Add m-esr52 at 52.6.0

22 files changed, 34450 insertions, 0 deletions

diff --git a/js/src/frontend/BytecodeCompiler.cpp b/js/src/frontend/BytecodeCompiler.cpp
new file mode 100644
index 0000000000..d4c758b6c2
--- /dev/null
+++ b/js/src/frontend/BytecodeCompiler.cpp
@@ -0,0 +1,738 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "frontend/BytecodeCompiler.h"
+
+#include "mozilla/IntegerPrintfMacros.h"
+
+#include "jscntxt.h"
+#include "jsscript.h"
+
+#include "builtin/ModuleObject.h"
+#include "frontend/BytecodeEmitter.h"
+#include "frontend/FoldConstants.h"
+#include "frontend/NameFunctions.h"
+#include "frontend/Parser.h"
+#include "vm/GlobalObject.h"
+#include "vm/TraceLogging.h"
+#include "wasm/AsmJS.h"
+
+#include "jsobjinlines.h"
+#include "jsscriptinlines.h"
+
+#include "vm/EnvironmentObject-inl.h"
+
+using namespace js;
+using namespace js::frontend;
+using mozilla::Maybe;
+
+class MOZ_STACK_CLASS AutoCompilationTraceLogger
+{
+  public:
+    AutoCompilationTraceLogger(ExclusiveContext* cx, const TraceLoggerTextId id,
+                               const ReadOnlyCompileOptions& options);
+
+  private:
+    TraceLoggerThread* logger;
+    TraceLoggerEvent event;
+    AutoTraceLog scriptLogger;
+    AutoTraceLog typeLogger;
+};
+
+// The BytecodeCompiler class contains resources common to compiling scripts and
+// function bodies.
+class MOZ_STACK_CLASS BytecodeCompiler
+{
+  public:
+    // Construct an object passing mandatory arguments.
+    BytecodeCompiler(ExclusiveContext* cx,
+                     LifoAlloc& alloc,
+                     const ReadOnlyCompileOptions& options,
+                     SourceBufferHolder& sourceBuffer,
+                     HandleScope enclosingScope,
+                     TraceLoggerTextId logId);
+
+    // Call setters for optional arguments.
+    void maybeSetSourceCompressor(SourceCompressionTask* sourceCompressor);
+    void setSourceArgumentsNotIncluded();
+
+    JSScript* compileGlobalScript(ScopeKind scopeKind);
+    JSScript* compileEvalScript(HandleObject environment, HandleScope enclosingScope);
+    ModuleObject* compileModule();
+    bool compileFunctionBody(MutableHandleFunction fun, Handle<PropertyNameVector> formals,
+                             GeneratorKind generatorKind, FunctionAsyncKind asyncKind);
+
+    ScriptSourceObject* sourceObjectPtr() const;
+
+  private:
+    JSScript* compileScript(HandleObject environment, SharedContext* sc);
+    bool checkLength();
+    bool createScriptSource();
+    bool maybeCompressSource();
+    bool canLazilyParse();
+    bool createParser();
+    bool createSourceAndParser();
+    bool createScript();
+    bool emplaceEmitter(Maybe<BytecodeEmitter>& emitter, SharedContext* sharedContext);
+    bool handleParseFailure(const Directives& newDirectives);
+    bool deoptimizeArgumentsInEnclosingScripts(JSContext* cx, HandleObject environment);
+    bool maybeCompleteCompressSource();
+
+    AutoCompilationTraceLogger traceLogger;
+    AutoKeepAtoms keepAtoms;
+
+    ExclusiveContext* cx;
+    LifoAlloc& alloc;
+    const ReadOnlyCompileOptions& options;
+    SourceBufferHolder& sourceBuffer;
+
+    RootedScope enclosingScope;
+    bool sourceArgumentsNotIncluded;
+
+    RootedScriptSource sourceObject;
+    ScriptSource* scriptSource;
+
+    Maybe<SourceCompressionTask> maybeSourceCompressor;
+    SourceCompressionTask* sourceCompressor;
+
+    Maybe<UsedNameTracker> usedNames;
+    Maybe<Parser<SyntaxParseHandler>> syntaxParser;
+    Maybe<Parser<FullParseHandler>> parser;
+
+    Directives directives;
+    TokenStream::Position startPosition;
+
+    RootedScript script;
+};
+
+AutoCompilationTraceLogger::AutoCompilationTraceLogger(ExclusiveContext* cx,
+        const TraceLoggerTextId id, const ReadOnlyCompileOptions& options)
+  : logger(cx->isJSContext() ? TraceLoggerForMainThread(cx->asJSContext()->runtime())
+                             : TraceLoggerForCurrentThread()),
+    event(logger, TraceLogger_AnnotateScripts, options),
+    scriptLogger(logger, event),
+    typeLogger(logger, id)
+{}
+
+BytecodeCompiler::BytecodeCompiler(ExclusiveContext* cx,
+                                   LifoAlloc& alloc,
+                                   const ReadOnlyCompileOptions& options,
+                                   SourceBufferHolder& sourceBuffer,
+                                   HandleScope enclosingScope,
+                                   TraceLoggerTextId logId)
+  : traceLogger(cx, logId, options),
+    keepAtoms(cx->perThreadData),
+    cx(cx),
+    alloc(alloc),
+    options(options),
+    sourceBuffer(sourceBuffer),
+    enclosingScope(cx, enclosingScope),
+    sourceArgumentsNotIncluded(false),
+    sourceObject(cx),
+    scriptSource(nullptr),
+    sourceCompressor(nullptr),
+    directives(options.strictOption),
+    startPosition(keepAtoms),
+    script(cx)
+{
+    MOZ_ASSERT(sourceBuffer.get());
+}
+
+void
+BytecodeCompiler::maybeSetSourceCompressor(SourceCompressionTask* sourceCompressor)
+{
+    this->sourceCompressor = sourceCompressor;
+}
+
+void
+BytecodeCompiler::setSourceArgumentsNotIncluded()
+{
+    sourceArgumentsNotIncluded = true;
+}
+
+bool
+BytecodeCompiler::checkLength()
+{
+    // Note this limit is simply so we can store sourceStart and sourceEnd in
+    // JSScript as 32-bits. It could be lifted fairly easily, since the compiler
+    // is using size_t internally already.
+    if (sourceBuffer.length() > UINT32_MAX) {
+        if (cx->isJSContext())
+            JS_ReportErrorNumberASCII(cx->asJSContext(), GetErrorMessage, nullptr,
+                                      JSMSG_SOURCE_TOO_LONG);
+        return false;
+    }
+    return true;
+}
+
+bool
+BytecodeCompiler::createScriptSource()
+{
+    if (!checkLength())
+        return false;
+
+    sourceObject = CreateScriptSourceObject(cx, options);
+    if (!sourceObject)
+        return false;
+
+    scriptSource = sourceObject->source();
+    return true;
+}
+
+bool
+BytecodeCompiler::maybeCompressSource()
+{
+    if (!sourceCompressor) {
+        maybeSourceCompressor.emplace(cx);
+        sourceCompressor = maybeSourceCompressor.ptr();
+    }
+
+    if (!cx->compartment()->behaviors().discardSource()) {
+        if (options.sourceIsLazy) {
+            scriptSource->setSourceRetrievable();
+        } else if (!scriptSource->setSourceCopy(cx, sourceBuffer, sourceArgumentsNotIncluded,
+                                                sourceCompressor))
+        {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeCompiler::canLazilyParse()
+{
+    return options.canLazilyParse &&
+           !(enclosingScope && enclosingScope->hasOnChain(ScopeKind::NonSyntactic)) &&
+           !cx->compartment()->behaviors().disableLazyParsing() &&
+           !cx->compartment()->behaviors().discardSource() &&
+           !options.sourceIsLazy &&
+           !cx->lcovEnabled();
+}
+
+bool
+BytecodeCompiler::createParser()
+{
+    usedNames.emplace(cx);
+    if (!usedNames->init())
+        return false;
+
+    if (canLazilyParse()) {
+        syntaxParser.emplace(cx, alloc, options, sourceBuffer.get(), sourceBuffer.length(),
+                             /* foldConstants = */ false, *usedNames,
+                             (Parser<SyntaxParseHandler>*) nullptr, (LazyScript*) nullptr);
+
+        if (!syntaxParser->checkOptions())
+            return false;
+    }
+
+    parser.emplace(cx, alloc, options, sourceBuffer.get(), sourceBuffer.length(),
+                   /* foldConstants = */ true, *usedNames, syntaxParser.ptrOr(nullptr), nullptr);
+    parser->sct = sourceCompressor;
+    parser->ss = scriptSource;
+    if (!parser->checkOptions())
+        return false;
+
+    parser->tokenStream.tell(&startPosition);
+    return true;
+}
+
+bool
+BytecodeCompiler::createSourceAndParser()
+{
+    return createScriptSource() &&
+           maybeCompressSource() &&
+           createParser();
+}
+
+bool
+BytecodeCompiler::createScript()
+{
+    script = JSScript::Create(cx, options,
+                              sourceObject, /* sourceStart = */ 0, sourceBuffer.length());
+    return script != nullptr;
+}
+
+bool
+BytecodeCompiler::emplaceEmitter(Maybe<BytecodeEmitter>& emitter, SharedContext* sharedContext)
+{
+    BytecodeEmitter::EmitterMode emitterMode =
+        options.selfHostingMode ? BytecodeEmitter::SelfHosting : BytecodeEmitter::Normal;
+    emitter.emplace(/* parent = */ nullptr, parser.ptr(), sharedContext, script,
+                    /* lazyScript = */ nullptr, options.lineno, emitterMode);
+    return emitter->init();
+}
+
+bool
+BytecodeCompiler::handleParseFailure(const Directives& newDirectives)
+{
+    if (parser->hadAbortedSyntaxParse()) {
+        // Hit some unrecoverable ambiguity during an inner syntax parse.
+        // Syntax parsing has now been disabled in the parser, so retry
+        // the parse.
+        parser->clearAbortedSyntaxParse();
+    } else if (parser->tokenStream.hadError() || directives == newDirectives) {
+        return false;
+    }
+
+    parser->tokenStream.seek(startPosition);
+
+    // Assignment must be monotonic to prevent reparsing iloops
+    MOZ_ASSERT_IF(directives.strict(), newDirectives.strict());
+    MOZ_ASSERT_IF(directives.asmJS(), newDirectives.asmJS());
+    directives = newDirectives;
+    return true;
+}
+
+bool
+BytecodeCompiler::deoptimizeArgumentsInEnclosingScripts(JSContext* cx, HandleObject environment)
+{
+    RootedObject env(cx, environment);
+    while (env->is<EnvironmentObject>() || env->is<DebugEnvironmentProxy>()) {
+        if (env->is<CallObject>()) {
+            RootedScript script(cx, env->as<CallObject>().callee().getOrCreateScript(cx));
+            if (!script)
+                return false;
+            if (script->argumentsHasVarBinding()) {
+                if (!JSScript::argumentsOptimizationFailed(cx, script))
+                    return false;
+            }
+        }
+        env = env->enclosingEnvironment();
+    }
+
+    return true;
+}
+
+bool
+BytecodeCompiler::maybeCompleteCompressSource()
+{
+    return !maybeSourceCompressor || maybeSourceCompressor->complete();
+}
+
+JSScript*
+BytecodeCompiler::compileScript(HandleObject environment, SharedContext* sc)
+{
+    if (!createSourceAndParser())
+        return nullptr;
+
+    if (!createScript())
+        return nullptr;
+
+    Maybe<BytecodeEmitter> emitter;
+    if (!emplaceEmitter(emitter, sc))
+        return nullptr;
+
+    for (;;) {
+        ParseNode* pn;
+        if (sc->isEvalContext())
+            pn = parser->evalBody(sc->asEvalContext());
+        else
+            pn = parser->globalBody(sc->asGlobalContext());
+
+        // Successfully parsed. Emit the script.
+        if (pn) {
+            if (sc->isEvalContext() && sc->hasDebuggerStatement() && cx->isJSContext()) {
+                // If the eval'ed script contains any debugger statement, force construction
+                // of arguments objects for the caller script and any other scripts it is
+                // transitively nested inside. The debugger can access any variable on the
+                // scope chain.
+                if (!deoptimizeArgumentsInEnclosingScripts(cx->asJSContext(), environment))
+                    return nullptr;
+            }
+            if (!NameFunctions(cx, pn))
+                return nullptr;
+            if (!emitter->emitScript(pn))
+                return nullptr;
+            parser->handler.freeTree(pn);
+
+            break;
+        }
+
+        // Maybe we aborted a syntax parse. See if we can try again.
+        if (!handleParseFailure(directives))
+            return nullptr;
+
+        // Reset UsedNameTracker state before trying again.
+        usedNames->reset();
+    }
+
+    if (!maybeCompleteCompressSource())
+        return nullptr;
+
+    MOZ_ASSERT_IF(cx->isJSContext(), !cx->asJSContext()->isExceptionPending());
+
+    return script;
+}
+
+JSScript*
+BytecodeCompiler::compileGlobalScript(ScopeKind scopeKind)
+{
+    GlobalSharedContext globalsc(cx, scopeKind, directives, options.extraWarningsOption);
+    return compileScript(nullptr, &globalsc);
+}
+
+JSScript*
+BytecodeCompiler::compileEvalScript(HandleObject environment, HandleScope enclosingScope)
+{
+    EvalSharedContext evalsc(cx, environment, enclosingScope,
+                             directives, options.extraWarningsOption);
+    return compileScript(environment, &evalsc);
+}
+
+ModuleObject*
+BytecodeCompiler::compileModule()
+{
+    if (!createSourceAndParser())
+        return nullptr;
+
+    Rooted<ModuleObject*> module(cx, ModuleObject::create(cx));
+    if (!module)
+        return nullptr;
+
+    if (!createScript())
+        return nullptr;
+
+    module->init(script);
+
+    ModuleBuilder builder(cx, module);
+    ModuleSharedContext modulesc(cx, module, enclosingScope, builder);
+    ParseNode* pn = parser->moduleBody(&modulesc);
+    if (!pn)
+        return nullptr;
+
+    if (!NameFunctions(cx, pn))
+        return nullptr;
+
+    Maybe<BytecodeEmitter> emitter;
+    if (!emplaceEmitter(emitter, &modulesc))
+        return nullptr;
+    if (!emitter->emitScript(pn->pn_body))
+        return nullptr;
+
+    parser->handler.freeTree(pn);
+
+    if (!builder.initModule())
+        return nullptr;
+
+    RootedModuleEnvironmentObject env(cx, ModuleEnvironmentObject::create(cx, module));
+    if (!env)
+        return nullptr;
+
+    module->setInitialEnvironment(env);
+
+    if (!maybeCompleteCompressSource())
+        return nullptr;
+
+    MOZ_ASSERT_IF(cx->isJSContext(), !cx->asJSContext()->isExceptionPending());
+    return module;
+}
+
+bool
+BytecodeCompiler::compileFunctionBody(MutableHandleFunction fun,
+                                      Handle<PropertyNameVector> formals,
+                                      GeneratorKind generatorKind,
+                                      FunctionAsyncKind asyncKind)
+{
+    MOZ_ASSERT(fun);
+    MOZ_ASSERT(fun->isTenured());
+
+    fun->setArgCount(formals.length());
+
+    if (!createSourceAndParser())
+        return false;
+
+    // Speculatively parse using the default directives implied by the context.
+    // If a directive is encountered (e.g., "use strict") that changes how the
+    // function should have been parsed, we backup and reparse with the new set
+    // of directives.
+
+    ParseNode* fn;
+    do {
+        Directives newDirectives = directives;
+        fn = parser->standaloneFunctionBody(fun, enclosingScope, formals, generatorKind, asyncKind,
+                                            directives, &newDirectives);
+        if (!fn && !handleParseFailure(newDirectives))
+            return false;
+    } while (!fn);
+
+    if (!NameFunctions(cx, fn))
+        return false;
+
+    if (fn->pn_funbox->function()->isInterpreted()) {
+        MOZ_ASSERT(fun == fn->pn_funbox->function());
+
+        if (!createScript())
+            return false;
+
+        Maybe<BytecodeEmitter> emitter;
+        if (!emplaceEmitter(emitter, fn->pn_funbox))
+            return false;
+        if (!emitter->emitFunctionScript(fn->pn_body))
+            return false;
+    } else {
+        fun.set(fn->pn_funbox->function());
+        MOZ_ASSERT(IsAsmJSModule(fun));
+    }
+
+    if (!maybeCompleteCompressSource())
+        return false;
+
+    return true;
+}
+
+ScriptSourceObject*
+BytecodeCompiler::sourceObjectPtr() const
+{
+    return sourceObject.get();
+}
+
+ScriptSourceObject*
+frontend::CreateScriptSourceObject(ExclusiveContext* cx, const ReadOnlyCompileOptions& options)
+{
+    ScriptSource* ss = cx->new_<ScriptSource>();
+    if (!ss)
+        return nullptr;
+    ScriptSourceHolder ssHolder(ss);
+
+    if (!ss->initFromOptions(cx, options))
+        return nullptr;
+
+    RootedScriptSource sso(cx, ScriptSourceObject::create(cx, ss));
+    if (!sso)
+        return nullptr;
+
+    // Off-thread compilations do all their GC heap allocation, including the
+    // SSO, in a temporary compartment. Hence, for the SSO to refer to the
+    // gc-heap-allocated values in |options|, it would need cross-compartment
+    // wrappers from the temporary compartment to the real compartment --- which
+    // would then be inappropriate once we merged the temporary and real
+    // compartments.
+    //
+    // Instead, we put off populating those SSO slots in off-thread compilations
+    // until after we've merged compartments.
+    if (cx->isJSContext()) {
+        if (!ScriptSourceObject::initFromOptions(cx->asJSContext(), sso, options))
+            return nullptr;
+    }
+
+    return sso;
+}
+
+// CompileScript independently returns the ScriptSourceObject (SSO) for the
+// compile.  This is used by off-main-thread script compilation (OMT-SC).
+//
+// OMT-SC cannot initialize the SSO when it is first constructed because the
+// SSO is allocated initially in a separate compartment.
+//
+// After OMT-SC, the separate compartment is merged with the main compartment,
+// at which point the JSScripts created become observable by the debugger via
+// memory-space scanning.
+//
+// Whatever happens to the top-level script compilation (even if it fails and
+// returns null), we must finish initializing the SSO.  This is because there
+// may be valid inner scripts observable by the debugger which reference the
+// partially-initialized SSO.
+class MOZ_STACK_CLASS AutoInitializeSourceObject
+{
+    BytecodeCompiler& compiler_;
+    ScriptSourceObject** sourceObjectOut_;
+
+  public:
+    AutoInitializeSourceObject(BytecodeCompiler& compiler, ScriptSourceObject** sourceObjectOut)
+      : compiler_(compiler),
+        sourceObjectOut_(sourceObjectOut)
+    { }
+
+    ~AutoInitializeSourceObject() {
+        if (sourceObjectOut_)
+            *sourceObjectOut_ = compiler_.sourceObjectPtr();
+    }
+};
+
+JSScript*
+frontend::CompileGlobalScript(ExclusiveContext* cx, LifoAlloc& alloc, ScopeKind scopeKind,
+                              const ReadOnlyCompileOptions& options,
+                              SourceBufferHolder& srcBuf,
+                              SourceCompressionTask* extraSct,
+                              ScriptSourceObject** sourceObjectOut)
+{
+    MOZ_ASSERT(scopeKind == ScopeKind::Global || scopeKind == ScopeKind::NonSyntactic);
+    BytecodeCompiler compiler(cx, alloc, options, srcBuf, /* enclosingScope = */ nullptr,
+                              TraceLogger_ParserCompileScript);
+    AutoInitializeSourceObject autoSSO(compiler, sourceObjectOut);
+    compiler.maybeSetSourceCompressor(extraSct);
+    return compiler.compileGlobalScript(scopeKind);
+}
+
+JSScript*
+frontend::CompileEvalScript(ExclusiveContext* cx, LifoAlloc& alloc,
+                            HandleObject environment, HandleScope enclosingScope,
+                            const ReadOnlyCompileOptions& options,
+                            SourceBufferHolder& srcBuf,
+                            SourceCompressionTask* extraSct,
+                            ScriptSourceObject** sourceObjectOut)
+{
+    BytecodeCompiler compiler(cx, alloc, options, srcBuf, enclosingScope,
+                              TraceLogger_ParserCompileScript);
+    AutoInitializeSourceObject autoSSO(compiler, sourceObjectOut);
+    compiler.maybeSetSourceCompressor(extraSct);
+    return compiler.compileEvalScript(environment, enclosingScope);
+}
+
+ModuleObject*
+frontend::CompileModule(ExclusiveContext* cx, const ReadOnlyCompileOptions& optionsInput,
+                        SourceBufferHolder& srcBuf, LifoAlloc& alloc,
+                        ScriptSourceObject** sourceObjectOut /* = nullptr */)
+{
+    MOZ_ASSERT(srcBuf.get());
+    MOZ_ASSERT_IF(sourceObjectOut, *sourceObjectOut == nullptr);
+
+    CompileOptions options(cx, optionsInput);
+    options.maybeMakeStrictMode(true); // ES6 10.2.1 Module code is always strict mode code.
+    options.setIsRunOnce(true);
+
+    RootedScope emptyGlobalScope(cx, &cx->global()->emptyGlobalScope());
+    BytecodeCompiler compiler(cx, alloc, options, srcBuf, emptyGlobalScope,
+                              TraceLogger_ParserCompileModule);
+    AutoInitializeSourceObject autoSSO(compiler, sourceObjectOut);
+    return compiler.compileModule();
+}
+
+ModuleObject*
+frontend::CompileModule(JSContext* cx, const ReadOnlyCompileOptions& options,
+                        SourceBufferHolder& srcBuf)
+{
+    if (!GlobalObject::ensureModulePrototypesCreated(cx, cx->global()))
+        return nullptr;
+
+    LifoAlloc& alloc = cx->asJSContext()->tempLifoAlloc();
+    RootedModuleObject module(cx, CompileModule(cx, options, srcBuf, alloc));
+    if (!module)
+        return nullptr;
+
+    // This happens in GlobalHelperThreadState::finishModuleParseTask() when a
+    // module is compiled off main thread.
+    if (!ModuleObject::Freeze(cx->asJSContext(), module))
+        return nullptr;
+
+    return module;
+}
+
+bool
+frontend::CompileLazyFunction(JSContext* cx, Handle<LazyScript*> lazy, const char16_t* chars, size_t length)
+{
+    MOZ_ASSERT(cx->compartment() == lazy->functionNonDelazifying()->compartment());
+
+    CompileOptions options(cx, lazy->version());
+    options.setMutedErrors(lazy->mutedErrors())
+           .setFileAndLine(lazy->filename(), lazy->lineno())
+           .setColumn(lazy->column())
+           .setNoScriptRval(false)
+           .setSelfHostingMode(false);
+
+    AutoCompilationTraceLogger traceLogger(cx, TraceLogger_ParserCompileLazy, options);
+
+    UsedNameTracker usedNames(cx);
+    if (!usedNames.init())
+        return false;
+    Parser<FullParseHandler> parser(cx, cx->tempLifoAlloc(), options, chars, length,
+                                    /* foldConstants = */ true, usedNames, nullptr, lazy);
+    if (!parser.checkOptions())
+        return false;
+
+    Rooted<JSFunction*> fun(cx, lazy->functionNonDelazifying());
+    MOZ_ASSERT(!lazy->isLegacyGenerator());
+    ParseNode* pn = parser.standaloneLazyFunction(fun, lazy->strict(), lazy->generatorKind(),
+                                                  lazy->asyncKind());
+    if (!pn)
+        return false;
+
+    if (!NameFunctions(cx, pn))
+        return false;
+
+    RootedScriptSource sourceObject(cx, lazy->sourceObject());
+    MOZ_ASSERT(sourceObject);
+
+    Rooted<JSScript*> script(cx, JSScript::Create(cx, options, sourceObject,
+                                                  lazy->begin(), lazy->end()));
+    if (!script)
+        return false;
+
+    if (lazy->isLikelyConstructorWrapper())
+        script->setLikelyConstructorWrapper();
+    if (lazy->hasBeenCloned())
+        script->setHasBeenCloned();
+
+    BytecodeEmitter bce(/* parent = */ nullptr, &parser, pn->pn_funbox, script, lazy,
+                        pn->pn_pos, BytecodeEmitter::LazyFunction);
+    if (!bce.init())
+        return false;
+
+    return bce.emitFunctionScript(pn->pn_body);
+}
+
+// Compile a JS function body, which might appear as the value of an event
+// handler attribute in an HTML <INPUT> tag, or in a Function() constructor.
+static bool
+CompileFunctionBody(JSContext* cx, MutableHandleFunction fun, const ReadOnlyCompileOptions& options,
+                    Handle<PropertyNameVector> formals, SourceBufferHolder& srcBuf,
+                    HandleScope enclosingScope, GeneratorKind generatorKind,
+                    FunctionAsyncKind asyncKind)
+{
+    MOZ_ASSERT(!options.isRunOnce);
+
+    // FIXME: make Function pass in two strings and parse them as arguments and
+    // ProgramElements respectively.
+
+    BytecodeCompiler compiler(cx, cx->tempLifoAlloc(), options, srcBuf, enclosingScope,
+                              TraceLogger_ParserCompileFunction);
+    compiler.setSourceArgumentsNotIncluded();
+    return compiler.compileFunctionBody(fun, formals, generatorKind, asyncKind);
+}
+
+bool
+frontend::CompileFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                              const ReadOnlyCompileOptions& options,
+                              Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf,
+                              HandleScope enclosingScope)
+{
+    return CompileFunctionBody(cx, fun, options, formals, srcBuf, enclosingScope, NotGenerator,
+                               SyncFunction);
+}
+
+bool
+frontend::CompileFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                              const ReadOnlyCompileOptions& options,
+                              Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf)
+{
+    RootedScope emptyGlobalScope(cx, &cx->global()->emptyGlobalScope());
+    return CompileFunctionBody(cx, fun, options, formals, srcBuf, emptyGlobalScope,
+                               NotGenerator, SyncFunction);
+}
+
+bool
+frontend::CompileStarGeneratorBody(JSContext* cx, MutableHandleFunction fun,
+                                   const ReadOnlyCompileOptions& options,
+                                   Handle<PropertyNameVector> formals,
+                                   JS::SourceBufferHolder& srcBuf)
+{
+    RootedScope emptyGlobalScope(cx, &cx->global()->emptyGlobalScope());
+    return CompileFunctionBody(cx, fun, options, formals, srcBuf, emptyGlobalScope,
+                               StarGenerator, SyncFunction);
+}
+
+bool
+frontend::CompileAsyncFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                                   const ReadOnlyCompileOptions& options,
+                                   Handle<PropertyNameVector> formals,
+                                   JS::SourceBufferHolder& srcBuf)
+{
+    RootedScope emptyGlobalScope(cx, &cx->global()->emptyGlobalScope());
+    return CompileFunctionBody(cx, fun, options, formals, srcBuf, emptyGlobalScope,
+                               StarGenerator, AsyncFunction);
+}
diff --git a/js/src/frontend/BytecodeCompiler.h b/js/src/frontend/BytecodeCompiler.h
new file mode 100644
index 0000000000..1d86f11607
--- /dev/null
+++ b/js/src/frontend/BytecodeCompiler.h
@@ -0,0 +1,108 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_BytecodeCompiler_h
+#define frontend_BytecodeCompiler_h
+
+#include "NamespaceImports.h"
+
+#include "vm/Scope.h"
+#include "vm/String.h"
+
+class JSLinearString;
+
+namespace js {
+
+class LazyScript;
+class LifoAlloc;
+class ModuleObject;
+class ScriptSourceObject;
+struct SourceCompressionTask;
+
+namespace frontend {
+
+JSScript*
+CompileGlobalScript(ExclusiveContext* cx, LifoAlloc& alloc, ScopeKind scopeKind,
+                    const ReadOnlyCompileOptions& options,
+                    SourceBufferHolder& srcBuf,
+                    SourceCompressionTask* extraSct = nullptr,
+                    ScriptSourceObject** sourceObjectOut = nullptr);
+
+JSScript*
+CompileEvalScript(ExclusiveContext* cx, LifoAlloc& alloc,
+                  HandleObject scopeChain, HandleScope enclosingScope,
+                  const ReadOnlyCompileOptions& options,
+                  SourceBufferHolder& srcBuf,
+                  SourceCompressionTask* extraSct = nullptr,
+                  ScriptSourceObject** sourceObjectOut = nullptr);
+
+ModuleObject*
+CompileModule(JSContext* cx, const ReadOnlyCompileOptions& options,
+              SourceBufferHolder& srcBuf);
+
+ModuleObject*
+CompileModule(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
+              SourceBufferHolder& srcBuf, LifoAlloc& alloc,
+              ScriptSourceObject** sourceObjectOut = nullptr);
+
+MOZ_MUST_USE bool
+CompileLazyFunction(JSContext* cx, Handle<LazyScript*> lazy, const char16_t* chars, size_t length);
+
+MOZ_MUST_USE bool
+CompileFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                    const ReadOnlyCompileOptions& options,
+                    Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf,
+                    HandleScope enclosingScope);
+
+// As above, but defaults to the global lexical scope as the enclosing scope.
+MOZ_MUST_USE bool
+CompileFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                    const ReadOnlyCompileOptions& options,
+                    Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf);
+
+MOZ_MUST_USE bool
+CompileStarGeneratorBody(JSContext* cx, MutableHandleFunction fun,
+                         const ReadOnlyCompileOptions& options,
+                         Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf);
+
+MOZ_MUST_USE bool
+CompileAsyncFunctionBody(JSContext* cx, MutableHandleFunction fun,
+                         const ReadOnlyCompileOptions& options,
+                         Handle<PropertyNameVector> formals, JS::SourceBufferHolder& srcBuf);
+
+ScriptSourceObject*
+CreateScriptSourceObject(ExclusiveContext* cx, const ReadOnlyCompileOptions& options);
+
+/*
+ * True if str consists of an IdentifierStart character, followed by one or
+ * more IdentifierPart characters, i.e. it matches the IdentifierName production
+ * in the language spec.
+ *
+ * This returns true even if str is a keyword like "if".
+ *
+ * Defined in TokenStream.cpp.
+ */
+bool
+IsIdentifier(JSLinearString* str);
+
+/*
+ * As above, but taking chars + length.
+ */
+bool
+IsIdentifier(const char16_t* chars, size_t length);
+
+/* True if str is a keyword. Defined in TokenStream.cpp. */
+bool
+IsKeyword(JSLinearString* str);
+
+/* GC marking. Defined in Parser.cpp. */
+void
+MarkParser(JSTracer* trc, JS::AutoGCRooter* parser);
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_BytecodeCompiler_h */
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
new file mode 100644
index 0000000000..1e9d8f2243
--- /dev/null
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -0,0 +1,10170 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * JS bytecode generation.
+ */
+
+#include "frontend/BytecodeEmitter.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PodOperations.h"
+
+#include <string.h>
+
+#include "jsapi.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsfun.h"
+#include "jsnum.h"
+#include "jsopcode.h"
+#include "jsscript.h"
+#include "jstypes.h"
+#include "jsutil.h"
+
+#include "frontend/Parser.h"
+#include "frontend/TokenStream.h"
+#include "vm/Debugger.h"
+#include "vm/GeneratorObject.h"
+#include "vm/Stack.h"
+#include "wasm/AsmJS.h"
+
+#include "jsatominlines.h"
+#include "jsobjinlines.h"
+#include "jsscriptinlines.h"
+
+#include "frontend/ParseNode-inl.h"
+#include "vm/EnvironmentObject-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+using namespace js::gc;
+using namespace js::frontend;
+
+using mozilla::AssertedCast;
+using mozilla::DebugOnly;
+using mozilla::Maybe;
+using mozilla::Nothing;
+using mozilla::NumberIsInt32;
+using mozilla::PodCopy;
+using mozilla::Some;
+
+class BreakableControl;
+class LabelControl;
+class LoopControl;
+class TryFinallyControl;
+
+static bool
+ParseNodeRequiresSpecialLineNumberNotes(ParseNode* pn)
+{
+    return pn->getKind() == PNK_WHILE || pn->getKind() == PNK_FOR;
+}
+
+// A cache that tracks superfluous TDZ checks.
+//
+// Each basic block should have a TDZCheckCache in scope. Some NestableControl
+// subclasses contain a TDZCheckCache.
+class BytecodeEmitter::TDZCheckCache : public Nestable<BytecodeEmitter::TDZCheckCache>
+{
+    PooledMapPtr<CheckTDZMap> cache_;
+
+    MOZ_MUST_USE bool ensureCache(BytecodeEmitter* bce) {
+        return cache_ || cache_.acquire(bce->cx);
+    }
+
+  public:
+    explicit TDZCheckCache(BytecodeEmitter* bce)
+      : Nestable<TDZCheckCache>(&bce->innermostTDZCheckCache),
+        cache_(bce->cx->frontendCollectionPool())
+    { }
+
+    Maybe<MaybeCheckTDZ> needsTDZCheck(BytecodeEmitter* bce, JSAtom* name);
+    MOZ_MUST_USE bool noteTDZCheck(BytecodeEmitter* bce, JSAtom* name, MaybeCheckTDZ check);
+};
+
+class BytecodeEmitter::NestableControl : public Nestable<BytecodeEmitter::NestableControl>
+{
+    StatementKind kind_;
+
+    // The innermost scope when this was pushed.
+    EmitterScope* emitterScope_;
+
+  protected:
+    NestableControl(BytecodeEmitter* bce, StatementKind kind)
+      : Nestable<NestableControl>(&bce->innermostNestableControl),
+        kind_(kind),
+        emitterScope_(bce->innermostEmitterScope)
+    { }
+
+  public:
+    using Nestable<NestableControl>::enclosing;
+    using Nestable<NestableControl>::findNearest;
+
+    StatementKind kind() const {
+        return kind_;
+    }
+
+    EmitterScope* emitterScope() const {
+        return emitterScope_;
+    }
+
+    template <typename T>
+    bool is() const;
+
+    template <typename T>
+    T& as() {
+        MOZ_ASSERT(this->is<T>());
+        return static_cast<T&>(*this);
+    }
+};
+
+// Template specializations are disallowed in different namespaces; specialize
+// all the NestableControl subtypes up front.
+namespace js {
+namespace frontend {
+
+template <>
+bool
+BytecodeEmitter::NestableControl::is<BreakableControl>() const
+{
+    return StatementKindIsUnlabeledBreakTarget(kind_) || kind_ == StatementKind::Label;
+}
+
+template <>
+bool
+BytecodeEmitter::NestableControl::is<LabelControl>() const
+{
+    return kind_ == StatementKind::Label;
+}
+
+template <>
+bool
+BytecodeEmitter::NestableControl::is<LoopControl>() const
+{
+    return StatementKindIsLoop(kind_);
+}
+
+template <>
+bool
+BytecodeEmitter::NestableControl::is<TryFinallyControl>() const
+{
+    return kind_ == StatementKind::Try || kind_ == StatementKind::Finally;
+}
+
+} // namespace frontend
+} // namespace js
+
+class BreakableControl : public BytecodeEmitter::NestableControl
+{
+  public:
+    // Offset of the last break.
+    JumpList breaks;
+
+    BreakableControl(BytecodeEmitter* bce, StatementKind kind)
+      : NestableControl(bce, kind)
+    {
+        MOZ_ASSERT(is<BreakableControl>());
+    }
+
+    MOZ_MUST_USE bool patchBreaks(BytecodeEmitter* bce) {
+        return bce->emitJumpTargetAndPatch(breaks);
+    }
+};
+
+class LabelControl : public BreakableControl
+{
+    RootedAtom label_;
+
+    // The code offset when this was pushed. Used for effectfulness checking.
+    ptrdiff_t startOffset_;
+
+  public:
+    LabelControl(BytecodeEmitter* bce, JSAtom* label, ptrdiff_t startOffset)
+      : BreakableControl(bce, StatementKind::Label),
+        label_(bce->cx, label),
+        startOffset_(startOffset)
+    { }
+
+    HandleAtom label() const {
+        return label_;
+    }
+
+    ptrdiff_t startOffset() const {
+        return startOffset_;
+    }
+};
+
+class LoopControl : public BreakableControl
+{
+    // Loops' children are emitted in dominance order, so they can always
+    // have a TDZCheckCache.
+    BytecodeEmitter::TDZCheckCache tdzCache_;
+
+    // Stack depth when this loop was pushed on the control stack.
+    int32_t stackDepth_;
+
+    // The loop nesting depth. Used as a hint to Ion.
+    uint32_t loopDepth_;
+
+    // Can we OSR into Ion from here? True unless there is non-loop state on the stack.
+    bool canIonOsr_;
+
+  public:
+    // The target of continue statement jumps, e.g., the update portion of a
+    // for(;;) loop.
+    JumpTarget continueTarget;
+
+    // Offset of the last continue in the loop.
+    JumpList continues;
+
+    LoopControl(BytecodeEmitter* bce, StatementKind loopKind)
+      : BreakableControl(bce, loopKind),
+        tdzCache_(bce),
+        continueTarget({ -1 })
+    {
+        MOZ_ASSERT(is<LoopControl>());
+
+        LoopControl* enclosingLoop = findNearest<LoopControl>(enclosing());
+
+        stackDepth_ = bce->stackDepth;
+        loopDepth_ = enclosingLoop ? enclosingLoop->loopDepth_ + 1 : 1;
+
+        int loopSlots;
+        if (loopKind == StatementKind::Spread)
+            loopSlots = 3;
+        else if (loopKind == StatementKind::ForInLoop || loopKind == StatementKind::ForOfLoop)
+            loopSlots = 2;
+        else
+            loopSlots = 0;
+
+        MOZ_ASSERT(loopSlots <= stackDepth_);
+
+        if (enclosingLoop) {
+            canIonOsr_ = (enclosingLoop->canIonOsr_ &&
+                          stackDepth_ == enclosingLoop->stackDepth_ + loopSlots);
+        } else {
+            canIonOsr_ = stackDepth_ == loopSlots;
+        }
+    }
+
+    uint32_t loopDepth() const {
+        return loopDepth_;
+    }
+
+    bool canIonOsr() const {
+        return canIonOsr_;
+    }
+
+    MOZ_MUST_USE bool patchBreaksAndContinues(BytecodeEmitter* bce) {
+        MOZ_ASSERT(continueTarget.offset != -1);
+        if (!patchBreaks(bce))
+            return false;
+        bce->patchJumpsToTarget(continues, continueTarget);
+        return true;
+    }
+};
+
+class TryFinallyControl : public BytecodeEmitter::NestableControl
+{
+    bool emittingSubroutine_;
+
+  public:
+    // The subroutine when emitting a finally block.
+    JumpList gosubs;
+
+    // Offset of the last catch guard, if any.
+    JumpList guardJump;
+
+    TryFinallyControl(BytecodeEmitter* bce, StatementKind kind)
+      : NestableControl(bce, kind),
+        emittingSubroutine_(false)
+    {
+        MOZ_ASSERT(is<TryFinallyControl>());
+    }
+
+    void setEmittingSubroutine() {
+        emittingSubroutine_ = true;
+    }
+
+    bool emittingSubroutine() const {
+        return emittingSubroutine_;
+    }
+};
+
+static bool
+ScopeKindIsInBody(ScopeKind kind)
+{
+    return kind == ScopeKind::Lexical ||
+           kind == ScopeKind::SimpleCatch ||
+           kind == ScopeKind::Catch ||
+           kind == ScopeKind::With ||
+           kind == ScopeKind::FunctionBodyVar ||
+           kind == ScopeKind::ParameterExpressionVar;
+}
+
+static inline void
+MarkAllBindingsClosedOver(LexicalScope::Data& data)
+{
+    BindingName* names = data.names;
+    for (uint32_t i = 0; i < data.length; i++)
+        names[i] = BindingName(names[i].name(), true);
+}
+
+// A scope that introduces bindings.
+class BytecodeEmitter::EmitterScope : public Nestable<BytecodeEmitter::EmitterScope>
+{
+    // The cache of bound names that may be looked up in the
+    // scope. Initially populated as the set of names this scope binds. As
+    // names are looked up in enclosing scopes, they are cached on the
+    // current scope.
+    PooledMapPtr<NameLocationMap> nameCache_;
+
+    // If this scope's cache does not include free names, such as the
+    // global scope, the NameLocation to return.
+    Maybe<NameLocation> fallbackFreeNameLocation_;
+
+    // True if there is a corresponding EnvironmentObject on the environment
+    // chain, false if all bindings are stored in frame slots on the stack.
+    bool hasEnvironment_;
+
+    // The number of enclosing environments. Used for error checking.
+    uint8_t environmentChainLength_;
+
+    // The next usable slot on the frame for not-closed over bindings.
+    //
+    // The initial frame slot when assigning slots to bindings is the
+    // enclosing scope's nextFrameSlot. For the first scope in a frame,
+    // the initial frame slot is 0.
+    uint32_t nextFrameSlot_;
+
+    // The index in the BytecodeEmitter's interned scope vector, otherwise
+    // ScopeNote::NoScopeIndex.
+    uint32_t scopeIndex_;
+
+    // If kind is Lexical, Catch, or With, the index in the BytecodeEmitter's
+    // block scope note list. Otherwise ScopeNote::NoScopeNote.
+    uint32_t noteIndex_;
+
+    MOZ_MUST_USE bool ensureCache(BytecodeEmitter* bce) {
+        return nameCache_.acquire(bce->cx);
+    }
+
+    template <typename BindingIter>
+    MOZ_MUST_USE bool checkSlotLimits(BytecodeEmitter* bce, const BindingIter& bi) {
+        if (bi.nextFrameSlot() >= LOCALNO_LIMIT ||
+            bi.nextEnvironmentSlot() >= ENVCOORD_SLOT_LIMIT)
+        {
+            return bce->reportError(nullptr, JSMSG_TOO_MANY_LOCALS);
+        }
+        return true;
+    }
+
+    MOZ_MUST_USE bool checkEnvironmentChainLength(BytecodeEmitter* bce) {
+        uint32_t hops;
+        if (EmitterScope* emitterScope = enclosing(&bce))
+            hops = emitterScope->environmentChainLength_;
+        else
+            hops = bce->sc->compilationEnclosingScope()->environmentChainLength();
+        if (hops >= ENVCOORD_HOPS_LIMIT - 1)
+            return bce->reportError(nullptr, JSMSG_TOO_DEEP, js_function_str);
+        environmentChainLength_ = mozilla::AssertedCast<uint8_t>(hops + 1);
+        return true;
+    }
+
+    void updateFrameFixedSlots(BytecodeEmitter* bce, const BindingIter& bi) {
+        nextFrameSlot_ = bi.nextFrameSlot();
+        if (nextFrameSlot_ > bce->maxFixedSlots)
+            bce->maxFixedSlots = nextFrameSlot_;
+        MOZ_ASSERT_IF(bce->sc->isFunctionBox() && bce->sc->asFunctionBox()->isGenerator(),
+                      bce->maxFixedSlots == 0);
+    }
+
+    MOZ_MUST_USE bool putNameInCache(BytecodeEmitter* bce, JSAtom* name, NameLocation loc) {
+        NameLocationMap& cache = *nameCache_;
+        NameLocationMap::AddPtr p = cache.lookupForAdd(name);
+        MOZ_ASSERT(!p);
+        if (!cache.add(p, name, loc)) {
+            ReportOutOfMemory(bce->cx);
+            return false;
+        }
+        return true;
+    }
+
+    Maybe<NameLocation> lookupInCache(BytecodeEmitter* bce, JSAtom* name) {
+        if (NameLocationMap::Ptr p = nameCache_->lookup(name))
+            return Some(p->value().wrapped);
+        if (fallbackFreeNameLocation_ && nameCanBeFree(bce, name))
+            return fallbackFreeNameLocation_;
+        return Nothing();
+    }
+
+    friend bool BytecodeEmitter::needsImplicitThis();
+
+    EmitterScope* enclosing(BytecodeEmitter** bce) const {
+        // There is an enclosing scope with access to the same frame.
+        if (EmitterScope* inFrame = enclosingInFrame())
+            return inFrame;
+
+        // We are currently compiling the enclosing script, look in the
+        // enclosing BCE.
+        if ((*bce)->parent) {
+            *bce = (*bce)->parent;
+            return (*bce)->innermostEmitterScope;
+        }
+
+        return nullptr;
+    }
+
+    Scope* enclosingScope(BytecodeEmitter* bce) const {
+        if (EmitterScope* es = enclosing(&bce))
+            return es->scope(bce);
+
+        // The enclosing script is already compiled or the current script is the
+        // global script.
+        return bce->sc->compilationEnclosingScope();
+    }
+
+    static bool nameCanBeFree(BytecodeEmitter* bce, JSAtom* name) {
+        // '.generator' cannot be accessed by name.
+        return name != bce->cx->names().dotGenerator;
+    }
+
+    static NameLocation searchInEnclosingScope(JSAtom* name, Scope* scope, uint8_t hops);
+    NameLocation searchAndCache(BytecodeEmitter* bce, JSAtom* name);
+
+    template <typename ScopeCreator>
+    MOZ_MUST_USE bool internScope(BytecodeEmitter* bce, ScopeCreator createScope);
+    template <typename ScopeCreator>
+    MOZ_MUST_USE bool internBodyScope(BytecodeEmitter* bce, ScopeCreator createScope);
+    MOZ_MUST_USE bool appendScopeNote(BytecodeEmitter* bce);
+
+    MOZ_MUST_USE bool deadZoneFrameSlotRange(BytecodeEmitter* bce, uint32_t slotStart,
+                                             uint32_t slotEnd);
+
+  public:
+    explicit EmitterScope(BytecodeEmitter* bce)
+      : Nestable<EmitterScope>(&bce->innermostEmitterScope),
+        nameCache_(bce->cx->frontendCollectionPool()),
+        hasEnvironment_(false),
+        environmentChainLength_(0),
+        nextFrameSlot_(0),
+        scopeIndex_(ScopeNote::NoScopeIndex),
+        noteIndex_(ScopeNote::NoScopeNoteIndex)
+    { }
+
+    void dump(BytecodeEmitter* bce);
+
+    MOZ_MUST_USE bool enterLexical(BytecodeEmitter* bce, ScopeKind kind,
+                                   Handle<LexicalScope::Data*> bindings);
+    MOZ_MUST_USE bool enterNamedLambda(BytecodeEmitter* bce, FunctionBox* funbox);
+    MOZ_MUST_USE bool enterComprehensionFor(BytecodeEmitter* bce,
+                                            Handle<LexicalScope::Data*> bindings);
+    MOZ_MUST_USE bool enterFunction(BytecodeEmitter* bce, FunctionBox* funbox);
+    MOZ_MUST_USE bool enterFunctionExtraBodyVar(BytecodeEmitter* bce, FunctionBox* funbox);
+    MOZ_MUST_USE bool enterParameterExpressionVar(BytecodeEmitter* bce);
+    MOZ_MUST_USE bool enterGlobal(BytecodeEmitter* bce, GlobalSharedContext* globalsc);
+    MOZ_MUST_USE bool enterEval(BytecodeEmitter* bce, EvalSharedContext* evalsc);
+    MOZ_MUST_USE bool enterModule(BytecodeEmitter* module, ModuleSharedContext* modulesc);
+    MOZ_MUST_USE bool enterWith(BytecodeEmitter* bce);
+    MOZ_MUST_USE bool deadZoneFrameSlots(BytecodeEmitter* bce);
+
+    MOZ_MUST_USE bool leave(BytecodeEmitter* bce, bool nonLocal = false);
+
+    uint32_t index() const {
+        MOZ_ASSERT(scopeIndex_ != ScopeNote::NoScopeIndex, "Did you forget to intern a Scope?");
+        return scopeIndex_;
+    }
+
+    uint32_t noteIndex() const {
+        return noteIndex_;
+    }
+
+    Scope* scope(const BytecodeEmitter* bce) const {
+        return bce->scopeList.vector[index()];
+    }
+
+    bool hasEnvironment() const {
+        return hasEnvironment_;
+    }
+
+    // The first frame slot used.
+    uint32_t frameSlotStart() const {
+        if (EmitterScope* inFrame = enclosingInFrame())
+            return inFrame->nextFrameSlot_;
+        return 0;
+    }
+
+    // The last frame slot used + 1.
+    uint32_t frameSlotEnd() const {
+        return nextFrameSlot_;
+    }
+
+    uint32_t numFrameSlots() const {
+        return frameSlotEnd() - frameSlotStart();
+    }
+
+    EmitterScope* enclosingInFrame() const {
+        return Nestable<EmitterScope>::enclosing();
+    }
+
+    NameLocation lookup(BytecodeEmitter* bce, JSAtom* name) {
+        if (Maybe<NameLocation> loc = lookupInCache(bce, name))
+            return *loc;
+        return searchAndCache(bce, name);
+    }
+
+    Maybe<NameLocation> locationBoundInScope(BytecodeEmitter* bce, JSAtom* name,
+                                             EmitterScope* target);
+};
+
+void
+BytecodeEmitter::EmitterScope::dump(BytecodeEmitter* bce)
+{
+    fprintf(stdout, "EmitterScope [%s] %p\n", ScopeKindString(scope(bce)->kind()), this);
+
+    for (NameLocationMap::Range r = nameCache_->all(); !r.empty(); r.popFront()) {
+        const NameLocation& l = r.front().value();
+
+        JSAutoByteString bytes;
+        if (!AtomToPrintableString(bce->cx, r.front().key(), &bytes))
+            return;
+        if (l.kind() != NameLocation::Kind::Dynamic)
+            fprintf(stdout, "  %s %s ", BindingKindString(l.bindingKind()), bytes.ptr());
+        else
+            fprintf(stdout, "  %s ", bytes.ptr());
+
+        switch (l.kind()) {
+          case NameLocation::Kind::Dynamic:
+            fprintf(stdout, "dynamic\n");
+            break;
+          case NameLocation::Kind::Global:
+            fprintf(stdout, "global\n");
+            break;
+          case NameLocation::Kind::Intrinsic:
+            fprintf(stdout, "intrinsic\n");
+            break;
+          case NameLocation::Kind::NamedLambdaCallee:
+            fprintf(stdout, "named lambda callee\n");
+            break;
+          case NameLocation::Kind::Import:
+            fprintf(stdout, "import\n");
+            break;
+          case NameLocation::Kind::ArgumentSlot:
+            fprintf(stdout, "arg slot=%u\n", l.argumentSlot());
+            break;
+          case NameLocation::Kind::FrameSlot:
+            fprintf(stdout, "frame slot=%u\n", l.frameSlot());
+            break;
+          case NameLocation::Kind::EnvironmentCoordinate:
+            fprintf(stdout, "environment hops=%u slot=%u\n",
+                    l.environmentCoordinate().hops(), l.environmentCoordinate().slot());
+            break;
+          case NameLocation::Kind::DynamicAnnexBVar:
+            fprintf(stdout, "dynamic annex b var\n");
+            break;
+        }
+    }
+
+    fprintf(stdout, "\n");
+}
+
+template <typename ScopeCreator>
+bool
+BytecodeEmitter::EmitterScope::internScope(BytecodeEmitter* bce, ScopeCreator createScope)
+{
+    RootedScope enclosing(bce->cx, enclosingScope(bce));
+    Scope* scope = createScope(bce->cx, enclosing);
+    if (!scope)
+        return false;
+    hasEnvironment_ = scope->hasEnvironment();
+    scopeIndex_ = bce->scopeList.length();
+    return bce->scopeList.append(scope);
+}
+
+template <typename ScopeCreator>
+bool
+BytecodeEmitter::EmitterScope::internBodyScope(BytecodeEmitter* bce, ScopeCreator createScope)
+{
+    MOZ_ASSERT(bce->bodyScopeIndex == UINT32_MAX, "There can be only one body scope");
+    bce->bodyScopeIndex = bce->scopeList.length();
+    return internScope(bce, createScope);
+}
+
+bool
+BytecodeEmitter::EmitterScope::appendScopeNote(BytecodeEmitter* bce)
+{
+    MOZ_ASSERT(ScopeKindIsInBody(scope(bce)->kind()) && enclosingInFrame(),
+               "Scope notes are not needed for body-level scopes.");
+    noteIndex_ = bce->scopeNoteList.length();
+    return bce->scopeNoteList.append(index(), bce->offset(), bce->inPrologue(),
+                                     enclosingInFrame() ? enclosingInFrame()->noteIndex()
+                                                        : ScopeNote::NoScopeNoteIndex);
+}
+
+#ifdef DEBUG
+static bool
+NameIsOnEnvironment(Scope* scope, JSAtom* name)
+{
+    for (BindingIter bi(scope); bi; bi++) {
+        // If found, the name must already be on the environment or an import,
+        // or else there is a bug in the closed-over name analysis in the
+        // Parser.
+        if (bi.name() == name) {
+            BindingLocation::Kind kind = bi.location().kind();
+
+            if (bi.hasArgumentSlot()) {
+                JSScript* script = scope->as<FunctionScope>().script();
+                if (!script->strict() && !script->functionHasParameterExprs()) {
+                    // Check for duplicate positional formal parameters.
+                    for (BindingIter bi2(bi); bi2 && bi2.hasArgumentSlot(); bi2++) {
+                        if (bi2.name() == name)
+                            kind = bi2.location().kind();
+                    }
+                }
+            }
+
+            return kind == BindingLocation::Kind::Global ||
+                   kind == BindingLocation::Kind::Environment ||
+                   kind == BindingLocation::Kind::Import;
+        }
+    }
+
+    // If not found, assume it's on the global or dynamically accessed.
+    return true;
+}
+#endif
+
+/* static */ NameLocation
+BytecodeEmitter::EmitterScope::searchInEnclosingScope(JSAtom* name, Scope* scope, uint8_t hops)
+{
+    for (ScopeIter si(scope); si; si++) {
+        MOZ_ASSERT(NameIsOnEnvironment(si.scope(), name));
+
+        bool hasEnv = si.hasSyntacticEnvironment();
+
+        switch (si.kind()) {
+          case ScopeKind::Function:
+            if (hasEnv) {
+                JSScript* script = si.scope()->as<FunctionScope>().script();
+                if (script->funHasExtensibleScope())
+                    return NameLocation::Dynamic();
+
+                for (BindingIter bi(si.scope()); bi; bi++) {
+                    if (bi.name() != name)
+                        continue;
+
+                    BindingLocation bindLoc = bi.location();
+                    if (bi.hasArgumentSlot() &&
+                        !script->strict() &&
+                        !script->functionHasParameterExprs())
+                    {
+                        // Check for duplicate positional formal parameters.
+                        for (BindingIter bi2(bi); bi2 && bi2.hasArgumentSlot(); bi2++) {
+                            if (bi2.name() == name)
+                                bindLoc = bi2.location();
+                        }
+                    }
+
+                    MOZ_ASSERT(bindLoc.kind() == BindingLocation::Kind::Environment);
+                    return NameLocation::EnvironmentCoordinate(bi.kind(), hops, bindLoc.slot());
+                }
+            }
+            break;
+
+          case ScopeKind::FunctionBodyVar:
+          case ScopeKind::ParameterExpressionVar:
+          case ScopeKind::Lexical:
+          case ScopeKind::NamedLambda:
+          case ScopeKind::StrictNamedLambda:
+          case ScopeKind::SimpleCatch:
+          case ScopeKind::Catch:
+            if (hasEnv) {
+                for (BindingIter bi(si.scope()); bi; bi++) {
+                    if (bi.name() != name)
+                        continue;
+
+                    // The name must already have been marked as closed
+                    // over. If this assertion is hit, there is a bug in the
+                    // name analysis.
+                    BindingLocation bindLoc = bi.location();
+                    MOZ_ASSERT(bindLoc.kind() == BindingLocation::Kind::Environment);
+                    return NameLocation::EnvironmentCoordinate(bi.kind(), hops, bindLoc.slot());
+                }
+            }
+            break;
+
+          case ScopeKind::Module:
+            if (hasEnv) {
+                for (BindingIter bi(si.scope()); bi; bi++) {
+                    if (bi.name() != name)
+                        continue;
+
+                    BindingLocation bindLoc = bi.location();
+
+                    // Imports are on the environment but are indirect
+                    // bindings and must be accessed dynamically instead of
+                    // using an EnvironmentCoordinate.
+                    if (bindLoc.kind() == BindingLocation::Kind::Import) {
+                        MOZ_ASSERT(si.kind() == ScopeKind::Module);
+                        return NameLocation::Import();
+                    }
+
+                    MOZ_ASSERT(bindLoc.kind() == BindingLocation::Kind::Environment);
+                    return NameLocation::EnvironmentCoordinate(bi.kind(), hops, bindLoc.slot());
+                }
+            }
+            break;
+
+          case ScopeKind::Eval:
+          case ScopeKind::StrictEval:
+            // As an optimization, if the eval doesn't have its own var
+            // environment and its immediate enclosing scope is a global
+            // scope, all accesses are global.
+            if (!hasEnv && si.scope()->enclosing()->is<GlobalScope>())
+                return NameLocation::Global(BindingKind::Var);
+            return NameLocation::Dynamic();
+
+          case ScopeKind::Global:
+            return NameLocation::Global(BindingKind::Var);
+
+          case ScopeKind::With:
+          case ScopeKind::NonSyntactic:
+            return NameLocation::Dynamic();
+        }
+
+        if (hasEnv) {
+            MOZ_ASSERT(hops < ENVCOORD_HOPS_LIMIT - 1);
+            hops++;
+        }
+    }
+
+    MOZ_CRASH("Malformed scope chain");
+}
+
+NameLocation
+BytecodeEmitter::EmitterScope::searchAndCache(BytecodeEmitter* bce, JSAtom* name)
+{
+    Maybe<NameLocation> loc;
+    uint8_t hops = hasEnvironment() ? 1 : 0;
+    DebugOnly<bool> inCurrentScript = enclosingInFrame();
+
+    // Start searching in the current compilation.
+    for (EmitterScope* es = enclosing(&bce); es; es = es->enclosing(&bce)) {
+        loc = es->lookupInCache(bce, name);
+        if (loc) {
+            if (loc->kind() == NameLocation::Kind::EnvironmentCoordinate)
+                *loc = loc->addHops(hops);
+            break;
+        }
+
+        if (es->hasEnvironment())
+            hops++;
+
+#ifdef DEBUG
+        if (!es->enclosingInFrame())
+            inCurrentScript = false;
+#endif
+    }
+
+    // If the name is not found in the current compilation, walk the Scope
+    // chain encompassing the compilation.
+    if (!loc) {
+        inCurrentScript = false;
+        loc = Some(searchInEnclosingScope(name, bce->sc->compilationEnclosingScope(), hops));
+    }
+
+    // Each script has its own frame. A free name that is accessed
+    // from an inner script must not be a frame slot access. If this
+    // assertion is hit, it is a bug in the free name analysis in the
+    // parser.
+    MOZ_ASSERT_IF(!inCurrentScript, loc->kind() != NameLocation::Kind::FrameSlot);
+
+    // It is always correct to not cache the location. Ignore OOMs to make
+    // lookups infallible.
+    if (!putNameInCache(bce, name, *loc))
+        bce->cx->recoverFromOutOfMemory();
+
+    return *loc;
+}
+
+Maybe<NameLocation>
+BytecodeEmitter::EmitterScope::locationBoundInScope(BytecodeEmitter* bce, JSAtom* name,
+                                                    EmitterScope* target)
+{
+    // The target scope must be an intra-frame enclosing scope of this
+    // one. Count the number of extra hops to reach it.
+    uint8_t extraHops = 0;
+    for (EmitterScope* es = this; es != target; es = es->enclosingInFrame()) {
+        if (es->hasEnvironment())
+            extraHops++;
+    }
+
+    // Caches are prepopulated with bound names. So if the name is bound in a
+    // particular scope, it must already be in the cache. Furthermore, don't
+    // consult the fallback location as we only care about binding names.
+    Maybe<NameLocation> loc;
+    if (NameLocationMap::Ptr p = target->nameCache_->lookup(name)) {
+        NameLocation l = p->value().wrapped;
+        if (l.kind() == NameLocation::Kind::EnvironmentCoordinate)
+            loc = Some(l.addHops(extraHops));
+        else
+            loc = Some(l);
+    }
+    return loc;
+}
+
+bool
+BytecodeEmitter::EmitterScope::deadZoneFrameSlotRange(BytecodeEmitter* bce, uint32_t slotStart,
+                                                      uint32_t slotEnd)
+{
+    // Lexical bindings throw ReferenceErrors if they are used before
+    // initialization. See ES6 8.1.1.1.6.
+    //
+    // For completeness, lexical bindings are initialized in ES6 by calling
+    // InitializeBinding, after which touching the binding will no longer
+    // throw reference errors. See 13.1.11, 9.2.13, 13.6.3.4, 13.6.4.6,
+    // 13.6.4.8, 13.14.5, 15.1.8, and 15.2.0.15.
+    if (slotStart != slotEnd) {
+        if (!bce->emit1(JSOP_UNINITIALIZED))
+            return false;
+        for (uint32_t slot = slotStart; slot < slotEnd; slot++) {
+            if (!bce->emitLocalOp(JSOP_INITLEXICAL, slot))
+                return false;
+        }
+        if (!bce->emit1(JSOP_POP))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::EmitterScope::deadZoneFrameSlots(BytecodeEmitter* bce)
+{
+    return deadZoneFrameSlotRange(bce, frameSlotStart(), frameSlotEnd());
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterLexical(BytecodeEmitter* bce, ScopeKind kind,
+                                            Handle<LexicalScope::Data*> bindings)
+{
+    MOZ_ASSERT(kind != ScopeKind::NamedLambda && kind != ScopeKind::StrictNamedLambda);
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // Marks all names as closed over if the the context requires it. This
+    // cannot be done in the Parser as we may not know if the context requires
+    // all bindings to be closed over until after parsing is finished. For
+    // example, legacy generators require all bindings to be closed over but
+    // it is unknown if a function is a legacy generator until the first
+    // 'yield' expression is parsed.
+    //
+    // This is not a problem with other scopes, as all other scopes with
+    // bindings are body-level. At the time of their creation, whether or not
+    // the context requires all bindings to be closed over is already known.
+    if (bce->sc->allBindingsClosedOver())
+        MarkAllBindingsClosedOver(*bindings);
+
+    // Resolve bindings.
+    TDZCheckCache* tdzCache = bce->innermostTDZCheckCache;
+    uint32_t firstFrameSlot = frameSlotStart();
+    BindingIter bi(*bindings, firstFrameSlot, /* isNamedLambda = */ false);
+    for (; bi; bi++) {
+        if (!checkSlotLimits(bce, bi))
+            return false;
+
+        NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+        if (!putNameInCache(bce, bi.name(), loc))
+            return false;
+
+        if (!tdzCache->noteTDZCheck(bce, bi.name(), CheckTDZ))
+            return false;
+    }
+
+    updateFrameFixedSlots(bce, bi);
+
+    // Create and intern the VM scope.
+    auto createScope = [kind, bindings, firstFrameSlot](ExclusiveContext* cx,
+                                                        HandleScope enclosing)
+    {
+        return LexicalScope::create(cx, kind, bindings, firstFrameSlot, enclosing);
+    };
+    if (!internScope(bce, createScope))
+        return false;
+
+    if (ScopeKindIsInBody(kind) && hasEnvironment()) {
+        // After interning the VM scope we can get the scope index.
+        if (!bce->emitInternedScopeOp(index(), JSOP_PUSHLEXICALENV))
+            return false;
+    }
+
+    // Lexical scopes need notes to be mapped from a pc.
+    if (!appendScopeNote(bce))
+        return false;
+
+    // Put frame slots in TDZ. Environment slots are poisoned during
+    // environment creation.
+    //
+    // This must be done after appendScopeNote to be considered in the extent
+    // of the scope.
+    if (!deadZoneFrameSlotRange(bce, firstFrameSlot, frameSlotEnd()))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterNamedLambda(BytecodeEmitter* bce, FunctionBox* funbox)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+    MOZ_ASSERT(funbox->namedLambdaBindings());
+
+    if (!ensureCache(bce))
+        return false;
+
+    // See comment in enterLexical about allBindingsClosedOver.
+    if (funbox->allBindingsClosedOver())
+        MarkAllBindingsClosedOver(*funbox->namedLambdaBindings());
+
+    BindingIter bi(*funbox->namedLambdaBindings(), LOCALNO_LIMIT, /* isNamedLambda = */ true);
+    MOZ_ASSERT(bi.kind() == BindingKind::NamedLambdaCallee);
+
+    // The lambda name, if not closed over, is accessed via JSOP_CALLEE and
+    // not a frame slot. Do not update frame slot information.
+    NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+    if (!putNameInCache(bce, bi.name(), loc))
+        return false;
+
+    bi++;
+    MOZ_ASSERT(!bi, "There should be exactly one binding in a NamedLambda scope");
+
+    auto createScope = [funbox](ExclusiveContext* cx, HandleScope enclosing) {
+        ScopeKind scopeKind =
+            funbox->strict() ? ScopeKind::StrictNamedLambda : ScopeKind::NamedLambda;
+        return LexicalScope::create(cx, scopeKind, funbox->namedLambdaBindings(),
+                                    LOCALNO_LIMIT, enclosing);
+    };
+    if (!internScope(bce, createScope))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterComprehensionFor(BytecodeEmitter* bce,
+                                                     Handle<LexicalScope::Data*> bindings)
+{
+    if (!enterLexical(bce, ScopeKind::Lexical, bindings))
+        return false;
+
+    // For comprehensions, initialize all lexical names up front to undefined
+    // because they're now a dead feature and don't interact properly with
+    // TDZ.
+    auto nop = [](BytecodeEmitter*, const NameLocation&, bool) {
+        return true;
+    };
+
+    if (!bce->emit1(JSOP_UNDEFINED))
+        return false;
+
+    RootedAtom name(bce->cx);
+    for (BindingIter bi(*bindings, frameSlotStart(), /* isNamedLambda = */ false); bi; bi++) {
+        name = bi.name();
+        if (!bce->emitInitializeName(name, nop))
+            return false;
+    }
+
+    if (!bce->emit1(JSOP_POP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterParameterExpressionVar(BytecodeEmitter* bce)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // Parameter expressions var scopes have no pre-set bindings and are
+    // always extensible, as they are needed for eval.
+    fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    // Create and intern the VM scope.
+    uint32_t firstFrameSlot = frameSlotStart();
+    auto createScope = [firstFrameSlot](ExclusiveContext* cx, HandleScope enclosing) {
+        return VarScope::create(cx, ScopeKind::ParameterExpressionVar,
+                                /* data = */ nullptr, firstFrameSlot,
+                                /* needsEnvironment = */ true, enclosing);
+    };
+    if (!internScope(bce, createScope))
+        return false;
+
+    MOZ_ASSERT(hasEnvironment());
+    if (!bce->emitInternedScopeOp(index(), JSOP_PUSHVARENV))
+        return false;
+
+    // The extra var scope needs a note to be mapped from a pc.
+    if (!appendScopeNote(bce))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterFunction(BytecodeEmitter* bce, FunctionBox* funbox)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    // If there are parameter expressions, there is an extra var scope.
+    if (!funbox->hasExtraBodyVarScope())
+        bce->setVarEmitterScope(this);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // Resolve body-level bindings, if there are any.
+    auto bindings = funbox->functionScopeBindings();
+    Maybe<uint32_t> lastLexicalSlot;
+    if (bindings) {
+        NameLocationMap& cache = *nameCache_;
+
+        BindingIter bi(*bindings, funbox->hasParameterExprs);
+        for (; bi; bi++) {
+            if (!checkSlotLimits(bce, bi))
+                return false;
+
+            NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+            NameLocationMap::AddPtr p = cache.lookupForAdd(bi.name());
+
+            // The only duplicate bindings that occur are simple formal
+            // parameters, in which case the last position counts, so update the
+            // location.
+            if (p) {
+                MOZ_ASSERT(bi.kind() == BindingKind::FormalParameter);
+                MOZ_ASSERT(!funbox->hasDestructuringArgs);
+                MOZ_ASSERT(!funbox->function()->hasRest());
+                p->value() = loc;
+                continue;
+            }
+
+            if (!cache.add(p, bi.name(), loc)) {
+                ReportOutOfMemory(bce->cx);
+                return false;
+            }
+        }
+
+        updateFrameFixedSlots(bce, bi);
+    } else {
+        nextFrameSlot_ = 0;
+    }
+
+    // If the function's scope may be extended at runtime due to sloppy direct
+    // eval and there is no extra var scope, any names beyond the function
+    // scope must be accessed dynamically as we don't know if the name will
+    // become a 'var' binding due to direct eval.
+    if (!funbox->hasParameterExprs && funbox->hasExtensibleScope())
+        fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    // In case of parameter expressions, the parameters are lexical
+    // bindings and have TDZ.
+    if (funbox->hasParameterExprs && nextFrameSlot_) {
+        uint32_t paramFrameSlotEnd = 0;
+        for (BindingIter bi(*bindings, true); bi; bi++) {
+            if (!BindingKindIsLexical(bi.kind()))
+                break;
+
+            NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+            if (loc.kind() == NameLocation::Kind::FrameSlot) {
+                MOZ_ASSERT(paramFrameSlotEnd <= loc.frameSlot());
+                paramFrameSlotEnd = loc.frameSlot() + 1;
+            }
+        }
+
+        if (!deadZoneFrameSlotRange(bce, 0, paramFrameSlotEnd))
+            return false;
+    }
+
+    // Create and intern the VM scope.
+    auto createScope = [funbox](ExclusiveContext* cx, HandleScope enclosing) {
+        RootedFunction fun(cx, funbox->function());
+        return FunctionScope::create(cx, funbox->functionScopeBindings(),
+                                     funbox->hasParameterExprs,
+                                     funbox->needsCallObjectRegardlessOfBindings(),
+                                     fun, enclosing);
+    };
+    if (!internBodyScope(bce, createScope))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterFunctionExtraBodyVar(BytecodeEmitter* bce, FunctionBox* funbox)
+{
+    MOZ_ASSERT(funbox->hasParameterExprs);
+    MOZ_ASSERT(funbox->extraVarScopeBindings() ||
+               funbox->needsExtraBodyVarEnvironmentRegardlessOfBindings());
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    // The extra var scope is never popped once it's entered. It replaces the
+    // function scope as the var emitter scope.
+    bce->setVarEmitterScope(this);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // Resolve body-level bindings, if there are any.
+    uint32_t firstFrameSlot = frameSlotStart();
+    if (auto bindings = funbox->extraVarScopeBindings()) {
+        BindingIter bi(*bindings, firstFrameSlot);
+        for (; bi; bi++) {
+            if (!checkSlotLimits(bce, bi))
+                return false;
+
+            NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+            if (!putNameInCache(bce, bi.name(), loc))
+                return false;
+        }
+
+        updateFrameFixedSlots(bce, bi);
+    } else {
+        nextFrameSlot_ = firstFrameSlot;
+    }
+
+    // If the extra var scope may be extended at runtime due to sloppy
+    // direct eval, any names beyond the var scope must be accessed
+    // dynamically as we don't know if the name will become a 'var' binding
+    // due to direct eval.
+    if (funbox->hasExtensibleScope())
+        fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    // Create and intern the VM scope.
+    auto createScope = [funbox, firstFrameSlot](ExclusiveContext* cx, HandleScope enclosing) {
+        return VarScope::create(cx, ScopeKind::FunctionBodyVar,
+                                funbox->extraVarScopeBindings(), firstFrameSlot,
+                                funbox->needsExtraBodyVarEnvironmentRegardlessOfBindings(),
+                                enclosing);
+    };
+    if (!internScope(bce, createScope))
+        return false;
+
+    if (hasEnvironment()) {
+        if (!bce->emitInternedScopeOp(index(), JSOP_PUSHVARENV))
+            return false;
+    }
+
+    // The extra var scope needs a note to be mapped from a pc.
+    if (!appendScopeNote(bce))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+class DynamicBindingIter : public BindingIter
+{
+  public:
+    explicit DynamicBindingIter(GlobalSharedContext* sc)
+      : BindingIter(*sc->bindings)
+    { }
+
+    explicit DynamicBindingIter(EvalSharedContext* sc)
+      : BindingIter(*sc->bindings, /* strict = */ false)
+    {
+        MOZ_ASSERT(!sc->strict());
+    }
+
+    JSOp bindingOp() const {
+        switch (kind()) {
+          case BindingKind::Var:
+            return JSOP_DEFVAR;
+          case BindingKind::Let:
+            return JSOP_DEFLET;
+          case BindingKind::Const:
+            return JSOP_DEFCONST;
+          default:
+            MOZ_CRASH("Bad BindingKind");
+        }
+    }
+};
+
+bool
+BytecodeEmitter::EmitterScope::enterGlobal(BytecodeEmitter* bce, GlobalSharedContext* globalsc)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    bce->setVarEmitterScope(this);
+
+    if (!ensureCache(bce))
+        return false;
+
+    if (bce->emitterMode == BytecodeEmitter::SelfHosting) {
+        // In self-hosting, it is incorrect to consult the global scope because
+        // self-hosted scripts are cloned into their target compartments before
+        // they are run. Instead of Global, Intrinsic is used for all names.
+        //
+        // Intrinsic lookups are redirected to the special intrinsics holder
+        // in the global object, into which any missing values are cloned
+        // lazily upon first access.
+        fallbackFreeNameLocation_ = Some(NameLocation::Intrinsic());
+
+        auto createScope = [](ExclusiveContext* cx, HandleScope enclosing) {
+            MOZ_ASSERT(!enclosing);
+            return &cx->global()->emptyGlobalScope();
+        };
+        return internBodyScope(bce, createScope);
+    }
+
+    // Resolve binding names and emit DEF{VAR,LET,CONST} prologue ops.
+    if (globalsc->bindings) {
+        for (DynamicBindingIter bi(globalsc); bi; bi++) {
+            NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+            JSAtom* name = bi.name();
+            if (!putNameInCache(bce, name, loc))
+                return false;
+
+            // Define the name in the prologue. Do not emit DEFVAR for
+            // functions that we'll emit DEFFUN for.
+            if (bi.isTopLevelFunction())
+                continue;
+
+            if (!bce->emitAtomOp(name, bi.bindingOp()))
+                return false;
+        }
+    }
+
+    // Note that to save space, we don't add free names to the cache for
+    // global scopes. They are assumed to be global vars in the syntactic
+    // global scope, dynamic accesses under non-syntactic global scope.
+    if (globalsc->scopeKind() == ScopeKind::Global)
+        fallbackFreeNameLocation_ = Some(NameLocation::Global(BindingKind::Var));
+    else
+        fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    auto createScope = [globalsc](ExclusiveContext* cx, HandleScope enclosing) {
+        MOZ_ASSERT(!enclosing);
+        return GlobalScope::create(cx, globalsc->scopeKind(), globalsc->bindings);
+    };
+    return internBodyScope(bce, createScope);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterEval(BytecodeEmitter* bce, EvalSharedContext* evalsc)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    bce->setVarEmitterScope(this);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // For simplicity, treat all free name lookups in eval scripts as dynamic.
+    fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    // Create the `var` scope. Note that there is also a lexical scope, created
+    // separately in emitScript().
+    auto createScope = [evalsc](ExclusiveContext* cx, HandleScope enclosing) {
+        ScopeKind scopeKind = evalsc->strict() ? ScopeKind::StrictEval : ScopeKind::Eval;
+        return EvalScope::create(cx, scopeKind, evalsc->bindings, enclosing);
+    };
+    if (!internBodyScope(bce, createScope))
+        return false;
+
+    if (hasEnvironment()) {
+        if (!bce->emitInternedScopeOp(index(), JSOP_PUSHVARENV))
+            return false;
+    } else {
+        // Resolve binding names and emit DEFVAR prologue ops if we don't have
+        // an environment (i.e., a sloppy eval not in a parameter expression).
+        // Eval scripts always have their own lexical scope, but non-strict
+        // scopes may introduce 'var' bindings to the nearest var scope.
+        //
+        // TODO: We may optimize strict eval bindings in the future to be on
+        // the frame. For now, handle everything dynamically.
+        if (!hasEnvironment() && evalsc->bindings) {
+            for (DynamicBindingIter bi(evalsc); bi; bi++) {
+                MOZ_ASSERT(bi.bindingOp() == JSOP_DEFVAR);
+
+                if (bi.isTopLevelFunction())
+                    continue;
+
+                if (!bce->emitAtomOp(bi.name(), JSOP_DEFVAR))
+                    return false;
+            }
+        }
+
+        // As an optimization, if the eval does not have its own var
+        // environment and is directly enclosed in a global scope, then all
+        // free name lookups are global.
+        if (scope(bce)->enclosing()->is<GlobalScope>())
+            fallbackFreeNameLocation_ = Some(NameLocation::Global(BindingKind::Var));
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterModule(BytecodeEmitter* bce, ModuleSharedContext* modulesc)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    bce->setVarEmitterScope(this);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // Resolve body-level bindings, if there are any.
+    TDZCheckCache* tdzCache = bce->innermostTDZCheckCache;
+    Maybe<uint32_t> firstLexicalFrameSlot;
+    if (ModuleScope::Data* bindings = modulesc->bindings) {
+        BindingIter bi(*bindings);
+        for (; bi; bi++) {
+            if (!checkSlotLimits(bce, bi))
+                return false;
+
+            NameLocation loc = NameLocation::fromBinding(bi.kind(), bi.location());
+            if (!putNameInCache(bce, bi.name(), loc))
+                return false;
+
+            if (BindingKindIsLexical(bi.kind())) {
+                if (loc.kind() == NameLocation::Kind::FrameSlot && !firstLexicalFrameSlot)
+                    firstLexicalFrameSlot = Some(loc.frameSlot());
+
+                if (!tdzCache->noteTDZCheck(bce, bi.name(), CheckTDZ))
+                    return false;
+            }
+        }
+
+        updateFrameFixedSlots(bce, bi);
+    } else {
+        nextFrameSlot_ = 0;
+    }
+
+    // Modules are toplevel, so any free names are global.
+    fallbackFreeNameLocation_ = Some(NameLocation::Global(BindingKind::Var));
+
+    // Put lexical frame slots in TDZ. Environment slots are poisoned during
+    // environment creation.
+    if (firstLexicalFrameSlot) {
+        if (!deadZoneFrameSlotRange(bce, *firstLexicalFrameSlot, frameSlotEnd()))
+            return false;
+    }
+
+    // Create and intern the VM scope.
+    auto createScope = [modulesc](ExclusiveContext* cx, HandleScope enclosing) {
+        return ModuleScope::create(cx, modulesc->bindings, modulesc->module(), enclosing);
+    };
+    if (!internBodyScope(bce, createScope))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::enterWith(BytecodeEmitter* bce)
+{
+    MOZ_ASSERT(this == bce->innermostEmitterScope);
+
+    if (!ensureCache(bce))
+        return false;
+
+    // 'with' make all accesses dynamic and unanalyzable.
+    fallbackFreeNameLocation_ = Some(NameLocation::Dynamic());
+
+    auto createScope = [](ExclusiveContext* cx, HandleScope enclosing) {
+        return WithScope::create(cx, enclosing);
+    };
+    if (!internScope(bce, createScope))
+        return false;
+
+    if (!bce->emitInternedScopeOp(index(), JSOP_ENTERWITH))
+        return false;
+
+    if (!appendScopeNote(bce))
+        return false;
+
+    return checkEnvironmentChainLength(bce);
+}
+
+bool
+BytecodeEmitter::EmitterScope::leave(BytecodeEmitter* bce, bool nonLocal)
+{
+    // If we aren't leaving the scope due to a non-local jump (e.g., break),
+    // we must be the innermost scope.
+    MOZ_ASSERT_IF(!nonLocal, this == bce->innermostEmitterScope);
+
+    ScopeKind kind = scope(bce)->kind();
+    switch (kind) {
+      case ScopeKind::Lexical:
+      case ScopeKind::SimpleCatch:
+      case ScopeKind::Catch:
+        if (!bce->emit1(hasEnvironment() ? JSOP_POPLEXICALENV : JSOP_DEBUGLEAVELEXICALENV))
+            return false;
+        break;
+
+      case ScopeKind::With:
+        if (!bce->emit1(JSOP_LEAVEWITH))
+            return false;
+        break;
+
+      case ScopeKind::ParameterExpressionVar:
+        MOZ_ASSERT(hasEnvironment());
+        if (!bce->emit1(JSOP_POPVARENV))
+            return false;
+        break;
+
+      case ScopeKind::Function:
+      case ScopeKind::FunctionBodyVar:
+      case ScopeKind::NamedLambda:
+      case ScopeKind::StrictNamedLambda:
+      case ScopeKind::Eval:
+      case ScopeKind::StrictEval:
+      case ScopeKind::Global:
+      case ScopeKind::NonSyntactic:
+      case ScopeKind::Module:
+        break;
+    }
+
+    // Finish up the scope if we are leaving it in LIFO fashion.
+    if (!nonLocal) {
+        // Popping scopes due to non-local jumps generate additional scope
+        // notes. See NonLocalExitControl::prepareForNonLocalJump.
+        if (ScopeKindIsInBody(kind)) {
+            // The extra function var scope is never popped once it's pushed,
+            // so its scope note extends until the end of any possible code.
+            uint32_t offset = kind == ScopeKind::FunctionBodyVar ? UINT32_MAX : bce->offset();
+            bce->scopeNoteList.recordEnd(noteIndex_, offset, bce->inPrologue());
+        }
+    }
+
+    return true;
+}
+
+Maybe<MaybeCheckTDZ>
+BytecodeEmitter::TDZCheckCache::needsTDZCheck(BytecodeEmitter* bce, JSAtom* name)
+{
+    if (!ensureCache(bce))
+        return Nothing();
+
+    CheckTDZMap::AddPtr p = cache_->lookupForAdd(name);
+    if (p)
+        return Some(p->value().wrapped);
+
+    MaybeCheckTDZ rv = CheckTDZ;
+    for (TDZCheckCache* it = enclosing(); it; it = it->enclosing()) {
+        if (it->cache_) {
+            if (CheckTDZMap::Ptr p2 = it->cache_->lookup(name)) {
+                rv = p2->value();
+                break;
+            }
+        }
+    }
+
+    if (!cache_->add(p, name, rv)) {
+        ReportOutOfMemory(bce->cx);
+        return Nothing();
+    }
+
+    return Some(rv);
+}
+
+bool
+BytecodeEmitter::TDZCheckCache::noteTDZCheck(BytecodeEmitter* bce, JSAtom* name,
+                                             MaybeCheckTDZ check)
+{
+    if (!ensureCache(bce))
+        return false;
+
+    CheckTDZMap::AddPtr p = cache_->lookupForAdd(name);
+    if (p) {
+        MOZ_ASSERT(!check, "TDZ only needs to be checked once per binding per basic block.");
+        p->value() = check;
+    } else {
+        if (!cache_->add(p, name, check))
+            return false;
+    }
+
+    return true;
+}
+
+BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
+                                 Parser<FullParseHandler>* parser, SharedContext* sc,
+                                 HandleScript script, Handle<LazyScript*> lazyScript,
+                                 uint32_t lineNum, EmitterMode emitterMode)
+  : sc(sc),
+    cx(sc->context),
+    parent(parent),
+    script(cx, script),
+    lazyScript(cx, lazyScript),
+    prologue(cx, lineNum),
+    main(cx, lineNum),
+    current(&main),
+    parser(parser),
+    atomIndices(cx->frontendCollectionPool()),
+    firstLine(lineNum),
+    maxFixedSlots(0),
+    maxStackDepth(0),
+    stackDepth(0),
+    arrayCompDepth(0),
+    emitLevel(0),
+    bodyScopeIndex(UINT32_MAX),
+    varEmitterScope(nullptr),
+    innermostNestableControl(nullptr),
+    innermostEmitterScope(nullptr),
+    innermostTDZCheckCache(nullptr),
+    constList(cx),
+    scopeList(cx),
+    tryNoteList(cx),
+    scopeNoteList(cx),
+    yieldOffsetList(cx),
+    typesetCount(0),
+    hasSingletons(false),
+    hasTryFinally(false),
+    emittingRunOnceLambda(false),
+    emitterMode(emitterMode),
+    functionBodyEndPosSet(false)
+{
+    MOZ_ASSERT_IF(emitterMode == LazyFunction, lazyScript);
+}
+
+BytecodeEmitter::BytecodeEmitter(BytecodeEmitter* parent,
+                                 Parser<FullParseHandler>* parser, SharedContext* sc,
+                                 HandleScript script, Handle<LazyScript*> lazyScript,
+                                 TokenPos bodyPosition, EmitterMode emitterMode)
+    : BytecodeEmitter(parent, parser, sc, script, lazyScript,
+                      parser->tokenStream.srcCoords.lineNum(bodyPosition.begin),
+                      emitterMode)
+{
+    setFunctionBodyEndPos(bodyPosition);
+}
+
+bool
+BytecodeEmitter::init()
+{
+    return atomIndices.acquire(cx);
+}
+
+template <typename Predicate /* (NestableControl*) -> bool */>
+BytecodeEmitter::NestableControl*
+BytecodeEmitter::findInnermostNestableControl(Predicate predicate) const
+{
+    return NestableControl::findNearest(innermostNestableControl, predicate);
+}
+
+template <typename T>
+T*
+BytecodeEmitter::findInnermostNestableControl() const
+{
+    return NestableControl::findNearest<T>(innermostNestableControl);
+}
+
+template <typename T, typename Predicate /* (T*) -> bool */>
+T*
+BytecodeEmitter::findInnermostNestableControl(Predicate predicate) const
+{
+    return NestableControl::findNearest<T>(innermostNestableControl, predicate);
+}
+
+NameLocation
+BytecodeEmitter::lookupName(JSAtom* name)
+{
+    return innermostEmitterScope->lookup(this, name);
+}
+
+Maybe<NameLocation>
+BytecodeEmitter::locationOfNameBoundInScope(JSAtom* name, EmitterScope* target)
+{
+    return innermostEmitterScope->locationBoundInScope(this, name, target);
+}
+
+Maybe<NameLocation>
+BytecodeEmitter::locationOfNameBoundInFunctionScope(JSAtom* name, EmitterScope* source)
+{
+    EmitterScope* funScope = source;
+    while (!funScope->scope(this)->is<FunctionScope>())
+        funScope = funScope->enclosingInFrame();
+    return source->locationBoundInScope(this, name, funScope);
+}
+
+bool
+BytecodeEmitter::emitCheck(ptrdiff_t delta, ptrdiff_t* offset)
+{
+    *offset = code().length();
+
+    // Start it off moderately large to avoid repeated resizings early on.
+    // ~98% of cases fit within 1024 bytes.
+    if (code().capacity() == 0 && !code().reserve(1024))
+        return false;
+
+    if (!code().growBy(delta)) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+    return true;
+}
+
+void
+BytecodeEmitter::updateDepth(ptrdiff_t target)
+{
+    jsbytecode* pc = code(target);
+
+    int nuses = StackUses(nullptr, pc);
+    int ndefs = StackDefs(nullptr, pc);
+
+    stackDepth -= nuses;
+    MOZ_ASSERT(stackDepth >= 0);
+    stackDepth += ndefs;
+
+    if ((uint32_t)stackDepth > maxStackDepth)
+        maxStackDepth = stackDepth;
+}
+
+#ifdef DEBUG
+bool
+BytecodeEmitter::checkStrictOrSloppy(JSOp op)
+{
+    if (IsCheckStrictOp(op) && !sc->strict())
+        return false;
+    if (IsCheckSloppyOp(op) && sc->strict())
+        return false;
+    return true;
+}
+#endif
+
+bool
+BytecodeEmitter::emit1(JSOp op)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+
+    ptrdiff_t offset;
+    if (!emitCheck(1, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emit2(JSOp op, uint8_t op1)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+
+    ptrdiff_t offset;
+    if (!emitCheck(2, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    code[1] = jsbytecode(op1);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emit3(JSOp op, jsbytecode op1, jsbytecode op2)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+
+    /* These should filter through emitVarOp. */
+    MOZ_ASSERT(!IsArgOp(op));
+    MOZ_ASSERT(!IsLocalOp(op));
+
+    ptrdiff_t offset;
+    if (!emitCheck(3, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    code[1] = op1;
+    code[2] = op2;
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitN(JSOp op, size_t extra, ptrdiff_t* offset)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+    ptrdiff_t length = 1 + ptrdiff_t(extra);
+
+    ptrdiff_t off;
+    if (!emitCheck(length, &off))
+        return false;
+
+    jsbytecode* code = this->code(off);
+    code[0] = jsbytecode(op);
+    /* The remaining |extra| bytes are set by the caller */
+
+    /*
+     * Don't updateDepth if op's use-count comes from the immediate
+     * operand yet to be stored in the extra bytes after op.
+     */
+    if (CodeSpec[op].nuses >= 0)
+        updateDepth(off);
+
+    if (offset)
+        *offset = off;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitJumpTarget(JumpTarget* target)
+{
+    ptrdiff_t off = offset();
+
+    // Alias consecutive jump targets.
+    if (off == current->lastTarget.offset + ptrdiff_t(JSOP_JUMPTARGET_LENGTH)) {
+        target->offset = current->lastTarget.offset;
+        return true;
+    }
+
+    target->offset = off;
+    current->lastTarget.offset = off;
+    if (!emit1(JSOP_JUMPTARGET))
+        return false;
+    return true;
+}
+
+void
+JumpList::push(jsbytecode* code, ptrdiff_t jumpOffset)
+{
+    SET_JUMP_OFFSET(&code[jumpOffset], offset - jumpOffset);
+    offset = jumpOffset;
+}
+
+void
+JumpList::patchAll(jsbytecode* code, JumpTarget target)
+{
+    ptrdiff_t delta;
+    for (ptrdiff_t jumpOffset = offset; jumpOffset != -1; jumpOffset += delta) {
+        jsbytecode* pc = &code[jumpOffset];
+        MOZ_ASSERT(IsJumpOpcode(JSOp(*pc)) || JSOp(*pc) == JSOP_LABEL);
+        delta = GET_JUMP_OFFSET(pc);
+        MOZ_ASSERT(delta < 0);
+        ptrdiff_t span = target.offset - jumpOffset;
+        SET_JUMP_OFFSET(pc, span);
+    }
+}
+
+bool
+BytecodeEmitter::emitJumpNoFallthrough(JSOp op, JumpList* jump)
+{
+    ptrdiff_t offset;
+    if (!emitCheck(5, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    MOZ_ASSERT(-1 <= jump->offset && jump->offset < offset);
+    jump->push(this->code(0), offset);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitJump(JSOp op, JumpList* jump)
+{
+    if (!emitJumpNoFallthrough(op, jump))
+        return false;
+    if (BytecodeFallsThrough(op)) {
+        JumpTarget fallthrough;
+        if (!emitJumpTarget(&fallthrough))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitBackwardJump(JSOp op, JumpTarget target, JumpList* jump, JumpTarget* fallthrough)
+{
+    if (!emitJumpNoFallthrough(op, jump))
+        return false;
+    patchJumpsToTarget(*jump, target);
+
+    // Unconditionally create a fallthrough for closing iterators, and as a
+    // target for break statements.
+    if (!emitJumpTarget(fallthrough))
+        return false;
+    return true;
+}
+
+void
+BytecodeEmitter::patchJumpsToTarget(JumpList jump, JumpTarget target)
+{
+    MOZ_ASSERT(-1 <= jump.offset && jump.offset <= offset());
+    MOZ_ASSERT(0 <= target.offset && target.offset <= offset());
+    MOZ_ASSERT_IF(jump.offset != -1 && target.offset + 4 <= offset(),
+                  BytecodeIsJumpTarget(JSOp(*code(target.offset))));
+    jump.patchAll(code(0), target);
+}
+
+bool
+BytecodeEmitter::emitJumpTargetAndPatch(JumpList jump)
+{
+    if (jump.offset == -1)
+        return true;
+    JumpTarget target;
+    if (!emitJumpTarget(&target))
+        return false;
+    patchJumpsToTarget(jump, target);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitCall(JSOp op, uint16_t argc, ParseNode* pn)
+{
+    if (pn && !updateSourceCoordNotes(pn->pn_pos.begin))
+        return false;
+    return emit3(op, ARGC_HI(argc), ARGC_LO(argc));
+}
+
+bool
+BytecodeEmitter::emitDupAt(unsigned slotFromTop)
+{
+    MOZ_ASSERT(slotFromTop < unsigned(stackDepth));
+
+    if (slotFromTop >= JS_BIT(24)) {
+        reportError(nullptr, JSMSG_TOO_MANY_LOCALS);
+        return false;
+    }
+
+    ptrdiff_t off;
+    if (!emitN(JSOP_DUPAT, 3, &off))
+        return false;
+
+    jsbytecode* pc = code(off);
+    SET_UINT24(pc, slotFromTop);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitCheckIsObj(CheckIsObjectKind kind)
+{
+    return emit2(JSOP_CHECKISOBJ, uint8_t(kind));
+}
+
+static inline unsigned
+LengthOfSetLine(unsigned line)
+{
+    return 1 /* SN_SETLINE */ + (line > SN_4BYTE_OFFSET_MASK ? 4 : 1);
+}
+
+/* Updates line number notes, not column notes. */
+bool
+BytecodeEmitter::updateLineNumberNotes(uint32_t offset)
+{
+    TokenStream* ts = &parser->tokenStream;
+    bool onThisLine;
+    if (!ts->srcCoords.isOnThisLine(offset, currentLine(), &onThisLine))
+        return ts->reportError(JSMSG_OUT_OF_MEMORY);
+    if (!onThisLine) {
+        unsigned line = ts->srcCoords.lineNum(offset);
+        unsigned delta = line - currentLine();
+
+        /*
+         * Encode any change in the current source line number by using
+         * either several SRC_NEWLINE notes or just one SRC_SETLINE note,
+         * whichever consumes less space.
+         *
+         * NB: We handle backward line number deltas (possible with for
+         * loops where the update part is emitted after the body, but its
+         * line number is <= any line number in the body) here by letting
+         * unsigned delta_ wrap to a very large number, which triggers a
+         * SRC_SETLINE.
+         */
+        current->currentLine = line;
+        current->lastColumn  = 0;
+        if (delta >= LengthOfSetLine(line)) {
+            if (!newSrcNote2(SRC_SETLINE, ptrdiff_t(line)))
+                return false;
+        } else {
+            do {
+                if (!newSrcNote(SRC_NEWLINE))
+                    return false;
+            } while (--delta != 0);
+        }
+    }
+    return true;
+}
+
+/* Updates the line number and column number information in the source notes. */
+bool
+BytecodeEmitter::updateSourceCoordNotes(uint32_t offset)
+{
+    if (!updateLineNumberNotes(offset))
+        return false;
+
+    uint32_t columnIndex = parser->tokenStream.srcCoords.columnIndex(offset);
+    ptrdiff_t colspan = ptrdiff_t(columnIndex) - ptrdiff_t(current->lastColumn);
+    if (colspan != 0) {
+        // If the column span is so large that we can't store it, then just
+        // discard this information. This can happen with minimized or otherwise
+        // machine-generated code. Even gigantic column numbers are still
+        // valuable if you have a source map to relate them to something real;
+        // but it's better to fail soft here.
+        if (!SN_REPRESENTABLE_COLSPAN(colspan))
+            return true;
+        if (!newSrcNote2(SRC_COLSPAN, SN_COLSPAN_TO_OFFSET(colspan)))
+            return false;
+        current->lastColumn = columnIndex;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitLoopHead(ParseNode* nextpn, JumpTarget* top)
+{
+    if (nextpn) {
+        /*
+         * Try to give the JSOP_LOOPHEAD the same line number as the next
+         * instruction. nextpn is often a block, in which case the next
+         * instruction typically comes from the first statement inside.
+         */
+        if (nextpn->isKind(PNK_LEXICALSCOPE))
+            nextpn = nextpn->scopeBody();
+        MOZ_ASSERT_IF(nextpn->isKind(PNK_STATEMENTLIST), nextpn->isArity(PN_LIST));
+        if (nextpn->isKind(PNK_STATEMENTLIST) && nextpn->pn_head)
+            nextpn = nextpn->pn_head;
+        if (!updateSourceCoordNotes(nextpn->pn_pos.begin))
+            return false;
+    }
+
+    *top = { offset() };
+    return emit1(JSOP_LOOPHEAD);
+}
+
+bool
+BytecodeEmitter::emitLoopEntry(ParseNode* nextpn, JumpList entryJump)
+{
+    if (nextpn) {
+        /* Update the line number, as for LOOPHEAD. */
+        if (nextpn->isKind(PNK_LEXICALSCOPE))
+            nextpn = nextpn->scopeBody();
+        MOZ_ASSERT_IF(nextpn->isKind(PNK_STATEMENTLIST), nextpn->isArity(PN_LIST));
+        if (nextpn->isKind(PNK_STATEMENTLIST) && nextpn->pn_head)
+            nextpn = nextpn->pn_head;
+        if (!updateSourceCoordNotes(nextpn->pn_pos.begin))
+            return false;
+    }
+
+    JumpTarget entry{ offset() };
+    patchJumpsToTarget(entryJump, entry);
+
+    LoopControl& loopInfo = innermostNestableControl->as<LoopControl>();
+    MOZ_ASSERT(loopInfo.loopDepth() > 0);
+
+    uint8_t loopDepthAndFlags = PackLoopEntryDepthHintAndFlags(loopInfo.loopDepth(),
+                                                               loopInfo.canIonOsr());
+    return emit2(JSOP_LOOPENTRY, loopDepthAndFlags);
+}
+
+void
+BytecodeEmitter::checkTypeSet(JSOp op)
+{
+    if (CodeSpec[op].format & JOF_TYPESET) {
+        if (typesetCount < UINT16_MAX)
+            typesetCount++;
+    }
+}
+
+bool
+BytecodeEmitter::emitUint16Operand(JSOp op, uint32_t operand)
+{
+    MOZ_ASSERT(operand <= UINT16_MAX);
+    if (!emit3(op, UINT16_HI(operand), UINT16_LO(operand)))
+        return false;
+    checkTypeSet(op);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitUint32Operand(JSOp op, uint32_t operand)
+{
+    ptrdiff_t off;
+    if (!emitN(op, 4, &off))
+        return false;
+    SET_UINT32(code(off), operand);
+    checkTypeSet(op);
+    return true;
+}
+
+bool
+BytecodeEmitter::flushPops(int* npops)
+{
+    MOZ_ASSERT(*npops != 0);
+    if (!emitUint16Operand(JSOP_POPN, *npops))
+        return false;
+
+    *npops = 0;
+    return true;
+}
+
+namespace {
+
+class NonLocalExitControl {
+    BytecodeEmitter* bce_;
+    const uint32_t savedScopeNoteIndex_;
+    const int savedDepth_;
+    uint32_t openScopeNoteIndex_;
+
+    NonLocalExitControl(const NonLocalExitControl&) = delete;
+
+    MOZ_MUST_USE bool leaveScope(BytecodeEmitter::EmitterScope* scope);
+
+  public:
+    explicit NonLocalExitControl(BytecodeEmitter* bce)
+      : bce_(bce),
+        savedScopeNoteIndex_(bce->scopeNoteList.length()),
+        savedDepth_(bce->stackDepth),
+        openScopeNoteIndex_(bce->innermostEmitterScope->noteIndex())
+    { }
+
+    ~NonLocalExitControl() {
+        for (uint32_t n = savedScopeNoteIndex_; n < bce_->scopeNoteList.length(); n++)
+            bce_->scopeNoteList.recordEnd(n, bce_->offset(), bce_->inPrologue());
+        bce_->stackDepth = savedDepth_;
+    }
+
+    MOZ_MUST_USE bool prepareForNonLocalJump(BytecodeEmitter::NestableControl* target);
+
+    MOZ_MUST_USE bool prepareForNonLocalJumpToOutermost() {
+        return prepareForNonLocalJump(nullptr);
+    }
+};
+
+bool
+NonLocalExitControl::leaveScope(BytecodeEmitter::EmitterScope* es)
+{
+    if (!es->leave(bce_, /* nonLocal = */ true))
+        return false;
+
+    // As we pop each scope due to the non-local jump, emit notes that
+    // record the extent of the enclosing scope. These notes will have
+    // their ends recorded in ~NonLocalExitControl().
+    uint32_t enclosingScopeIndex = ScopeNote::NoScopeIndex;
+    if (es->enclosingInFrame())
+        enclosingScopeIndex = es->enclosingInFrame()->index();
+    if (!bce_->scopeNoteList.append(enclosingScopeIndex, bce_->offset(), bce_->inPrologue(),
+                                    openScopeNoteIndex_))
+        return false;
+    openScopeNoteIndex_ = bce_->scopeNoteList.length() - 1;
+
+    return true;
+}
+
+/*
+ * Emit additional bytecode(s) for non-local jumps.
+ */
+bool
+NonLocalExitControl::prepareForNonLocalJump(BytecodeEmitter::NestableControl* target)
+{
+    using NestableControl = BytecodeEmitter::NestableControl;
+    using EmitterScope = BytecodeEmitter::EmitterScope;
+
+    EmitterScope* es = bce_->innermostEmitterScope;
+    int npops = 0;
+
+    auto flushPops = [&npops](BytecodeEmitter* bce) {
+        if (npops && !bce->flushPops(&npops))
+            return false;
+        return true;
+    };
+
+    // Walk the nestable control stack and patch jumps.
+    for (NestableControl* control = bce_->innermostNestableControl;
+         control != target;
+         control = control->enclosing())
+    {
+        // Walk the scope stack and leave the scopes we entered. Leaving a scope
+        // may emit administrative ops like JSOP_POPLEXICALENV but never anything
+        // that manipulates the stack.
+        for (; es != control->emitterScope(); es = es->enclosingInFrame()) {
+            if (!leaveScope(es))
+                return false;
+        }
+
+        switch (control->kind()) {
+          case StatementKind::Finally: {
+            TryFinallyControl& finallyControl = control->as<TryFinallyControl>();
+            if (finallyControl.emittingSubroutine()) {
+                /*
+                 * There's a [exception or hole, retsub pc-index] pair and the
+                 * possible return value on the stack that we need to pop.
+                 */
+                npops += 3;
+            } else {
+                if (!flushPops(bce_))
+                    return false;
+                if (!bce_->emitJump(JSOP_GOSUB, &finallyControl.gosubs))
+                    return false;
+            }
+            break;
+          }
+
+          case StatementKind::ForOfLoop:
+            npops += 2;
+            break;
+
+          case StatementKind::ForInLoop:
+            /* The iterator and the current value are on the stack. */
+            npops += 1;
+            if (!flushPops(bce_))
+                return false;
+            if (!bce_->emit1(JSOP_ENDITER))
+                return false;
+            break;
+
+          default:
+            break;
+        }
+    }
+
+    EmitterScope* targetEmitterScope = target ? target->emitterScope() : bce_->varEmitterScope;
+    for (; es != targetEmitterScope; es = es->enclosingInFrame()) {
+        if (!leaveScope(es))
+            return false;
+    }
+
+    return flushPops(bce_);
+}
+
+}  // anonymous namespace
+
+bool
+BytecodeEmitter::emitGoto(NestableControl* target, JumpList* jumplist, SrcNoteType noteType)
+{
+    NonLocalExitControl nle(this);
+
+    if (!nle.prepareForNonLocalJump(target))
+        return false;
+
+    if (noteType != SRC_NULL) {
+        if (!newSrcNote(noteType))
+            return false;
+    }
+
+    return emitJump(JSOP_GOTO, jumplist);
+}
+
+Scope*
+BytecodeEmitter::innermostScope() const
+{
+    return innermostEmitterScope->scope(this);
+}
+
+bool
+BytecodeEmitter::emitIndex32(JSOp op, uint32_t index)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+
+    const size_t len = 1 + UINT32_INDEX_LEN;
+    MOZ_ASSERT(len == size_t(CodeSpec[op].length));
+
+    ptrdiff_t offset;
+    if (!emitCheck(len, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    SET_UINT32_INDEX(code, index);
+    checkTypeSet(op);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitIndexOp(JSOp op, uint32_t index)
+{
+    MOZ_ASSERT(checkStrictOrSloppy(op));
+
+    const size_t len = CodeSpec[op].length;
+    MOZ_ASSERT(len >= 1 + UINT32_INDEX_LEN);
+
+    ptrdiff_t offset;
+    if (!emitCheck(len, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = jsbytecode(op);
+    SET_UINT32_INDEX(code, index);
+    checkTypeSet(op);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitAtomOp(JSAtom* atom, JSOp op)
+{
+    MOZ_ASSERT(atom);
+    MOZ_ASSERT(JOF_OPTYPE(op) == JOF_ATOM);
+
+    // .generator lookups should be emitted as JSOP_GETALIASEDVAR instead of
+    // JSOP_GETNAME etc, to bypass |with| objects on the scope chain.
+    // It's safe to emit .this lookups though because |with| objects skip
+    // those.
+    MOZ_ASSERT_IF(op == JSOP_GETNAME || op == JSOP_GETGNAME,
+                  atom != cx->names().dotGenerator);
+
+    if (op == JSOP_GETPROP && atom == cx->names().length) {
+        /* Specialize length accesses for the interpreter. */
+        op = JSOP_LENGTH;
+    }
+
+    uint32_t index;
+    if (!makeAtomIndex(atom, &index))
+        return false;
+
+    return emitIndexOp(op, index);
+}
+
+bool
+BytecodeEmitter::emitAtomOp(ParseNode* pn, JSOp op)
+{
+    MOZ_ASSERT(pn->pn_atom != nullptr);
+    return emitAtomOp(pn->pn_atom, op);
+}
+
+bool
+BytecodeEmitter::emitInternedScopeOp(uint32_t index, JSOp op)
+{
+    MOZ_ASSERT(JOF_OPTYPE(op) == JOF_SCOPE);
+    MOZ_ASSERT(index < scopeList.length());
+    return emitIndex32(op, index);
+}
+
+bool
+BytecodeEmitter::emitInternedObjectOp(uint32_t index, JSOp op)
+{
+    MOZ_ASSERT(JOF_OPTYPE(op) == JOF_OBJECT);
+    MOZ_ASSERT(index < objectList.length);
+    return emitIndex32(op, index);
+}
+
+bool
+BytecodeEmitter::emitObjectOp(ObjectBox* objbox, JSOp op)
+{
+    return emitInternedObjectOp(objectList.add(objbox), op);
+}
+
+bool
+BytecodeEmitter::emitObjectPairOp(ObjectBox* objbox1, ObjectBox* objbox2, JSOp op)
+{
+    uint32_t index = objectList.add(objbox1);
+    objectList.add(objbox2);
+    return emitInternedObjectOp(index, op);
+}
+
+bool
+BytecodeEmitter::emitRegExp(uint32_t index)
+{
+    return emitIndex32(JSOP_REGEXP, index);
+}
+
+bool
+BytecodeEmitter::emitLocalOp(JSOp op, uint32_t slot)
+{
+    MOZ_ASSERT(JOF_OPTYPE(op) != JOF_ENVCOORD);
+    MOZ_ASSERT(IsLocalOp(op));
+
+    ptrdiff_t off;
+    if (!emitN(op, LOCALNO_LEN, &off))
+        return false;
+
+    SET_LOCALNO(code(off), slot);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitArgOp(JSOp op, uint16_t slot)
+{
+    MOZ_ASSERT(IsArgOp(op));
+    ptrdiff_t off;
+    if (!emitN(op, ARGNO_LEN, &off))
+        return false;
+
+    SET_ARGNO(code(off), slot);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitEnvCoordOp(JSOp op, EnvironmentCoordinate ec)
+{
+    MOZ_ASSERT(JOF_OPTYPE(op) == JOF_ENVCOORD);
+
+    unsigned n = ENVCOORD_HOPS_LEN + ENVCOORD_SLOT_LEN;
+    MOZ_ASSERT(int(n) + 1 /* op */ == CodeSpec[op].length);
+
+    ptrdiff_t off;
+    if (!emitN(op, n, &off))
+        return false;
+
+    jsbytecode* pc = code(off);
+    SET_ENVCOORD_HOPS(pc, ec.hops());
+    pc += ENVCOORD_HOPS_LEN;
+    SET_ENVCOORD_SLOT(pc, ec.slot());
+    pc += ENVCOORD_SLOT_LEN;
+    checkTypeSet(op);
+    return true;
+}
+
+static JSOp
+GetIncDecInfo(ParseNodeKind kind, bool* post)
+{
+    MOZ_ASSERT(kind == PNK_POSTINCREMENT || kind == PNK_PREINCREMENT ||
+               kind == PNK_POSTDECREMENT || kind == PNK_PREDECREMENT);
+    *post = kind == PNK_POSTINCREMENT || kind == PNK_POSTDECREMENT;
+    return (kind == PNK_POSTINCREMENT || kind == PNK_PREINCREMENT) ? JSOP_ADD : JSOP_SUB;
+}
+
+JSOp
+BytecodeEmitter::strictifySetNameOp(JSOp op)
+{
+    switch (op) {
+      case JSOP_SETNAME:
+        if (sc->strict())
+            op = JSOP_STRICTSETNAME;
+        break;
+      case JSOP_SETGNAME:
+        if (sc->strict())
+            op = JSOP_STRICTSETGNAME;
+        break;
+        default:;
+    }
+    return op;
+}
+
+bool
+BytecodeEmitter::checkSideEffects(ParseNode* pn, bool* answer)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+ restart:
+
+    switch (pn->getKind()) {
+      // Trivial cases with no side effects.
+      case PNK_NOP:
+      case PNK_STRING:
+      case PNK_TEMPLATE_STRING:
+      case PNK_REGEXP:
+      case PNK_TRUE:
+      case PNK_FALSE:
+      case PNK_NULL:
+      case PNK_ELISION:
+      case PNK_GENERATOR:
+      case PNK_NUMBER:
+      case PNK_OBJECT_PROPERTY_NAME:
+        MOZ_ASSERT(pn->isArity(PN_NULLARY));
+        *answer = false;
+        return true;
+
+      // |this| can throw in derived class constructors, including nested arrow
+      // functions or eval.
+      case PNK_THIS:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = sc->needsThisTDZChecks();
+        return true;
+
+      // Trivial binary nodes with more token pos holders.
+      case PNK_NEWTARGET:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT(pn->pn_left->isKind(PNK_POSHOLDER));
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_POSHOLDER));
+        *answer = false;
+        return true;
+
+      case PNK_BREAK:
+      case PNK_CONTINUE:
+      case PNK_DEBUGGER:
+        MOZ_ASSERT(pn->isArity(PN_NULLARY));
+        *answer = true;
+        return true;
+
+      // Watch out for getters!
+      case PNK_DOT:
+        MOZ_ASSERT(pn->isArity(PN_NAME));
+        *answer = true;
+        return true;
+
+      // Unary cases with side effects only if the child has them.
+      case PNK_TYPEOFEXPR:
+      case PNK_VOID:
+      case PNK_NOT:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        return checkSideEffects(pn->pn_kid, answer);
+
+      // Even if the name expression is effect-free, performing ToPropertyKey on
+      // it might not be effect-free:
+      //
+      //   RegExp.prototype.toString = () => { throw 42; };
+      //   ({ [/regex/]: 0 }); // ToPropertyKey(/regex/) throws 42
+      //
+      //   function Q() {
+      //     ({ [new.target]: 0 });
+      //   }
+      //   Q.toString = () => { throw 17; };
+      //   new Q; // new.target will be Q, ToPropertyKey(Q) throws 17
+      case PNK_COMPUTED_NAME:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // Looking up or evaluating the associated name could throw.
+      case PNK_TYPEOFNAME:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // These unary cases have side effects on the enclosing object/array,
+      // sure.  But that's not the question this function answers: it's
+      // whether the operation may have a side effect on something *other* than
+      // the result of the overall operation in which it's embedded.  The
+      // answer to that is no, for an object literal having a mutated prototype
+      // and an array comprehension containing no other effectful operations
+      // only produce a value, without affecting anything else.
+      case PNK_MUTATEPROTO:
+      case PNK_ARRAYPUSH:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        return checkSideEffects(pn->pn_kid, answer);
+
+      // Unary cases with obvious side effects.
+      case PNK_PREINCREMENT:
+      case PNK_POSTINCREMENT:
+      case PNK_PREDECREMENT:
+      case PNK_POSTDECREMENT:
+      case PNK_THROW:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // These might invoke valueOf/toString, even with a subexpression without
+      // side effects!  Consider |+{ valueOf: null, toString: null }|.
+      case PNK_BITNOT:
+      case PNK_POS:
+      case PNK_NEG:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // This invokes the (user-controllable) iterator protocol.
+      case PNK_SPREAD:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      case PNK_YIELD_STAR:
+      case PNK_YIELD:
+      case PNK_AWAIT:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      // Deletion generally has side effects, even if isolated cases have none.
+      case PNK_DELETENAME:
+      case PNK_DELETEPROP:
+      case PNK_DELETEELEM:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // Deletion of a non-Reference expression has side effects only through
+      // evaluating the expression.
+      case PNK_DELETEEXPR: {
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        ParseNode* expr = pn->pn_kid;
+        return checkSideEffects(expr, answer);
+      }
+
+      case PNK_SEMI:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        if (ParseNode* expr = pn->pn_kid)
+            return checkSideEffects(expr, answer);
+        *answer = false;
+        return true;
+
+      // Binary cases with obvious side effects.
+      case PNK_ASSIGN:
+      case PNK_ADDASSIGN:
+      case PNK_SUBASSIGN:
+      case PNK_BITORASSIGN:
+      case PNK_BITXORASSIGN:
+      case PNK_BITANDASSIGN:
+      case PNK_LSHASSIGN:
+      case PNK_RSHASSIGN:
+      case PNK_URSHASSIGN:
+      case PNK_MULASSIGN:
+      case PNK_DIVASSIGN:
+      case PNK_MODASSIGN:
+      case PNK_POWASSIGN:
+      case PNK_SETTHIS:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      case PNK_STATEMENTLIST:
+      case PNK_CATCHLIST:
+      // Strict equality operations and logical operators are well-behaved and
+      // perform no conversions.
+      case PNK_OR:
+      case PNK_AND:
+      case PNK_STRICTEQ:
+      case PNK_STRICTNE:
+      // Any subexpression of a comma expression could be effectful.
+      case PNK_COMMA:
+        MOZ_ASSERT(pn->pn_count > 0);
+        MOZ_FALLTHROUGH;
+      // Subcomponents of a literal may be effectful.
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        for (ParseNode* item = pn->pn_head; item; item = item->pn_next) {
+            if (!checkSideEffects(item, answer))
+                return false;
+            if (*answer)
+                return true;
+        }
+        return true;
+
+      // Most other binary operations (parsed as lists in SpiderMonkey) may
+      // perform conversions triggering side effects.  Math operations perform
+      // ToNumber and may fail invoking invalid user-defined toString/valueOf:
+      // |5 < { toString: null }|.  |instanceof| throws if provided a
+      // non-object constructor: |null instanceof null|.  |in| throws if given
+      // a non-object RHS: |5 in null|.
+      case PNK_BITOR:
+      case PNK_BITXOR:
+      case PNK_BITAND:
+      case PNK_EQ:
+      case PNK_NE:
+      case PNK_LT:
+      case PNK_LE:
+      case PNK_GT:
+      case PNK_GE:
+      case PNK_INSTANCEOF:
+      case PNK_IN:
+      case PNK_LSH:
+      case PNK_RSH:
+      case PNK_URSH:
+      case PNK_ADD:
+      case PNK_SUB:
+      case PNK_STAR:
+      case PNK_DIV:
+      case PNK_MOD:
+      case PNK_POW:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        MOZ_ASSERT(pn->pn_count >= 2);
+        *answer = true;
+        return true;
+
+      case PNK_COLON:
+      case PNK_CASE:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        if (!checkSideEffects(pn->pn_left, answer))
+            return false;
+        if (*answer)
+            return true;
+        return checkSideEffects(pn->pn_right, answer);
+
+      // More getters.
+      case PNK_ELEM:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      // These affect visible names in this code, or in other code.
+      case PNK_IMPORT:
+      case PNK_EXPORT_FROM:
+      case PNK_EXPORT_DEFAULT:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      // Likewise.
+      case PNK_EXPORT:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        *answer = true;
+        return true;
+
+      // Every part of a loop might be effect-free, but looping infinitely *is*
+      // an effect.  (Language lawyer trivia: C++ says threads can be assumed
+      // to exit or have side effects, C++14 [intro.multithread]p27, so a C++
+      // implementation's equivalent of the below could set |*answer = false;|
+      // if all loop sub-nodes set |*answer = false|!)
+      case PNK_DOWHILE:
+      case PNK_WHILE:
+      case PNK_FOR:
+      case PNK_COMPREHENSIONFOR:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      // Declarations affect the name set of the relevant scope.
+      case PNK_VAR:
+      case PNK_CONST:
+      case PNK_LET:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        *answer = true;
+        return true;
+
+      case PNK_IF:
+      case PNK_CONDITIONAL:
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        if (!checkSideEffects(pn->pn_kid1, answer))
+            return false;
+        if (*answer)
+            return true;
+        if (!checkSideEffects(pn->pn_kid2, answer))
+            return false;
+        if (*answer)
+            return true;
+        if ((pn = pn->pn_kid3))
+            goto restart;
+        return true;
+
+      // Function calls can invoke non-local code.
+      case PNK_NEW:
+      case PNK_CALL:
+      case PNK_TAGGED_TEMPLATE:
+      case PNK_SUPERCALL:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        *answer = true;
+        return true;
+
+      // Classes typically introduce names.  Even if no name is introduced,
+      // the heritage and/or class body (through computed property names)
+      // usually have effects.
+      case PNK_CLASS:
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        *answer = true;
+        return true;
+
+      // |with| calls |ToObject| on its expression and so throws if that value
+      // is null/undefined.
+      case PNK_WITH:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      case PNK_RETURN:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      case PNK_NAME:
+        MOZ_ASSERT(pn->isArity(PN_NAME));
+        *answer = true;
+        return true;
+
+      // Shorthands could trigger getters: the |x| in the object literal in
+      // |with ({ get x() { throw 42; } }) ({ x });|, for example, triggers
+      // one.  (Of course, it isn't necessary to use |with| for a shorthand to
+      // trigger a getter.)
+      case PNK_SHORTHAND:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        *answer = true;
+        return true;
+
+      case PNK_FUNCTION:
+        MOZ_ASSERT(pn->isArity(PN_CODE));
+        /*
+         * A named function, contrary to ES3, is no longer effectful, because
+         * we bind its name lexically (using JSOP_CALLEE) instead of creating
+         * an Object instance and binding a readonly, permanent property in it
+         * (the object and binding can be detected and hijacked or captured).
+         * This is a bug fix to ES3; it is fixed in ES3.1 drafts.
+         */
+        *answer = false;
+        return true;
+
+      case PNK_MODULE:
+        *answer = false;
+        return true;
+
+      // Generator expressions have no side effects on their own.
+      case PNK_GENEXP:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        *answer = false;
+        return true;
+
+      case PNK_TRY:
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        if (!checkSideEffects(pn->pn_kid1, answer))
+            return false;
+        if (*answer)
+            return true;
+        if (ParseNode* catchList = pn->pn_kid2) {
+            MOZ_ASSERT(catchList->isKind(PNK_CATCHLIST));
+            if (!checkSideEffects(catchList, answer))
+                return false;
+            if (*answer)
+                return true;
+        }
+        if (ParseNode* finallyBlock = pn->pn_kid3) {
+            if (!checkSideEffects(finallyBlock, answer))
+                return false;
+        }
+        return true;
+
+      case PNK_CATCH:
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        if (!checkSideEffects(pn->pn_kid1, answer))
+            return false;
+        if (*answer)
+            return true;
+        if (ParseNode* cond = pn->pn_kid2) {
+            if (!checkSideEffects(cond, answer))
+                return false;
+            if (*answer)
+                return true;
+        }
+        return checkSideEffects(pn->pn_kid3, answer);
+
+      case PNK_SWITCH:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        if (!checkSideEffects(pn->pn_left, answer))
+            return false;
+        return *answer || checkSideEffects(pn->pn_right, answer);
+
+      case PNK_LABEL:
+        MOZ_ASSERT(pn->isArity(PN_NAME));
+        return checkSideEffects(pn->expr(), answer);
+
+      case PNK_LEXICALSCOPE:
+        MOZ_ASSERT(pn->isArity(PN_SCOPE));
+        return checkSideEffects(pn->scopeBody(), answer);
+
+      // We could methodically check every interpolated expression, but it's
+      // probably not worth the trouble.  Treat template strings as effect-free
+      // only if they don't contain any substitutions.
+      case PNK_TEMPLATE_STRING_LIST:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        MOZ_ASSERT(pn->pn_count > 0);
+        MOZ_ASSERT((pn->pn_count % 2) == 1,
+                   "template strings must alternate template and substitution "
+                   "parts");
+        *answer = pn->pn_count > 1;
+        return true;
+
+      case PNK_ARRAYCOMP:
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        MOZ_ASSERT(pn->pn_count == 1);
+        return checkSideEffects(pn->pn_head, answer);
+
+      // This should be unreachable but is left as-is for now.
+      case PNK_PARAMSBODY:
+        *answer = true;
+        return true;
+
+      case PNK_FORIN:           // by PNK_FOR/PNK_COMPREHENSIONFOR
+      case PNK_FOROF:           // by PNK_FOR/PNK_COMPREHENSIONFOR
+      case PNK_FORHEAD:         // by PNK_FOR/PNK_COMPREHENSIONFOR
+      case PNK_CLASSMETHOD:     // by PNK_CLASS
+      case PNK_CLASSNAMES:      // by PNK_CLASS
+      case PNK_CLASSMETHODLIST: // by PNK_CLASS
+      case PNK_IMPORT_SPEC_LIST: // by PNK_IMPORT
+      case PNK_IMPORT_SPEC:      // by PNK_IMPORT
+      case PNK_EXPORT_BATCH_SPEC:// by PNK_EXPORT
+      case PNK_EXPORT_SPEC_LIST: // by PNK_EXPORT
+      case PNK_EXPORT_SPEC:      // by PNK_EXPORT
+      case PNK_CALLSITEOBJ:      // by PNK_TAGGED_TEMPLATE
+      case PNK_POSHOLDER:        // by PNK_NEWTARGET
+      case PNK_SUPERBASE:        // by PNK_ELEM and others
+        MOZ_CRASH("handled by parent nodes");
+
+      case PNK_LIMIT: // invalid sentinel value
+        MOZ_CRASH("invalid node kind");
+    }
+
+    MOZ_CRASH("invalid, unenumerated ParseNodeKind value encountered in "
+              "BytecodeEmitter::checkSideEffects");
+}
+
+bool
+BytecodeEmitter::isInLoop()
+{
+    return findInnermostNestableControl<LoopControl>();
+}
+
+bool
+BytecodeEmitter::checkSingletonContext()
+{
+    if (!script->treatAsRunOnce() || sc->isFunctionBox() || isInLoop())
+        return false;
+    hasSingletons = true;
+    return true;
+}
+
+bool
+BytecodeEmitter::checkRunOnceContext()
+{
+    return checkSingletonContext() || (!isInLoop() && isRunOnceLambda());
+}
+
+bool
+BytecodeEmitter::needsImplicitThis()
+{
+    // Short-circuit if there is an enclosing 'with' scope.
+    if (sc->inWith())
+        return true;
+
+    // Otherwise see if the current point is under a 'with'.
+    for (EmitterScope* es = innermostEmitterScope; es; es = es->enclosingInFrame()) {
+        if (es->scope(this)->kind() == ScopeKind::With)
+            return true;
+    }
+
+    return false;
+}
+
+bool
+BytecodeEmitter::maybeSetDisplayURL()
+{
+    if (tokenStream()->hasDisplayURL()) {
+        if (!parser->ss->setDisplayURL(cx, tokenStream()->displayURL()))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::maybeSetSourceMap()
+{
+    if (tokenStream()->hasSourceMapURL()) {
+        MOZ_ASSERT(!parser->ss->hasSourceMapURL());
+        if (!parser->ss->setSourceMapURL(cx, tokenStream()->sourceMapURL()))
+            return false;
+    }
+
+    /*
+     * Source map URLs passed as a compile option (usually via a HTTP source map
+     * header) override any source map urls passed as comment pragmas.
+     */
+    if (parser->options().sourceMapURL()) {
+        // Warn about the replacement, but use the new one.
+        if (parser->ss->hasSourceMapURL()) {
+            if(!parser->report(ParseWarning, false, nullptr, JSMSG_ALREADY_HAS_PRAGMA,
+                               parser->ss->filename(), "//# sourceMappingURL"))
+                return false;
+        }
+
+        if (!parser->ss->setSourceMapURL(cx, parser->options().sourceMapURL()))
+            return false;
+    }
+
+    return true;
+}
+
+void
+BytecodeEmitter::tellDebuggerAboutCompiledScript(ExclusiveContext* cx)
+{
+    // Note: when parsing off thread the resulting scripts need to be handed to
+    // the debugger after rejoining to the main thread.
+    if (!cx->isJSContext())
+        return;
+
+    // Lazy scripts are never top level (despite always being invoked with a
+    // nullptr parent), and so the hook should never be fired.
+    if (emitterMode != LazyFunction && !parent) {
+        Debugger::onNewScript(cx->asJSContext(), script);
+    }
+}
+
+inline TokenStream*
+BytecodeEmitter::tokenStream()
+{
+    return &parser->tokenStream;
+}
+
+bool
+BytecodeEmitter::reportError(ParseNode* pn, unsigned errorNumber, ...)
+{
+    TokenPos pos = pn ? pn->pn_pos : tokenStream()->currentToken().pos;
+
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = tokenStream()->reportCompileErrorNumberVA(pos.begin, JSREPORT_ERROR,
+                                                            errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+bool
+BytecodeEmitter::reportStrictWarning(ParseNode* pn, unsigned errorNumber, ...)
+{
+    TokenPos pos = pn ? pn->pn_pos : tokenStream()->currentToken().pos;
+
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = tokenStream()->reportStrictWarningErrorNumberVA(pos.begin, errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+bool
+BytecodeEmitter::reportStrictModeError(ParseNode* pn, unsigned errorNumber, ...)
+{
+    TokenPos pos = pn ? pn->pn_pos : tokenStream()->currentToken().pos;
+
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = tokenStream()->reportStrictModeErrorNumberVA(pos.begin, sc->strict(),
+                                                               errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+bool
+BytecodeEmitter::emitNewInit(JSProtoKey key)
+{
+    const size_t len = 1 + UINT32_INDEX_LEN;
+    ptrdiff_t offset;
+    if (!emitCheck(len, &offset))
+        return false;
+
+    jsbytecode* code = this->code(offset);
+    code[0] = JSOP_NEWINIT;
+    code[1] = jsbytecode(key);
+    code[2] = 0;
+    code[3] = 0;
+    code[4] = 0;
+    checkTypeSet(JSOP_NEWINIT);
+    updateDepth(offset);
+    return true;
+}
+
+bool
+BytecodeEmitter::iteratorResultShape(unsigned* shape)
+{
+    // No need to do any guessing for the object kind, since we know exactly how
+    // many properties we plan to have.
+    gc::AllocKind kind = gc::GetGCObjectKind(2);
+    RootedPlainObject obj(cx, NewBuiltinClassInstance<PlainObject>(cx, kind, TenuredObject));
+    if (!obj)
+        return false;
+
+    Rooted<jsid> value_id(cx, AtomToId(cx->names().value));
+    Rooted<jsid> done_id(cx, AtomToId(cx->names().done));
+    if (!NativeDefineProperty(cx, obj, value_id, UndefinedHandleValue, nullptr, nullptr,
+                              JSPROP_ENUMERATE))
+    {
+        return false;
+    }
+    if (!NativeDefineProperty(cx, obj, done_id, UndefinedHandleValue, nullptr, nullptr,
+                              JSPROP_ENUMERATE))
+    {
+        return false;
+    }
+
+    ObjectBox* objbox = parser->newObjectBox(obj);
+    if (!objbox)
+        return false;
+
+    *shape = objectList.add(objbox);
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitPrepareIteratorResult()
+{
+    unsigned shape;
+    if (!iteratorResultShape(&shape))
+        return false;
+    return emitIndex32(JSOP_NEWOBJECT, shape);
+}
+
+bool
+BytecodeEmitter::emitFinishIteratorResult(bool done)
+{
+    uint32_t value_id;
+    if (!makeAtomIndex(cx->names().value, &value_id))
+        return false;
+    uint32_t done_id;
+    if (!makeAtomIndex(cx->names().done, &done_id))
+        return false;
+
+    if (!emitIndex32(JSOP_INITPROP, value_id))
+        return false;
+    if (!emit1(done ? JSOP_TRUE : JSOP_FALSE))
+        return false;
+    if (!emitIndex32(JSOP_INITPROP, done_id))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitGetNameAtLocation(JSAtom* name, const NameLocation& loc, bool callContext)
+{
+    switch (loc.kind()) {
+      case NameLocation::Kind::Dynamic:
+        if (!emitAtomOp(name, JSOP_GETNAME))
+            return false;
+        break;
+
+      case NameLocation::Kind::Global:
+        if (!emitAtomOp(name, JSOP_GETGNAME))
+            return false;
+        break;
+
+      case NameLocation::Kind::Intrinsic:
+        if (!emitAtomOp(name, JSOP_GETINTRINSIC))
+            return false;
+        break;
+
+      case NameLocation::Kind::NamedLambdaCallee:
+        if (!emit1(JSOP_CALLEE))
+            return false;
+        break;
+
+      case NameLocation::Kind::Import:
+        if (!emitAtomOp(name, JSOP_GETIMPORT))
+            return false;
+        break;
+
+      case NameLocation::Kind::ArgumentSlot:
+        if (!emitArgOp(JSOP_GETARG, loc.argumentSlot()))
+            return false;
+        break;
+
+      case NameLocation::Kind::FrameSlot:
+        if (loc.isLexical()) {
+            if (!emitTDZCheckIfNeeded(name, loc))
+                return false;
+        }
+        if (!emitLocalOp(JSOP_GETLOCAL, loc.frameSlot()))
+            return false;
+        break;
+
+      case NameLocation::Kind::EnvironmentCoordinate:
+        if (loc.isLexical()) {
+            if (!emitTDZCheckIfNeeded(name, loc))
+                return false;
+        }
+        if (!emitEnvCoordOp(JSOP_GETALIASEDVAR, loc.environmentCoordinate()))
+            return false;
+        break;
+
+      case NameLocation::Kind::DynamicAnnexBVar:
+        MOZ_CRASH("Synthesized vars for Annex B.3.3 should only be used in initialization");
+    }
+
+    // Need to provide |this| value for call.
+    if (callContext) {
+        switch (loc.kind()) {
+          case NameLocation::Kind::Dynamic: {
+            JSOp thisOp = needsImplicitThis() ? JSOP_IMPLICITTHIS : JSOP_GIMPLICITTHIS;
+            if (!emitAtomOp(name, thisOp))
+                return false;
+            break;
+          }
+
+          case NameLocation::Kind::Global:
+            if (!emitAtomOp(name, JSOP_GIMPLICITTHIS))
+                return false;
+            break;
+
+          case NameLocation::Kind::Intrinsic:
+          case NameLocation::Kind::NamedLambdaCallee:
+          case NameLocation::Kind::Import:
+          case NameLocation::Kind::ArgumentSlot:
+          case NameLocation::Kind::FrameSlot:
+          case NameLocation::Kind::EnvironmentCoordinate:
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+            break;
+
+          case NameLocation::Kind::DynamicAnnexBVar:
+            MOZ_CRASH("Synthesized vars for Annex B.3.3 should only be used in initialization");
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitGetName(ParseNode* pn, bool callContext)
+{
+    return emitGetName(pn->name(), callContext);
+}
+
+template <typename RHSEmitter>
+bool
+BytecodeEmitter::emitSetOrInitializeNameAtLocation(HandleAtom name, const NameLocation& loc,
+                                                   RHSEmitter emitRhs, bool initialize)
+{
+    bool emittedBindOp = false;
+
+    switch (loc.kind()) {
+      case NameLocation::Kind::Dynamic:
+      case NameLocation::Kind::Import:
+      case NameLocation::Kind::DynamicAnnexBVar: {
+        uint32_t atomIndex;
+        if (!makeAtomIndex(name, &atomIndex))
+            return false;
+        if (loc.kind() == NameLocation::Kind::DynamicAnnexBVar) {
+            // Annex B vars always go on the nearest variable environment,
+            // even if lexical environments in between contain same-named
+            // bindings.
+            if (!emit1(JSOP_BINDVAR))
+                return false;
+        } else {
+            if (!emitIndexOp(JSOP_BINDNAME, atomIndex))
+                return false;
+        }
+        emittedBindOp = true;
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (!emitIndexOp(strictifySetNameOp(JSOP_SETNAME), atomIndex))
+            return false;
+        break;
+      }
+
+      case NameLocation::Kind::Global: {
+        JSOp op;
+        uint32_t atomIndex;
+        if (!makeAtomIndex(name, &atomIndex))
+            return false;
+        if (loc.isLexical() && initialize) {
+            // INITGLEXICAL always gets the global lexical scope. It doesn't
+            // need a BINDGNAME.
+            MOZ_ASSERT(innermostScope()->is<GlobalScope>());
+            op = JSOP_INITGLEXICAL;
+        } else {
+            if (!emitIndexOp(JSOP_BINDGNAME, atomIndex))
+                return false;
+            emittedBindOp = true;
+            op = strictifySetNameOp(JSOP_SETGNAME);
+        }
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (!emitIndexOp(op, atomIndex))
+            return false;
+        break;
+      }
+
+      case NameLocation::Kind::Intrinsic:
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (!emitAtomOp(name, JSOP_SETINTRINSIC))
+            return false;
+        break;
+
+      case NameLocation::Kind::NamedLambdaCallee:
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        // Assigning to the named lambda is a no-op in sloppy mode but
+        // throws in strict mode.
+        if (sc->strict() && !emit1(JSOP_THROWSETCALLEE))
+            return false;
+        break;
+
+      case NameLocation::Kind::ArgumentSlot: {
+        // If we assign to a positional formal parameter and the arguments
+        // object is unmapped (strict mode or function with
+        // default/rest/destructing args), parameters do not alias
+        // arguments[i], and to make the arguments object reflect initial
+        // parameter values prior to any mutation we create it eagerly
+        // whenever parameters are (or might, in the case of calls to eval)
+        // assigned.
+        FunctionBox* funbox = sc->asFunctionBox();
+        if (funbox->argumentsHasLocalBinding() && !funbox->hasMappedArgsObj())
+            funbox->setDefinitelyNeedsArgsObj();
+
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (!emitArgOp(JSOP_SETARG, loc.argumentSlot()))
+            return false;
+        break;
+      }
+
+      case NameLocation::Kind::FrameSlot: {
+        JSOp op = JSOP_SETLOCAL;
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (loc.isLexical()) {
+            if (initialize) {
+                op = JSOP_INITLEXICAL;
+            } else {
+                if (loc.isConst())
+                    op = JSOP_THROWSETCONST;
+
+                if (!emitTDZCheckIfNeeded(name, loc))
+                    return false;
+            }
+        }
+        if (!emitLocalOp(op, loc.frameSlot()))
+            return false;
+        if (op == JSOP_INITLEXICAL) {
+            if (!innermostTDZCheckCache->noteTDZCheck(this, name, DontCheckTDZ))
+                return false;
+        }
+        break;
+      }
+
+      case NameLocation::Kind::EnvironmentCoordinate: {
+        JSOp op = JSOP_SETALIASEDVAR;
+        if (!emitRhs(this, loc, emittedBindOp))
+            return false;
+        if (loc.isLexical()) {
+            if (initialize) {
+                op = JSOP_INITALIASEDLEXICAL;
+            } else {
+                if (loc.isConst())
+                    op = JSOP_THROWSETALIASEDCONST;
+
+                if (!emitTDZCheckIfNeeded(name, loc))
+                    return false;
+            }
+        }
+        if (loc.bindingKind() == BindingKind::NamedLambdaCallee) {
+            // Assigning to the named lambda is a no-op in sloppy mode and throws
+            // in strict mode.
+            op = JSOP_THROWSETALIASEDCONST;
+            if (sc->strict() && !emitEnvCoordOp(op, loc.environmentCoordinate()))
+                return false;
+        } else {
+            if (!emitEnvCoordOp(op, loc.environmentCoordinate()))
+                return false;
+        }
+        if (op == JSOP_INITALIASEDLEXICAL) {
+            if (!innermostTDZCheckCache->noteTDZCheck(this, name, DontCheckTDZ))
+                return false;
+        }
+        break;
+      }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitTDZCheckIfNeeded(JSAtom* name, const NameLocation& loc)
+{
+    // Dynamic accesses have TDZ checks built into their VM code and should
+    // never emit explicit TDZ checks.
+    MOZ_ASSERT(loc.hasKnownSlot());
+    MOZ_ASSERT(loc.isLexical());
+
+    Maybe<MaybeCheckTDZ> check = innermostTDZCheckCache->needsTDZCheck(this, name);
+    if (!check)
+        return false;
+
+    // We've already emitted a check in this basic block.
+    if (*check == DontCheckTDZ)
+        return true;
+
+    if (loc.kind() == NameLocation::Kind::FrameSlot) {
+        if (!emitLocalOp(JSOP_CHECKLEXICAL, loc.frameSlot()))
+            return false;
+    } else {
+        if (!emitEnvCoordOp(JSOP_CHECKALIASEDLEXICAL, loc.environmentCoordinate()))
+            return false;
+    }
+
+    return innermostTDZCheckCache->noteTDZCheck(this, name, DontCheckTDZ);
+}
+
+bool
+BytecodeEmitter::emitPropLHS(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_DOT));
+    MOZ_ASSERT(!pn->as<PropertyAccess>().isSuper());
+
+    ParseNode* pn2 = pn->pn_expr;
+
+    /*
+     * If the object operand is also a dotted property reference, reverse the
+     * list linked via pn_expr temporarily so we can iterate over it from the
+     * bottom up (reversing again as we go), to avoid excessive recursion.
+     */
+    if (pn2->isKind(PNK_DOT) && !pn2->as<PropertyAccess>().isSuper()) {
+        ParseNode* pndot = pn2;
+        ParseNode* pnup = nullptr;
+        ParseNode* pndown;
+        for (;;) {
+            /* Reverse pndot->pn_expr to point up, not down. */
+            pndown = pndot->pn_expr;
+            pndot->pn_expr = pnup;
+            if (!pndown->isKind(PNK_DOT) || pndown->as<PropertyAccess>().isSuper())
+                break;
+            pnup = pndot;
+            pndot = pndown;
+        }
+
+        /* pndown is a primary expression, not a dotted property reference. */
+        if (!emitTree(pndown))
+            return false;
+
+        do {
+            /* Walk back up the list, emitting annotated name ops. */
+            if (!emitAtomOp(pndot, JSOP_GETPROP))
+                return false;
+
+            /* Reverse the pn_expr link again. */
+            pnup = pndot->pn_expr;
+            pndot->pn_expr = pndown;
+            pndown = pndot;
+        } while ((pndot = pnup) != nullptr);
+        return true;
+    }
+
+    // The non-optimized case.
+    return emitTree(pn2);
+}
+
+bool
+BytecodeEmitter::emitSuperPropLHS(ParseNode* superBase, bool isCall)
+{
+    if (!emitGetThisForSuperBase(superBase))
+        return false;
+    if (isCall && !emit1(JSOP_DUP))
+        return false;
+    if (!emit1(JSOP_SUPERBASE))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitPropOp(ParseNode* pn, JSOp op)
+{
+    MOZ_ASSERT(pn->isArity(PN_NAME));
+
+    if (!emitPropLHS(pn))
+        return false;
+
+    if (op == JSOP_CALLPROP && !emit1(JSOP_DUP))
+        return false;
+
+    if (!emitAtomOp(pn, op))
+        return false;
+
+    if (op == JSOP_CALLPROP && !emit1(JSOP_SWAP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSuperPropOp(ParseNode* pn, JSOp op, bool isCall)
+{
+    ParseNode* base = &pn->as<PropertyAccess>().expression();
+    if (!emitSuperPropLHS(base, isCall))
+        return false;
+
+    if (!emitAtomOp(pn, op))
+        return false;
+
+    if (isCall && !emit1(JSOP_SWAP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitPropIncDec(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->pn_kid->isKind(PNK_DOT));
+
+    bool post;
+    bool isSuper = pn->pn_kid->as<PropertyAccess>().isSuper();
+    JSOp binop = GetIncDecInfo(pn->getKind(), &post);
+
+    if (isSuper) {
+        ParseNode* base = &pn->pn_kid->as<PropertyAccess>().expression();
+        if (!emitSuperPropLHS(base))                // THIS OBJ
+            return false;
+        if (!emit1(JSOP_DUP2))                      // THIS OBJ THIS OBJ
+            return false;
+    } else {
+        if (!emitPropLHS(pn->pn_kid))               // OBJ
+            return false;
+        if (!emit1(JSOP_DUP))                       // OBJ OBJ
+            return false;
+    }
+    if (!emitAtomOp(pn->pn_kid, isSuper? JSOP_GETPROP_SUPER : JSOP_GETPROP)) // OBJ V
+        return false;
+    if (!emit1(JSOP_POS))                           // OBJ N
+        return false;
+    if (post && !emit1(JSOP_DUP))                   // OBJ N? N
+        return false;
+    if (!emit1(JSOP_ONE))                           // OBJ N? N 1
+        return false;
+    if (!emit1(binop))                              // OBJ N? N+1
+        return false;
+
+    if (post) {
+        if (!emit2(JSOP_PICK, 2 + isSuper))        // N? N+1 OBJ
+            return false;
+        if (!emit1(JSOP_SWAP))                     // N? OBJ N+1
+            return false;
+        if (isSuper) {
+            if (!emit2(JSOP_PICK, 3))              // N THIS N+1 OBJ
+                return false;
+            if (!emit1(JSOP_SWAP))                 // N THIS OBJ N+1
+                return false;
+        }
+    }
+
+    JSOp setOp = isSuper ? sc->strict() ? JSOP_STRICTSETPROP_SUPER : JSOP_SETPROP_SUPER
+                         : sc->strict() ? JSOP_STRICTSETPROP : JSOP_SETPROP;
+    if (!emitAtomOp(pn->pn_kid, setOp))             // N? N+1
+        return false;
+    if (post && !emit1(JSOP_POP))                   // RESULT
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitNameIncDec(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->pn_kid->isKind(PNK_NAME));
+
+    bool post;
+    JSOp binop = GetIncDecInfo(pn->getKind(), &post);
+
+    auto emitRhs = [pn, post, binop](BytecodeEmitter* bce, const NameLocation& loc,
+                                     bool emittedBindOp)
+    {
+        JSAtom* name = pn->pn_kid->name();
+        if (!bce->emitGetNameAtLocation(name, loc, false)) // SCOPE? V
+            return false;
+        if (!bce->emit1(JSOP_POS))                         // SCOPE? N
+            return false;
+        if (post && !bce->emit1(JSOP_DUP))                 // SCOPE? N? N
+            return false;
+        if (!bce->emit1(JSOP_ONE))                         // SCOPE? N? N 1
+            return false;
+        if (!bce->emit1(binop))                            // SCOPE? N? N+1
+            return false;
+
+        if (post && emittedBindOp) {
+            if (!bce->emit2(JSOP_PICK, 2))                 // N? N+1 SCOPE?
+                return false;
+            if (!bce->emit1(JSOP_SWAP))                    // N? SCOPE? N+1
+                return false;
+        }
+
+        return true;
+    };
+
+    if (!emitSetName(pn->pn_kid, emitRhs))
+        return false;
+
+    if (post && !emit1(JSOP_POP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitElemOperands(ParseNode* pn, EmitElemOption opts)
+{
+    MOZ_ASSERT(pn->isArity(PN_BINARY));
+
+    if (!emitTree(pn->pn_left))
+        return false;
+
+    if (opts == EmitElemOption::IncDec) {
+        if (!emit1(JSOP_CHECKOBJCOERCIBLE))
+            return false;
+    } else if (opts == EmitElemOption::Call) {
+        if (!emit1(JSOP_DUP))
+            return false;
+    }
+
+    if (!emitTree(pn->pn_right))
+        return false;
+
+    if (opts == EmitElemOption::Set) {
+        if (!emit2(JSOP_PICK, 2))
+            return false;
+    } else if (opts == EmitElemOption::IncDec || opts == EmitElemOption::CompoundAssign) {
+        if (!emit1(JSOP_TOID))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSuperElemOperands(ParseNode* pn, EmitElemOption opts)
+{
+    MOZ_ASSERT(pn->isKind(PNK_ELEM) && pn->as<PropertyByValue>().isSuper());
+
+    // The ordering here is somewhat screwy. We need to evaluate the propval
+    // first, by spec. Do a little dance to not emit more than one JSOP_THIS.
+    // Since JSOP_THIS might throw in derived class constructors, we cannot
+    // just push it earlier as the receiver. We have to swap it down instead.
+
+    if (!emitTree(pn->pn_right))
+        return false;
+
+    // We need to convert the key to an object id first, so that we do not do
+    // it inside both the GETELEM and the SETELEM.
+    if (opts == EmitElemOption::IncDec || opts == EmitElemOption::CompoundAssign) {
+        if (!emit1(JSOP_TOID))
+            return false;
+    }
+
+    if (!emitGetThisForSuperBase(pn->pn_left))
+        return false;
+
+    if (opts == EmitElemOption::Call) {
+        if (!emit1(JSOP_SWAP))
+            return false;
+
+        // We need another |this| on top, also
+        if (!emitDupAt(1))
+            return false;
+    }
+
+    if (!emit1(JSOP_SUPERBASE))
+        return false;
+
+    if (opts == EmitElemOption::Set && !emit2(JSOP_PICK, 3))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitElemOpBase(JSOp op)
+{
+    if (!emit1(op))
+        return false;
+
+    checkTypeSet(op);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitElemOp(ParseNode* pn, JSOp op)
+{
+    EmitElemOption opts = EmitElemOption::Get;
+    if (op == JSOP_CALLELEM)
+        opts = EmitElemOption::Call;
+    else if (op == JSOP_SETELEM || op == JSOP_STRICTSETELEM)
+        opts = EmitElemOption::Set;
+
+    return emitElemOperands(pn, opts) && emitElemOpBase(op);
+}
+
+bool
+BytecodeEmitter::emitSuperElemOp(ParseNode* pn, JSOp op, bool isCall)
+{
+    EmitElemOption opts = EmitElemOption::Get;
+    if (isCall)
+        opts = EmitElemOption::Call;
+    else if (op == JSOP_SETELEM_SUPER || op == JSOP_STRICTSETELEM_SUPER)
+        opts = EmitElemOption::Set;
+
+    if (!emitSuperElemOperands(pn, opts))
+        return false;
+    if (!emitElemOpBase(op))
+        return false;
+
+    if (isCall && !emit1(JSOP_SWAP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitElemIncDec(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->pn_kid->isKind(PNK_ELEM));
+
+    bool isSuper = pn->pn_kid->as<PropertyByValue>().isSuper();
+
+    // We need to convert the key to an object id first, so that we do not do
+    // it inside both the GETELEM and the SETELEM. This is done by
+    // emit(Super)ElemOperands.
+    if (isSuper) {
+        if (!emitSuperElemOperands(pn->pn_kid, EmitElemOption::IncDec))
+            return false;
+    } else {
+        if (!emitElemOperands(pn->pn_kid, EmitElemOption::IncDec))
+            return false;
+    }
+
+    bool post;
+    JSOp binop = GetIncDecInfo(pn->getKind(), &post);
+
+    JSOp getOp;
+    if (isSuper) {
+        // There's no such thing as JSOP_DUP3, so we have to be creative.
+        // Note that pushing things again is no fewer JSOps.
+        if (!emitDupAt(2))                              // KEY THIS OBJ KEY
+            return false;
+        if (!emitDupAt(2))                              // KEY THIS OBJ KEY THIS
+            return false;
+        if (!emitDupAt(2))                              // KEY THIS OBJ KEY THIS OBJ
+            return false;
+        getOp = JSOP_GETELEM_SUPER;
+    } else {
+                                                        // OBJ KEY
+        if (!emit1(JSOP_DUP2))                          // OBJ KEY OBJ KEY
+            return false;
+        getOp = JSOP_GETELEM;
+    }
+    if (!emitElemOpBase(getOp))                         // OBJ KEY V
+        return false;
+    if (!emit1(JSOP_POS))                               // OBJ KEY N
+        return false;
+    if (post && !emit1(JSOP_DUP))                       // OBJ KEY N? N
+        return false;
+    if (!emit1(JSOP_ONE))                               // OBJ KEY N? N 1
+        return false;
+    if (!emit1(binop))                                  // OBJ KEY N? N+1
+        return false;
+
+    if (post) {
+        if (isSuper) {
+            // We have one more value to rotate around, because of |this|
+            // on the stack
+            if (!emit2(JSOP_PICK, 4))
+                return false;
+        }
+        if (!emit2(JSOP_PICK, 3 + isSuper))             // KEY N N+1 OBJ
+            return false;
+        if (!emit2(JSOP_PICK, 3 + isSuper))             // N N+1 OBJ KEY
+            return false;
+        if (!emit2(JSOP_PICK, 2 + isSuper))             // N OBJ KEY N+1
+            return false;
+    }
+
+    JSOp setOp = isSuper ? (sc->strict() ? JSOP_STRICTSETELEM_SUPER : JSOP_SETELEM_SUPER)
+                         : (sc->strict() ? JSOP_STRICTSETELEM : JSOP_SETELEM);
+    if (!emitElemOpBase(setOp))                         // N? N+1
+        return false;
+    if (post && !emit1(JSOP_POP))                       // RESULT
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitCallIncDec(ParseNode* incDec)
+{
+    MOZ_ASSERT(incDec->isKind(PNK_PREINCREMENT) ||
+               incDec->isKind(PNK_POSTINCREMENT) ||
+               incDec->isKind(PNK_PREDECREMENT) ||
+               incDec->isKind(PNK_POSTDECREMENT));
+
+    MOZ_ASSERT(incDec->pn_kid->isKind(PNK_CALL));
+
+    ParseNode* call = incDec->pn_kid;
+    if (!emitTree(call))                                // CALLRESULT
+        return false;
+    if (!emit1(JSOP_POS))                               // N
+        return false;
+
+    // The increment/decrement has no side effects, so proceed to throw for
+    // invalid assignment target.
+    return emitUint16Operand(JSOP_THROWMSG, JSMSG_BAD_LEFTSIDE_OF_ASS);
+}
+
+bool
+BytecodeEmitter::emitNumberOp(double dval)
+{
+    int32_t ival;
+    if (NumberIsInt32(dval, &ival)) {
+        if (ival == 0)
+            return emit1(JSOP_ZERO);
+        if (ival == 1)
+            return emit1(JSOP_ONE);
+        if ((int)(int8_t)ival == ival)
+            return emit2(JSOP_INT8, uint8_t(int8_t(ival)));
+
+        uint32_t u = uint32_t(ival);
+        if (u < JS_BIT(16)) {
+            if (!emitUint16Operand(JSOP_UINT16, u))
+                return false;
+        } else if (u < JS_BIT(24)) {
+            ptrdiff_t off;
+            if (!emitN(JSOP_UINT24, 3, &off))
+                return false;
+            SET_UINT24(code(off), u);
+        } else {
+            ptrdiff_t off;
+            if (!emitN(JSOP_INT32, 4, &off))
+                return false;
+            SET_INT32(code(off), ival);
+        }
+        return true;
+    }
+
+    if (!constList.append(DoubleValue(dval)))
+        return false;
+
+    return emitIndex32(JSOP_DOUBLE, constList.length() - 1);
+}
+
+/*
+ * Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047.
+ * LLVM is deciding to inline this function which uses a lot of stack space
+ * into emitTree which is recursive and uses relatively little stack space.
+ */
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitSwitch(ParseNode* pn)
+{
+    ParseNode* cases = pn->pn_right;
+    MOZ_ASSERT(cases->isKind(PNK_LEXICALSCOPE) || cases->isKind(PNK_STATEMENTLIST));
+
+    // Emit code for the discriminant.
+    if (!emitTree(pn->pn_left))
+        return false;
+
+    // Enter the scope before pushing the switch BreakableControl since all
+    // breaks are under this scope.
+    Maybe<TDZCheckCache> tdzCache;
+    Maybe<EmitterScope> emitterScope;
+    if (cases->isKind(PNK_LEXICALSCOPE)) {
+        if (!cases->isEmptyScope()) {
+            tdzCache.emplace(this);
+            emitterScope.emplace(this);
+            if (!emitterScope->enterLexical(this, ScopeKind::Lexical, cases->scopeBindings()))
+                return false;
+        }
+
+        // Advance |cases| to refer to the switch case list.
+        cases = cases->scopeBody();
+
+        // A switch statement may contain hoisted functions inside its
+        // cases. The PNX_FUNCDEFS flag is propagated from the STATEMENTLIST
+        // bodies of the cases to the case list.
+        if (cases->pn_xflags & PNX_FUNCDEFS) {
+            MOZ_ASSERT(emitterScope);
+            for (ParseNode* caseNode = cases->pn_head; caseNode; caseNode = caseNode->pn_next) {
+                if (caseNode->pn_right->pn_xflags & PNX_FUNCDEFS) {
+                    if (!emitHoistedFunctionsInList(caseNode->pn_right))
+                        return false;
+                }
+            }
+        }
+    }
+
+    // After entering the scope, push the switch control.
+    BreakableControl controlInfo(this, StatementKind::Switch);
+
+    ptrdiff_t top = offset();
+
+    // Switch bytecodes run from here till end of final case.
+    uint32_t caseCount = cases->pn_count;
+    if (caseCount > JS_BIT(16)) {
+        parser->tokenStream.reportError(JSMSG_TOO_MANY_CASES);
+        return false;
+    }
+
+    // Try for most optimal, fall back if not dense ints.
+    JSOp switchOp = JSOP_TABLESWITCH;
+    uint32_t tableLength = 0;
+    int32_t low, high;
+    bool hasDefault = false;
+    CaseClause* firstCase = cases->pn_head ? &cases->pn_head->as<CaseClause>() : nullptr;
+    if (caseCount == 0 ||
+        (caseCount == 1 && (hasDefault = firstCase->isDefault())))
+    {
+        caseCount = 0;
+        low = 0;
+        high = -1;
+    } else {
+        Vector<jsbitmap, 128, SystemAllocPolicy> intmap;
+        int32_t intmapBitLength = 0;
+
+        low  = JSVAL_INT_MAX;
+        high = JSVAL_INT_MIN;
+
+        for (CaseClause* caseNode = firstCase; caseNode; caseNode = caseNode->next()) {
+            if (caseNode->isDefault()) {
+                hasDefault = true;
+                caseCount--;  // one of the "cases" was the default
+                continue;
+            }
+
+            if (switchOp == JSOP_CONDSWITCH)
+                continue;
+
+            MOZ_ASSERT(switchOp == JSOP_TABLESWITCH);
+
+            ParseNode* caseValue = caseNode->caseExpression();
+
+            if (caseValue->getKind() != PNK_NUMBER) {
+                switchOp = JSOP_CONDSWITCH;
+                continue;
+            }
+
+            int32_t i;
+            if (!NumberIsInt32(caseValue->pn_dval, &i)) {
+                switchOp = JSOP_CONDSWITCH;
+                continue;
+            }
+
+            if (unsigned(i + int(JS_BIT(15))) >= unsigned(JS_BIT(16))) {
+                switchOp = JSOP_CONDSWITCH;
+                continue;
+            }
+            if (i < low)
+                low = i;
+            if (i > high)
+                high = i;
+
+            // Check for duplicates, which require a JSOP_CONDSWITCH.
+            // We bias i by 65536 if it's negative, and hope that's a rare
+            // case (because it requires a malloc'd bitmap).
+            if (i < 0)
+                i += JS_BIT(16);
+            if (i >= intmapBitLength) {
+                size_t newLength = (i / JS_BITMAP_NBITS) + 1;
+                if (!intmap.resize(newLength))
+                    return false;
+                intmapBitLength = newLength * JS_BITMAP_NBITS;
+            }
+            if (JS_TEST_BIT(intmap, i)) {
+                switchOp = JSOP_CONDSWITCH;
+                continue;
+            }
+            JS_SET_BIT(intmap, i);
+        }
+
+        // Compute table length and select condswitch instead if overlarge or
+        // more than half-sparse.
+        if (switchOp == JSOP_TABLESWITCH) {
+            tableLength = uint32_t(high - low + 1);
+            if (tableLength >= JS_BIT(16) || tableLength > 2 * caseCount)
+                switchOp = JSOP_CONDSWITCH;
+        }
+    }
+
+    // The note has one or two offsets: first tells total switch code length;
+    // second (if condswitch) tells offset to first JSOP_CASE.
+    unsigned noteIndex;
+    size_t switchSize;
+    if (switchOp == JSOP_CONDSWITCH) {
+        // 0 bytes of immediate for unoptimized switch.
+        switchSize = 0;
+        if (!newSrcNote3(SRC_CONDSWITCH, 0, 0, &noteIndex))
+            return false;
+    } else {
+        MOZ_ASSERT(switchOp == JSOP_TABLESWITCH);
+
+        // 3 offsets (len, low, high) before the table, 1 per entry.
+        switchSize = size_t(JUMP_OFFSET_LEN * (3 + tableLength));
+        if (!newSrcNote2(SRC_TABLESWITCH, 0, &noteIndex))
+            return false;
+    }
+
+    // Emit switchOp followed by switchSize bytes of jump or lookup table.
+    MOZ_ASSERT(top == offset());
+    if (!emitN(switchOp, switchSize))
+        return false;
+
+    Vector<CaseClause*, 32, SystemAllocPolicy> table;
+
+    JumpList condSwitchDefaultOff;
+    if (switchOp == JSOP_CONDSWITCH) {
+        unsigned caseNoteIndex;
+        bool beforeCases = true;
+        ptrdiff_t lastCaseOffset = -1;
+
+        // The case conditions need their own TDZ cache since they might not
+        // all execute.
+        TDZCheckCache tdzCache(this);
+
+        // Emit code for evaluating cases and jumping to case statements.
+        for (CaseClause* caseNode = firstCase; caseNode; caseNode = caseNode->next()) {
+            ParseNode* caseValue = caseNode->caseExpression();
+
+            // If the expression is a literal, suppress line number emission so
+            // that debugging works more naturally.
+            if (caseValue) {
+                if (!emitTree(caseValue,
+                              caseValue->isLiteral() ? SUPPRESS_LINENOTE : EMIT_LINENOTE))
+                {
+                    return false;
+                }
+            }
+
+            if (!beforeCases) {
+                // prevCase is the previous JSOP_CASE's bytecode offset.
+                if (!setSrcNoteOffset(caseNoteIndex, 0, offset() - lastCaseOffset))
+                    return false;
+            }
+            if (!caseValue) {
+                // This is the default clause.
+                continue;
+            }
+
+            if (!newSrcNote2(SRC_NEXTCASE, 0, &caseNoteIndex))
+                return false;
+
+            // The case clauses are produced before any of the case body. The
+            // JumpList is saved on the parsed tree, then later restored and
+            // patched when generating the cases body.
+            JumpList caseJump;
+            if (!emitJump(JSOP_CASE, &caseJump))
+                return false;
+            caseNode->setOffset(caseJump.offset);
+            lastCaseOffset = caseJump.offset;
+
+            if (beforeCases) {
+                // Switch note's second offset is to first JSOP_CASE.
+                unsigned noteCount = notes().length();
+                if (!setSrcNoteOffset(noteIndex, 1, lastCaseOffset - top))
+                    return false;
+                unsigned noteCountDelta = notes().length() - noteCount;
+                if (noteCountDelta != 0)
+                    caseNoteIndex += noteCountDelta;
+                beforeCases = false;
+            }
+        }
+
+        // If we didn't have an explicit default (which could fall in between
+        // cases, preventing us from fusing this setSrcNoteOffset with the call
+        // in the loop above), link the last case to the implicit default for
+        // the benefit of IonBuilder.
+        if (!hasDefault &&
+            !beforeCases &&
+            !setSrcNoteOffset(caseNoteIndex, 0, offset() - lastCaseOffset))
+        {
+            return false;
+        }
+
+        // Emit default even if no explicit default statement.
+        if (!emitJump(JSOP_DEFAULT, &condSwitchDefaultOff))
+            return false;
+    } else {
+        MOZ_ASSERT(switchOp == JSOP_TABLESWITCH);
+
+        // skip default offset.
+        jsbytecode* pc = code(top + JUMP_OFFSET_LEN);
+
+        // Fill in switch bounds, which we know fit in 16-bit offsets.
+        SET_JUMP_OFFSET(pc, low);
+        pc += JUMP_OFFSET_LEN;
+        SET_JUMP_OFFSET(pc, high);
+        pc += JUMP_OFFSET_LEN;
+
+        if (tableLength != 0) {
+            if (!table.growBy(tableLength))
+                return false;
+
+            for (CaseClause* caseNode = firstCase; caseNode; caseNode = caseNode->next()) {
+                if (ParseNode* caseValue = caseNode->caseExpression()) {
+                    MOZ_ASSERT(caseValue->isKind(PNK_NUMBER));
+
+                    int32_t i = int32_t(caseValue->pn_dval);
+                    MOZ_ASSERT(double(i) == caseValue->pn_dval);
+
+                    i -= low;
+                    MOZ_ASSERT(uint32_t(i) < tableLength);
+                    MOZ_ASSERT(!table[i]);
+                    table[i] = caseNode;
+                }
+            }
+        }
+    }
+
+    JumpTarget defaultOffset{ -1 };
+
+    // Emit code for each case's statements.
+    for (CaseClause* caseNode = firstCase; caseNode; caseNode = caseNode->next()) {
+        if (switchOp == JSOP_CONDSWITCH && !caseNode->isDefault()) {
+            // The case offset got saved in the caseNode structure after
+            // emitting the JSOP_CASE jump instruction above.
+            JumpList caseCond;
+            caseCond.offset = caseNode->offset();
+            if (!emitJumpTargetAndPatch(caseCond))
+                return false;
+        }
+
+        JumpTarget here;
+        if (!emitJumpTarget(&here))
+            return false;
+        if (caseNode->isDefault())
+            defaultOffset = here;
+
+        // If this is emitted as a TABLESWITCH, we'll need to know this case's
+        // offset later when emitting the table. Store it in the node's
+        // pn_offset (giving the field a different meaning vs. how we used it
+        // on the immediately preceding line of code).
+        caseNode->setOffset(here.offset);
+
+        TDZCheckCache tdzCache(this);
+
+        if (!emitTree(caseNode->statementList()))
+            return false;
+    }
+
+    if (!hasDefault) {
+        // If no default case, offset for default is to end of switch.
+        if (!emitJumpTarget(&defaultOffset))
+            return false;
+    }
+    MOZ_ASSERT(defaultOffset.offset != -1);
+
+    // Set the default offset (to end of switch if no default).
+    jsbytecode* pc;
+    if (switchOp == JSOP_CONDSWITCH) {
+        pc = nullptr;
+        patchJumpsToTarget(condSwitchDefaultOff, defaultOffset);
+    } else {
+        MOZ_ASSERT(switchOp == JSOP_TABLESWITCH);
+        pc = code(top);
+        SET_JUMP_OFFSET(pc, defaultOffset.offset - top);
+        pc += JUMP_OFFSET_LEN;
+    }
+
+    // Set the SRC_SWITCH note's offset operand to tell end of switch.
+    if (!setSrcNoteOffset(noteIndex, 0, lastNonJumpTargetOffset() - top))
+        return false;
+
+    if (switchOp == JSOP_TABLESWITCH) {
+        // Skip over the already-initialized switch bounds.
+        pc += 2 * JUMP_OFFSET_LEN;
+
+        // Fill in the jump table, if there is one.
+        for (uint32_t i = 0; i < tableLength; i++) {
+            CaseClause* caseNode = table[i];
+            ptrdiff_t off = caseNode ? caseNode->offset() - top : 0;
+            SET_JUMP_OFFSET(pc, off);
+            pc += JUMP_OFFSET_LEN;
+        }
+    }
+
+    // Patch breaks before leaving the scope, as all breaks are under the
+    // lexical scope if it exists.
+    if (!controlInfo.patchBreaks(this))
+        return false;
+
+    if (emitterScope && !emitterScope->leave(this))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::isRunOnceLambda()
+{
+    // The run once lambda flags set by the parser are approximate, and we look
+    // at properties of the function itself before deciding to emit a function
+    // as a run once lambda.
+
+    if (!(parent && parent->emittingRunOnceLambda) &&
+        (emitterMode != LazyFunction || !lazyScript->treatAsRunOnce()))
+    {
+        return false;
+    }
+
+    FunctionBox* funbox = sc->asFunctionBox();
+    return !funbox->argumentsHasLocalBinding() &&
+           !funbox->isGenerator() &&
+           !funbox->function()->name();
+}
+
+bool
+BytecodeEmitter::emitYieldOp(JSOp op)
+{
+    if (op == JSOP_FINALYIELDRVAL)
+        return emit1(JSOP_FINALYIELDRVAL);
+
+    MOZ_ASSERT(op == JSOP_INITIALYIELD || op == JSOP_YIELD);
+
+    ptrdiff_t off;
+    if (!emitN(op, 3, &off))
+        return false;
+
+    uint32_t yieldIndex = yieldOffsetList.length();
+    if (yieldIndex >= JS_BIT(24)) {
+        reportError(nullptr, JSMSG_TOO_MANY_YIELDS);
+        return false;
+    }
+
+    SET_UINT24(code(off), yieldIndex);
+
+    if (!yieldOffsetList.append(offset()))
+        return false;
+
+    return emit1(JSOP_DEBUGAFTERYIELD);
+}
+
+bool
+BytecodeEmitter::emitSetThis(ParseNode* pn)
+{
+    // PNK_SETTHIS is used to update |this| after a super() call in a derived
+    // class constructor.
+
+    MOZ_ASSERT(pn->isKind(PNK_SETTHIS));
+    MOZ_ASSERT(pn->pn_left->isKind(PNK_NAME));
+
+    RootedAtom name(cx, pn->pn_left->name());
+    auto emitRhs = [&name, pn](BytecodeEmitter* bce, const NameLocation&, bool) {
+        // Emit the new |this| value.
+        if (!bce->emitTree(pn->pn_right))
+            return false;
+        // Get the original |this| and throw if we already initialized
+        // it. Do *not* use the NameLocation argument, as that's the special
+        // lexical location below to deal with super() semantics.
+        if (!bce->emitGetName(name))
+            return false;
+        if (!bce->emit1(JSOP_CHECKTHISREINIT))
+            return false;
+        if (!bce->emit1(JSOP_POP))
+            return false;
+        return true;
+    };
+
+    // The 'this' binding is not lexical, but due to super() semantics this
+    // initialization needs to be treated as a lexical one.
+    NameLocation loc = lookupName(name);
+    NameLocation lexicalLoc;
+    if (loc.kind() == NameLocation::Kind::FrameSlot) {
+        lexicalLoc = NameLocation::FrameSlot(BindingKind::Let, loc.frameSlot());
+    } else if (loc.kind() == NameLocation::Kind::EnvironmentCoordinate) {
+        EnvironmentCoordinate coord = loc.environmentCoordinate();
+        uint8_t hops = AssertedCast<uint8_t>(coord.hops());
+        lexicalLoc = NameLocation::EnvironmentCoordinate(BindingKind::Let, hops, coord.slot());
+    } else {
+        MOZ_ASSERT(loc.kind() == NameLocation::Kind::Dynamic);
+        lexicalLoc = loc;
+    }
+
+    return emitSetOrInitializeNameAtLocation(name, lexicalLoc, emitRhs, true);
+}
+
+bool
+BytecodeEmitter::emitScript(ParseNode* body)
+{
+    TDZCheckCache tdzCache(this);
+    EmitterScope emitterScope(this);
+    if (sc->isGlobalContext()) {
+        switchToPrologue();
+        if (!emitterScope.enterGlobal(this, sc->asGlobalContext()))
+            return false;
+        switchToMain();
+    } else if (sc->isEvalContext()) {
+        switchToPrologue();
+        if (!emitterScope.enterEval(this, sc->asEvalContext()))
+            return false;
+        switchToMain();
+    } else {
+        MOZ_ASSERT(sc->isModuleContext());
+        if (!emitterScope.enterModule(this, sc->asModuleContext()))
+            return false;
+    }
+
+    setFunctionBodyEndPos(body->pn_pos);
+
+    if (sc->isEvalContext() && !sc->strict() &&
+        body->isKind(PNK_LEXICALSCOPE) && !body->isEmptyScope())
+    {
+        // Sloppy eval scripts may need to emit DEFFUNs in the prologue. If there is
+        // an immediately enclosed lexical scope, we need to enter the lexical
+        // scope in the prologue for the DEFFUNs to pick up the right
+        // environment chain.
+        EmitterScope lexicalEmitterScope(this);
+
+        switchToPrologue();
+        if (!lexicalEmitterScope.enterLexical(this, ScopeKind::Lexical, body->scopeBindings()))
+            return false;
+        switchToMain();
+
+        if (!emitLexicalScopeBody(body->scopeBody()))
+            return false;
+
+        if (!lexicalEmitterScope.leave(this))
+            return false;
+    } else {
+        if (!emitTree(body))
+            return false;
+    }
+
+    if (!emit1(JSOP_RETRVAL))
+        return false;
+
+    if (!emitterScope.leave(this))
+        return false;
+
+    if (!JSScript::fullyInitFromEmitter(cx, script, this))
+        return false;
+
+    // URL and source map information must be set before firing
+    // Debugger::onNewScript.
+    if (!maybeSetDisplayURL() || !maybeSetSourceMap())
+        return false;
+
+    tellDebuggerAboutCompiledScript(cx);
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitFunctionScript(ParseNode* body)
+{
+    FunctionBox* funbox = sc->asFunctionBox();
+
+    // The ordering of these EmitterScopes is important. The named lambda
+    // scope needs to enclose the function scope needs to enclose the extra
+    // var scope.
+
+    Maybe<EmitterScope> namedLambdaEmitterScope;
+    if (funbox->namedLambdaBindings()) {
+        namedLambdaEmitterScope.emplace(this);
+        if (!namedLambdaEmitterScope->enterNamedLambda(this, funbox))
+            return false;
+    }
+
+    /*
+     * Emit a prologue for run-once scripts which will deoptimize JIT code
+     * if the script ends up running multiple times via foo.caller related
+     * shenanigans.
+     *
+     * Also mark the script so that initializers created within it may be
+     * given more precise types.
+     */
+    if (isRunOnceLambda()) {
+        script->setTreatAsRunOnce();
+        MOZ_ASSERT(!script->hasRunOnce());
+
+        switchToPrologue();
+        if (!emit1(JSOP_RUNONCE))
+            return false;
+        switchToMain();
+    }
+
+    setFunctionBodyEndPos(body->pn_pos);
+    if (!emitTree(body))
+        return false;
+
+    if (!updateSourceCoordNotes(body->pn_pos.end))
+        return false;
+
+    // Always end the script with a JSOP_RETRVAL. Some other parts of the
+    // codebase depend on this opcode,
+    // e.g. InterpreterRegs::setToEndOfScript.
+    if (!emit1(JSOP_RETRVAL))
+        return false;
+
+    if (namedLambdaEmitterScope) {
+        if (!namedLambdaEmitterScope->leave(this))
+            return false;
+        namedLambdaEmitterScope.reset();
+    }
+
+    if (!JSScript::fullyInitFromEmitter(cx, script, this))
+        return false;
+
+    // URL and source map information must be set before firing
+    // Debugger::onNewScript. Only top-level functions need this, as compiling
+    // the outer scripts of nested functions already processed the source.
+    if (emitterMode != LazyFunction && !parent) {
+        if (!maybeSetDisplayURL() || !maybeSetSourceMap())
+            return false;
+
+        tellDebuggerAboutCompiledScript(cx);
+    }
+
+    return true;
+}
+
+template <typename NameEmitter>
+bool
+BytecodeEmitter::emitDestructuringDeclsWithEmitter(ParseNode* pattern, NameEmitter emitName)
+{
+    if (pattern->isKind(PNK_ARRAY)) {
+        for (ParseNode* element = pattern->pn_head; element; element = element->pn_next) {
+            if (element->isKind(PNK_ELISION))
+                continue;
+            ParseNode* target = element;
+            if (element->isKind(PNK_SPREAD)) {
+                target = element->pn_kid;
+            }
+            if (target->isKind(PNK_ASSIGN))
+                target = target->pn_left;
+            if (target->isKind(PNK_NAME)) {
+                if (!emitName(this, target))
+                    return false;
+            } else {
+                if (!emitDestructuringDeclsWithEmitter(target, emitName))
+                    return false;
+            }
+        }
+        return true;
+    }
+
+    MOZ_ASSERT(pattern->isKind(PNK_OBJECT));
+    for (ParseNode* member = pattern->pn_head; member; member = member->pn_next) {
+        MOZ_ASSERT(member->isKind(PNK_MUTATEPROTO) ||
+                   member->isKind(PNK_COLON) ||
+                   member->isKind(PNK_SHORTHAND));
+
+        ParseNode* target = member->isKind(PNK_MUTATEPROTO) ? member->pn_kid : member->pn_right;
+
+        if (target->isKind(PNK_ASSIGN))
+            target = target->pn_left;
+        if (target->isKind(PNK_NAME)) {
+            if (!emitName(this, target))
+                return false;
+        } else {
+            if (!emitDestructuringDeclsWithEmitter(target, emitName))
+                return false;
+        }
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDestructuringLHS(ParseNode* target, DestructuringFlavor flav)
+{
+    // Now emit the lvalue opcode sequence. If the lvalue is a nested
+    // destructuring initialiser-form, call ourselves to handle it, then pop
+    // the matched value. Otherwise emit an lvalue bytecode sequence followed
+    // by an assignment op.
+    if (target->isKind(PNK_SPREAD))
+        target = target->pn_kid;
+    else if (target->isKind(PNK_ASSIGN))
+        target = target->pn_left;
+    if (target->isKind(PNK_ARRAY) || target->isKind(PNK_OBJECT)) {
+        if (!emitDestructuringOps(target, flav))
+            return false;
+        // Per its post-condition, emitDestructuringOps has left the
+        // to-be-destructured value on top of the stack.
+        if (!emit1(JSOP_POP))
+            return false;
+    } else {
+        switch (target->getKind()) {
+          case PNK_NAME: {
+            auto emitSwapScopeAndRhs = [](BytecodeEmitter* bce, const NameLocation&,
+                                          bool emittedBindOp)
+            {
+                if (emittedBindOp) {
+                    // This is like ordinary assignment, but with one
+                    // difference.
+                    //
+                    // In `a = b`, we first determine a binding for `a` (using
+                    // JSOP_BINDNAME or JSOP_BINDGNAME), then we evaluate `b`,
+                    // then a JSOP_SETNAME instruction.
+                    //
+                    // In `[a] = [b]`, per spec, `b` is evaluated first, then
+                    // we determine a binding for `a`. Then we need to do
+                    // assignment-- but the operands are on the stack in the
+                    // wrong order for JSOP_SETPROP, so we have to add a
+                    // JSOP_SWAP.
+                    //
+                    // In the cases where we are emitting a name op, emit a
+                    // swap because of this.
+                    return bce->emit1(JSOP_SWAP);
+                }
+
+                // In cases of emitting a frame slot or environment slot,
+                // nothing needs be done.
+                return true;
+            };
+
+            RootedAtom name(cx, target->name());
+            switch (flav) {
+              case DestructuringDeclaration:
+                if (!emitInitializeName(name, emitSwapScopeAndRhs))
+                    return false;
+                break;
+
+              case DestructuringFormalParameterInVarScope: {
+                // If there's an parameter expression var scope, the
+                // destructuring declaration needs to initialize the name in
+                // the function scope. The innermost scope is the var scope,
+                // and its enclosing scope is the function scope.
+                EmitterScope* funScope = innermostEmitterScope->enclosingInFrame();
+                NameLocation paramLoc = *locationOfNameBoundInScope(name, funScope);
+                if (!emitSetOrInitializeNameAtLocation(name, paramLoc, emitSwapScopeAndRhs, true))
+                    return false;
+                break;
+              }
+
+              case DestructuringAssignment:
+                if (!emitSetName(name, emitSwapScopeAndRhs))
+                    return false;
+                break;
+            }
+
+            break;
+          }
+
+          case PNK_DOT: {
+            // See the (PNK_NAME, JSOP_SETNAME) case above.
+            //
+            // In `a.x = b`, `a` is evaluated first, then `b`, then a
+            // JSOP_SETPROP instruction.
+            //
+            // In `[a.x] = [b]`, per spec, `b` is evaluated before `a`. Then we
+            // need a property set -- but the operands are on the stack in the
+            // wrong order for JSOP_SETPROP, so we have to add a JSOP_SWAP.
+            JSOp setOp;
+            if (target->as<PropertyAccess>().isSuper()) {
+                if (!emitSuperPropLHS(&target->as<PropertyAccess>().expression()))
+                    return false;
+                if (!emit2(JSOP_PICK, 2))
+                    return false;
+                setOp = sc->strict() ? JSOP_STRICTSETPROP_SUPER : JSOP_SETPROP_SUPER;
+            } else {
+                if (!emitTree(target->pn_expr))
+                    return false;
+                if (!emit1(JSOP_SWAP))
+                    return false;
+                setOp = sc->strict() ? JSOP_STRICTSETPROP : JSOP_SETPROP;
+            }
+            if (!emitAtomOp(target, setOp))
+                return false;
+            break;
+          }
+
+          case PNK_ELEM: {
+            // See the comment at `case PNK_DOT:` above. This case,
+            // `[a[x]] = [b]`, is handled much the same way. The JSOP_SWAP
+            // is emitted by emitElemOperands.
+            if (target->as<PropertyByValue>().isSuper()) {
+                JSOp setOp = sc->strict() ? JSOP_STRICTSETELEM_SUPER : JSOP_SETELEM_SUPER;
+                if (!emitSuperElemOp(target, setOp))
+                    return false;
+            } else {
+                JSOp setOp = sc->strict() ? JSOP_STRICTSETELEM : JSOP_SETELEM;
+                if (!emitElemOp(target, setOp))
+                    return false;
+            }
+            break;
+          }
+
+          case PNK_CALL:
+            MOZ_ASSERT_UNREACHABLE("Parser::reportIfNotValidSimpleAssignmentTarget "
+                                   "rejects function calls as assignment "
+                                   "targets in destructuring assignments");
+            break;
+
+          default:
+            MOZ_CRASH("emitDestructuringLHS: bad lhs kind");
+        }
+
+        // Pop the assigned value.
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitConditionallyExecutedDestructuringLHS(ParseNode* target, DestructuringFlavor flav)
+{
+    TDZCheckCache tdzCache(this);
+    return emitDestructuringLHS(target, flav);
+}
+
+bool
+BytecodeEmitter::emitIteratorNext(ParseNode* pn, bool allowSelfHosted)
+{
+    MOZ_ASSERT(allowSelfHosted || emitterMode != BytecodeEmitter::SelfHosting,
+               ".next() iteration is prohibited in self-hosted code because it "
+               "can run user-modifiable iteration code");
+
+    if (!emit1(JSOP_DUP))                                 // ... ITER ITER
+        return false;
+    if (!emitAtomOp(cx->names().next, JSOP_CALLPROP))     // ... ITER NEXT
+        return false;
+    if (!emit1(JSOP_SWAP))                                // ... NEXT ITER
+        return false;
+    if (!emitCall(JSOP_CALL, 0, pn))                      // ... RESULT
+        return false;
+    if (!emitCheckIsObj(CheckIsObjectKind::IteratorNext)) // ... RESULT
+        return false;
+    checkTypeSet(JSOP_CALL);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDefault(ParseNode* defaultExpr)
+{
+    if (!emit1(JSOP_DUP))                                 // VALUE VALUE
+        return false;
+    if (!emit1(JSOP_UNDEFINED))                           // VALUE VALUE UNDEFINED
+        return false;
+    if (!emit1(JSOP_STRICTEQ))                            // VALUE EQL?
+        return false;
+    // Emit source note to enable ion compilation.
+    if (!newSrcNote(SRC_IF))
+        return false;
+    JumpList jump;
+    if (!emitJump(JSOP_IFEQ, &jump))                      // VALUE
+        return false;
+    if (!emit1(JSOP_POP))                                 // .
+        return false;
+    if (!emitConditionallyExecutedTree(defaultExpr))      // DEFAULTVALUE
+        return false;
+    if (!emitJumpTargetAndPatch(jump))
+        return false;
+    return true;
+}
+
+class MOZ_STACK_CLASS IfThenElseEmitter
+{
+    BytecodeEmitter* bce_;
+    JumpList jumpAroundThen_;
+    JumpList jumpsAroundElse_;
+    unsigned noteIndex_;
+    int32_t thenDepth_;
+#ifdef DEBUG
+    int32_t pushed_;
+    bool calculatedPushed_;
+#endif
+    enum State {
+        Start,
+        If,
+        Cond,
+        IfElse,
+        Else,
+        End
+    };
+    State state_;
+
+  public:
+    explicit IfThenElseEmitter(BytecodeEmitter* bce)
+      : bce_(bce),
+        noteIndex_(-1),
+        thenDepth_(0),
+#ifdef DEBUG
+        pushed_(0),
+        calculatedPushed_(false),
+#endif
+        state_(Start)
+    {}
+
+    ~IfThenElseEmitter()
+    {}
+
+  private:
+    bool emitIf(State nextState) {
+        MOZ_ASSERT(state_ == Start || state_ == Else);
+        MOZ_ASSERT(nextState == If || nextState == IfElse || nextState == Cond);
+
+        // Clear jumpAroundThen_ offset that points previous JSOP_IFEQ.
+        if (state_ == Else)
+            jumpAroundThen_ = JumpList();
+
+        // Emit an annotated branch-if-false around the then part.
+        SrcNoteType type = nextState == If ? SRC_IF : nextState == IfElse ? SRC_IF_ELSE : SRC_COND;
+        if (!bce_->newSrcNote(type, &noteIndex_))
+            return false;
+        if (!bce_->emitJump(JSOP_IFEQ, &jumpAroundThen_))
+            return false;
+
+        // To restore stack depth in else part, save depth of the then part.
+#ifdef DEBUG
+        // If DEBUG, this is also necessary to calculate |pushed_|.
+        thenDepth_ = bce_->stackDepth;
+#else
+        if (nextState == IfElse || nextState == Cond)
+            thenDepth_ = bce_->stackDepth;
+#endif
+        state_ = nextState;
+        return true;
+    }
+
+  public:
+    bool emitIf() {
+        return emitIf(If);
+    }
+
+    bool emitCond() {
+        return emitIf(Cond);
+    }
+
+    bool emitIfElse() {
+        return emitIf(IfElse);
+    }
+
+    bool emitElse() {
+        MOZ_ASSERT(state_ == IfElse || state_ == Cond);
+
+        calculateOrCheckPushed();
+
+        // Emit a jump from the end of our then part around the else part. The
+        // patchJumpsToTarget call at the bottom of this function will fix up
+        // the offset with jumpsAroundElse value.
+        if (!bce_->emitJump(JSOP_GOTO, &jumpsAroundElse_))
+            return false;
+
+        // Ensure the branch-if-false comes here, then emit the else.
+        if (!bce_->emitJumpTargetAndPatch(jumpAroundThen_))
+            return false;
+
+        // Annotate SRC_IF_ELSE or SRC_COND with the offset from branch to
+        // jump, for IonMonkey's benefit.  We can't just "back up" from the pc
+        // of the else clause, because we don't know whether an extended
+        // jump was required to leap from the end of the then clause over
+        // the else clause.
+        if (!bce_->setSrcNoteOffset(noteIndex_, 0,
+                                    jumpsAroundElse_.offset - jumpAroundThen_.offset))
+        {
+            return false;
+        }
+
+        // Restore stack depth of the then part.
+        bce_->stackDepth = thenDepth_;
+        state_ = Else;
+        return true;
+    }
+
+    bool emitEnd() {
+        MOZ_ASSERT(state_ == If || state_ == Else);
+
+        calculateOrCheckPushed();
+
+        if (state_ == If) {
+            // No else part, fixup the branch-if-false to come here.
+            if (!bce_->emitJumpTargetAndPatch(jumpAroundThen_))
+                return false;
+        }
+
+        // Patch all the jumps around else parts.
+        if (!bce_->emitJumpTargetAndPatch(jumpsAroundElse_))
+            return false;
+
+        state_ = End;
+        return true;
+    }
+
+    void calculateOrCheckPushed() {
+#ifdef DEBUG
+        if (!calculatedPushed_) {
+            pushed_ = bce_->stackDepth - thenDepth_;
+            calculatedPushed_ = true;
+        } else {
+            MOZ_ASSERT(pushed_ == bce_->stackDepth - thenDepth_);
+        }
+#endif
+    }
+
+#ifdef DEBUG
+    int32_t pushed() const {
+        return pushed_;
+    }
+
+    int32_t popped() const {
+        return -pushed_;
+    }
+#endif
+};
+
+bool
+BytecodeEmitter::emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlavor flav)
+{
+    MOZ_ASSERT(pattern->isKind(PNK_ARRAY));
+    MOZ_ASSERT(pattern->isArity(PN_LIST));
+    MOZ_ASSERT(this->stackDepth != 0);
+
+    // Here's pseudo code for |let [a, b, , c=y, ...d] = x;|
+    //
+    //   let x, y;
+    //   let a, b, c, d;
+    //   let tmp, done, iter, result; // stack values
+    //
+    //   iter = x[Symbol.iterator]();
+    //
+    //   // ==== emitted by loop for a ====
+    //   result = iter.next();
+    //   done = result.done;
+    //
+    //   if (done) {
+    //     a = undefined;
+    //
+    //     result = undefined;
+    //     done = true;
+    //   } else {
+    //     a = result.value;
+    //
+    //     // Do next element's .next() and .done access here
+    //     result = iter.next();
+    //     done = result.done;
+    //   }
+    //
+    //   // ==== emitted by loop for b ====
+    //   if (done) {
+    //     b = undefined;
+    //
+    //     result = undefined;
+    //     done = true;
+    //   } else {
+    //     b = result.value;
+    //
+    //     result = iter.next();
+    //     done = result.done;
+    //   }
+    //
+    //   // ==== emitted by loop for elision ====
+    //   if (done) {
+    //     result = undefined
+    //     done = true
+    //   } else {
+    //     result.value;
+    //
+    //     result = iter.next();
+    //     done = result.done;
+    //   }
+    //
+    //   // ==== emitted by loop for c ====
+    //   if (done) {
+    //     c = y;
+    //   } else {
+    //     tmp = result.value;
+    //     if (tmp === undefined)
+    //       tmp = y;
+    //     c = tmp;
+    //
+    //     // Don't do next element's .next() and .done access if
+    //     // this is the last non-spread element.
+    //   }
+    //
+    //   // ==== emitted by loop for d ====
+    //   if (done) {
+    //     // Assing empty array when completed
+    //     d = [];
+    //   } else {
+    //     d = [...iter];
+    //   }
+
+    /*
+     * Use an iterator to destructure the RHS, instead of index lookup. We
+     * must leave the *original* value on the stack.
+     */
+    if (!emit1(JSOP_DUP))                                         // ... OBJ OBJ
+        return false;
+    if (!emitIterator())                                          // ... OBJ? ITER
+        return false;
+    bool needToPopIterator = true;
+
+    for (ParseNode* member = pattern->pn_head; member; member = member->pn_next) {
+        bool isHead = member == pattern->pn_head;
+        if (member->isKind(PNK_SPREAD)) {
+            IfThenElseEmitter ifThenElse(this);
+            if (!isHead) {
+                // If spread is not the first element of the pattern,
+                // iterator can already be completed.
+                if (!ifThenElse.emitIfElse())                     // ... OBJ? ITER
+                    return false;
+
+                if (!emit1(JSOP_POP))                             // ... OBJ?
+                    return false;
+                if (!emitUint32Operand(JSOP_NEWARRAY, 0))         // ... OBJ? ARRAY
+                    return false;
+                if (!emitConditionallyExecutedDestructuringLHS(member, flav)) // ... OBJ?
+                    return false;
+
+                if (!ifThenElse.emitElse())                       // ... OBJ? ITER
+                    return false;
+            }
+
+            // If iterator is not completed, create a new array with the rest
+            // of the iterator.
+            if (!emitUint32Operand(JSOP_NEWARRAY, 0))             // ... OBJ? ITER ARRAY
+                return false;
+            if (!emitNumberOp(0))                                 // ... OBJ? ITER ARRAY INDEX
+                return false;
+            if (!emitSpread())                                    // ... OBJ? ARRAY INDEX
+                return false;
+            if (!emit1(JSOP_POP))                                 // ... OBJ? ARRAY
+                return false;
+            if (!emitConditionallyExecutedDestructuringLHS(member, flav)) // ... OBJ?
+                return false;
+
+            if (!isHead) {
+                if (!ifThenElse.emitEnd())
+                    return false;
+                MOZ_ASSERT(ifThenElse.popped() == 1);
+            }
+            needToPopIterator = false;
+            MOZ_ASSERT(!member->pn_next);
+            break;
+        }
+
+        ParseNode* pndefault = nullptr;
+        ParseNode* subpattern = member;
+        if (subpattern->isKind(PNK_ASSIGN)) {
+            pndefault = subpattern->pn_right;
+            subpattern = subpattern->pn_left;
+        }
+
+        bool isElision = subpattern->isKind(PNK_ELISION);
+        bool hasNextNonSpread = member->pn_next && !member->pn_next->isKind(PNK_SPREAD);
+        bool hasNextSpread = member->pn_next && member->pn_next->isKind(PNK_SPREAD);
+
+        MOZ_ASSERT(!subpattern->isKind(PNK_SPREAD));
+
+        auto emitNext = [pattern](ExclusiveContext* cx, BytecodeEmitter* bce) {
+            if (!bce->emit1(JSOP_DUP))                            // ... OBJ? ITER ITER
+                return false;
+            if (!bce->emitIteratorNext(pattern))                  // ... OBJ? ITER RESULT
+                return false;
+            if (!bce->emit1(JSOP_DUP))                            // ... OBJ? ITER RESULT RESULT
+                return false;
+            if (!bce->emitAtomOp(cx->names().done, JSOP_GETPROP)) // ... OBJ? ITER RESULT DONE?
+                return false;
+            return true;
+        };
+
+        if (isHead) {
+            if (!emitNext(cx, this))                              // ... OBJ? ITER RESULT DONE?
+                return false;
+        }
+
+        IfThenElseEmitter ifThenElse(this);
+        if (!ifThenElse.emitIfElse())                             // ... OBJ? ITER RESULT
+            return false;
+
+        if (!emit1(JSOP_POP))                                     // ... OBJ? ITER
+            return false;
+        if (pndefault) {
+            // Emit only pndefault tree here, as undefined check in emitDefault
+            // should always be true.
+            if (!emitConditionallyExecutedTree(pndefault))        // ... OBJ? ITER VALUE
+                return false;
+        } else {
+            if (!isElision) {
+                if (!emit1(JSOP_UNDEFINED))                       // ... OBJ? ITER UNDEFINED
+                    return false;
+                if (!emit1(JSOP_NOP_DESTRUCTURING))
+                    return false;
+            }
+        }
+        if (!isElision) {
+            if (!emitConditionallyExecutedDestructuringLHS(subpattern, flav)) // ... OBJ? ITER
+                return false;
+        } else if (pndefault) {
+            if (!emit1(JSOP_POP))                                 // ... OBJ? ITER
+                return false;
+        }
+
+        // Setup next element's result when the iterator is done.
+        if (hasNextNonSpread) {
+            if (!emit1(JSOP_UNDEFINED))                           // ... OBJ? ITER RESULT
+                return false;
+            if (!emit1(JSOP_NOP_DESTRUCTURING))
+                return false;
+            if (!emit1(JSOP_TRUE))                                // ... OBJ? ITER RESULT DONE?
+                return false;
+        } else if (hasNextSpread) {
+            if (!emit1(JSOP_TRUE))                                // ... OBJ? ITER DONE?
+                return false;
+        }
+
+        if (!ifThenElse.emitElse())                               // ... OBJ? ITER RESULT
+            return false;
+
+        if (!emitAtomOp(cx->names().value, JSOP_GETPROP))         // ... OBJ? ITER VALUE
+            return false;
+
+        if (pndefault) {
+            if (!emitDefault(pndefault))                          // ... OBJ? ITER VALUE
+                return false;
+        }
+
+        if (!isElision) {
+            if (!emitConditionallyExecutedDestructuringLHS(subpattern, flav)) // ... OBJ? ITER
+                return false;
+        } else {
+            if (!emit1(JSOP_POP))                                 // ... OBJ? ITER
+                return false;
+        }
+
+        // Setup next element's result when the iterator is not done.
+        if (hasNextNonSpread) {
+            if (!emitNext(cx, this))                              // ... OBJ? ITER RESULT DONE?
+                return false;
+        } else if (hasNextSpread) {
+            if (!emit1(JSOP_FALSE))                               // ... OBJ? ITER DONE?
+                return false;
+        }
+
+        if (!ifThenElse.emitEnd())
+            return false;
+        if (hasNextNonSpread)
+            MOZ_ASSERT(ifThenElse.pushed() == 1);
+        else if (hasNextSpread)
+            MOZ_ASSERT(ifThenElse.pushed() == 0);
+        else
+            MOZ_ASSERT(ifThenElse.popped() == 1);
+    }
+
+    if (needToPopIterator) {
+        if (!emit1(JSOP_POP))                                     // ... OBJ?
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitComputedPropertyName(ParseNode* computedPropName)
+{
+    MOZ_ASSERT(computedPropName->isKind(PNK_COMPUTED_NAME));
+    return emitTree(computedPropName->pn_kid) && emit1(JSOP_TOID);
+}
+
+bool
+BytecodeEmitter::emitDestructuringOpsObject(ParseNode* pattern, DestructuringFlavor flav)
+{
+    MOZ_ASSERT(pattern->isKind(PNK_OBJECT));
+    MOZ_ASSERT(pattern->isArity(PN_LIST));
+
+    MOZ_ASSERT(this->stackDepth > 0);                             // ... RHS
+
+    if (!emitRequireObjectCoercible())                            // ... RHS
+        return false;
+
+    for (ParseNode* member = pattern->pn_head; member; member = member->pn_next) {
+        // Duplicate the value being destructured to use as a reference base.
+        if (!emit1(JSOP_DUP))                                     // ... RHS RHS
+            return false;
+
+        // Now push the property name currently being matched, which is the
+        // current property name "label" on the left of a colon in the object
+        // initialiser.
+        bool needsGetElem = true;
+
+        ParseNode* subpattern;
+        if (member->isKind(PNK_MUTATEPROTO)) {
+            if (!emitAtomOp(cx->names().proto, JSOP_GETPROP))     // ... RHS PROP
+                return false;
+            needsGetElem = false;
+            subpattern = member->pn_kid;
+        } else {
+            MOZ_ASSERT(member->isKind(PNK_COLON) || member->isKind(PNK_SHORTHAND));
+
+            ParseNode* key = member->pn_left;
+            if (key->isKind(PNK_NUMBER)) {
+                if (!emitNumberOp(key->pn_dval))                  // ... RHS RHS KEY
+                    return false;
+            } else if (key->isKind(PNK_OBJECT_PROPERTY_NAME) || key->isKind(PNK_STRING)) {
+                PropertyName* name = key->pn_atom->asPropertyName();
+
+                // The parser already checked for atoms representing indexes and
+                // used PNK_NUMBER instead, but also watch for ids which TI treats
+                // as indexes for simplification of downstream analysis.
+                jsid id = NameToId(name);
+                if (id != IdToTypeId(id)) {
+                    if (!emitTree(key))                           // ... RHS RHS KEY
+                        return false;
+                } else {
+                    if (!emitAtomOp(name, JSOP_GETPROP))          // ...RHS PROP
+                        return false;
+                    needsGetElem = false;
+                }
+            } else {
+                if (!emitComputedPropertyName(key))               // ... RHS RHS KEY
+                    return false;
+            }
+
+            subpattern = member->pn_right;
+        }
+
+        // Get the property value if not done already.
+        if (needsGetElem && !emitElemOpBase(JSOP_GETELEM))        // ... RHS PROP
+            return false;
+
+        if (subpattern->isKind(PNK_ASSIGN)) {
+            if (!emitDefault(subpattern->pn_right))
+                return false;
+            subpattern = subpattern->pn_left;
+        }
+
+        // Destructure PROP per this member's subpattern.
+        if (!emitDestructuringLHS(subpattern, flav))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDestructuringOps(ParseNode* pattern, DestructuringFlavor flav)
+{
+    if (pattern->isKind(PNK_ARRAY))
+        return emitDestructuringOpsArray(pattern, flav);
+    return emitDestructuringOpsObject(pattern, flav);
+}
+
+bool
+BytecodeEmitter::emitTemplateString(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isArity(PN_LIST));
+
+    bool pushedString = false;
+
+    for (ParseNode* pn2 = pn->pn_head; pn2 != NULL; pn2 = pn2->pn_next) {
+        bool isString = (pn2->getKind() == PNK_STRING || pn2->getKind() == PNK_TEMPLATE_STRING);
+
+        // Skip empty strings. These are very common: a template string like
+        // `${a}${b}` has three empty strings and without this optimization
+        // we'd emit four JSOP_ADD operations instead of just one.
+        if (isString && pn2->pn_atom->empty())
+            continue;
+
+        if (!isString) {
+            // We update source notes before emitting the expression
+            if (!updateSourceCoordNotes(pn2->pn_pos.begin))
+                return false;
+        }
+
+        if (!emitTree(pn2))
+            return false;
+
+        if (!isString) {
+            // We need to convert the expression to a string
+            if (!emit1(JSOP_TOSTRING))
+                return false;
+        }
+
+        if (pushedString) {
+            // We've pushed two strings onto the stack. Add them together, leaving just one.
+            if (!emit1(JSOP_ADD))
+                return false;
+        } else {
+            pushedString = true;
+        }
+    }
+
+    if (!pushedString) {
+        // All strings were empty, this can happen for something like `${""}`.
+        // Just push an empty string.
+        if (!emitAtomOp(cx->names().empty, JSOP_STRING))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDeclarationList(ParseNode* declList)
+{
+    MOZ_ASSERT(declList->isArity(PN_LIST));
+
+    ParseNode* next;
+    for (ParseNode* decl = declList->pn_head; decl; decl = next) {
+        if (!updateSourceCoordNotes(decl->pn_pos.begin))
+            return false;
+        next = decl->pn_next;
+
+        if (decl->isKind(PNK_ASSIGN)) {
+            MOZ_ASSERT(decl->isOp(JSOP_NOP));
+
+            ParseNode* pattern = decl->pn_left;
+            MOZ_ASSERT(pattern->isKind(PNK_ARRAY) || pattern->isKind(PNK_OBJECT));
+
+            if (!emitTree(decl->pn_right))
+                return false;
+
+            if (!emitDestructuringOps(pattern, DestructuringDeclaration))
+                return false;
+
+            if (!emit1(JSOP_POP))
+                return false;
+        } else {
+            if (!emitSingleDeclaration(declList, decl, decl->expr()))
+                return false;
+        }
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSingleDeclaration(ParseNode* declList, ParseNode* decl,
+                                       ParseNode* initializer)
+{
+    MOZ_ASSERT(decl->isKind(PNK_NAME));
+
+    // Nothing to do for initializer-less 'var' declarations, as there's no TDZ.
+    if (!initializer && declList->isKind(PNK_VAR))
+        return true;
+
+    auto emitRhs = [initializer, declList](BytecodeEmitter* bce, const NameLocation&, bool) {
+        if (!initializer) {
+            // Lexical declarations are initialized to undefined without an
+            // initializer.
+            MOZ_ASSERT(declList->isKind(PNK_LET),
+                       "var declarations without initializers handled above, "
+                       "and const declarations must have initializers");
+            return bce->emit1(JSOP_UNDEFINED);
+        }
+
+        MOZ_ASSERT(initializer);
+        return bce->emitTree(initializer);
+    };
+
+    if (!emitInitializeName(decl, emitRhs))
+        return false;
+
+    // Pop the RHS.
+    return emit1(JSOP_POP);
+}
+
+static bool
+EmitAssignmentRhs(BytecodeEmitter* bce, ParseNode* rhs, uint8_t offset)
+{
+    // If there is a RHS tree, emit the tree.
+    if (rhs)
+        return bce->emitTree(rhs);
+
+    // Otherwise the RHS value to assign is already on the stack, i.e., the
+    // next enumeration value in a for-in or for-of loop. Depending on how
+    // many other values have been pushed on the stack, we need to get the
+    // already-pushed RHS value.
+    if (offset != 1 && !bce->emit2(JSOP_PICK, offset - 1))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitAssignment(ParseNode* lhs, JSOp op, ParseNode* rhs)
+{
+    // Name assignments are handled separately because choosing ops and when
+    // to emit BINDNAME is involved and should avoid duplication.
+    if (lhs->isKind(PNK_NAME)) {
+        auto emitRhs = [op, lhs, rhs](BytecodeEmitter* bce, const NameLocation& lhsLoc,
+                                      bool emittedBindOp)
+        {
+            // For compound assignments, first get the LHS value, then emit
+            // the RHS and the op.
+            if (op != JSOP_NOP) {
+                if (lhsLoc.kind() == NameLocation::Kind::Dynamic) {
+                    // For dynamic accesses we can do better than a GETNAME
+                    // since the assignment already emitted a BINDNAME on the
+                    // top of the stack. As an optimization, use that to get
+                    // the name.
+                    if (!bce->emit1(JSOP_DUP))
+                        return false;
+                    if (!bce->emitAtomOp(lhs, JSOP_GETXPROP))
+                        return false;
+                } else {
+                    if (!bce->emitGetNameAtLocation(lhs->name(), lhsLoc))
+                        return false;
+                }
+            }
+
+            // Emit the RHS. If we emitted a BIND[G]NAME, then the scope is on
+            // the top of the stack and we need to pick the right RHS value.
+            if (!EmitAssignmentRhs(bce, rhs, emittedBindOp ? 2 : 1))
+                return false;
+
+            // Emit the compound assignment op if there is one.
+            if (op != JSOP_NOP && !bce->emit1(op))
+                return false;
+
+            return true;
+        };
+
+        return emitSetName(lhs, emitRhs);
+    }
+
+    // Deal with non-name assignments.
+    uint32_t atomIndex = (uint32_t) -1;
+    uint8_t offset = 1;
+
+    switch (lhs->getKind()) {
+      case PNK_DOT:
+        if (lhs->as<PropertyAccess>().isSuper()) {
+            if (!emitSuperPropLHS(&lhs->as<PropertyAccess>().expression()))
+                return false;
+            offset += 2;
+        } else {
+            if (!emitTree(lhs->expr()))
+                return false;
+            offset += 1;
+        }
+        if (!makeAtomIndex(lhs->pn_atom, &atomIndex))
+            return false;
+        break;
+      case PNK_ELEM: {
+        MOZ_ASSERT(lhs->isArity(PN_BINARY));
+        EmitElemOption opt = op == JSOP_NOP ? EmitElemOption::Get : EmitElemOption::CompoundAssign;
+        if (lhs->as<PropertyByValue>().isSuper()) {
+            if (!emitSuperElemOperands(lhs, opt))
+                return false;
+            offset += 3;
+        } else {
+            if (!emitElemOperands(lhs, opt))
+                return false;
+            offset += 2;
+        }
+        break;
+      }
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+        break;
+      case PNK_CALL:
+        if (!emitTree(lhs))
+            return false;
+
+        // Assignment to function calls is forbidden, but we have to make the
+        // call first.  Now we can throw.
+        if (!emitUint16Operand(JSOP_THROWMSG, JSMSG_BAD_LEFTSIDE_OF_ASS))
+            return false;
+
+        // Rebalance the stack to placate stack-depth assertions.
+        if (!emit1(JSOP_POP))
+            return false;
+        break;
+      default:
+        MOZ_ASSERT(0);
+    }
+
+    if (op != JSOP_NOP) {
+        MOZ_ASSERT(rhs);
+        switch (lhs->getKind()) {
+          case PNK_DOT: {
+            JSOp getOp;
+            if (lhs->as<PropertyAccess>().isSuper()) {
+                if (!emit1(JSOP_DUP2))
+                    return false;
+                getOp = JSOP_GETPROP_SUPER;
+            } else {
+                if (!emit1(JSOP_DUP))
+                    return false;
+                bool isLength = (lhs->pn_atom == cx->names().length);
+                getOp = isLength ? JSOP_LENGTH : JSOP_GETPROP;
+            }
+            if (!emitIndex32(getOp, atomIndex))
+                return false;
+            break;
+          }
+          case PNK_ELEM: {
+            JSOp elemOp;
+            if (lhs->as<PropertyByValue>().isSuper()) {
+                if (!emitDupAt(2))
+                    return false;
+                if (!emitDupAt(2))
+                    return false;
+                if (!emitDupAt(2))
+                    return false;
+                elemOp = JSOP_GETELEM_SUPER;
+            } else {
+                if (!emit1(JSOP_DUP2))
+                    return false;
+                elemOp = JSOP_GETELEM;
+            }
+            if (!emitElemOpBase(elemOp))
+                return false;
+            break;
+          }
+          case PNK_CALL:
+            // We just emitted a JSOP_THROWMSG and popped the call's return
+            // value.  Push a random value to make sure the stack depth is
+            // correct.
+            if (!emit1(JSOP_NULL))
+                return false;
+            break;
+          default:;
+        }
+    }
+
+    if (!EmitAssignmentRhs(this, rhs, offset))
+        return false;
+
+    /* If += etc., emit the binary operator with a source note. */
+    if (op != JSOP_NOP) {
+        if (!newSrcNote(SRC_ASSIGNOP))
+            return false;
+        if (!emit1(op))
+            return false;
+    }
+
+    /* Finally, emit the specialized assignment bytecode. */
+    switch (lhs->getKind()) {
+      case PNK_DOT: {
+        JSOp setOp = lhs->as<PropertyAccess>().isSuper() ?
+                       (sc->strict() ? JSOP_STRICTSETPROP_SUPER : JSOP_SETPROP_SUPER) :
+                       (sc->strict() ? JSOP_STRICTSETPROP : JSOP_SETPROP);
+        if (!emitIndexOp(setOp, atomIndex))
+            return false;
+        break;
+      }
+      case PNK_CALL:
+        // We threw above, so nothing to do here.
+        break;
+      case PNK_ELEM: {
+        JSOp setOp = lhs->as<PropertyByValue>().isSuper() ?
+                       sc->strict() ? JSOP_STRICTSETELEM_SUPER : JSOP_SETELEM_SUPER :
+                       sc->strict() ? JSOP_STRICTSETELEM : JSOP_SETELEM;
+        if (!emit1(setOp))
+            return false;
+        break;
+      }
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+        if (!emitDestructuringOps(lhs, DestructuringAssignment))
+            return false;
+        break;
+      default:
+        MOZ_ASSERT(0);
+    }
+    return true;
+}
+
+bool
+ParseNode::getConstantValue(ExclusiveContext* cx, AllowConstantObjects allowObjects,
+                            MutableHandleValue vp, Value* compare, size_t ncompare,
+                            NewObjectKind newKind)
+{
+    MOZ_ASSERT(newKind == TenuredObject || newKind == SingletonObject);
+
+    switch (getKind()) {
+      case PNK_NUMBER:
+        vp.setNumber(pn_dval);
+        return true;
+      case PNK_TEMPLATE_STRING:
+      case PNK_STRING:
+        vp.setString(pn_atom);
+        return true;
+      case PNK_TRUE:
+        vp.setBoolean(true);
+        return true;
+      case PNK_FALSE:
+        vp.setBoolean(false);
+        return true;
+      case PNK_NULL:
+        vp.setNull();
+        return true;
+      case PNK_CALLSITEOBJ:
+      case PNK_ARRAY: {
+        unsigned count;
+        ParseNode* pn;
+
+        if (allowObjects == DontAllowObjects) {
+            vp.setMagic(JS_GENERIC_MAGIC);
+            return true;
+        }
+
+        ObjectGroup::NewArrayKind arrayKind = ObjectGroup::NewArrayKind::Normal;
+        if (allowObjects == ForCopyOnWriteArray) {
+            arrayKind = ObjectGroup::NewArrayKind::CopyOnWrite;
+            allowObjects = DontAllowObjects;
+        }
+
+        if (getKind() == PNK_CALLSITEOBJ) {
+            count = pn_count - 1;
+            pn = pn_head->pn_next;
+        } else {
+            MOZ_ASSERT(isOp(JSOP_NEWINIT) && !(pn_xflags & PNX_NONCONST));
+            count = pn_count;
+            pn = pn_head;
+        }
+
+        AutoValueVector values(cx);
+        if (!values.appendN(MagicValue(JS_ELEMENTS_HOLE), count))
+            return false;
+        size_t idx;
+        for (idx = 0; pn; idx++, pn = pn->pn_next) {
+            if (!pn->getConstantValue(cx, allowObjects, values[idx], values.begin(), idx))
+                return false;
+            if (values[idx].isMagic(JS_GENERIC_MAGIC)) {
+                vp.setMagic(JS_GENERIC_MAGIC);
+                return true;
+            }
+        }
+        MOZ_ASSERT(idx == count);
+
+        JSObject* obj = ObjectGroup::newArrayObject(cx, values.begin(), values.length(),
+                                                    newKind, arrayKind);
+        if (!obj)
+            return false;
+
+        if (!CombineArrayElementTypes(cx, obj, compare, ncompare))
+            return false;
+
+        vp.setObject(*obj);
+        return true;
+      }
+      case PNK_OBJECT: {
+        MOZ_ASSERT(isOp(JSOP_NEWINIT));
+        MOZ_ASSERT(!(pn_xflags & PNX_NONCONST));
+
+        if (allowObjects == DontAllowObjects) {
+            vp.setMagic(JS_GENERIC_MAGIC);
+            return true;
+        }
+        MOZ_ASSERT(allowObjects == AllowObjects);
+
+        Rooted<IdValueVector> properties(cx, IdValueVector(cx));
+
+        RootedValue value(cx), idvalue(cx);
+        for (ParseNode* pn = pn_head; pn; pn = pn->pn_next) {
+            if (!pn->pn_right->getConstantValue(cx, allowObjects, &value))
+                return false;
+            if (value.isMagic(JS_GENERIC_MAGIC)) {
+                vp.setMagic(JS_GENERIC_MAGIC);
+                return true;
+            }
+
+            ParseNode* pnid = pn->pn_left;
+            if (pnid->isKind(PNK_NUMBER)) {
+                idvalue = NumberValue(pnid->pn_dval);
+            } else {
+                MOZ_ASSERT(pnid->isKind(PNK_OBJECT_PROPERTY_NAME) || pnid->isKind(PNK_STRING));
+                MOZ_ASSERT(pnid->pn_atom != cx->names().proto);
+                idvalue = StringValue(pnid->pn_atom);
+            }
+
+            RootedId id(cx);
+            if (!ValueToId<CanGC>(cx, idvalue, &id))
+                return false;
+
+            if (!properties.append(IdValuePair(id, value)))
+                return false;
+        }
+
+        JSObject* obj = ObjectGroup::newPlainObject(cx, properties.begin(), properties.length(),
+                                                    newKind);
+        if (!obj)
+            return false;
+
+        if (!CombinePlainObjectPropertyTypes(cx, obj, compare, ncompare))
+            return false;
+
+        vp.setObject(*obj);
+        return true;
+      }
+      default:
+        MOZ_CRASH("Unexpected node");
+    }
+    return false;
+}
+
+bool
+BytecodeEmitter::emitSingletonInitialiser(ParseNode* pn)
+{
+    NewObjectKind newKind = (pn->getKind() == PNK_OBJECT) ? SingletonObject : TenuredObject;
+
+    RootedValue value(cx);
+    if (!pn->getConstantValue(cx, ParseNode::AllowObjects, &value, nullptr, 0, newKind))
+        return false;
+
+    MOZ_ASSERT_IF(newKind == SingletonObject, value.toObject().isSingleton());
+
+    ObjectBox* objbox = parser->newObjectBox(&value.toObject());
+    if (!objbox)
+        return false;
+
+    return emitObjectOp(objbox, JSOP_OBJECT);
+}
+
+bool
+BytecodeEmitter::emitCallSiteObject(ParseNode* pn)
+{
+    RootedValue value(cx);
+    if (!pn->getConstantValue(cx, ParseNode::AllowObjects, &value))
+        return false;
+
+    MOZ_ASSERT(value.isObject());
+
+    ObjectBox* objbox1 = parser->newObjectBox(&value.toObject());
+    if (!objbox1)
+        return false;
+
+    if (!pn->as<CallSiteNode>().getRawArrayValue(cx, &value))
+        return false;
+
+    MOZ_ASSERT(value.isObject());
+
+    ObjectBox* objbox2 = parser->newObjectBox(&value.toObject());
+    if (!objbox2)
+        return false;
+
+    return emitObjectPairOp(objbox1, objbox2, JSOP_CALLSITEOBJ);
+}
+
+/* See the SRC_FOR source note offsetBias comments later in this file. */
+JS_STATIC_ASSERT(JSOP_NOP_LENGTH == 1);
+JS_STATIC_ASSERT(JSOP_POP_LENGTH == 1);
+
+namespace {
+
+class EmitLevelManager
+{
+    BytecodeEmitter* bce;
+  public:
+    explicit EmitLevelManager(BytecodeEmitter* bce) : bce(bce) { bce->emitLevel++; }
+    ~EmitLevelManager() { bce->emitLevel--; }
+};
+
+} /* anonymous namespace */
+
+bool
+BytecodeEmitter::emitCatch(ParseNode* pn)
+{
+    // We must be nested under a try-finally statement.
+    TryFinallyControl& controlInfo = innermostNestableControl->as<TryFinallyControl>();
+
+    /* Pick up the pending exception and bind it to the catch variable. */
+    if (!emit1(JSOP_EXCEPTION))
+        return false;
+
+    /*
+     * Dup the exception object if there is a guard for rethrowing to use
+     * it later when rethrowing or in other catches.
+     */
+    if (pn->pn_kid2 && !emit1(JSOP_DUP))
+        return false;
+
+    ParseNode* pn2 = pn->pn_kid1;
+    switch (pn2->getKind()) {
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+        if (!emitDestructuringOps(pn2, DestructuringDeclaration))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+        break;
+
+      case PNK_NAME:
+        if (!emitLexicalInitialization(pn2))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+        break;
+
+      default:
+        MOZ_ASSERT(0);
+    }
+
+    // If there is a guard expression, emit it and arrange to jump to the next
+    // catch block if the guard expression is false.
+    if (pn->pn_kid2) {
+        if (!emitTree(pn->pn_kid2))
+            return false;
+
+        // If the guard expression is false, fall through, pop the block scope,
+        // and jump to the next catch block.  Otherwise jump over that code and
+        // pop the dupped exception.
+        JumpList guardCheck;
+        if (!emitJump(JSOP_IFNE, &guardCheck))
+            return false;
+
+        {
+            NonLocalExitControl nle(this);
+
+            // Move exception back to cx->exception to prepare for
+            // the next catch.
+            if (!emit1(JSOP_THROWING))
+                return false;
+
+            // Leave the scope for this catch block.
+            if (!nle.prepareForNonLocalJump(&controlInfo))
+                return false;
+
+            // Jump to the next handler added by emitTry.
+            if (!emitJump(JSOP_GOTO, &controlInfo.guardJump))
+                return false;
+        }
+
+        // Back to normal control flow.
+        if (!emitJumpTargetAndPatch(guardCheck))
+            return false;
+
+        // Pop duplicated exception object as we no longer need it.
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+
+    /* Emit the catch body. */
+    return emitTree(pn->pn_kid3);
+}
+
+// Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See the
+// comment on EmitSwitch.
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitTry(ParseNode* pn)
+{
+    // Track jumps-over-catches and gosubs-to-finally for later fixup.
+    //
+    // When a finally block is active, non-local jumps (including
+    // jumps-over-catches) result in a GOSUB being written into the bytecode
+    // stream and fixed-up later.
+    //
+    TryFinallyControl controlInfo(this, pn->pn_kid3 ? StatementKind::Finally : StatementKind::Try);
+
+    // Since an exception can be thrown at any place inside the try block,
+    // we need to restore the stack and the scope chain before we transfer
+    // the control to the exception handler.
+    //
+    // For that we store in a try note associated with the catch or
+    // finally block the stack depth upon the try entry. The interpreter
+    // uses this depth to properly unwind the stack and the scope chain.
+    //
+    int depth = stackDepth;
+
+    // Record the try location, then emit the try block.
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_TRY, &noteIndex))
+        return false;
+    if (!emit1(JSOP_TRY))
+        return false;
+
+    ptrdiff_t tryStart = offset();
+    if (!emitTree(pn->pn_kid1))
+        return false;
+    MOZ_ASSERT(depth == stackDepth);
+
+    // GOSUB to finally, if present.
+    if (pn->pn_kid3) {
+        if (!emitJump(JSOP_GOSUB, &controlInfo.gosubs))
+            return false;
+    }
+
+    // Source note points to the jump at the end of the try block.
+    if (!setSrcNoteOffset(noteIndex, 0, offset() - tryStart + JSOP_TRY_LENGTH))
+        return false;
+
+    // Emit jump over catch and/or finally.
+    JumpList catchJump;
+    if (!emitJump(JSOP_GOTO, &catchJump))
+        return false;
+
+    JumpTarget tryEnd;
+    if (!emitJumpTarget(&tryEnd))
+        return false;
+
+    // If this try has a catch block, emit it.
+    ParseNode* catchList = pn->pn_kid2;
+    if (catchList) {
+        MOZ_ASSERT(catchList->isKind(PNK_CATCHLIST));
+
+        // The emitted code for a catch block looks like:
+        //
+        // [pushlexicalenv]             only if any local aliased
+        // exception
+        // if there is a catchguard:
+        //   dup
+        // setlocal 0; pop              assign or possibly destructure exception
+        // if there is a catchguard:
+        //   < catchguard code >
+        //   ifne POST
+        //   debugleaveblock
+        //   [poplexicalenv]            only if any local aliased
+        //   throwing                   pop exception to cx->exception
+        //   goto <next catch block>
+        //   POST: pop
+        // < catch block contents >
+        // debugleaveblock
+        // [poplexicalenv]              only if any local aliased
+        // goto <end of catch blocks>   non-local; finally applies
+        //
+        // If there's no catch block without a catchguard, the last <next catch
+        // block> points to rethrow code.  This code will [gosub] to the finally
+        // code if appropriate, and is also used for the catch-all trynote for
+        // capturing exceptions thrown from catch{} blocks.
+        //
+        for (ParseNode* pn3 = catchList->pn_head; pn3; pn3 = pn3->pn_next) {
+            MOZ_ASSERT(this->stackDepth == depth);
+
+            // Clear the frame's return value that might have been set by the
+            // try block:
+            //
+            //   eval("try { 1; throw 2 } catch(e) {}"); // undefined, not 1
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+            if (!emit1(JSOP_SETRVAL))
+                return false;
+
+            // Emit the lexical scope and catch body.
+            MOZ_ASSERT(pn3->isKind(PNK_LEXICALSCOPE));
+            if (!emitTree(pn3))
+                return false;
+
+            // gosub <finally>, if required.
+            if (pn->pn_kid3) {
+                if (!emitJump(JSOP_GOSUB, &controlInfo.gosubs))
+                    return false;
+                MOZ_ASSERT(this->stackDepth == depth);
+            }
+
+            // Jump over the remaining catch blocks.  This will get fixed
+            // up to jump to after catch/finally.
+            if (!emitJump(JSOP_GOTO, &catchJump))
+                return false;
+
+            // If this catch block had a guard clause, patch the guard jump to
+            // come here.
+            if (controlInfo.guardJump.offset != -1) {
+                if (!emitJumpTargetAndPatch(controlInfo.guardJump))
+                    return false;
+                controlInfo.guardJump.offset = -1;
+
+                // If this catch block is the last one, rethrow, delegating
+                // execution of any finally block to the exception handler.
+                if (!pn3->pn_next) {
+                    if (!emit1(JSOP_EXCEPTION))
+                        return false;
+                    if (!emit1(JSOP_THROW))
+                        return false;
+                }
+            }
+        }
+    }
+
+    MOZ_ASSERT(this->stackDepth == depth);
+
+    // Emit the finally handler, if there is one.
+    JumpTarget finallyStart{ 0 };
+    if (pn->pn_kid3) {
+        if (!emitJumpTarget(&finallyStart))
+            return false;
+
+        // Fix up the gosubs that might have been emitted before non-local
+        // jumps to the finally code.
+        patchJumpsToTarget(controlInfo.gosubs, finallyStart);
+
+        // Indicate that we're emitting a subroutine body.
+        controlInfo.setEmittingSubroutine();
+        if (!updateSourceCoordNotes(pn->pn_kid3->pn_pos.begin))
+            return false;
+        if (!emit1(JSOP_FINALLY))
+            return false;
+        if (!emit1(JSOP_GETRVAL))
+            return false;
+
+        // Clear the frame's return value to make break/continue return
+        // correct value even if there's no other statement before them:
+        //
+        //   eval("x: try { 1 } finally { break x; }");  // undefined, not 1
+        if (!emit1(JSOP_UNDEFINED))
+            return false;
+        if (!emit1(JSOP_SETRVAL))
+            return false;
+
+        if (!emitTree(pn->pn_kid3))
+            return false;
+        if (!emit1(JSOP_SETRVAL))
+            return false;
+        if (!emit1(JSOP_RETSUB))
+            return false;
+        hasTryFinally = true;
+        MOZ_ASSERT(this->stackDepth == depth);
+    }
+
+    // ReconstructPCStack needs a NOP here to mark the end of the last catch block.
+    if (!emit1(JSOP_NOP))
+        return false;
+
+    // Fix up the end-of-try/catch jumps to come here.
+    if (!emitJumpTargetAndPatch(catchJump))
+        return false;
+
+    // Add the try note last, to let post-order give us the right ordering
+    // (first to last for a given nesting level, inner to outer by level).
+    if (catchList && !tryNoteList.append(JSTRY_CATCH, depth, tryStart, tryEnd.offset))
+        return false;
+
+    // If we've got a finally, mark try+catch region with additional
+    // trynote to catch exceptions (re)thrown from a catch block or
+    // for the try{}finally{} case.
+    if (pn->pn_kid3 && !tryNoteList.append(JSTRY_FINALLY, depth, tryStart, finallyStart.offset))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitIf(ParseNode* pn)
+{
+    IfThenElseEmitter ifThenElse(this);
+
+  if_again:
+    /* Emit code for the condition before pushing stmtInfo. */
+    if (!emitConditionallyExecutedTree(pn->pn_kid1))
+        return false;
+
+    ParseNode* elseNode = pn->pn_kid3;
+    if (elseNode) {
+        if (!ifThenElse.emitIfElse())
+            return false;
+    } else {
+        if (!ifThenElse.emitIf())
+            return false;
+    }
+
+    /* Emit code for the then part. */
+    if (!emitConditionallyExecutedTree(pn->pn_kid2))
+        return false;
+
+    if (elseNode) {
+        if (!ifThenElse.emitElse())
+            return false;
+
+        if (elseNode->isKind(PNK_IF)) {
+            pn = elseNode;
+            goto if_again;
+        }
+
+        /* Emit code for the else part. */
+        if (!emitConditionallyExecutedTree(elseNode))
+            return false;
+    }
+
+    if (!ifThenElse.emitEnd())
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitHoistedFunctionsInList(ParseNode* list)
+{
+    MOZ_ASSERT(list->pn_xflags & PNX_FUNCDEFS);
+
+    for (ParseNode* pn = list->pn_head; pn; pn = pn->pn_next) {
+        ParseNode* maybeFun = pn;
+
+        if (!sc->strict()) {
+            while (maybeFun->isKind(PNK_LABEL))
+                maybeFun = maybeFun->as<LabeledStatement>().statement();
+        }
+
+        if (maybeFun->isKind(PNK_FUNCTION) && maybeFun->functionIsHoisted()) {
+            if (!emitTree(maybeFun))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitLexicalScopeBody(ParseNode* body, EmitLineNumberNote emitLineNote)
+{
+    if (body->isKind(PNK_STATEMENTLIST) && body->pn_xflags & PNX_FUNCDEFS) {
+        // This block contains function statements whose definitions are
+        // hoisted to the top of the block. Emit these as a separate pass
+        // before the rest of the block.
+        if (!emitHoistedFunctionsInList(body))
+            return false;
+    }
+
+    // Line notes were updated by emitLexicalScope.
+    return emitTree(body, emitLineNote);
+}
+
+// Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
+// the comment on emitSwitch.
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitLexicalScope(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_LEXICALSCOPE));
+
+    TDZCheckCache tdzCache(this);
+
+    ParseNode* body = pn->scopeBody();
+    if (pn->isEmptyScope())
+        return emitLexicalScopeBody(body);
+
+    // Update line number notes before emitting TDZ poison in
+    // EmitterScope::enterLexical to avoid spurious pausing on seemingly
+    // non-effectful lines in Debugger.
+    //
+    // For example, consider the following code.
+    //
+    // L1: {
+    // L2:   let x = 42;
+    // L3: }
+    //
+    // If line number notes were not updated before the TDZ poison, the TDZ
+    // poison bytecode sequence of 'uninitialized; initlexical' will have line
+    // number L1, and the Debugger will pause there.
+    if (!ParseNodeRequiresSpecialLineNumberNotes(body)) {
+        ParseNode* pnForPos = body;
+        if (body->isKind(PNK_STATEMENTLIST) && body->pn_head)
+            pnForPos = body->pn_head;
+        if (!updateLineNumberNotes(pnForPos->pn_pos.begin))
+            return false;
+    }
+
+    EmitterScope emitterScope(this);
+    ScopeKind kind;
+    if (body->isKind(PNK_CATCH))
+        kind = body->pn_kid1->isKind(PNK_NAME) ? ScopeKind::SimpleCatch : ScopeKind::Catch;
+    else
+        kind = ScopeKind::Lexical;
+
+    if (!emitterScope.enterLexical(this, kind, pn->scopeBindings()))
+        return false;
+
+    if (body->isKind(PNK_FOR)) {
+        // for loops need to emit {FRESHEN,RECREATE}LEXICALENV if there are
+        // lexical declarations in the head. Signal this by passing a
+        // non-nullptr lexical scope.
+        if (!emitFor(body, &emitterScope))
+            return false;
+    } else {
+        if (!emitLexicalScopeBody(body, SUPPRESS_LINENOTE))
+            return false;
+    }
+
+    return emitterScope.leave(this);
+}
+
+bool
+BytecodeEmitter::emitWith(ParseNode* pn)
+{
+    if (!emitTree(pn->pn_left))
+        return false;
+
+    EmitterScope emitterScope(this);
+    if (!emitterScope.enterWith(this))
+        return false;
+
+    if (!emitTree(pn->pn_right))
+        return false;
+
+    return emitterScope.leave(this);
+}
+
+bool
+BytecodeEmitter::emitRequireObjectCoercible()
+{
+    // For simplicity, handle this in self-hosted code, at cost of 13 bytes of
+    // bytecode versus 1 byte for a dedicated opcode.  As more places need this
+    // behavior, we may want to reconsider this tradeoff.
+
+#ifdef DEBUG
+    auto depth = this->stackDepth;
+#endif
+    MOZ_ASSERT(depth > 0);                 // VAL
+    if (!emit1(JSOP_DUP))                  // VAL VAL
+        return false;
+
+    // Note that "intrinsic" is a misnomer: we're calling a *self-hosted*
+    // function that's not an intrinsic!  But it nonetheless works as desired.
+    if (!emitAtomOp(cx->names().RequireObjectCoercible,
+                    JSOP_GETINTRINSIC))    // VAL VAL REQUIREOBJECTCOERCIBLE
+    {
+        return false;
+    }
+    if (!emit1(JSOP_UNDEFINED))            // VAL VAL REQUIREOBJECTCOERCIBLE UNDEFINED
+        return false;
+    if (!emit2(JSOP_PICK, 2))              // VAL REQUIREOBJECTCOERCIBLE UNDEFINED VAL
+        return false;
+    if (!emitCall(JSOP_CALL, 1))           // VAL IGNORED
+        return false;
+    checkTypeSet(JSOP_CALL);
+
+    if (!emit1(JSOP_POP))                  // VAL
+        return false;
+
+    MOZ_ASSERT(depth == this->stackDepth);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitIterator()
+{
+    // Convert iterable to iterator.
+    if (!emit1(JSOP_DUP))                                         // OBJ OBJ
+        return false;
+    if (!emit2(JSOP_SYMBOL, uint8_t(JS::SymbolCode::iterator)))   // OBJ OBJ @@ITERATOR
+        return false;
+    if (!emitElemOpBase(JSOP_CALLELEM))                           // OBJ ITERFN
+        return false;
+    if (!emit1(JSOP_SWAP))                                        // ITERFN OBJ
+        return false;
+    if (!emitCall(JSOP_CALLITER, 0))                              // ITER
+        return false;
+    checkTypeSet(JSOP_CALLITER);
+    if (!emitCheckIsObj(CheckIsObjectKind::GetIterator))          // ITER
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSpread(bool allowSelfHosted)
+{
+    LoopControl loopInfo(this, StatementKind::Spread);
+
+    // Jump down to the loop condition to minimize overhead assuming at least
+    // one iteration, as the other loop forms do.  Annotate so IonMonkey can
+    // find the loop-closing jump.
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR_OF, &noteIndex))
+        return false;
+
+    // Jump down to the loop condition to minimize overhead, assuming at least
+    // one iteration.  (This is also what we do for loops; whether this
+    // assumption holds for spreads is an unanswered question.)
+    JumpList initialJump;
+    if (!emitJump(JSOP_GOTO, &initialJump))               // ITER ARR I (during the goto)
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(nullptr, &top))                     // ITER ARR I
+        return false;
+
+    // When we enter the goto above, we have ITER ARR I on the stack.  But when
+    // we reach this point on the loop backedge (if spreading produces at least
+    // one value), we've additionally pushed a RESULT iteration value.
+    // Increment manually to reflect this.
+    this->stackDepth++;
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    {
+#ifdef DEBUG
+        auto loopDepth = this->stackDepth;
+#endif
+
+        // Emit code to assign result.value to the iteration variable.
+        if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ITER ARR I VALUE
+            return false;
+        if (!emit1(JSOP_INITELEM_INC))                    // ITER ARR (I+1)
+            return false;
+
+        MOZ_ASSERT(this->stackDepth == loopDepth - 1);
+
+        // Spread operations can't contain |continue|, so don't bother setting loop
+        // and enclosing "update" offsets, as we do with for-loops.
+
+        // COME FROM the beginning of the loop to here.
+        if (!emitLoopEntry(nullptr, initialJump))         // ITER ARR I
+            return false;
+
+        if (!emitDupAt(2))                                // ITER ARR I ITER
+            return false;
+        if (!emitIteratorNext(nullptr, allowSelfHosted))  // ITER ARR I RESULT
+            return false;
+        if (!emit1(JSOP_DUP))                             // ITER ARR I RESULT RESULT
+            return false;
+        if (!emitAtomOp(cx->names().done, JSOP_GETPROP))  // ITER ARR I RESULT DONE?
+            return false;
+
+        if (!emitBackwardJump(JSOP_IFEQ, top, &beq, &breakTarget)) // ITER ARR I RESULT
+            return false;
+
+        MOZ_ASSERT(this->stackDepth == loopDepth);
+    }
+
+    // Let Ion know where the closing jump of this loop is.
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - initialJump.offset))
+        return false;
+
+    // No breaks or continues should occur in spreads.
+    MOZ_ASSERT(loopInfo.breaks.offset == -1);
+    MOZ_ASSERT(loopInfo.continues.offset == -1);
+
+    if (!tryNoteList.append(JSTRY_FOR_OF, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    if (!emit2(JSOP_PICK, 3))                             // ARR FINAL_INDEX RESULT ITER
+        return false;
+
+    return emitUint16Operand(JSOP_POPN, 2);               // ARR FINAL_INDEX
+}
+
+bool
+BytecodeEmitter::emitInitializeForInOrOfTarget(ParseNode* forHead)
+{
+    MOZ_ASSERT(forHead->isKind(PNK_FORIN) || forHead->isKind(PNK_FOROF));
+    MOZ_ASSERT(forHead->isArity(PN_TERNARY));
+
+    MOZ_ASSERT(this->stackDepth >= 1,
+               "must have a per-iteration value for initializing");
+
+    ParseNode* target = forHead->pn_kid1;
+    MOZ_ASSERT(!forHead->pn_kid2);
+
+    // If the for-in/of loop didn't have a variable declaration, per-loop
+    // initialization is just assigning the iteration value to a target
+    // expression.
+    if (!parser->handler.isDeclarationList(target))
+        return emitAssignment(target, JSOP_NOP, nullptr); // ... ITERVAL
+
+    // Otherwise, per-loop initialization is (possibly) declaration
+    // initialization.  If the declaration is a lexical declaration, it must be
+    // initialized.  If the declaration is a variable declaration, an
+    // assignment to that name (which does *not* necessarily assign to the
+    // variable!) must be generated.
+
+    if (!updateSourceCoordNotes(target->pn_pos.begin))
+        return false;
+
+    MOZ_ASSERT(target->isForLoopDeclaration());
+    target = parser->handler.singleBindingFromDeclaration(target);
+
+    if (target->isKind(PNK_NAME)) {
+        auto emitSwapScopeAndRhs = [](BytecodeEmitter* bce, const NameLocation&,
+                                      bool emittedBindOp)
+        {
+            if (emittedBindOp) {
+                // Per-iteration initialization in for-in/of loops computes the
+                // iteration value *before* initializing.  Thus the
+                // initializing value may be buried under a bind-specific value
+                // on the stack.  Swap it to the top of the stack.
+                MOZ_ASSERT(bce->stackDepth >= 2);
+                return bce->emit1(JSOP_SWAP);
+            }
+
+            // In cases of emitting a frame slot or environment slot,
+            // nothing needs be done.
+            MOZ_ASSERT(bce->stackDepth >= 1);
+            return true;
+        };
+
+        // The caller handles removing the iteration value from the stack.
+        return emitInitializeName(target, emitSwapScopeAndRhs);
+    }
+
+    MOZ_ASSERT(!target->isKind(PNK_ASSIGN),
+               "for-in/of loop destructuring declarations can't have initializers");
+
+    MOZ_ASSERT(target->isKind(PNK_ARRAY) || target->isKind(PNK_OBJECT));
+    return emitDestructuringOps(target, DestructuringDeclaration);
+}
+
+bool
+BytecodeEmitter::emitForOf(ParseNode* forOfLoop, EmitterScope* headLexicalEmitterScope)
+{
+    MOZ_ASSERT(forOfLoop->isKind(PNK_FOR));
+    MOZ_ASSERT(forOfLoop->isArity(PN_BINARY));
+
+    ParseNode* forOfHead = forOfLoop->pn_left;
+    MOZ_ASSERT(forOfHead->isKind(PNK_FOROF));
+    MOZ_ASSERT(forOfHead->isArity(PN_TERNARY));
+
+    // Evaluate the expression being iterated.
+    ParseNode* forHeadExpr = forOfHead->pn_kid3;
+    if (!emitTree(forHeadExpr))                           // ITERABLE
+        return false;
+    if (!emitIterator())                                  // ITER
+        return false;
+
+    // For-of loops have both the iterator and the value on the stack. Push
+    // undefined to balance the stack.
+    if (!emit1(JSOP_UNDEFINED))                           // ITER RESULT
+        return false;
+
+    LoopControl loopInfo(this, StatementKind::ForOfLoop);
+
+    // Annotate so IonMonkey can find the loop-closing jump.
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR_OF, &noteIndex))
+        return false;
+
+    JumpList initialJump;
+    if (!emitJump(JSOP_GOTO, &initialJump))               // ITER RESULT
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(nullptr, &top))                     // ITER RESULT
+        return false;
+
+    // If the loop had an escaping lexical declaration, replace the current
+    // environment with an dead zoned one to implement TDZ semantics.
+    if (headLexicalEmitterScope) {
+        // The environment chain only includes an environment for the for-of
+        // loop head *if* a scope binding is captured, thereby requiring
+        // recreation each iteration. If a lexical scope exists for the head,
+        // it must be the innermost one. If that scope has closed-over
+        // bindings inducing an environment, recreate the current environment.
+        DebugOnly<ParseNode*> forOfTarget = forOfHead->pn_kid1;
+        MOZ_ASSERT(forOfTarget->isKind(PNK_LET) || forOfTarget->isKind(PNK_CONST));
+        MOZ_ASSERT(headLexicalEmitterScope == innermostEmitterScope);
+        MOZ_ASSERT(headLexicalEmitterScope->scope(this)->kind() == ScopeKind::Lexical);
+
+        if (headLexicalEmitterScope->hasEnvironment()) {
+            if (!emit1(JSOP_RECREATELEXICALENV))          // ITER RESULT
+                return false;
+        }
+
+        // For uncaptured bindings, put them back in TDZ.
+        if (!headLexicalEmitterScope->deadZoneFrameSlots(this))
+            return false;
+    }
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    {
+#ifdef DEBUG
+        auto loopDepth = this->stackDepth;
+#endif
+
+        // Emit code to assign result.value to the iteration variable.
+        if (!emit1(JSOP_DUP))                             // ITER RESULT RESULT
+            return false;
+        if (!emitAtomOp(cx->names().value, JSOP_GETPROP)) // ITER RESULT VALUE
+            return false;
+
+        if (!emitInitializeForInOrOfTarget(forOfHead))    // ITER RESULT VALUE
+            return false;
+
+        if (!emit1(JSOP_POP))                             // ITER RESULT
+            return false;
+
+        MOZ_ASSERT(this->stackDepth == loopDepth,
+                   "the stack must be balanced around the initializing "
+                   "operation");
+
+        // Perform the loop body.
+        ParseNode* forBody = forOfLoop->pn_right;
+        if (!emitTree(forBody))                           // ITER RESULT
+            return false;
+
+        // Set offset for continues.
+        loopInfo.continueTarget = { offset() };
+
+        if (!emitLoopEntry(forHeadExpr, initialJump))     // ITER RESULT
+            return false;
+
+        if (!emit1(JSOP_POP))                             // ITER
+            return false;
+        if (!emit1(JSOP_DUP))                             // ITER ITER
+            return false;
+
+        if (!emitIteratorNext(forOfHead))                 // ITER RESULT
+            return false;
+        if (!emit1(JSOP_DUP))                             // ITER RESULT RESULT
+            return false;
+        if (!emitAtomOp(cx->names().done, JSOP_GETPROP))  // ITER RESULT DONE?
+            return false;
+
+        if (!emitBackwardJump(JSOP_IFEQ, top, &beq, &breakTarget))
+            return false;                                 // ITER RESULT
+
+        MOZ_ASSERT(this->stackDepth == loopDepth);
+    }
+
+    // Let Ion know where the closing jump of this loop is.
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - initialJump.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    if (!tryNoteList.append(JSTRY_FOR_OF, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    return emitUint16Operand(JSOP_POPN, 2);               //
+}
+
+bool
+BytecodeEmitter::emitForIn(ParseNode* forInLoop, EmitterScope* headLexicalEmitterScope)
+{
+    MOZ_ASSERT(forInLoop->isKind(PNK_FOR));
+    MOZ_ASSERT(forInLoop->isArity(PN_BINARY));
+    MOZ_ASSERT(forInLoop->isOp(JSOP_ITER));
+
+    ParseNode* forInHead = forInLoop->pn_left;
+    MOZ_ASSERT(forInHead->isKind(PNK_FORIN));
+    MOZ_ASSERT(forInHead->isArity(PN_TERNARY));
+
+    // Annex B: Evaluate the var-initializer expression if present.
+    // |for (var i = initializer in expr) { ... }|
+    ParseNode* forInTarget = forInHead->pn_kid1;
+    if (parser->handler.isDeclarationList(forInTarget)) {
+        ParseNode* decl = parser->handler.singleBindingFromDeclaration(forInTarget);
+        if (decl->isKind(PNK_NAME)) {
+            if (ParseNode* initializer = decl->expr()) {
+                MOZ_ASSERT(forInTarget->isKind(PNK_VAR),
+                           "for-in initializers are only permitted for |var| declarations");
+
+                if (!updateSourceCoordNotes(decl->pn_pos.begin))
+                    return false;
+
+                auto emitRhs = [initializer](BytecodeEmitter* bce, const NameLocation&, bool) {
+                    return bce->emitTree(initializer);
+                };
+
+                if (!emitInitializeName(decl, emitRhs))
+                    return false;
+
+                // Pop the initializer.
+                if (!emit1(JSOP_POP))
+                    return false;
+            }
+        }
+    }
+
+    // Evaluate the expression being iterated.
+    ParseNode* expr = forInHead->pn_kid3;
+    if (!emitTree(expr))                                  // EXPR
+        return false;
+
+    // Convert the value to the appropriate sort of iterator object for the
+    // loop variant (for-in, for-each-in, or destructuring for-in).
+    unsigned iflags = forInLoop->pn_iflags;
+    MOZ_ASSERT(0 == (iflags & ~(JSITER_FOREACH | JSITER_ENUMERATE)));
+    if (!emit2(JSOP_ITER, AssertedCast<uint8_t>(iflags))) // ITER
+        return false;
+
+    // For-in loops have both the iterator and the value on the stack. Push
+    // undefined to balance the stack.
+    if (!emit1(JSOP_UNDEFINED))                           // ITER ITERVAL
+        return false;
+
+    LoopControl loopInfo(this, StatementKind::ForInLoop);
+
+    /* Annotate so IonMonkey can find the loop-closing jump. */
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR_IN, &noteIndex))
+        return false;
+
+    // Jump down to the loop condition to minimize overhead (assuming at least
+    // one iteration, just like the other loop forms).
+    JumpList initialJump;
+    if (!emitJump(JSOP_GOTO, &initialJump))               // ITER ITERVAL
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(nullptr, &top))                     // ITER ITERVAL
+        return false;
+
+    // If the loop had an escaping lexical declaration, replace the current
+    // environment with an dead zoned one to implement TDZ semantics.
+    if (headLexicalEmitterScope) {
+        // The environment chain only includes an environment for the for-in
+        // loop head *if* a scope binding is captured, thereby requiring
+        // recreation each iteration. If a lexical scope exists for the head,
+        // it must be the innermost one. If that scope has closed-over
+        // bindings inducing an environment, recreate the current environment.
+        MOZ_ASSERT(forInTarget->isKind(PNK_LET) || forInTarget->isKind(PNK_CONST));
+        MOZ_ASSERT(headLexicalEmitterScope == innermostEmitterScope);
+        MOZ_ASSERT(headLexicalEmitterScope->scope(this)->kind() == ScopeKind::Lexical);
+
+        if (headLexicalEmitterScope->hasEnvironment()) {
+            if (!emit1(JSOP_RECREATELEXICALENV))          // ITER ITERVAL
+                return false;
+        }
+
+        // For uncaptured bindings, put them back in TDZ.
+        if (!headLexicalEmitterScope->deadZoneFrameSlots(this))
+            return false;
+    }
+
+    {
+#ifdef DEBUG
+        auto loopDepth = this->stackDepth;
+#endif
+        MOZ_ASSERT(loopDepth >= 2);
+
+        if (!emitInitializeForInOrOfTarget(forInHead))    // ITER ITERVAL
+            return false;
+
+        MOZ_ASSERT(this->stackDepth == loopDepth,
+                   "iterator and iterval must be left on the stack");
+    }
+
+    // Perform the loop body.
+    ParseNode* forBody = forInLoop->pn_right;
+    if (!emitTree(forBody))                               // ITER ITERVAL
+        return false;
+
+    // Set offset for continues.
+    loopInfo.continueTarget = { offset() };
+
+    if (!emitLoopEntry(nullptr, initialJump))             // ITER ITERVAL
+        return false;
+    if (!emit1(JSOP_POP))                                 // ITER
+        return false;
+    if (!emit1(JSOP_MOREITER))                            // ITER NEXTITERVAL?
+        return false;
+    if (!emit1(JSOP_ISNOITER))                            // ITER NEXTITERVAL? ISNOITER
+        return false;
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFEQ, top, &beq, &breakTarget))
+        return false;                                     // ITER NEXTITERVAL
+
+    // Set the srcnote offset so we can find the closing jump.
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - initialJump.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    // Pop the enumeration value.
+    if (!emit1(JSOP_POP))                                 // ITER
+        return false;
+
+    if (!tryNoteList.append(JSTRY_FOR_IN, this->stackDepth, top.offset, offset()))
+        return false;
+
+    return emit1(JSOP_ENDITER);                           //
+}
+
+/* C-style `for (init; cond; update) ...` loop. */
+bool
+BytecodeEmitter::emitCStyleFor(ParseNode* pn, EmitterScope* headLexicalEmitterScope)
+{
+    LoopControl loopInfo(this, StatementKind::ForLoop);
+
+    ParseNode* forHead = pn->pn_left;
+    ParseNode* forBody = pn->pn_right;
+
+    // If the head of this for-loop declared any lexical variables, the parser
+    // wrapped this PNK_FOR node in a PNK_LEXICALSCOPE representing the
+    // implicit scope of those variables. By the time we get here, we have
+    // already entered that scope. So far, so good.
+    //
+    // ### Scope freshening
+    //
+    // Each iteration of a `for (let V...)` loop creates a fresh loop variable
+    // binding for V, even if the loop is a C-style `for(;;)` loop:
+    //
+    //     var funcs = [];
+    //     for (let i = 0; i < 2; i++)
+    //         funcs.push(function() { return i; });
+    //     assertEq(funcs[0](), 0);  // the two closures capture...
+    //     assertEq(funcs[1](), 1);  // ...two different `i` bindings
+    //
+    // This is implemented by "freshening" the implicit block -- changing the
+    // scope chain to a fresh clone of the instantaneous block object -- each
+    // iteration, just before evaluating the "update" in for(;;) loops.
+    //
+    // No freshening occurs in `for (const ...;;)` as there's no point: you
+    // can't reassign consts. This is observable through the Debugger API. (The
+    // ES6 spec also skips cloning the environment in this case.)
+    bool forLoopRequiresFreshening = false;
+    if (ParseNode* init = forHead->pn_kid1) {
+        // Emit the `init` clause, whether it's an expression or a variable
+        // declaration. (The loop variables were hoisted into an enclosing
+        // scope, but we still need to emit code for the initializers.)
+        if (!updateSourceCoordNotes(init->pn_pos.begin))
+            return false;
+        if (!emitTree(init))
+            return false;
+
+        if (!init->isForLoopDeclaration()) {
+            // 'init' is an expression, not a declaration. emitTree left its
+            // value on the stack.
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+
+        // ES 13.7.4.8 step 2. The initial freshening.
+        //
+        // If an initializer let-declaration may be captured during loop iteration,
+        // the current scope has an environment.  If so, freshen the current
+        // environment to expose distinct bindings for each loop iteration.
+        forLoopRequiresFreshening = init->isKind(PNK_LET) && headLexicalEmitterScope;
+        if (forLoopRequiresFreshening) {
+            // The environment chain only includes an environment for the for(;;)
+            // loop head's let-declaration *if* a scope binding is captured, thus
+            // requiring a fresh environment each iteration. If a lexical scope
+            // exists for the head, it must be the innermost one. If that scope
+            // has closed-over bindings inducing an environment, recreate the
+            // current environment.
+            MOZ_ASSERT(headLexicalEmitterScope == innermostEmitterScope);
+            MOZ_ASSERT(headLexicalEmitterScope->scope(this)->kind() == ScopeKind::Lexical);
+
+            if (headLexicalEmitterScope->hasEnvironment()) {
+                if (!emit1(JSOP_FRESHENLEXICALENV))
+                    return false;
+            }
+        }
+    }
+
+    /*
+     * NB: the SRC_FOR note has offsetBias 1 (JSOP_NOP_LENGTH).
+     * Use tmp to hold the biased srcnote "top" offset, which differs
+     * from the top local variable by the length of the JSOP_GOTO
+     * emitted in between tmp and top if this loop has a condition.
+     */
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR, &noteIndex))
+        return false;
+    if (!emit1(JSOP_NOP))
+        return false;
+    ptrdiff_t tmp = offset();
+
+    JumpList jmp;
+    if (forHead->pn_kid2) {
+        /* Goto the loop condition, which branches back to iterate. */
+        if (!emitJump(JSOP_GOTO, &jmp))
+            return false;
+    }
+
+    /* Emit code for the loop body. */
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(forBody, &top))
+        return false;
+    if (jmp.offset == -1 && !emitLoopEntry(forBody, jmp))
+        return false;
+
+    if (!emitConditionallyExecutedTree(forBody))
+        return false;
+
+    // Set loop and enclosing "update" offsets, for continue.  Note that we
+    // continue to immediately *before* the block-freshening: continuing must
+    // refresh the block.
+    if (!emitJumpTarget(&loopInfo.continueTarget))
+        return false;
+
+    // ES 13.7.4.8 step 3.e. The per-iteration freshening.
+    if (forLoopRequiresFreshening) {
+        MOZ_ASSERT(headLexicalEmitterScope == innermostEmitterScope);
+        MOZ_ASSERT(headLexicalEmitterScope->scope(this)->kind() == ScopeKind::Lexical);
+
+        if (headLexicalEmitterScope->hasEnvironment()) {
+            if (!emit1(JSOP_FRESHENLEXICALENV))
+                return false;
+        }
+    }
+
+    // Check for update code to do before the condition (if any).
+    // The update code may not be executed at all; it needs its own TDZ cache.
+    if (ParseNode* update = forHead->pn_kid3) {
+        TDZCheckCache tdzCache(this);
+
+        if (!updateSourceCoordNotes(update->pn_pos.begin))
+            return false;
+        if (!emitTree(update))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+
+        /* Restore the absolute line number for source note readers. */
+        uint32_t lineNum = parser->tokenStream.srcCoords.lineNum(pn->pn_pos.end);
+        if (currentLine() != lineNum) {
+            if (!newSrcNote2(SRC_SETLINE, ptrdiff_t(lineNum)))
+                return false;
+            current->currentLine = lineNum;
+            current->lastColumn = 0;
+        }
+    }
+
+    ptrdiff_t tmp3 = offset();
+
+    if (forHead->pn_kid2) {
+        /* Fix up the goto from top to target the loop condition. */
+        MOZ_ASSERT(jmp.offset >= 0);
+        if (!emitLoopEntry(forHead->pn_kid2, jmp))
+            return false;
+
+        if (!emitTree(forHead->pn_kid2))
+            return false;
+    } else if (!forHead->pn_kid3) {
+        // If there is no condition clause and no update clause, mark
+        // the loop-ending "goto" with the location of the "for".
+        // This ensures that the debugger will stop on each loop
+        // iteration.
+        if (!updateSourceCoordNotes(pn->pn_pos.begin))
+            return false;
+    }
+
+    /* Set the first note offset so we can find the loop condition. */
+    if (!setSrcNoteOffset(noteIndex, 0, tmp3 - tmp))
+        return false;
+    if (!setSrcNoteOffset(noteIndex, 1, loopInfo.continueTarget.offset - tmp))
+        return false;
+
+    /* If no loop condition, just emit a loop-closing jump. */
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(forHead->pn_kid2 ? JSOP_IFNE : JSOP_GOTO, top, &beq, &breakTarget))
+        return false;
+
+    /* The third note offset helps us find the loop-closing jump. */
+    if (!setSrcNoteOffset(noteIndex, 2, beq.offset - tmp))
+        return false;
+
+    if (!tryNoteList.append(JSTRY_LOOP, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitFor(ParseNode* pn, EmitterScope* headLexicalEmitterScope)
+{
+    MOZ_ASSERT(pn->isKind(PNK_FOR));
+
+    if (pn->pn_left->isKind(PNK_FORHEAD))
+        return emitCStyleFor(pn, headLexicalEmitterScope);
+
+    if (!updateLineNumberNotes(pn->pn_pos.begin))
+        return false;
+
+    if (pn->pn_left->isKind(PNK_FORIN))
+        return emitForIn(pn, headLexicalEmitterScope);
+
+    MOZ_ASSERT(pn->pn_left->isKind(PNK_FOROF));
+    return emitForOf(pn, headLexicalEmitterScope);
+}
+
+bool
+BytecodeEmitter::emitComprehensionForInOrOfVariables(ParseNode* pn, bool* lexicalScope)
+{
+    // ES6 specifies that lexical for-loop variables get a fresh binding each
+    // iteration, and that evaluation of the expression looped over occurs with
+    // these variables dead zoned.  But these rules only apply to *standard*
+    // for-in/of loops, and we haven't extended these requirements to
+    // comprehension syntax.
+
+    *lexicalScope = pn->isKind(PNK_LEXICALSCOPE);
+    if (*lexicalScope) {
+        // This is initially-ES7-tracked syntax, now with considerably murkier
+        // outlook. The scope work is done by the caller by instantiating an
+        // EmitterScope. There's nothing to do here.
+    } else {
+        // This is legacy comprehension syntax.  We'll have PNK_LET here, using
+        // a lexical scope provided by/for the entire comprehension.  Name
+        // analysis assumes declarations initialize lets, but as we're handling
+        // this declaration manually, we must also initialize manually to avoid
+        // triggering dead zone checks.
+        MOZ_ASSERT(pn->isKind(PNK_LET));
+        MOZ_ASSERT(pn->pn_count == 1);
+
+        if (!emitDeclarationList(pn))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitComprehensionForOf(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_COMPREHENSIONFOR));
+
+    ParseNode* forHead = pn->pn_left;
+    MOZ_ASSERT(forHead->isKind(PNK_FOROF));
+
+    ParseNode* forHeadExpr = forHead->pn_kid3;
+    ParseNode* forBody = pn->pn_right;
+
+    ParseNode* loopDecl = forHead->pn_kid1;
+    bool lexicalScope = false;
+    if (!emitComprehensionForInOrOfVariables(loopDecl, &lexicalScope))
+        return false;
+
+    // For-of loops run with two values on the stack: the iterator and the
+    // current result object.
+
+    // Evaluate the expression to the right of 'of'.
+    if (!emitTree(forHeadExpr))                // EXPR
+        return false;
+    if (!emitIterator())                       // ITER
+        return false;
+
+    // Push a dummy result so that we properly enter iteration midstream.
+    if (!emit1(JSOP_UNDEFINED))                // ITER RESULT
+        return false;
+
+    // Enter the block before the loop body, after evaluating the obj.
+    // Initialize let bindings with undefined when entering, as the name
+    // assigned to is a plain assignment.
+    TDZCheckCache tdzCache(this);
+    Maybe<EmitterScope> emitterScope;
+    ParseNode* loopVariableName;
+    if (lexicalScope) {
+        loopVariableName = parser->handler.singleBindingFromDeclaration(loopDecl->pn_expr);
+        emitterScope.emplace(this);
+        if (!emitterScope->enterComprehensionFor(this, loopDecl->scopeBindings()))
+            return false;
+    } else {
+        loopVariableName = parser->handler.singleBindingFromDeclaration(loopDecl);
+    }
+
+    LoopControl loopInfo(this, StatementKind::ForOfLoop);
+
+    // Jump down to the loop condition to minimize overhead assuming at least
+    // one iteration, as the other loop forms do.  Annotate so IonMonkey can
+    // find the loop-closing jump.
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR_OF, &noteIndex))
+        return false;
+    JumpList jmp;
+    if (!emitJump(JSOP_GOTO, &jmp))
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(nullptr, &top))
+        return false;
+
+#ifdef DEBUG
+    int loopDepth = this->stackDepth;
+#endif
+
+    // Emit code to assign result.value to the iteration variable.
+    if (!emit1(JSOP_DUP))                                 // ITER RESULT RESULT
+        return false;
+    if (!emitAtomOp(cx->names().value, JSOP_GETPROP))     // ITER RESULT VALUE
+        return false;
+    if (!emitAssignment(loopVariableName, JSOP_NOP, nullptr)) // ITER RESULT VALUE
+        return false;
+    if (!emit1(JSOP_POP))                                 // ITER RESULT
+        return false;
+
+    // The stack should be balanced around the assignment opcode sequence.
+    MOZ_ASSERT(this->stackDepth == loopDepth);
+
+    // Emit code for the loop body.
+    if (!emitTree(forBody))
+        return false;
+
+    // Set offset for continues.
+    loopInfo.continueTarget = { offset() };
+
+    if (!emitLoopEntry(forHeadExpr, jmp))
+        return false;
+
+    if (!emit1(JSOP_POP))                                 // ITER
+        return false;
+    if (!emit1(JSOP_DUP))                                 // ITER ITER
+        return false;
+    if (!emitIteratorNext(forHead))                       // ITER RESULT
+        return false;
+    if (!emit1(JSOP_DUP))                                 // ITER RESULT RESULT
+        return false;
+    if (!emitAtomOp(cx->names().done, JSOP_GETPROP))      // ITER RESULT DONE?
+        return false;
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFEQ, top, &beq, &breakTarget)) // ITER RESULT
+        return false;
+
+    MOZ_ASSERT(this->stackDepth == loopDepth);
+
+    // Let Ion know where the closing jump of this loop is.
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - jmp.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    if (!tryNoteList.append(JSTRY_FOR_OF, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    if (emitterScope) {
+        if (!emitterScope->leave(this))
+            return false;
+        emitterScope.reset();
+    }
+
+    // Pop the result and the iter.
+    return emitUint16Operand(JSOP_POPN, 2);               //
+}
+
+bool
+BytecodeEmitter::emitComprehensionForIn(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_COMPREHENSIONFOR));
+
+    ParseNode* forHead = pn->pn_left;
+    MOZ_ASSERT(forHead->isKind(PNK_FORIN));
+
+    ParseNode* forBody = pn->pn_right;
+
+    ParseNode* loopDecl = forHead->pn_kid1;
+    bool lexicalScope = false;
+    if (loopDecl && !emitComprehensionForInOrOfVariables(loopDecl, &lexicalScope))
+        return false;
+
+    // Evaluate the expression to the right of 'in'.
+    if (!emitTree(forHead->pn_kid3))
+        return false;
+
+    /*
+     * Emit a bytecode to convert top of stack value to the iterator
+     * object depending on the loop variant (for-in, for-each-in, or
+     * destructuring for-in).
+     */
+    MOZ_ASSERT(pn->isOp(JSOP_ITER));
+    if (!emit2(JSOP_ITER, (uint8_t) pn->pn_iflags))
+        return false;
+
+    // For-in loops have both the iterator and the value on the stack. Push
+    // undefined to balance the stack.
+    if (!emit1(JSOP_UNDEFINED))
+        return false;
+
+    // Enter the block before the loop body, after evaluating the obj.
+    // Initialize let bindings with undefined when entering, as the name
+    // assigned to is a plain assignment.
+    TDZCheckCache tdzCache(this);
+    Maybe<EmitterScope> emitterScope;
+    if (lexicalScope) {
+        emitterScope.emplace(this);
+        if (!emitterScope->enterComprehensionFor(this, loopDecl->scopeBindings()))
+            return false;
+    }
+
+    LoopControl loopInfo(this, StatementKind::ForInLoop);
+
+    /* Annotate so IonMonkey can find the loop-closing jump. */
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_FOR_IN, &noteIndex))
+        return false;
+
+    /*
+     * Jump down to the loop condition to minimize overhead assuming at
+     * least one iteration, as the other loop forms do.
+     */
+    JumpList jmp;
+    if (!emitJump(JSOP_GOTO, &jmp))
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitLoopHead(nullptr, &top))
+        return false;
+
+#ifdef DEBUG
+    int loopDepth = this->stackDepth;
+#endif
+
+    // Emit code to assign the enumeration value to the left hand side, but
+    // also leave it on the stack.
+    if (!emitAssignment(forHead->pn_kid2, JSOP_NOP, nullptr))
+        return false;
+
+    /* The stack should be balanced around the assignment opcode sequence. */
+    MOZ_ASSERT(this->stackDepth == loopDepth);
+
+    /* Emit code for the loop body. */
+    if (!emitTree(forBody))
+        return false;
+
+    // Set offset for continues.
+    loopInfo.continueTarget = { offset() };
+
+    if (!emitLoopEntry(nullptr, jmp))
+        return false;
+    if (!emit1(JSOP_POP))
+        return false;
+    if (!emit1(JSOP_MOREITER))
+        return false;
+    if (!emit1(JSOP_ISNOITER))
+        return false;
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFEQ, top, &beq, &breakTarget))
+        return false;
+
+    /* Set the srcnote offset so we can find the closing jump. */
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - jmp.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    // Pop the enumeration value.
+    if (!emit1(JSOP_POP))
+        return false;
+
+    JumpTarget endIter{ offset() };
+    if (!tryNoteList.append(JSTRY_FOR_IN, this->stackDepth, top.offset, endIter.offset))
+        return false;
+    if (!emit1(JSOP_ENDITER))
+        return false;
+
+    if (emitterScope) {
+        if (!emitterScope->leave(this))
+            return false;
+        emitterScope.reset();
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitComprehensionFor(ParseNode* compFor)
+{
+    MOZ_ASSERT(compFor->pn_left->isKind(PNK_FORIN) ||
+               compFor->pn_left->isKind(PNK_FOROF));
+
+    if (!updateLineNumberNotes(compFor->pn_pos.begin))
+        return false;
+
+    return compFor->pn_left->isKind(PNK_FORIN)
+           ? emitComprehensionForIn(compFor)
+           : emitComprehensionForOf(compFor);
+}
+
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitFunction(ParseNode* pn, bool needsProto)
+{
+    FunctionBox* funbox = pn->pn_funbox;
+    RootedFunction fun(cx, funbox->function());
+    RootedAtom name(cx, fun->name());
+    MOZ_ASSERT_IF(fun->isInterpretedLazy(), fun->lazyScript());
+    MOZ_ASSERT_IF(pn->isOp(JSOP_FUNWITHPROTO), needsProto);
+
+    /*
+     * Set the |wasEmitted| flag in the funbox once the function has been
+     * emitted. Function definitions that need hoisting to the top of the
+     * function will be seen by emitFunction in two places.
+     */
+    if (funbox->wasEmitted && pn->functionIsHoisted()) {
+        // Annex B block-scoped functions are hoisted like any other
+        // block-scoped function to the top of their scope. When their
+        // definitions are seen for the second time, we need to emit the
+        // assignment that assigns the function to the outer 'var' binding.
+        if (funbox->isAnnexB) {
+            auto emitRhs = [&name](BytecodeEmitter* bce, const NameLocation&, bool) {
+                // The RHS is the value of the lexically bound name in the
+                // innermost scope.
+                return bce->emitGetName(name);
+            };
+
+            // Get the location of the 'var' binding in the body scope. The
+            // name must be found, else there is a bug in the Annex B handling
+            // in Parser.
+            //
+            // In sloppy eval contexts, this location is dynamic.
+            Maybe<NameLocation> lhsLoc = locationOfNameBoundInScope(name, varEmitterScope);
+
+            // If there are parameter expressions, the var name could be a
+            // parameter.
+            if (!lhsLoc && sc->isFunctionBox() && sc->asFunctionBox()->hasExtraBodyVarScope())
+                lhsLoc = locationOfNameBoundInScope(name, varEmitterScope->enclosingInFrame());
+
+            if (!lhsLoc) {
+                lhsLoc = Some(NameLocation::DynamicAnnexBVar());
+            } else {
+                MOZ_ASSERT(lhsLoc->bindingKind() == BindingKind::Var ||
+                           lhsLoc->bindingKind() == BindingKind::FormalParameter ||
+                           (lhsLoc->bindingKind() == BindingKind::Let &&
+                            sc->asFunctionBox()->hasParameterExprs));
+            }
+
+            if (!emitSetOrInitializeNameAtLocation(name, *lhsLoc, emitRhs, false))
+                return false;
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+
+        MOZ_ASSERT_IF(fun->hasScript(), fun->nonLazyScript());
+        MOZ_ASSERT(pn->functionIsHoisted());
+        return true;
+    }
+
+    funbox->wasEmitted = true;
+
+    /*
+     * Mark as singletons any function which will only be executed once, or
+     * which is inner to a lambda we only expect to run once. In the latter
+     * case, if the lambda runs multiple times then CloneFunctionObject will
+     * make a deep clone of its contents.
+     */
+    if (fun->isInterpreted()) {
+        bool singleton = checkRunOnceContext();
+        if (!JSFunction::setTypeForScriptedFunction(cx, fun, singleton))
+            return false;
+
+        SharedContext* outersc = sc;
+        if (fun->isInterpretedLazy()) {
+            // We need to update the static scope chain regardless of whether
+            // the LazyScript has already been initialized, due to the case
+            // where we previously successfully compiled an inner function's
+            // lazy script but failed to compile the outer script after the
+            // fact. If we attempt to compile the outer script again, the
+            // static scope chain will be newly allocated and will mismatch
+            // the previously compiled LazyScript's.
+            ScriptSourceObject* source = &script->sourceObject()->as<ScriptSourceObject>();
+            fun->lazyScript()->setEnclosingScopeAndSource(innermostScope(), source);
+            if (emittingRunOnceLambda)
+                fun->lazyScript()->setTreatAsRunOnce();
+        } else {
+            MOZ_ASSERT_IF(outersc->strict(), funbox->strictScript);
+
+            // Inherit most things (principals, version, etc) from the
+            // parent.  Use default values for the rest.
+            Rooted<JSScript*> parent(cx, script);
+            MOZ_ASSERT(parent->getVersion() == parser->options().version);
+            MOZ_ASSERT(parent->mutedErrors() == parser->options().mutedErrors());
+            const TransitiveCompileOptions& transitiveOptions = parser->options();
+            CompileOptions options(cx, transitiveOptions);
+
+            Rooted<JSObject*> sourceObject(cx, script->sourceObject());
+            Rooted<JSScript*> script(cx, JSScript::Create(cx, options, sourceObject,
+                                                          funbox->bufStart, funbox->bufEnd));
+            if (!script)
+                return false;
+
+            BytecodeEmitter bce2(this, parser, funbox, script, /* lazyScript = */ nullptr,
+                                 pn->pn_pos, emitterMode);
+            if (!bce2.init())
+                return false;
+
+            /* We measured the max scope depth when we parsed the function. */
+            if (!bce2.emitFunctionScript(pn->pn_body))
+                return false;
+
+            if (funbox->isLikelyConstructorWrapper())
+                script->setLikelyConstructorWrapper();
+        }
+
+        if (outersc->isFunctionBox())
+            outersc->asFunctionBox()->setHasInnerFunctions();
+    } else {
+        MOZ_ASSERT(IsAsmJSModule(fun));
+    }
+
+    /* Make the function object a literal in the outer script's pool. */
+    unsigned index = objectList.add(pn->pn_funbox);
+
+    /* Non-hoisted functions simply emit their respective op. */
+    if (!pn->functionIsHoisted()) {
+        /* JSOP_LAMBDA_ARROW is always preceded by a new.target */
+        MOZ_ASSERT(fun->isArrow() == (pn->getOp() == JSOP_LAMBDA_ARROW));
+        if (funbox->isAsync()) {
+            MOZ_ASSERT(!needsProto);
+            return emitAsyncWrapper(index, funbox->needsHomeObject(), fun->isArrow());
+        }
+
+        if (fun->isArrow()) {
+            if (sc->allowNewTarget()) {
+                if (!emit1(JSOP_NEWTARGET))
+                    return false;
+            } else {
+                if (!emit1(JSOP_NULL))
+                    return false;
+            }
+        }
+
+        if (needsProto) {
+            MOZ_ASSERT(pn->getOp() == JSOP_FUNWITHPROTO || pn->getOp() == JSOP_LAMBDA);
+            pn->setOp(JSOP_FUNWITHPROTO);
+        }
+
+        if (pn->getOp() == JSOP_DEFFUN) {
+            if (!emitIndex32(JSOP_LAMBDA, index))
+                return false;
+            return emit1(JSOP_DEFFUN);
+        }
+
+        return emitIndex32(pn->getOp(), index);
+    }
+
+    MOZ_ASSERT(!needsProto);
+
+    bool topLevelFunction;
+    if (sc->isFunctionBox() || (sc->isEvalContext() && sc->strict())) {
+        // No nested functions inside other functions are top-level.
+        topLevelFunction = false;
+    } else {
+        // In sloppy eval scripts, top-level functions in are accessed
+        // dynamically. In global and module scripts, top-level functions are
+        // those bound in the var scope.
+        NameLocation loc = lookupName(name);
+        topLevelFunction = loc.kind() == NameLocation::Kind::Dynamic ||
+                           loc.bindingKind() == BindingKind::Var;
+    }
+
+    if (topLevelFunction) {
+        if (sc->isModuleContext()) {
+            // For modules, we record the function and instantiate the binding
+            // during ModuleDeclarationInstantiation(), before the script is run.
+
+            RootedModuleObject module(cx, sc->asModuleContext()->module());
+            if (!module->noteFunctionDeclaration(cx, name, fun))
+                return false;
+        } else {
+            MOZ_ASSERT(sc->isGlobalContext() || sc->isEvalContext());
+            MOZ_ASSERT(pn->getOp() == JSOP_NOP);
+            switchToPrologue();
+            if (funbox->isAsync()) {
+                if (!emitAsyncWrapper(index, fun->isMethod(), fun->isArrow()))
+                    return false;
+            } else {
+                if (!emitIndex32(JSOP_LAMBDA, index))
+                    return false;
+            }
+            if (!emit1(JSOP_DEFFUN))
+                return false;
+            if (!updateSourceCoordNotes(pn->pn_pos.begin))
+                return false;
+            switchToMain();
+        }
+    } else {
+        // For functions nested within functions and blocks, make a lambda and
+        // initialize the binding name of the function in the current scope.
+
+        bool isAsync = funbox->isAsync();
+        auto emitLambda = [index, isAsync](BytecodeEmitter* bce, const NameLocation&, bool) {
+            if (isAsync) {
+                return bce->emitAsyncWrapper(index, /* needsHomeObject = */ false,
+                                             /* isArrow = */ false);
+            }
+            return bce->emitIndexOp(JSOP_LAMBDA, index);
+        };
+
+        if (!emitInitializeName(name, emitLambda))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitAsyncWrapperLambda(unsigned index, bool isArrow) {
+    if (isArrow) {
+        if (sc->allowNewTarget()) {
+            if (!emit1(JSOP_NEWTARGET))
+                return false;
+        } else {
+            if (!emit1(JSOP_NULL))
+                return false;
+        }
+        if (!emitIndex32(JSOP_LAMBDA_ARROW, index))
+            return false;
+    } else {
+        if (!emitIndex32(JSOP_LAMBDA, index))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitAsyncWrapper(unsigned index, bool needsHomeObject, bool isArrow)
+{
+    // needsHomeObject can be true for propertyList for extended class.
+    // In that case push both unwrapped and wrapped function, in order to
+    // initialize home object of unwrapped function, and set wrapped function
+    // as a property.
+    //
+    //   lambda       // unwrapped
+    //   dup          // unwrapped unwrapped
+    //   toasync      // unwrapped wrapped
+    //
+    // Emitted code is surrounded by the following code.
+    //
+    //                    // classObj classCtor classProto
+    //   (emitted code)   // classObj classCtor classProto unwrapped wrapped
+    //   swap             // classObj classCtor classProto wrapped unwrapped
+    //   inithomeobject 1 // classObj classCtor classProto wrapped unwrapped
+    //                    //   initialize the home object of unwrapped
+    //                    //   with classProto here
+    //   pop              // classObj classCtor classProto wrapped
+    //   inithiddenprop   // classObj classCtor classProto wrapped
+    //                    //   initialize the property of the classProto
+    //                    //   with wrapped function here
+    //   pop              // classObj classCtor classProto
+    //
+    // needsHomeObject is false for other cases, push wrapped function only.
+    if (!emitAsyncWrapperLambda(index, isArrow))
+        return false;
+    if (needsHomeObject) {
+        if (!emit1(JSOP_DUP))
+            return false;
+    }
+    if (!emit1(JSOP_TOASYNC))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDo(ParseNode* pn)
+{
+    /* Emit an annotated nop so IonBuilder can recognize the 'do' loop. */
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_WHILE, &noteIndex))
+        return false;
+    if (!emit1(JSOP_NOP))
+        return false;
+
+    unsigned noteIndex2;
+    if (!newSrcNote(SRC_WHILE, &noteIndex2))
+        return false;
+
+    /* Compile the loop body. */
+    JumpTarget top;
+    if (!emitLoopHead(pn->pn_left, &top))
+        return false;
+
+    LoopControl loopInfo(this, StatementKind::DoLoop);
+
+    JumpList empty;
+    if (!emitLoopEntry(nullptr, empty))
+        return false;
+
+    if (!emitTree(pn->pn_left))
+        return false;
+
+    // Set the offset for continues.
+    if (!emitJumpTarget(&loopInfo.continueTarget))
+        return false;
+
+    /* Compile the loop condition, now that continues know where to go. */
+    if (!emitTree(pn->pn_right))
+        return false;
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFNE, top, &beq, &breakTarget))
+        return false;
+
+    if (!tryNoteList.append(JSTRY_LOOP, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    /*
+     * Update the annotations with the update and back edge positions, for
+     * IonBuilder.
+     *
+     * Be careful: We must set noteIndex2 before noteIndex in case the noteIndex
+     * note gets bigger.
+     */
+    if (!setSrcNoteOffset(noteIndex2, 0, beq.offset - top.offset))
+        return false;
+    if (!setSrcNoteOffset(noteIndex, 0, 1 + (loopInfo.continueTarget.offset - top.offset)))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitWhile(ParseNode* pn)
+{
+    /*
+     * Minimize bytecodes issued for one or more iterations by jumping to
+     * the condition below the body and closing the loop if the condition
+     * is true with a backward branch. For iteration count i:
+     *
+     *  i    test at the top                 test at the bottom
+     *  =    ===============                 ==================
+     *  0    ifeq-pass                       goto; ifne-fail
+     *  1    ifeq-fail; goto; ifne-pass      goto; ifne-pass; ifne-fail
+     *  2    2*(ifeq-fail; goto); ifeq-pass  goto; 2*ifne-pass; ifne-fail
+     *  . . .
+     *  N    N*(ifeq-fail; goto); ifeq-pass  goto; N*ifne-pass; ifne-fail
+     */
+
+    // If we have a single-line while, like "while (x) ;", we want to
+    // emit the line note before the initial goto, so that the
+    // debugger sees a single entry point.  This way, if there is a
+    // breakpoint on the line, it will only fire once; and "next"ing
+    // will skip the whole loop.  However, for the multi-line case we
+    // want to emit the line note after the initial goto, so that
+    // "cont" stops on each iteration -- but without a stop before the
+    // first iteration.
+    if (parser->tokenStream.srcCoords.lineNum(pn->pn_pos.begin) ==
+        parser->tokenStream.srcCoords.lineNum(pn->pn_pos.end) &&
+        !updateSourceCoordNotes(pn->pn_pos.begin))
+        return false;
+
+    JumpTarget top{ -1 };
+    if (!emitJumpTarget(&top))
+        return false;
+
+    LoopControl loopInfo(this, StatementKind::WhileLoop);
+    loopInfo.continueTarget = top;
+
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_WHILE, &noteIndex))
+        return false;
+
+    JumpList jmp;
+    if (!emitJump(JSOP_GOTO, &jmp))
+        return false;
+
+    if (!emitLoopHead(pn->pn_right, &top))
+        return false;
+
+    if (!emitConditionallyExecutedTree(pn->pn_right))
+        return false;
+
+    if (!emitLoopEntry(pn->pn_left, jmp))
+        return false;
+    if (!emitTree(pn->pn_left))
+        return false;
+
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFNE, top, &beq, &breakTarget))
+        return false;
+
+    if (!tryNoteList.append(JSTRY_LOOP, stackDepth, top.offset, breakTarget.offset))
+        return false;
+
+    if (!setSrcNoteOffset(noteIndex, 0, beq.offset - jmp.offset))
+        return false;
+
+    if (!loopInfo.patchBreaksAndContinues(this))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitBreak(PropertyName* label)
+{
+    BreakableControl* target;
+    SrcNoteType noteType;
+    if (label) {
+        // Any statement with the matching label may be the break target.
+        auto hasSameLabel = [label](LabelControl* labelControl) {
+            return labelControl->label() == label;
+        };
+        target = findInnermostNestableControl<LabelControl>(hasSameLabel);
+        noteType = SRC_BREAK2LABEL;
+    } else {
+        auto isNotLabel = [](BreakableControl* control) {
+            return !control->is<LabelControl>();
+        };
+        target = findInnermostNestableControl<BreakableControl>(isNotLabel);
+        noteType = (target->kind() == StatementKind::Switch) ? SRC_SWITCHBREAK : SRC_BREAK;
+    }
+
+    return emitGoto(target, &target->breaks, noteType);
+}
+
+bool
+BytecodeEmitter::emitContinue(PropertyName* label)
+{
+    LoopControl* target = nullptr;
+    if (label) {
+        // Find the loop statement enclosed by the matching label.
+        NestableControl* control = innermostNestableControl;
+        while (!control->is<LabelControl>() || control->as<LabelControl>().label() != label) {
+            if (control->is<LoopControl>())
+                target = &control->as<LoopControl>();
+            control = control->enclosing();
+        }
+    } else {
+        target = findInnermostNestableControl<LoopControl>();
+    }
+    return emitGoto(target, &target->continues, SRC_CONTINUE);
+}
+
+bool
+BytecodeEmitter::emitGetFunctionThis(ParseNode* pn)
+{
+    MOZ_ASSERT(sc->thisBinding() == ThisBinding::Function);
+    MOZ_ASSERT(pn->isKind(PNK_NAME));
+    MOZ_ASSERT(pn->name() == cx->names().dotThis);
+
+    if (!emitTree(pn))
+        return false;
+    if (sc->needsThisTDZChecks() && !emit1(JSOP_CHECKTHIS))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitGetThisForSuperBase(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_SUPERBASE));
+    return emitGetFunctionThis(pn->pn_kid);
+}
+
+bool
+BytecodeEmitter::emitThisLiteral(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_THIS));
+
+    if (ParseNode* thisName = pn->pn_kid)
+        return emitGetFunctionThis(thisName);
+
+    if (sc->thisBinding() == ThisBinding::Module)
+        return emit1(JSOP_UNDEFINED);
+
+    MOZ_ASSERT(sc->thisBinding() == ThisBinding::Global);
+    return emit1(JSOP_GLOBALTHIS);
+}
+
+bool
+BytecodeEmitter::emitCheckDerivedClassConstructorReturn()
+{
+    MOZ_ASSERT(lookupName(cx->names().dotThis).hasKnownSlot());
+    if (!emitGetName(cx->names().dotThis))
+        return false;
+    if (!emit1(JSOP_CHECKRETURN))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitReturn(ParseNode* pn)
+{
+    if (!updateSourceCoordNotes(pn->pn_pos.begin))
+        return false;
+
+    if (sc->isFunctionBox() && sc->asFunctionBox()->isStarGenerator()) {
+        if (!emitPrepareIteratorResult())
+            return false;
+    }
+
+    /* Push a return value */
+    if (ParseNode* pn2 = pn->pn_kid) {
+        if (!emitTree(pn2))
+            return false;
+    } else {
+        /* No explicit return value provided */
+        if (!emit1(JSOP_UNDEFINED))
+            return false;
+    }
+
+    if (sc->isFunctionBox() && sc->asFunctionBox()->isStarGenerator()) {
+        if (!emitFinishIteratorResult(true))
+            return false;
+    }
+
+    // We know functionBodyEndPos is set because "return" is only
+    // valid in a function, and so we've passed through
+    // emitFunctionScript.
+    MOZ_ASSERT(functionBodyEndPosSet);
+    if (!updateSourceCoordNotes(functionBodyEndPos))
+        return false;
+
+    /*
+     * EmitNonLocalJumpFixup may add fixup bytecode to close open try
+     * blocks having finally clauses and to exit intermingled let blocks.
+     * We can't simply transfer control flow to our caller in that case,
+     * because we must gosub to those finally clauses from inner to outer,
+     * with the correct stack pointer (i.e., after popping any with,
+     * for/in, etc., slots nested inside the finally's try).
+     *
+     * In this case we mutate JSOP_RETURN into JSOP_SETRVAL and add an
+     * extra JSOP_RETRVAL after the fixups.
+     */
+    ptrdiff_t top = offset();
+
+    bool isGenerator = sc->isFunctionBox() && sc->asFunctionBox()->isGenerator();
+    bool isDerivedClassConstructor =
+        sc->isFunctionBox() && sc->asFunctionBox()->isDerivedClassConstructor();
+
+    if (!emit1((isGenerator || isDerivedClassConstructor) ? JSOP_SETRVAL : JSOP_RETURN))
+        return false;
+
+    // Make sure that we emit this before popping the blocks in prepareForNonLocalJump,
+    // to ensure that the error is thrown while the scope-chain is still intact.
+    if (isDerivedClassConstructor) {
+        if (!emitCheckDerivedClassConstructorReturn())
+            return false;
+    }
+
+    NonLocalExitControl nle(this);
+
+    if (!nle.prepareForNonLocalJumpToOutermost())
+        return false;
+
+    if (isGenerator) {
+        // We know that .generator is on the function scope, as we just exited
+        // all nested scopes.
+        NameLocation loc =
+            *locationOfNameBoundInFunctionScope(cx->names().dotGenerator, varEmitterScope);
+        if (!emitGetNameAtLocation(cx->names().dotGenerator, loc))
+            return false;
+        if (!emitYieldOp(JSOP_FINALYIELDRVAL))
+            return false;
+    } else if (isDerivedClassConstructor) {
+        MOZ_ASSERT(code()[top] == JSOP_SETRVAL);
+        if (!emit1(JSOP_RETRVAL))
+            return false;
+    } else if (top + static_cast<ptrdiff_t>(JSOP_RETURN_LENGTH) != offset()) {
+        code()[top] = JSOP_SETRVAL;
+        if (!emit1(JSOP_RETRVAL))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitYield(ParseNode* pn)
+{
+    MOZ_ASSERT(sc->isFunctionBox());
+
+    if (pn->getOp() == JSOP_YIELD) {
+        if (sc->asFunctionBox()->isStarGenerator()) {
+            if (!emitPrepareIteratorResult())
+                return false;
+        }
+        if (pn->pn_left) {
+            if (!emitTree(pn->pn_left))
+                return false;
+        } else {
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+        }
+        if (sc->asFunctionBox()->isStarGenerator()) {
+            if (!emitFinishIteratorResult(false))
+                return false;
+        }
+    } else {
+        MOZ_ASSERT(pn->getOp() == JSOP_INITIALYIELD);
+    }
+
+    if (!emitTree(pn->pn_right))
+        return false;
+
+    if (!emitYieldOp(pn->getOp()))
+        return false;
+
+    if (pn->getOp() == JSOP_INITIALYIELD && !emit1(JSOP_POP))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitYieldStar(ParseNode* iter, ParseNode* gen)
+{
+    MOZ_ASSERT(sc->isFunctionBox());
+    MOZ_ASSERT(sc->asFunctionBox()->isStarGenerator());
+
+    if (!emitTree(iter))                                         // ITERABLE
+        return false;
+    if (!emitIterator())                                         // ITER
+        return false;
+
+    // Initial send value is undefined.
+    if (!emit1(JSOP_UNDEFINED))                                  // ITER RECEIVED
+        return false;
+
+    int depth = stackDepth;
+    MOZ_ASSERT(depth >= 2);
+
+    JumpList send;
+    if (!emitJump(JSOP_GOTO, &send))                             // goto send
+        return false;
+
+    // Try prologue.                                             // ITER RESULT
+    unsigned noteIndex;
+    if (!newSrcNote(SRC_TRY, &noteIndex))
+        return false;
+    JumpTarget tryStart{ offset() };
+    if (!emit1(JSOP_TRY))                                        // tryStart:
+        return false;
+    MOZ_ASSERT(this->stackDepth == depth);
+
+    // Load the generator object.
+    if (!emitTree(gen))                                          // ITER RESULT GENOBJ
+        return false;
+
+    // Yield RESULT as-is, without re-boxing.
+    if (!emitYieldOp(JSOP_YIELD))                                // ITER RECEIVED
+        return false;
+
+    // Try epilogue.
+    if (!setSrcNoteOffset(noteIndex, 0, offset() - tryStart.offset))
+        return false;
+    if (!emitJump(JSOP_GOTO, &send))                             // goto send
+        return false;
+
+    JumpTarget tryEnd;
+    if (!emitJumpTarget(&tryEnd))                                // tryEnd:
+        return false;
+
+    // Catch location.
+    stackDepth = uint32_t(depth);                                // ITER RESULT
+    if (!emit1(JSOP_POP))                                        // ITER
+        return false;
+    // THROW? = 'throw' in ITER
+    if (!emit1(JSOP_EXCEPTION))                                  // ITER EXCEPTION
+        return false;
+    if (!emit1(JSOP_SWAP))                                       // EXCEPTION ITER
+        return false;
+    if (!emit1(JSOP_DUP))                                        // EXCEPTION ITER ITER
+        return false;
+    if (!emitAtomOp(cx->names().throw_, JSOP_STRING))            // EXCEPTION ITER ITER "throw"
+        return false;
+    if (!emit1(JSOP_SWAP))                                       // EXCEPTION ITER "throw" ITER
+        return false;
+    if (!emit1(JSOP_IN))                                         // EXCEPTION ITER THROW?
+        return false;
+    // if (THROW?) goto delegate
+    JumpList checkThrow;
+    if (!emitJump(JSOP_IFNE, &checkThrow))                       // EXCEPTION ITER
+        return false;
+    if (!emit1(JSOP_POP))                                        // EXCEPTION
+        return false;
+    if (!emit1(JSOP_THROW))                                      // throw EXCEPTION
+        return false;
+
+    if (!emitJumpTargetAndPatch(checkThrow))                     // delegate:
+        return false;
+    // RESULT = ITER.throw(EXCEPTION)                            // EXCEPTION ITER
+    stackDepth = uint32_t(depth);
+    if (!emit1(JSOP_DUP))                                        // EXCEPTION ITER ITER
+        return false;
+    if (!emit1(JSOP_DUP))                                        // EXCEPTION ITER ITER ITER
+        return false;
+    if (!emitAtomOp(cx->names().throw_, JSOP_CALLPROP))          // EXCEPTION ITER ITER THROW
+        return false;
+    if (!emit1(JSOP_SWAP))                                       // EXCEPTION ITER THROW ITER
+        return false;
+    if (!emit2(JSOP_PICK, 3))                                    // ITER THROW ITER EXCEPTION
+        return false;
+    if (!emitCall(JSOP_CALL, 1, iter))                           // ITER RESULT
+        return false;
+    checkTypeSet(JSOP_CALL);
+    MOZ_ASSERT(this->stackDepth == depth);
+    JumpList checkResult;
+    if (!emitJump(JSOP_GOTO, &checkResult))                      // goto checkResult
+        return false;
+
+    // Catch epilogue.
+
+    // This is a peace offering to ReconstructPCStack.  See the note in EmitTry.
+    if (!emit1(JSOP_NOP))
+        return false;
+    if (!tryNoteList.append(JSTRY_CATCH, depth, tryStart.offset + JSOP_TRY_LENGTH, tryEnd.offset))
+        return false;
+
+    // After the try/catch block: send the received value to the iterator.
+    if (!emitJumpTargetAndPatch(send))                           // send:
+        return false;
+
+    // Send location.
+    // result = iter.next(received)                              // ITER RECEIVED
+    if (!emit1(JSOP_SWAP))                                       // RECEIVED ITER
+        return false;
+    if (!emit1(JSOP_DUP))                                        // RECEIVED ITER ITER
+        return false;
+    if (!emit1(JSOP_DUP))                                        // RECEIVED ITER ITER ITER
+        return false;
+    if (!emitAtomOp(cx->names().next, JSOP_CALLPROP))            // RECEIVED ITER ITER NEXT
+        return false;
+    if (!emit1(JSOP_SWAP))                                       // RECEIVED ITER NEXT ITER
+        return false;
+    if (!emit2(JSOP_PICK, 3))                                    // ITER NEXT ITER RECEIVED
+        return false;
+    if (!emitCall(JSOP_CALL, 1, iter))                           // ITER RESULT
+        return false;
+    if (!emitCheckIsObj(CheckIsObjectKind::IteratorNext))        // ITER RESULT
+        return false;
+    checkTypeSet(JSOP_CALL);
+    MOZ_ASSERT(this->stackDepth == depth);
+
+    if (!emitJumpTargetAndPatch(checkResult))                    // checkResult:
+        return false;
+
+    // if (!result.done) goto tryStart;                          // ITER RESULT
+    if (!emit1(JSOP_DUP))                                        // ITER RESULT RESULT
+        return false;
+    if (!emitAtomOp(cx->names().done, JSOP_GETPROP))             // ITER RESULT DONE
+        return false;
+    // if (!DONE) goto tryStart;
+    JumpList beq;
+    JumpTarget breakTarget{ -1 };
+    if (!emitBackwardJump(JSOP_IFEQ, tryStart, &beq, &breakTarget)) // ITER RESULT
+        return false;
+
+    // result.value
+    if (!emit1(JSOP_SWAP))                                       // RESULT ITER
+        return false;
+    if (!emit1(JSOP_POP))                                        // RESULT
+        return false;
+    if (!emitAtomOp(cx->names().value, JSOP_GETPROP))            // VALUE
+        return false;
+
+    MOZ_ASSERT(this->stackDepth == depth - 1);
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitStatementList(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isArity(PN_LIST));
+    for (ParseNode* pn2 = pn->pn_head; pn2; pn2 = pn2->pn_next) {
+        if (!emitTree(pn2))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitStatement(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_SEMI));
+
+    ParseNode* pn2 = pn->pn_kid;
+    if (!pn2)
+        return true;
+
+    if (!updateSourceCoordNotes(pn->pn_pos.begin))
+        return false;
+
+    /*
+     * Top-level or called-from-a-native JS_Execute/EvaluateScript,
+     * debugger, and eval frames may need the value of the ultimate
+     * expression statement as the script's result, despite the fact
+     * that it appears useless to the compiler.
+     *
+     * API users may also set the JSOPTION_NO_SCRIPT_RVAL option when
+     * calling JS_Compile* to suppress JSOP_SETRVAL.
+     */
+    bool wantval = false;
+    bool useful = false;
+    if (sc->isFunctionBox())
+        MOZ_ASSERT(!script->noScriptRval());
+    else
+        useful = wantval = !script->noScriptRval();
+
+    /* Don't eliminate expressions with side effects. */
+    if (!useful) {
+        if (!checkSideEffects(pn2, &useful))
+            return false;
+
+        /*
+         * Don't eliminate apparently useless expressions if they are labeled
+         * expression statements. The startOffset() test catches the case
+         * where we are nesting in emitTree for a labeled compound statement.
+         */
+        if (innermostNestableControl &&
+            innermostNestableControl->is<LabelControl>() &&
+            innermostNestableControl->as<LabelControl>().startOffset() >= offset())
+        {
+            useful = true;
+        }
+    }
+
+    if (useful) {
+        JSOp op = wantval ? JSOP_SETRVAL : JSOP_POP;
+        MOZ_ASSERT_IF(pn2->isKind(PNK_ASSIGN), pn2->isOp(JSOP_NOP));
+        if (!emitTree(pn2))
+            return false;
+        if (!emit1(op))
+            return false;
+    } else if (pn->isDirectivePrologueMember()) {
+        // Don't complain about directive prologue members; just don't emit
+        // their code.
+    } else {
+        if (JSAtom* atom = pn->isStringExprStatement()) {
+            // Warn if encountering a non-directive prologue member string
+            // expression statement, that is inconsistent with the current
+            // directive prologue.  That is, a script *not* starting with
+            // "use strict" should warn for any "use strict" statements seen
+            // later in the script, because such statements are misleading.
+            const char* directive = nullptr;
+            if (atom == cx->names().useStrict) {
+                if (!sc->strictScript)
+                    directive = js_useStrict_str;
+            } else if (atom == cx->names().useAsm) {
+                if (sc->isFunctionBox()) {
+                    if (IsAsmJSModule(sc->asFunctionBox()->function()))
+                        directive = js_useAsm_str;
+                }
+            }
+
+            if (directive) {
+                if (!reportStrictWarning(pn2, JSMSG_CONTRARY_NONDIRECTIVE, directive))
+                    return false;
+            }
+        } else {
+            current->currentLine = parser->tokenStream.srcCoords.lineNum(pn2->pn_pos.begin);
+            current->lastColumn = 0;
+            if (!reportStrictWarning(pn2, JSMSG_USELESS_EXPR))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitDeleteName(ParseNode* node)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETENAME));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode* nameExpr = node->pn_kid;
+    MOZ_ASSERT(nameExpr->isKind(PNK_NAME));
+
+    return emitAtomOp(nameExpr, JSOP_DELNAME);
+}
+
+bool
+BytecodeEmitter::emitDeleteProperty(ParseNode* node)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEPROP));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode* propExpr = node->pn_kid;
+    MOZ_ASSERT(propExpr->isKind(PNK_DOT));
+
+    if (propExpr->as<PropertyAccess>().isSuper()) {
+        // Still have to calculate the base, even though we are are going
+        // to throw unconditionally, as calculating the base could also
+        // throw.
+        if (!emit1(JSOP_SUPERBASE))
+            return false;
+
+        return emitUint16Operand(JSOP_THROWMSG, JSMSG_CANT_DELETE_SUPER);
+    }
+
+    JSOp delOp = sc->strict() ? JSOP_STRICTDELPROP : JSOP_DELPROP;
+    return emitPropOp(propExpr, delOp);
+}
+
+bool
+BytecodeEmitter::emitDeleteElement(ParseNode* node)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEELEM));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode* elemExpr = node->pn_kid;
+    MOZ_ASSERT(elemExpr->isKind(PNK_ELEM));
+
+    if (elemExpr->as<PropertyByValue>().isSuper()) {
+        // Still have to calculate everything, even though we're gonna throw
+        // since it may have side effects
+        if (!emitTree(elemExpr->pn_right))
+            return false;
+
+        if (!emit1(JSOP_SUPERBASE))
+            return false;
+        if (!emitUint16Operand(JSOP_THROWMSG, JSMSG_CANT_DELETE_SUPER))
+            return false;
+
+        // Another wrinkle: Balance the stack from the emitter's point of view.
+        // Execution will not reach here, as the last bytecode threw.
+        return emit1(JSOP_POP);
+    }
+
+    JSOp delOp = sc->strict() ? JSOP_STRICTDELELEM : JSOP_DELELEM;
+    return emitElemOp(elemExpr, delOp);
+}
+
+bool
+BytecodeEmitter::emitDeleteExpression(ParseNode* node)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEEXPR));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode* expression = node->pn_kid;
+
+    // If useless, just emit JSOP_TRUE; otherwise convert |delete <expr>| to
+    // effectively |<expr>, true|.
+    bool useful = false;
+    if (!checkSideEffects(expression, &useful))
+        return false;
+
+    if (useful) {
+        if (!emitTree(expression))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+
+    return emit1(JSOP_TRUE);
+}
+
+static const char *
+SelfHostedCallFunctionName(JSAtom* name, ExclusiveContext* cx)
+{
+    if (name == cx->names().callFunction)
+        return "callFunction";
+    if (name == cx->names().callContentFunction)
+        return "callContentFunction";
+    if (name == cx->names().constructContentFunction)
+        return "constructContentFunction";
+
+    MOZ_CRASH("Unknown self-hosted call function name");
+}
+
+bool
+BytecodeEmitter::emitSelfHostedCallFunction(ParseNode* pn)
+{
+    // Special-casing of callFunction to emit bytecode that directly
+    // invokes the callee with the correct |this| object and arguments.
+    // callFunction(fun, thisArg, arg0, arg1) thus becomes:
+    // - emit lookup for fun
+    // - emit lookup for thisArg
+    // - emit lookups for arg0, arg1
+    //
+    // argc is set to the amount of actually emitted args and the
+    // emitting of args below is disabled by setting emitArgs to false.
+    ParseNode* pn2 = pn->pn_head;
+    const char* errorName = SelfHostedCallFunctionName(pn2->name(), cx);
+
+    if (pn->pn_count < 3) {
+        reportError(pn, JSMSG_MORE_ARGS_NEEDED, errorName, "2", "s");
+        return false;
+    }
+
+    JSOp callOp = pn->getOp();
+    if (callOp != JSOP_CALL) {
+        reportError(pn, JSMSG_NOT_CONSTRUCTOR, errorName);
+        return false;
+    }
+
+    bool constructing = pn2->name() == cx->names().constructContentFunction;
+    ParseNode* funNode = pn2->pn_next;
+    if (constructing)
+        callOp = JSOP_NEW;
+    else if (funNode->getKind() == PNK_NAME && funNode->name() == cx->names().std_Function_apply)
+        callOp = JSOP_FUNAPPLY;
+
+    if (!emitTree(funNode))
+        return false;
+
+#ifdef DEBUG
+    if (emitterMode == BytecodeEmitter::SelfHosting &&
+        pn2->name() == cx->names().callFunction)
+    {
+        if (!emit1(JSOP_DEBUGCHECKSELFHOSTED))
+            return false;
+    }
+#endif
+
+    ParseNode* thisOrNewTarget = funNode->pn_next;
+    if (constructing) {
+        // Save off the new.target value, but here emit a proper |this| for a
+        // constructing call.
+        if (!emit1(JSOP_IS_CONSTRUCTING))
+            return false;
+    } else {
+        // It's |this|, emit it.
+        if (!emitTree(thisOrNewTarget))
+            return false;
+    }
+
+    for (ParseNode* argpn = thisOrNewTarget->pn_next; argpn; argpn = argpn->pn_next) {
+        if (!emitTree(argpn))
+            return false;
+    }
+
+    if (constructing) {
+        if (!emitTree(thisOrNewTarget))
+            return false;
+    }
+
+    uint32_t argc = pn->pn_count - 3;
+    if (!emitCall(callOp, argc))
+        return false;
+
+    checkTypeSet(callOp);
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSelfHostedResumeGenerator(ParseNode* pn)
+{
+    // Syntax: resumeGenerator(gen, value, 'next'|'throw'|'close')
+    if (pn->pn_count != 4) {
+        reportError(pn, JSMSG_MORE_ARGS_NEEDED, "resumeGenerator", "1", "s");
+        return false;
+    }
+
+    ParseNode* funNode = pn->pn_head;  // The resumeGenerator node.
+
+    ParseNode* genNode = funNode->pn_next;
+    if (!emitTree(genNode))
+        return false;
+
+    ParseNode* valNode = genNode->pn_next;
+    if (!emitTree(valNode))
+        return false;
+
+    ParseNode* kindNode = valNode->pn_next;
+    MOZ_ASSERT(kindNode->isKind(PNK_STRING));
+    uint16_t operand = GeneratorObject::getResumeKind(cx, kindNode->pn_atom);
+    MOZ_ASSERT(!kindNode->pn_next);
+
+    if (!emitCall(JSOP_RESUME, operand))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSelfHostedForceInterpreter(ParseNode* pn)
+{
+    if (!emit1(JSOP_FORCEINTERPRETER))
+        return false;
+    if (!emit1(JSOP_UNDEFINED))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSelfHostedAllowContentSpread(ParseNode* pn)
+{
+    if (pn->pn_count != 2) {
+        reportError(pn, JSMSG_MORE_ARGS_NEEDED, "allowContentSpread", "1", "");
+        return false;
+    }
+
+    // We're just here as a sentinel. Pass the value through directly.
+    return emitTree(pn->pn_head->pn_next);
+}
+
+bool
+BytecodeEmitter::isRestParameter(ParseNode* pn, bool* result)
+{
+    if (!sc->isFunctionBox()) {
+        *result = false;
+        return true;
+    }
+
+    FunctionBox* funbox = sc->asFunctionBox();
+    RootedFunction fun(cx, funbox->function());
+    if (!fun->hasRest()) {
+        *result = false;
+        return true;
+    }
+
+    if (!pn->isKind(PNK_NAME)) {
+        if (emitterMode == BytecodeEmitter::SelfHosting && pn->isKind(PNK_CALL)) {
+            ParseNode* pn2 = pn->pn_head;
+            if (pn2->getKind() == PNK_NAME && pn2->name() == cx->names().allowContentSpread)
+                return isRestParameter(pn2->pn_next, result);
+        }
+        *result = false;
+        return true;
+    }
+
+    JSAtom* name = pn->name();
+    Maybe<NameLocation> paramLoc = locationOfNameBoundInFunctionScope(name);
+    if (paramLoc && lookupName(name) == *paramLoc) {
+        FunctionScope::Data* bindings = funbox->functionScopeBindings();
+        if (bindings->nonPositionalFormalStart > 0) {
+            // |paramName| can be nullptr when the rest destructuring syntax is
+            // used: `function f(...[]) {}`.
+            JSAtom* paramName = bindings->names[bindings->nonPositionalFormalStart - 1].name();
+            *result = paramName && name == paramName;
+            return true;
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitOptimizeSpread(ParseNode* arg0, JumpList* jmp, bool* emitted)
+{
+    // Emit a pereparation code to optimize the spread call with a rest
+    // parameter:
+    //
+    //   function f(...args) {
+    //     g(...args);
+    //   }
+    //
+    // If the spread operand is a rest parameter and it's optimizable array,
+    // skip spread operation and pass it directly to spread call operation.
+    // See the comment in OptimizeSpreadCall in Interpreter.cpp for the
+    // optimizable conditons.
+    bool result = false;
+    if (!isRestParameter(arg0, &result))
+        return false;
+
+    if (!result) {
+        *emitted = false;
+        return true;
+    }
+
+    if (!emitTree(arg0))
+        return false;
+
+    if (!emit1(JSOP_OPTIMIZE_SPREADCALL))
+        return false;
+
+    if (!emitJump(JSOP_IFNE, jmp))
+        return false;
+
+    if (!emit1(JSOP_POP))
+        return false;
+
+    *emitted = true;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitCallOrNew(ParseNode* pn)
+{
+    bool callop = pn->isKind(PNK_CALL) || pn->isKind(PNK_TAGGED_TEMPLATE);
+    /*
+     * Emit callable invocation or operator new (constructor call) code.
+     * First, emit code for the left operand to evaluate the callable or
+     * constructable object expression.
+     *
+     * For operator new, we emit JSOP_GETPROP instead of JSOP_CALLPROP, etc.
+     * This is necessary to interpose the lambda-initialized method read
+     * barrier -- see the code in jsinterp.cpp for JSOP_LAMBDA followed by
+     * JSOP_{SET,INIT}PROP.
+     *
+     * Then (or in a call case that has no explicit reference-base
+     * object) we emit JSOP_UNDEFINED to produce the undefined |this|
+     * value required for calls (which non-strict mode functions
+     * will box into the global object).
+     */
+    uint32_t argc = pn->pn_count - 1;
+
+    if (argc >= ARGC_LIMIT) {
+        parser->tokenStream.reportError(callop
+                                        ? JSMSG_TOO_MANY_FUN_ARGS
+                                        : JSMSG_TOO_MANY_CON_ARGS);
+        return false;
+    }
+
+    ParseNode* pn2 = pn->pn_head;
+    bool spread = JOF_OPTYPE(pn->getOp()) == JOF_BYTE;
+    switch (pn2->getKind()) {
+      case PNK_NAME:
+        if (emitterMode == BytecodeEmitter::SelfHosting && !spread) {
+            // Calls to "forceInterpreter", "callFunction",
+            // "callContentFunction", or "resumeGenerator" in self-hosted
+            // code generate inline bytecode.
+            if (pn2->name() == cx->names().callFunction ||
+                pn2->name() == cx->names().callContentFunction ||
+                pn2->name() == cx->names().constructContentFunction)
+            {
+                return emitSelfHostedCallFunction(pn);
+            }
+            if (pn2->name() == cx->names().resumeGenerator)
+                return emitSelfHostedResumeGenerator(pn);
+            if (pn2->name() == cx->names().forceInterpreter)
+                return emitSelfHostedForceInterpreter(pn);
+            if (pn2->name() == cx->names().allowContentSpread)
+                return emitSelfHostedAllowContentSpread(pn);
+            // Fall through.
+        }
+        if (!emitGetName(pn2, callop))
+            return false;
+        break;
+      case PNK_DOT:
+        MOZ_ASSERT(emitterMode != BytecodeEmitter::SelfHosting);
+        if (pn2->as<PropertyAccess>().isSuper()) {
+            if (!emitSuperPropOp(pn2, JSOP_GETPROP_SUPER, /* isCall = */ callop))
+                return false;
+        } else {
+            if (!emitPropOp(pn2, callop ? JSOP_CALLPROP : JSOP_GETPROP))
+                return false;
+        }
+
+        break;
+      case PNK_ELEM:
+        MOZ_ASSERT(emitterMode != BytecodeEmitter::SelfHosting);
+        if (pn2->as<PropertyByValue>().isSuper()) {
+            if (!emitSuperElemOp(pn2, JSOP_GETELEM_SUPER, /* isCall = */ callop))
+                return false;
+        } else {
+            if (!emitElemOp(pn2, callop ? JSOP_CALLELEM : JSOP_GETELEM))
+                return false;
+            if (callop) {
+                if (!emit1(JSOP_SWAP))
+                    return false;
+            }
+        }
+
+        break;
+      case PNK_FUNCTION:
+        /*
+         * Top level lambdas which are immediately invoked should be
+         * treated as only running once. Every time they execute we will
+         * create new types and scripts for their contents, to increase
+         * the quality of type information within them and enable more
+         * backend optimizations. Note that this does not depend on the
+         * lambda being invoked at most once (it may be named or be
+         * accessed via foo.caller indirection), as multiple executions
+         * will just cause the inner scripts to be repeatedly cloned.
+         */
+        MOZ_ASSERT(!emittingRunOnceLambda);
+        if (checkRunOnceContext()) {
+            emittingRunOnceLambda = true;
+            if (!emitTree(pn2))
+                return false;
+            emittingRunOnceLambda = false;
+        } else {
+            if (!emitTree(pn2))
+                return false;
+        }
+        callop = false;
+        break;
+      case PNK_SUPERBASE:
+        MOZ_ASSERT(pn->isKind(PNK_SUPERCALL));
+        MOZ_ASSERT(parser->handler.isSuperBase(pn2));
+        if (!emit1(JSOP_SUPERFUN))
+            return false;
+        break;
+      default:
+        if (!emitTree(pn2))
+            return false;
+        callop = false;             /* trigger JSOP_UNDEFINED after */
+        break;
+    }
+
+    bool isNewOp = pn->getOp() == JSOP_NEW || pn->getOp() == JSOP_SPREADNEW ||
+                   pn->getOp() == JSOP_SUPERCALL || pn->getOp() == JSOP_SPREADSUPERCALL;
+
+
+    // Emit room for |this|.
+    if (!callop) {
+        if (isNewOp) {
+            if (!emit1(JSOP_IS_CONSTRUCTING))
+                return false;
+        } else {
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+        }
+    }
+
+    /*
+     * Emit code for each argument in order, then emit the JSOP_*CALL or
+     * JSOP_NEW bytecode with a two-byte immediate telling how many args
+     * were pushed on the operand stack.
+     */
+    if (!spread) {
+        for (ParseNode* pn3 = pn2->pn_next; pn3; pn3 = pn3->pn_next) {
+            if (!emitTree(pn3))
+                return false;
+        }
+
+        if (isNewOp) {
+            if (pn->isKind(PNK_SUPERCALL)) {
+                if (!emit1(JSOP_NEWTARGET))
+                    return false;
+            } else {
+                // Repush the callee as new.target
+                if (!emitDupAt(argc + 1))
+                    return false;
+            }
+        }
+    } else {
+        ParseNode* args = pn2->pn_next;
+        JumpList jmp;
+        bool optCodeEmitted = false;
+        if (argc == 1) {
+            if (!emitOptimizeSpread(args->pn_kid, &jmp, &optCodeEmitted))
+                return false;
+        }
+
+        if (!emitArray(args, argc, JSOP_SPREADCALLARRAY))
+            return false;
+
+        if (optCodeEmitted) {
+            if (!emitJumpTargetAndPatch(jmp))
+                return false;
+        }
+
+        if (isNewOp) {
+            if (pn->isKind(PNK_SUPERCALL)) {
+                if (!emit1(JSOP_NEWTARGET))
+                    return false;
+            } else {
+                if (!emitDupAt(2))
+                    return false;
+            }
+        }
+    }
+
+    if (!spread) {
+        if (!emitCall(pn->getOp(), argc, pn))
+            return false;
+    } else {
+        if (!emit1(pn->getOp()))
+            return false;
+    }
+    checkTypeSet(pn->getOp());
+    if (pn->isOp(JSOP_EVAL) ||
+        pn->isOp(JSOP_STRICTEVAL) ||
+        pn->isOp(JSOP_SPREADEVAL) ||
+        pn->isOp(JSOP_STRICTSPREADEVAL))
+    {
+        uint32_t lineNum = parser->tokenStream.srcCoords.lineNum(pn->pn_pos.begin);
+        if (!emitUint32Operand(JSOP_LINENO, lineNum))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitRightAssociative(ParseNode* pn)
+{
+    // ** is the only right-associative operator.
+    MOZ_ASSERT(pn->isKind(PNK_POW));
+    MOZ_ASSERT(pn->isArity(PN_LIST));
+
+    // Right-associative operator chain.
+    for (ParseNode* subexpr = pn->pn_head; subexpr; subexpr = subexpr->pn_next) {
+        if (!emitTree(subexpr))
+            return false;
+    }
+    for (uint32_t i = 0; i < pn->pn_count - 1; i++) {
+        if (!emit1(JSOP_POW))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitLeftAssociative(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isArity(PN_LIST));
+
+    // Left-associative operator chain.
+    if (!emitTree(pn->pn_head))
+        return false;
+    JSOp op = pn->getOp();
+    ParseNode* nextExpr = pn->pn_head->pn_next;
+    do {
+        if (!emitTree(nextExpr))
+            return false;
+        if (!emit1(op))
+            return false;
+    } while ((nextExpr = nextExpr->pn_next));
+    return true;
+}
+
+bool
+BytecodeEmitter::emitLogical(ParseNode* pn)
+{
+    MOZ_ASSERT(pn->isArity(PN_LIST));
+
+    /*
+     * JSOP_OR converts the operand on the stack to boolean, leaves the original
+     * value on the stack and jumps if true; otherwise it falls into the next
+     * bytecode, which pops the left operand and then evaluates the right operand.
+     * The jump goes around the right operand evaluation.
+     *
+     * JSOP_AND converts the operand on the stack to boolean and jumps if false;
+     * otherwise it falls into the right operand's bytecode.
+     */
+
+    TDZCheckCache tdzCache(this);
+
+    /* Left-associative operator chain: avoid too much recursion. */
+    ParseNode* pn2 = pn->pn_head;
+    if (!emitTree(pn2))
+        return false;
+    JSOp op = pn->getOp();
+    JumpList jump;
+    if (!emitJump(op, &jump))
+        return false;
+    if (!emit1(JSOP_POP))
+        return false;
+
+    /* Emit nodes between the head and the tail. */
+    while ((pn2 = pn2->pn_next)->pn_next) {
+        if (!emitTree(pn2))
+            return false;
+        if (!emitJump(op, &jump))
+            return false;
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+    if (!emitTree(pn2))
+        return false;
+
+    if (!emitJumpTargetAndPatch(jump))
+        return false;
+    return true;
+}
+
+bool
+BytecodeEmitter::emitSequenceExpr(ParseNode* pn)
+{
+    for (ParseNode* child = pn->pn_head; ; child = child->pn_next) {
+        if (!updateSourceCoordNotes(child->pn_pos.begin))
+            return false;
+        if (!emitTree(child))
+            return false;
+        if (!child->pn_next)
+            break;
+        if (!emit1(JSOP_POP))
+            return false;
+    }
+    return true;
+}
+
+// Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
+// the comment on emitSwitch.
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitIncOrDec(ParseNode* pn)
+{
+    switch (pn->pn_kid->getKind()) {
+      case PNK_DOT:
+        return emitPropIncDec(pn);
+      case PNK_ELEM:
+        return emitElemIncDec(pn);
+      case PNK_CALL:
+        return emitCallIncDec(pn);
+      default:
+        return emitNameIncDec(pn);
+    }
+
+    return true;
+}
+
+// Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
+// the comment on emitSwitch.
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitLabeledStatement(const LabeledStatement* pn)
+{
+    /*
+     * Emit a JSOP_LABEL instruction. The argument is the offset to the statement
+     * following the labeled statement.
+     */
+    uint32_t index;
+    if (!makeAtomIndex(pn->label(), &index))
+        return false;
+
+    JumpList top;
+    if (!emitJump(JSOP_LABEL, &top))
+        return false;
+
+    /* Emit code for the labeled statement. */
+    LabelControl controlInfo(this, pn->label(), offset());
+
+    if (!emitTree(pn->statement()))
+        return false;
+
+    /* Patch the JSOP_LABEL offset. */
+    JumpTarget brk{ lastNonJumpTargetOffset() };
+    patchJumpsToTarget(top, brk);
+
+    if (!controlInfo.patchBreaks(this))
+        return false;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitConditionalExpression(ConditionalExpression& conditional)
+{
+    /* Emit the condition, then branch if false to the else part. */
+    if (!emitTree(&conditional.condition()))
+        return false;
+
+    IfThenElseEmitter ifThenElse(this);
+    if (!ifThenElse.emitCond())
+        return false;
+
+    if (!emitConditionallyExecutedTree(&conditional.thenExpression()))
+        return false;
+
+    if (!ifThenElse.emitElse())
+        return false;
+
+    if (!emitConditionallyExecutedTree(&conditional.elseExpression()))
+        return false;
+
+    if (!ifThenElse.emitEnd())
+        return false;
+    MOZ_ASSERT(ifThenElse.pushed() == 1);
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitPropertyList(ParseNode* pn, MutableHandlePlainObject objp, PropListType type)
+{
+    for (ParseNode* propdef = pn->pn_head; propdef; propdef = propdef->pn_next) {
+        if (!updateSourceCoordNotes(propdef->pn_pos.begin))
+            return false;
+
+        // Handle __proto__: v specially because *only* this form, and no other
+        // involving "__proto__", performs [[Prototype]] mutation.
+        if (propdef->isKind(PNK_MUTATEPROTO)) {
+            MOZ_ASSERT(type == ObjectLiteral);
+            if (!emitTree(propdef->pn_kid))
+                return false;
+            objp.set(nullptr);
+            if (!emit1(JSOP_MUTATEPROTO))
+                return false;
+            continue;
+        }
+
+        bool extraPop = false;
+        if (type == ClassBody && propdef->as<ClassMethod>().isStatic()) {
+            extraPop = true;
+            if (!emit1(JSOP_DUP2))
+                return false;
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+
+        /* Emit an index for t[2] for later consumption by JSOP_INITELEM. */
+        ParseNode* key = propdef->pn_left;
+        bool isIndex = false;
+        if (key->isKind(PNK_NUMBER)) {
+            if (!emitNumberOp(key->pn_dval))
+                return false;
+            isIndex = true;
+        } else if (key->isKind(PNK_OBJECT_PROPERTY_NAME) || key->isKind(PNK_STRING)) {
+            // EmitClass took care of constructor already.
+            if (type == ClassBody && key->pn_atom == cx->names().constructor &&
+                !propdef->as<ClassMethod>().isStatic())
+            {
+                continue;
+            }
+
+            // The parser already checked for atoms representing indexes and
+            // used PNK_NUMBER instead, but also watch for ids which TI treats
+            // as indexes for simpliciation of downstream analysis.
+            jsid id = NameToId(key->pn_atom->asPropertyName());
+            if (id != IdToTypeId(id)) {
+                if (!emitTree(key))
+                    return false;
+                isIndex = true;
+            }
+        } else {
+            if (!emitComputedPropertyName(key))
+                return false;
+            isIndex = true;
+        }
+
+        /* Emit code for the property initializer. */
+        if (!emitTree(propdef->pn_right))
+            return false;
+
+        JSOp op = propdef->getOp();
+        MOZ_ASSERT(op == JSOP_INITPROP ||
+                   op == JSOP_INITPROP_GETTER ||
+                   op == JSOP_INITPROP_SETTER);
+
+        if (op == JSOP_INITPROP_GETTER || op == JSOP_INITPROP_SETTER)
+            objp.set(nullptr);
+
+        if (propdef->pn_right->isKind(PNK_FUNCTION) &&
+            propdef->pn_right->pn_funbox->needsHomeObject())
+        {
+            MOZ_ASSERT(propdef->pn_right->pn_funbox->function()->allowSuperProperty());
+            bool isAsync = propdef->pn_right->pn_funbox->isAsync();
+            if (isAsync) {
+                if (!emit1(JSOP_SWAP))
+                    return false;
+            }
+            if (!emit2(JSOP_INITHOMEOBJECT, isIndex + isAsync))
+                return false;
+            if (isAsync) {
+                if (!emit1(JSOP_POP))
+                    return false;
+            }
+        }
+
+        // Class methods are not enumerable.
+        if (type == ClassBody) {
+            switch (op) {
+              case JSOP_INITPROP:        op = JSOP_INITHIDDENPROP;          break;
+              case JSOP_INITPROP_GETTER: op = JSOP_INITHIDDENPROP_GETTER;   break;
+              case JSOP_INITPROP_SETTER: op = JSOP_INITHIDDENPROP_SETTER;   break;
+              default: MOZ_CRASH("Invalid op");
+            }
+        }
+
+        if (isIndex) {
+            objp.set(nullptr);
+            switch (op) {
+              case JSOP_INITPROP:               op = JSOP_INITELEM;              break;
+              case JSOP_INITHIDDENPROP:         op = JSOP_INITHIDDENELEM;        break;
+              case JSOP_INITPROP_GETTER:        op = JSOP_INITELEM_GETTER;       break;
+              case JSOP_INITHIDDENPROP_GETTER:  op = JSOP_INITHIDDENELEM_GETTER; break;
+              case JSOP_INITPROP_SETTER:        op = JSOP_INITELEM_SETTER;       break;
+              case JSOP_INITHIDDENPROP_SETTER:  op = JSOP_INITHIDDENELEM_SETTER; break;
+              default: MOZ_CRASH("Invalid op");
+            }
+            if (!emit1(op))
+                return false;
+        } else {
+            MOZ_ASSERT(key->isKind(PNK_OBJECT_PROPERTY_NAME) || key->isKind(PNK_STRING));
+
+            uint32_t index;
+            if (!makeAtomIndex(key->pn_atom, &index))
+                return false;
+
+            if (objp) {
+                MOZ_ASSERT(type == ObjectLiteral);
+                MOZ_ASSERT(!IsHiddenInitOp(op));
+                MOZ_ASSERT(!objp->inDictionaryMode());
+                Rooted<jsid> id(cx, AtomToId(key->pn_atom));
+                RootedValue undefinedValue(cx, UndefinedValue());
+                if (!NativeDefineProperty(cx, objp, id, undefinedValue, nullptr, nullptr,
+                                          JSPROP_ENUMERATE))
+                {
+                    return false;
+                }
+                if (objp->inDictionaryMode())
+                    objp.set(nullptr);
+            }
+
+            if (!emitIndex32(op, index))
+                return false;
+        }
+
+        if (extraPop) {
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+    }
+    return true;
+}
+
+// Using MOZ_NEVER_INLINE in here is a workaround for llvm.org/pr14047. See
+// the comment on emitSwitch.
+MOZ_NEVER_INLINE bool
+BytecodeEmitter::emitObject(ParseNode* pn)
+{
+    if (!(pn->pn_xflags & PNX_NONCONST) && pn->pn_head && checkSingletonContext())
+        return emitSingletonInitialiser(pn);
+
+    /*
+     * Emit code for {p:a, '%q':b, 2:c} that is equivalent to constructing
+     * a new object and defining (in source order) each property on the object
+     * (or mutating the object's [[Prototype]], in the case of __proto__).
+     */
+    ptrdiff_t offset = this->offset();
+    if (!emitNewInit(JSProto_Object))
+        return false;
+
+    /*
+     * Try to construct the shape of the object as we go, so we can emit a
+     * JSOP_NEWOBJECT with the final shape instead.
+     */
+    RootedPlainObject obj(cx);
+    // No need to do any guessing for the object kind, since we know exactly
+    // how many properties we plan to have.
+    gc::AllocKind kind = gc::GetGCObjectKind(pn->pn_count);
+    obj = NewBuiltinClassInstance<PlainObject>(cx, kind, TenuredObject);
+    if (!obj)
+        return false;
+
+    if (!emitPropertyList(pn, &obj, ObjectLiteral))
+        return false;
+
+    if (obj) {
+        /*
+         * The object survived and has a predictable shape: update the original
+         * bytecode.
+         */
+        ObjectBox* objbox = parser->newObjectBox(obj);
+        if (!objbox)
+            return false;
+
+        static_assert(JSOP_NEWINIT_LENGTH == JSOP_NEWOBJECT_LENGTH,
+                      "newinit and newobject must have equal length to edit in-place");
+
+        uint32_t index = objectList.add(objbox);
+        jsbytecode* code = this->code(offset);
+        code[0] = JSOP_NEWOBJECT;
+        code[1] = jsbytecode(index >> 24);
+        code[2] = jsbytecode(index >> 16);
+        code[3] = jsbytecode(index >> 8);
+        code[4] = jsbytecode(index);
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitArrayComp(ParseNode* pn)
+{
+    if (!emitNewInit(JSProto_Array))
+        return false;
+
+    /*
+     * Pass the new array's stack index to the PNK_ARRAYPUSH case via
+     * arrayCompDepth, then simply traverse the PNK_FOR node and
+     * its kids under pn2 to generate this comprehension.
+     */
+    MOZ_ASSERT(stackDepth > 0);
+    uint32_t saveDepth = arrayCompDepth;
+    arrayCompDepth = (uint32_t) (stackDepth - 1);
+    if (!emitTree(pn->pn_head))
+        return false;
+    arrayCompDepth = saveDepth;
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitArrayLiteral(ParseNode* pn)
+{
+    if (!(pn->pn_xflags & PNX_NONCONST) && pn->pn_head) {
+        if (checkSingletonContext()) {
+            // Bake in the object entirely if it will only be created once.
+            return emitSingletonInitialiser(pn);
+        }
+
+        // If the array consists entirely of primitive values, make a
+        // template object with copy on write elements that can be reused
+        // every time the initializer executes.
+        if (emitterMode != BytecodeEmitter::SelfHosting && pn->pn_count != 0) {
+            RootedValue value(cx);
+            if (!pn->getConstantValue(cx, ParseNode::ForCopyOnWriteArray, &value))
+                return false;
+            if (!value.isMagic(JS_GENERIC_MAGIC)) {
+                // Note: the group of the template object might not yet reflect
+                // that the object has copy on write elements. When the
+                // interpreter or JIT compiler fetches the template, it should
+                // use ObjectGroup::getOrFixupCopyOnWriteObject to make sure the
+                // group for the template is accurate. We don't do this here as we
+                // want to use ObjectGroup::allocationSiteGroup, which requires a
+                // finished script.
+                JSObject* obj = &value.toObject();
+                MOZ_ASSERT(obj->is<ArrayObject>() &&
+                           obj->as<ArrayObject>().denseElementsAreCopyOnWrite());
+
+                ObjectBox* objbox = parser->newObjectBox(obj);
+                if (!objbox)
+                    return false;
+
+                return emitObjectOp(objbox, JSOP_NEWARRAY_COPYONWRITE);
+            }
+        }
+    }
+
+    return emitArray(pn->pn_head, pn->pn_count, JSOP_NEWARRAY);
+}
+
+bool
+BytecodeEmitter::emitArray(ParseNode* pn, uint32_t count, JSOp op)
+{
+
+    /*
+     * Emit code for [a, b, c] that is equivalent to constructing a new
+     * array and in source order evaluating each element value and adding
+     * it to the array, without invoking latent setters.  We use the
+     * JSOP_NEWINIT and JSOP_INITELEM_ARRAY bytecodes to ignore setters and
+     * to avoid dup'ing and popping the array as each element is added, as
+     * JSOP_SETELEM/JSOP_SETPROP would do.
+     */
+    MOZ_ASSERT(op == JSOP_NEWARRAY || op == JSOP_SPREADCALLARRAY);
+
+    uint32_t nspread = 0;
+    for (ParseNode* elt = pn; elt; elt = elt->pn_next) {
+        if (elt->isKind(PNK_SPREAD))
+            nspread++;
+    }
+
+    // Array literal's length is limited to NELEMENTS_LIMIT in parser.
+    static_assert(NativeObject::MAX_DENSE_ELEMENTS_COUNT <= INT32_MAX,
+                  "array literals' maximum length must not exceed limits "
+                  "required by BaselineCompiler::emit_JSOP_NEWARRAY, "
+                  "BaselineCompiler::emit_JSOP_INITELEM_ARRAY, "
+                  "and DoSetElemFallback's handling of JSOP_INITELEM_ARRAY");
+    MOZ_ASSERT(count >= nspread);
+    MOZ_ASSERT(count <= NativeObject::MAX_DENSE_ELEMENTS_COUNT,
+               "the parser must throw an error if the array exceeds maximum "
+               "length");
+
+    // For arrays with spread, this is a very pessimistic allocation, the
+    // minimum possible final size.
+    if (!emitUint32Operand(op, count - nspread))                    // ARRAY
+        return false;
+
+    ParseNode* pn2 = pn;
+    uint32_t index;
+    bool afterSpread = false;
+    for (index = 0; pn2; index++, pn2 = pn2->pn_next) {
+        if (!afterSpread && pn2->isKind(PNK_SPREAD)) {
+            afterSpread = true;
+            if (!emitNumberOp(index))                               // ARRAY INDEX
+                return false;
+        }
+        if (!updateSourceCoordNotes(pn2->pn_pos.begin))
+            return false;
+
+        bool allowSelfHostedSpread = false;
+        if (pn2->isKind(PNK_ELISION)) {
+            if (!emit1(JSOP_HOLE))
+                return false;
+        } else {
+            ParseNode* expr;
+            if (pn2->isKind(PNK_SPREAD)) {
+                expr = pn2->pn_kid;
+
+                if (emitterMode == BytecodeEmitter::SelfHosting &&
+                    expr->isKind(PNK_CALL) &&
+                    expr->pn_head->name() == cx->names().allowContentSpread)
+                {
+                    allowSelfHostedSpread = true;
+                }
+            } else {
+                expr = pn2;
+            }
+            if (!emitTree(expr))                                         // ARRAY INDEX? VALUE
+                return false;
+        }
+        if (pn2->isKind(PNK_SPREAD)) {
+            if (!emitIterator())                                         // ARRAY INDEX ITER
+                return false;
+            if (!emit2(JSOP_PICK, 2))                                    // INDEX ITER ARRAY
+                return false;
+            if (!emit2(JSOP_PICK, 2))                                    // ITER ARRAY INDEX
+                return false;
+            if (!emitSpread(allowSelfHostedSpread))                      // ARRAY INDEX
+                return false;
+        } else if (afterSpread) {
+            if (!emit1(JSOP_INITELEM_INC))
+                return false;
+        } else {
+            if (!emitUint32Operand(JSOP_INITELEM_ARRAY, index))
+                return false;
+        }
+    }
+    MOZ_ASSERT(index == count);
+    if (afterSpread) {
+        if (!emit1(JSOP_POP))                                            // ARRAY
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitUnary(ParseNode* pn)
+{
+    if (!updateSourceCoordNotes(pn->pn_pos.begin))
+        return false;
+
+    /* Unary op, including unary +/-. */
+    JSOp op = pn->getOp();
+    ParseNode* pn2 = pn->pn_kid;
+
+    if (!emitTree(pn2))
+        return false;
+
+    return emit1(op);
+}
+
+bool
+BytecodeEmitter::emitTypeof(ParseNode* node, JSOp op)
+{
+    MOZ_ASSERT(op == JSOP_TYPEOF || op == JSOP_TYPEOFEXPR);
+
+    if (!updateSourceCoordNotes(node->pn_pos.begin))
+        return false;
+
+    if (!emitTree(node->pn_kid))
+        return false;
+
+    return emit1(op);
+}
+
+bool
+BytecodeEmitter::emitFunctionFormalParametersAndBody(ParseNode *pn)
+{
+    MOZ_ASSERT(pn->isKind(PNK_PARAMSBODY));
+
+    ParseNode* funBody = pn->last();
+    FunctionBox* funbox = sc->asFunctionBox();
+
+    TDZCheckCache tdzCache(this);
+
+    if (funbox->hasParameterExprs) {
+        EmitterScope funEmitterScope(this);
+        if (!funEmitterScope.enterFunction(this, funbox))
+            return false;
+
+        if (!emitInitializeFunctionSpecialNames())
+            return false;
+
+        if (!emitFunctionFormalParameters(pn))
+            return false;
+
+        {
+            Maybe<EmitterScope> extraVarEmitterScope;
+
+            if (funbox->hasExtraBodyVarScope()) {
+                extraVarEmitterScope.emplace(this);
+                if (!extraVarEmitterScope->enterFunctionExtraBodyVar(this, funbox))
+                    return false;
+
+                // After emitting expressions for all parameters, copy over any
+                // formal parameters which have been redeclared as vars. For
+                // example, in the following, the var y in the body scope is 42:
+                //
+                //   function f(x, y = 42) { var y; }
+                //
+                RootedAtom name(cx);
+                if (funbox->extraVarScopeBindings() && funbox->functionScopeBindings()) {
+                    for (BindingIter bi(*funbox->functionScopeBindings(), true); bi; bi++) {
+                        name = bi.name();
+
+                        // There may not be a var binding of the same name.
+                        if (!locationOfNameBoundInScope(name, extraVarEmitterScope.ptr()))
+                            continue;
+
+                        // The '.this' and '.generator' function special
+                        // bindings should never appear in the extra var
+                        // scope. 'arguments', however, may.
+                        MOZ_ASSERT(name != cx->names().dotThis &&
+                                   name != cx->names().dotGenerator);
+
+                        NameLocation paramLoc = *locationOfNameBoundInScope(name, &funEmitterScope);
+                        auto emitRhs = [&name, &paramLoc](BytecodeEmitter* bce,
+                                                          const NameLocation&, bool)
+                        {
+                            return bce->emitGetNameAtLocation(name, paramLoc);
+                        };
+
+                        if (!emitInitializeName(name, emitRhs))
+                            return false;
+                        if (!emit1(JSOP_POP))
+                            return false;
+                    }
+                }
+            }
+
+            if (!emitFunctionBody(funBody))
+                return false;
+
+            if (extraVarEmitterScope && !extraVarEmitterScope->leave(this))
+                return false;
+        }
+
+        return funEmitterScope.leave(this);
+    }
+
+    // No parameter expressions. Enter the function body scope and emit
+    // everything.
+    //
+    // One caveat is that Debugger considers ops in the prologue to be
+    // unreachable (i.e. cannot set a breakpoint on it). If there are no
+    // parameter exprs, any unobservable environment ops (like pushing the
+    // call object, setting '.this', etc) need to go in the prologue, else it
+    // messes up breakpoint tests.
+    EmitterScope emitterScope(this);
+
+    switchToPrologue();
+    if (!emitterScope.enterFunction(this, funbox))
+        return false;
+
+    if (!emitInitializeFunctionSpecialNames())
+        return false;
+    switchToMain();
+
+    if (!emitFunctionFormalParameters(pn))
+        return false;
+
+    if (!emitFunctionBody(funBody))
+        return false;
+
+    return emitterScope.leave(this);
+}
+
+bool
+BytecodeEmitter::emitFunctionFormalParameters(ParseNode* pn)
+{
+    ParseNode* funBody = pn->last();
+    FunctionBox* funbox = sc->asFunctionBox();
+    EmitterScope* funScope = innermostEmitterScope;
+
+    bool hasParameterExprs = funbox->hasParameterExprs;
+    bool hasRest = funbox->function()->hasRest();
+
+    uint16_t argSlot = 0;
+    for (ParseNode* arg = pn->pn_head; arg != funBody; arg = arg->pn_next, argSlot++) {
+        ParseNode* bindingElement = arg;
+        ParseNode* initializer = nullptr;
+        if (arg->isKind(PNK_ASSIGN)) {
+            bindingElement = arg->pn_left;
+            initializer = arg->pn_right;
+        }
+
+        // Left-hand sides are either simple names or destructuring patterns.
+        MOZ_ASSERT(bindingElement->isKind(PNK_NAME) ||
+                   bindingElement->isKind(PNK_ARRAY) ||
+                   bindingElement->isKind(PNK_ARRAYCOMP) ||
+                   bindingElement->isKind(PNK_OBJECT));
+
+        // The rest parameter doesn't have an initializer.
+        bool isRest = hasRest && arg->pn_next == funBody;
+        MOZ_ASSERT_IF(isRest, !initializer);
+
+        bool isDestructuring = !bindingElement->isKind(PNK_NAME);
+
+        // ES 14.1.19 says if BindingElement contains an expression in the
+        // production FormalParameter : BindingElement, it is evaluated in a
+        // new var environment. This is needed to prevent vars from escaping
+        // direct eval in parameter expressions.
+        Maybe<EmitterScope> paramExprVarScope;
+        if (funbox->hasDirectEvalInParameterExpr && (isDestructuring || initializer)) {
+            paramExprVarScope.emplace(this);
+            if (!paramExprVarScope->enterParameterExpressionVar(this))
+                return false;
+        }
+
+        // First push the RHS if there is a default expression or if it is
+        // rest.
+
+        if (initializer) {
+            // If we have an initializer, emit the initializer and assign it
+            // to the argument slot. TDZ is taken care of afterwards.
+            MOZ_ASSERT(hasParameterExprs);
+            if (!emitArgOp(JSOP_GETARG, argSlot))
+                return false;
+            if (!emit1(JSOP_DUP))
+                return false;
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+            if (!emit1(JSOP_STRICTEQ))
+                return false;
+            // Emit source note to enable Ion compilation.
+            if (!newSrcNote(SRC_IF))
+                return false;
+            JumpList jump;
+            if (!emitJump(JSOP_IFEQ, &jump))
+                return false;
+            if (!emit1(JSOP_POP))
+                return false;
+            if (!emitConditionallyExecutedTree(initializer))
+                return false;
+            if (!emitJumpTargetAndPatch(jump))
+                return false;
+        } else if (isRest) {
+            if (!emit1(JSOP_REST))
+                return false;
+            checkTypeSet(JSOP_REST);
+        }
+
+        // Initialize the parameter name.
+
+        if (isDestructuring) {
+            // If we had an initializer or the rest parameter, the value is
+            // already on the stack.
+            if (!initializer && !isRest && !emitArgOp(JSOP_GETARG, argSlot))
+                return false;
+
+            // If there's an parameter expression var scope, the destructuring
+            // declaration needs to initialize the name in the function scope,
+            // which is not the innermost scope.
+            if (!emitDestructuringOps(bindingElement,
+                                      paramExprVarScope
+                                      ? DestructuringFormalParameterInVarScope
+                                      : DestructuringDeclaration))
+            {
+                return false;
+            }
+
+            if (!emit1(JSOP_POP))
+                return false;
+        } else {
+            RootedAtom paramName(cx, bindingElement->name());
+            NameLocation paramLoc = *locationOfNameBoundInScope(paramName, funScope);
+
+            if (hasParameterExprs) {
+                auto emitRhs = [argSlot, initializer, isRest](BytecodeEmitter* bce,
+                                                              const NameLocation&, bool)
+                {
+                    // If we had an initializer or a rest parameter, the value is
+                    // already on the stack.
+                    if (!initializer && !isRest)
+                        return bce->emitArgOp(JSOP_GETARG, argSlot);
+                    return true;
+                };
+
+                if (!emitSetOrInitializeNameAtLocation(paramName, paramLoc, emitRhs, true))
+                    return false;
+                if (!emit1(JSOP_POP))
+                    return false;
+            } else if (isRest) {
+                // The rest value is already on top of the stack.
+                auto nop = [](BytecodeEmitter*, const NameLocation&, bool) {
+                    return true;
+                };
+
+                if (!emitSetOrInitializeNameAtLocation(paramName, paramLoc, nop, true))
+                    return false;
+                if (!emit1(JSOP_POP))
+                    return false;
+            }
+        }
+
+        if (paramExprVarScope) {
+            if (!paramExprVarScope->leave(this))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitInitializeFunctionSpecialNames()
+{
+    FunctionBox* funbox = sc->asFunctionBox();
+
+    auto emitInitializeFunctionSpecialName = [](BytecodeEmitter* bce, HandlePropertyName name,
+                                                JSOp op)
+    {
+        // A special name must be slotful, either on the frame or on the
+        // call environment.
+        MOZ_ASSERT(bce->lookupName(name).hasKnownSlot());
+
+        auto emitInitial = [op](BytecodeEmitter* bce, const NameLocation&, bool) {
+            return bce->emit1(op);
+        };
+
+        if (!bce->emitInitializeName(name, emitInitial))
+            return false;
+        if (!bce->emit1(JSOP_POP))
+            return false;
+
+        return true;
+    };
+
+    // Do nothing if the function doesn't have an arguments binding.
+    if (funbox->argumentsHasLocalBinding()) {
+        if (!emitInitializeFunctionSpecialName(this, cx->names().arguments, JSOP_ARGUMENTS))
+            return false;
+    }
+
+    // Do nothing if the function doesn't have a this-binding (this
+    // happens for instance if it doesn't use this/eval or if it's an
+    // arrow function).
+    if (funbox->hasThisBinding()) {
+        if (!emitInitializeFunctionSpecialName(this, cx->names().dotThis, JSOP_FUNCTIONTHIS))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitFunctionBody(ParseNode* funBody)
+{
+    FunctionBox* funbox = sc->asFunctionBox();
+
+    if (!emitTree(funBody))
+        return false;
+
+    if (funbox->isGenerator()) {
+        // If we fall off the end of a generator, do a final yield.
+        if (funbox->isStarGenerator() && !emitPrepareIteratorResult())
+            return false;
+
+        if (!emit1(JSOP_UNDEFINED))
+            return false;
+
+        if (sc->asFunctionBox()->isStarGenerator() && !emitFinishIteratorResult(true))
+            return false;
+
+        if (!emit1(JSOP_SETRVAL))
+            return false;
+
+        NameLocation loc = *locationOfNameBoundInFunctionScope(cx->names().dotGenerator);
+        if (!emitGetNameAtLocation(cx->names().dotGenerator, loc))
+            return false;
+
+        // No need to check for finally blocks, etc as in EmitReturn.
+        if (!emitYieldOp(JSOP_FINALYIELDRVAL))
+            return false;
+    } else {
+        // Non-generator functions just return |undefined|. The
+        // JSOP_RETRVAL emitted below will do that, except if the
+        // script has a finally block: there can be a non-undefined
+        // value in the return value slot. Make sure the return value
+        // is |undefined|.
+        if (hasTryFinally) {
+            if (!emit1(JSOP_UNDEFINED))
+                return false;
+            if (!emit1(JSOP_SETRVAL))
+                return false;
+        }
+    }
+
+    if (funbox->isDerivedClassConstructor()) {
+        if (!emitCheckDerivedClassConstructorReturn())
+            return false;
+    }
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitLexicalInitialization(ParseNode* pn)
+{
+    // The caller has pushed the RHS to the top of the stack. Assert that the
+    // name is lexical and no BIND[G]NAME ops were emitted.
+    auto assertLexical = [](BytecodeEmitter*, const NameLocation& loc, bool emittedBindOp) {
+        MOZ_ASSERT(loc.isLexical());
+        MOZ_ASSERT(!emittedBindOp);
+        return true;
+    };
+    return emitInitializeName(pn, assertLexical);
+}
+
+// This follows ES6 14.5.14 (ClassDefinitionEvaluation) and ES6 14.5.15
+// (BindingClassDeclarationEvaluation).
+bool
+BytecodeEmitter::emitClass(ParseNode* pn)
+{
+    ClassNode& classNode = pn->as<ClassNode>();
+
+    ClassNames* names = classNode.names();
+
+    ParseNode* heritageExpression = classNode.heritage();
+
+    ParseNode* classMethods = classNode.methodList();
+    ParseNode* constructor = nullptr;
+    for (ParseNode* mn = classMethods->pn_head; mn; mn = mn->pn_next) {
+        ClassMethod& method = mn->as<ClassMethod>();
+        ParseNode& methodName = method.name();
+        if (!method.isStatic() &&
+            (methodName.isKind(PNK_OBJECT_PROPERTY_NAME) || methodName.isKind(PNK_STRING)) &&
+            methodName.pn_atom == cx->names().constructor)
+        {
+            constructor = &method.method();
+            break;
+        }
+    }
+
+    bool savedStrictness = sc->setLocalStrictMode(true);
+
+    Maybe<TDZCheckCache> tdzCache;
+    Maybe<EmitterScope> emitterScope;
+    if (names) {
+        tdzCache.emplace(this);
+        emitterScope.emplace(this);
+        if (!emitterScope->enterLexical(this, ScopeKind::Lexical, classNode.scopeBindings()))
+            return false;
+    }
+
+    // This is kind of silly. In order to the get the home object defined on
+    // the constructor, we have to make it second, but we want the prototype
+    // on top for EmitPropertyList, because we expect static properties to be
+    // rarer. The result is a few more swaps than we would like. Such is life.
+    if (heritageExpression) {
+        if (!emitTree(heritageExpression))
+            return false;
+        if (!emit1(JSOP_CLASSHERITAGE))
+            return false;
+        if (!emit1(JSOP_OBJWITHPROTO))
+            return false;
+
+        // JSOP_CLASSHERITAGE leaves both protos on the stack. After
+        // creating the prototype, swap it to the bottom to make the
+        // constructor.
+        if (!emit1(JSOP_SWAP))
+            return false;
+    } else {
+        if (!emitNewInit(JSProto_Object))
+            return false;
+    }
+
+    if (constructor) {
+        if (!emitFunction(constructor, !!heritageExpression))
+            return false;
+        if (constructor->pn_funbox->needsHomeObject()) {
+            if (!emit2(JSOP_INITHOMEOBJECT, 0))
+                return false;
+        }
+    } else {
+        JSAtom *name = names ? names->innerBinding()->pn_atom : cx->names().empty;
+        if (heritageExpression) {
+            if (!emitAtomOp(name, JSOP_DERIVEDCONSTRUCTOR))
+                return false;
+        } else {
+            if (!emitAtomOp(name, JSOP_CLASSCONSTRUCTOR))
+                return false;
+        }
+    }
+
+    if (!emit1(JSOP_SWAP))
+        return false;
+
+    if (!emit1(JSOP_DUP2))
+        return false;
+    if (!emitAtomOp(cx->names().prototype, JSOP_INITLOCKEDPROP))
+        return false;
+    if (!emitAtomOp(cx->names().constructor, JSOP_INITHIDDENPROP))
+        return false;
+
+    RootedPlainObject obj(cx);
+    if (!emitPropertyList(classMethods, &obj, ClassBody))
+        return false;
+
+    if (!emit1(JSOP_POP))
+        return false;
+
+    if (names) {
+        ParseNode* innerName = names->innerBinding();
+        if (!emitLexicalInitialization(innerName))
+            return false;
+
+        // Pop the inner scope.
+        if (!emitterScope->leave(this))
+            return false;
+        emitterScope.reset();
+
+        ParseNode* outerName = names->outerBinding();
+        if (outerName) {
+            if (!emitLexicalInitialization(outerName))
+                return false;
+            // Only class statements make outer bindings, and they do not leave
+            // themselves on the stack.
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+    }
+
+    MOZ_ALWAYS_TRUE(sc->setLocalStrictMode(savedStrictness));
+
+    return true;
+}
+
+bool
+BytecodeEmitter::emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    EmitLevelManager elm(this);
+
+    /* Emit notes to tell the current bytecode's source line number.
+       However, a couple trees require special treatment; see the
+       relevant emitter functions for details. */
+    if (emitLineNote == EMIT_LINENOTE && !ParseNodeRequiresSpecialLineNumberNotes(pn)) {
+        if (!updateLineNumberNotes(pn->pn_pos.begin))
+            return false;
+    }
+
+    switch (pn->getKind()) {
+      case PNK_FUNCTION:
+        if (!emitFunction(pn))
+            return false;
+        break;
+
+      case PNK_PARAMSBODY:
+        if (!emitFunctionFormalParametersAndBody(pn))
+            return false;
+        break;
+
+      case PNK_IF:
+        if (!emitIf(pn))
+            return false;
+        break;
+
+      case PNK_SWITCH:
+        if (!emitSwitch(pn))
+            return false;
+        break;
+
+      case PNK_WHILE:
+        if (!emitWhile(pn))
+            return false;
+        break;
+
+      case PNK_DOWHILE:
+        if (!emitDo(pn))
+            return false;
+        break;
+
+      case PNK_FOR:
+        if (!emitFor(pn))
+            return false;
+        break;
+
+      case PNK_COMPREHENSIONFOR:
+        if (!emitComprehensionFor(pn))
+            return false;
+        break;
+
+      case PNK_BREAK:
+        if (!emitBreak(pn->as<BreakStatement>().label()))
+            return false;
+        break;
+
+      case PNK_CONTINUE:
+        if (!emitContinue(pn->as<ContinueStatement>().label()))
+            return false;
+        break;
+
+      case PNK_WITH:
+        if (!emitWith(pn))
+            return false;
+        break;
+
+      case PNK_TRY:
+        if (!emitTry(pn))
+            return false;
+        break;
+
+      case PNK_CATCH:
+        if (!emitCatch(pn))
+            return false;
+        break;
+
+      case PNK_VAR:
+        if (!emitDeclarationList(pn))
+            return false;
+        break;
+
+      case PNK_RETURN:
+        if (!emitReturn(pn))
+            return false;
+        break;
+
+      case PNK_YIELD_STAR:
+        if (!emitYieldStar(pn->pn_left, pn->pn_right))
+            return false;
+        break;
+
+      case PNK_GENERATOR:
+        if (!emit1(JSOP_GENERATOR))
+            return false;
+        break;
+
+      case PNK_YIELD:
+      case PNK_AWAIT:
+        if (!emitYield(pn))
+            return false;
+        break;
+
+      case PNK_STATEMENTLIST:
+        if (!emitStatementList(pn))
+            return false;
+        break;
+
+      case PNK_SEMI:
+        if (!emitStatement(pn))
+            return false;
+        break;
+
+      case PNK_LABEL:
+        if (!emitLabeledStatement(&pn->as<LabeledStatement>()))
+            return false;
+        break;
+
+      case PNK_COMMA:
+        if (!emitSequenceExpr(pn))
+            return false;
+        break;
+
+      case PNK_ASSIGN:
+      case PNK_ADDASSIGN:
+      case PNK_SUBASSIGN:
+      case PNK_BITORASSIGN:
+      case PNK_BITXORASSIGN:
+      case PNK_BITANDASSIGN:
+      case PNK_LSHASSIGN:
+      case PNK_RSHASSIGN:
+      case PNK_URSHASSIGN:
+      case PNK_MULASSIGN:
+      case PNK_DIVASSIGN:
+      case PNK_MODASSIGN:
+      case PNK_POWASSIGN:
+        if (!emitAssignment(pn->pn_left, pn->getOp(), pn->pn_right))
+            return false;
+        break;
+
+      case PNK_CONDITIONAL:
+        if (!emitConditionalExpression(pn->as<ConditionalExpression>()))
+            return false;
+        break;
+
+      case PNK_OR:
+      case PNK_AND:
+        if (!emitLogical(pn))
+            return false;
+        break;
+
+      case PNK_ADD:
+      case PNK_SUB:
+      case PNK_BITOR:
+      case PNK_BITXOR:
+      case PNK_BITAND:
+      case PNK_STRICTEQ:
+      case PNK_EQ:
+      case PNK_STRICTNE:
+      case PNK_NE:
+      case PNK_LT:
+      case PNK_LE:
+      case PNK_GT:
+      case PNK_GE:
+      case PNK_IN:
+      case PNK_INSTANCEOF:
+      case PNK_LSH:
+      case PNK_RSH:
+      case PNK_URSH:
+      case PNK_STAR:
+      case PNK_DIV:
+      case PNK_MOD:
+        if (!emitLeftAssociative(pn))
+            return false;
+        break;
+
+      case PNK_POW:
+        if (!emitRightAssociative(pn))
+            return false;
+        break;
+
+      case PNK_TYPEOFNAME:
+        if (!emitTypeof(pn, JSOP_TYPEOF))
+            return false;
+        break;
+
+      case PNK_TYPEOFEXPR:
+        if (!emitTypeof(pn, JSOP_TYPEOFEXPR))
+            return false;
+        break;
+
+      case PNK_THROW:
+      case PNK_VOID:
+      case PNK_NOT:
+      case PNK_BITNOT:
+      case PNK_POS:
+      case PNK_NEG:
+        if (!emitUnary(pn))
+            return false;
+        break;
+
+      case PNK_PREINCREMENT:
+      case PNK_PREDECREMENT:
+      case PNK_POSTINCREMENT:
+      case PNK_POSTDECREMENT:
+        if (!emitIncOrDec(pn))
+            return false;
+        break;
+
+      case PNK_DELETENAME:
+        if (!emitDeleteName(pn))
+            return false;
+        break;
+
+      case PNK_DELETEPROP:
+        if (!emitDeleteProperty(pn))
+            return false;
+        break;
+
+      case PNK_DELETEELEM:
+        if (!emitDeleteElement(pn))
+            return false;
+        break;
+
+      case PNK_DELETEEXPR:
+        if (!emitDeleteExpression(pn))
+            return false;
+        break;
+
+      case PNK_DOT:
+        if (pn->as<PropertyAccess>().isSuper()) {
+            if (!emitSuperPropOp(pn, JSOP_GETPROP_SUPER))
+                return false;
+        } else {
+            if (!emitPropOp(pn, JSOP_GETPROP))
+                return false;
+        }
+        break;
+
+      case PNK_ELEM:
+        if (pn->as<PropertyByValue>().isSuper()) {
+            if (!emitSuperElemOp(pn, JSOP_GETELEM_SUPER))
+                return false;
+        } else {
+            if (!emitElemOp(pn, JSOP_GETELEM))
+                return false;
+        }
+        break;
+
+      case PNK_NEW:
+      case PNK_TAGGED_TEMPLATE:
+      case PNK_CALL:
+      case PNK_GENEXP:
+      case PNK_SUPERCALL:
+        if (!emitCallOrNew(pn))
+            return false;
+        break;
+
+      case PNK_LEXICALSCOPE:
+        if (!emitLexicalScope(pn))
+            return false;
+        break;
+
+      case PNK_CONST:
+      case PNK_LET:
+        if (!emitDeclarationList(pn))
+            return false;
+        break;
+
+      case PNK_IMPORT:
+        MOZ_ASSERT(sc->isModuleContext());
+        break;
+
+      case PNK_EXPORT:
+        MOZ_ASSERT(sc->isModuleContext());
+        if (pn->pn_kid->getKind() != PNK_EXPORT_SPEC_LIST) {
+            if (!emitTree(pn->pn_kid))
+                return false;
+        }
+        break;
+
+      case PNK_EXPORT_DEFAULT:
+        MOZ_ASSERT(sc->isModuleContext());
+        if (!emitTree(pn->pn_kid))
+            return false;
+        if (pn->pn_right) {
+            if (!emitLexicalInitialization(pn->pn_right))
+                return false;
+            if (!emit1(JSOP_POP))
+                return false;
+        }
+        break;
+
+      case PNK_EXPORT_FROM:
+        MOZ_ASSERT(sc->isModuleContext());
+        break;
+
+      case PNK_ARRAYPUSH:
+        /*
+         * The array object's stack index is in arrayCompDepth. See below
+         * under the array initialiser code generator for array comprehension
+         * special casing.
+         */
+        if (!emitTree(pn->pn_kid))
+            return false;
+        if (!emitDupAt(this->stackDepth - 1 - arrayCompDepth))
+            return false;
+        if (!emit1(JSOP_ARRAYPUSH))
+            return false;
+        break;
+
+      case PNK_CALLSITEOBJ:
+        if (!emitCallSiteObject(pn))
+            return false;
+        break;
+
+      case PNK_ARRAY:
+        if (!emitArrayLiteral(pn))
+            return false;
+        break;
+
+      case PNK_ARRAYCOMP:
+        if (!emitArrayComp(pn))
+            return false;
+        break;
+
+      case PNK_OBJECT:
+        if (!emitObject(pn))
+            return false;
+        break;
+
+      case PNK_NAME:
+        if (!emitGetName(pn))
+            return false;
+        break;
+
+      case PNK_TEMPLATE_STRING_LIST:
+        if (!emitTemplateString(pn))
+            return false;
+        break;
+
+      case PNK_TEMPLATE_STRING:
+      case PNK_STRING:
+        if (!emitAtomOp(pn, JSOP_STRING))
+            return false;
+        break;
+
+      case PNK_NUMBER:
+        if (!emitNumberOp(pn->pn_dval))
+            return false;
+        break;
+
+      case PNK_REGEXP:
+        if (!emitRegExp(objectList.add(pn->as<RegExpLiteral>().objbox())))
+            return false;
+        break;
+
+      case PNK_TRUE:
+      case PNK_FALSE:
+      case PNK_NULL:
+        if (!emit1(pn->getOp()))
+            return false;
+        break;
+
+      case PNK_THIS:
+        if (!emitThisLiteral(pn))
+            return false;
+        break;
+
+      case PNK_DEBUGGER:
+        if (!updateSourceCoordNotes(pn->pn_pos.begin))
+            return false;
+        if (!emit1(JSOP_DEBUGGER))
+            return false;
+        break;
+
+      case PNK_NOP:
+        MOZ_ASSERT(pn->getArity() == PN_NULLARY);
+        break;
+
+      case PNK_CLASS:
+        if (!emitClass(pn))
+            return false;
+        break;
+
+      case PNK_NEWTARGET:
+        if (!emit1(JSOP_NEWTARGET))
+            return false;
+        break;
+
+      case PNK_SETTHIS:
+        if (!emitSetThis(pn))
+            return false;
+        break;
+
+      case PNK_POSHOLDER:
+        MOZ_FALLTHROUGH_ASSERT("Should never try to emit PNK_POSHOLDER");
+
+      default:
+        MOZ_ASSERT(0);
+    }
+
+    /* bce->emitLevel == 1 means we're last on the stack, so finish up. */
+    if (emitLevel == 1) {
+        if (!updateSourceCoordNotes(pn->pn_pos.end))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::emitConditionallyExecutedTree(ParseNode* pn)
+{
+    // Code that may be conditionally executed always need their own TDZ
+    // cache.
+    TDZCheckCache tdzCache(this);
+    return emitTree(pn);
+}
+
+static bool
+AllocSrcNote(ExclusiveContext* cx, SrcNotesVector& notes, unsigned* index)
+{
+    // Start it off moderately large to avoid repeated resizings early on.
+    // ~99% of cases fit within 256 bytes.
+    if (notes.capacity() == 0 && !notes.reserve(256))
+        return false;
+
+    if (!notes.growBy(1)) {
+        ReportOutOfMemory(cx);
+        return false;
+    }
+
+    *index = notes.length() - 1;
+    return true;
+}
+
+bool
+BytecodeEmitter::newSrcNote(SrcNoteType type, unsigned* indexp)
+{
+    SrcNotesVector& notes = this->notes();
+    unsigned index;
+    if (!AllocSrcNote(cx, notes, &index))
+        return false;
+
+    /*
+     * Compute delta from the last annotated bytecode's offset.  If it's too
+     * big to fit in sn, allocate one or more xdelta notes and reset sn.
+     */
+    ptrdiff_t offset = this->offset();
+    ptrdiff_t delta = offset - lastNoteOffset();
+    current->lastNoteOffset = offset;
+    if (delta >= SN_DELTA_LIMIT) {
+        do {
+            ptrdiff_t xdelta = Min(delta, SN_XDELTA_MASK);
+            SN_MAKE_XDELTA(&notes[index], xdelta);
+            delta -= xdelta;
+            if (!AllocSrcNote(cx, notes, &index))
+                return false;
+        } while (delta >= SN_DELTA_LIMIT);
+    }
+
+    /*
+     * Initialize type and delta, then allocate the minimum number of notes
+     * needed for type's arity.  Usually, we won't need more, but if an offset
+     * does take two bytes, setSrcNoteOffset will grow notes.
+     */
+    SN_MAKE_NOTE(&notes[index], type, delta);
+    for (int n = (int)js_SrcNoteSpec[type].arity; n > 0; n--) {
+        if (!newSrcNote(SRC_NULL))
+            return false;
+    }
+
+    if (indexp)
+        *indexp = index;
+    return true;
+}
+
+bool
+BytecodeEmitter::newSrcNote2(SrcNoteType type, ptrdiff_t offset, unsigned* indexp)
+{
+    unsigned index;
+    if (!newSrcNote(type, &index))
+        return false;
+    if (!setSrcNoteOffset(index, 0, offset))
+        return false;
+    if (indexp)
+        *indexp = index;
+    return true;
+}
+
+bool
+BytecodeEmitter::newSrcNote3(SrcNoteType type, ptrdiff_t offset1, ptrdiff_t offset2,
+                             unsigned* indexp)
+{
+    unsigned index;
+    if (!newSrcNote(type, &index))
+        return false;
+    if (!setSrcNoteOffset(index, 0, offset1))
+        return false;
+    if (!setSrcNoteOffset(index, 1, offset2))
+        return false;
+    if (indexp)
+        *indexp = index;
+    return true;
+}
+
+bool
+BytecodeEmitter::addToSrcNoteDelta(jssrcnote* sn, ptrdiff_t delta)
+{
+    /*
+     * Called only from finishTakingSrcNotes to add to main script note
+     * deltas, and only by a small positive amount.
+     */
+    MOZ_ASSERT(current == &main);
+    MOZ_ASSERT((unsigned) delta < (unsigned) SN_XDELTA_LIMIT);
+
+    ptrdiff_t base = SN_DELTA(sn);
+    ptrdiff_t limit = SN_IS_XDELTA(sn) ? SN_XDELTA_LIMIT : SN_DELTA_LIMIT;
+    ptrdiff_t newdelta = base + delta;
+    if (newdelta < limit) {
+        SN_SET_DELTA(sn, newdelta);
+    } else {
+        jssrcnote xdelta;
+        SN_MAKE_XDELTA(&xdelta, delta);
+        if (!main.notes.insert(sn, xdelta))
+            return false;
+    }
+    return true;
+}
+
+bool
+BytecodeEmitter::setSrcNoteOffset(unsigned index, unsigned which, ptrdiff_t offset)
+{
+    if (!SN_REPRESENTABLE_OFFSET(offset)) {
+        parser->tokenStream.reportError(JSMSG_NEED_DIET, js_script_str);
+        return false;
+    }
+
+    SrcNotesVector& notes = this->notes();
+
+    /* Find the offset numbered which (i.e., skip exactly which offsets). */
+    jssrcnote* sn = &notes[index];
+    MOZ_ASSERT(SN_TYPE(sn) != SRC_XDELTA);
+    MOZ_ASSERT((int) which < js_SrcNoteSpec[SN_TYPE(sn)].arity);
+    for (sn++; which; sn++, which--) {
+        if (*sn & SN_4BYTE_OFFSET_FLAG)
+            sn += 3;
+    }
+
+    /*
+     * See if the new offset requires four bytes either by being too big or if
+     * the offset has already been inflated (in which case, we need to stay big
+     * to not break the srcnote encoding if this isn't the last srcnote).
+     */
+    if (offset > (ptrdiff_t)SN_4BYTE_OFFSET_MASK || (*sn & SN_4BYTE_OFFSET_FLAG)) {
+        /* Maybe this offset was already set to a four-byte value. */
+        if (!(*sn & SN_4BYTE_OFFSET_FLAG)) {
+            /* Insert three dummy bytes that will be overwritten shortly. */
+            jssrcnote dummy = 0;
+            if (!(sn = notes.insert(sn, dummy)) ||
+                !(sn = notes.insert(sn, dummy)) ||
+                !(sn = notes.insert(sn, dummy)))
+            {
+                ReportOutOfMemory(cx);
+                return false;
+            }
+        }
+        *sn++ = (jssrcnote)(SN_4BYTE_OFFSET_FLAG | (offset >> 24));
+        *sn++ = (jssrcnote)(offset >> 16);
+        *sn++ = (jssrcnote)(offset >> 8);
+    }
+    *sn = (jssrcnote)offset;
+    return true;
+}
+
+bool
+BytecodeEmitter::finishTakingSrcNotes(uint32_t* out)
+{
+    MOZ_ASSERT(current == &main);
+
+    unsigned prologueCount = prologue.notes.length();
+    if (prologueCount && prologue.currentLine != firstLine) {
+        switchToPrologue();
+        if (!newSrcNote2(SRC_SETLINE, ptrdiff_t(firstLine)))
+            return false;
+        switchToMain();
+    } else {
+        /*
+         * Either no prologue srcnotes, or no line number change over prologue.
+         * We don't need a SRC_SETLINE, but we may need to adjust the offset
+         * of the first main note, by adding to its delta and possibly even
+         * prepending SRC_XDELTA notes to it to account for prologue bytecodes
+         * that came at and after the last annotated bytecode.
+         */
+        ptrdiff_t offset = prologueOffset() - prologue.lastNoteOffset;
+        MOZ_ASSERT(offset >= 0);
+        if (offset > 0 && main.notes.length() != 0) {
+            /* NB: Use as much of the first main note's delta as we can. */
+            jssrcnote* sn = main.notes.begin();
+            ptrdiff_t delta = SN_IS_XDELTA(sn)
+                            ? SN_XDELTA_MASK - (*sn & SN_XDELTA_MASK)
+                            : SN_DELTA_MASK - (*sn & SN_DELTA_MASK);
+            if (offset < delta)
+                delta = offset;
+            for (;;) {
+                if (!addToSrcNoteDelta(sn, delta))
+                    return false;
+                offset -= delta;
+                if (offset == 0)
+                    break;
+                delta = Min(offset, SN_XDELTA_MASK);
+                sn = main.notes.begin();
+            }
+        }
+    }
+
+    // The prologue count might have changed, so we can't reuse prologueCount.
+    // The + 1 is to account for the final SN_MAKE_TERMINATOR that is appended
+    // when the notes are copied to their final destination by CopySrcNotes.
+    *out = prologue.notes.length() + main.notes.length() + 1;
+    return true;
+}
+
+void
+BytecodeEmitter::copySrcNotes(jssrcnote* destination, uint32_t nsrcnotes)
+{
+    unsigned prologueCount = prologue.notes.length();
+    unsigned mainCount = main.notes.length();
+    unsigned totalCount = prologueCount + mainCount;
+    MOZ_ASSERT(totalCount == nsrcnotes - 1);
+    if (prologueCount)
+        PodCopy(destination, prologue.notes.begin(), prologueCount);
+    PodCopy(destination + prologueCount, main.notes.begin(), mainCount);
+    SN_MAKE_TERMINATOR(&destination[totalCount]);
+}
+
+void
+CGConstList::finish(ConstArray* array)
+{
+    MOZ_ASSERT(length() == array->length);
+
+    for (unsigned i = 0; i < length(); i++)
+        array->vector[i] = list[i];
+}
+
+bool
+CGObjectList::isAdded(ObjectBox* objbox)
+{
+    // An objbox added to CGObjectList as non-first element has non-null
+    // emitLink member.  The first element has null emitLink.
+    // Check for firstbox to cover the first element.
+    return objbox->emitLink || objbox == firstbox;
+}
+
+/*
+ * Find the index of the given object for code generator.
+ *
+ * Since the emitter refers to each parsed object only once, for the index we
+ * use the number of already indexed objects. We also add the object to a list
+ * to convert the list to a fixed-size array when we complete code generation,
+ * see js::CGObjectList::finish below.
+ */
+unsigned
+CGObjectList::add(ObjectBox* objbox)
+{
+    if (isAdded(objbox))
+        return indexOf(objbox->object);
+
+    objbox->emitLink = lastbox;
+    lastbox = objbox;
+
+    // See the comment in CGObjectList::isAdded.
+    if (!firstbox)
+        firstbox = objbox;
+    return length++;
+}
+
+unsigned
+CGObjectList::indexOf(JSObject* obj)
+{
+    MOZ_ASSERT(length > 0);
+    unsigned index = length - 1;
+    for (ObjectBox* box = lastbox; box->object != obj; box = box->emitLink)
+        index--;
+    return index;
+}
+
+void
+CGObjectList::finish(ObjectArray* array)
+{
+    MOZ_ASSERT(length <= INDEX_LIMIT);
+    MOZ_ASSERT(length == array->length);
+
+    js::GCPtrObject* cursor = array->vector + array->length;
+    ObjectBox* objbox = lastbox;
+    do {
+        --cursor;
+        MOZ_ASSERT(!*cursor);
+        MOZ_ASSERT(objbox->object->isTenured());
+        *cursor = objbox->object;
+
+        ObjectBox* tmp = objbox->emitLink;
+        // Clear emitLink for CGObjectList::isAdded.
+        objbox->emitLink = nullptr;
+        objbox = tmp;
+    } while (objbox != nullptr);
+    MOZ_ASSERT(cursor == array->vector);
+}
+
+ObjectBox*
+CGObjectList::find(uint32_t index)
+{
+    MOZ_ASSERT(index < length);
+    ObjectBox* box = lastbox;
+    for (unsigned n = length - 1; n > index; n--)
+        box = box->emitLink;
+    return box;
+}
+
+void
+CGScopeList::finish(ScopeArray* array)
+{
+    MOZ_ASSERT(length() <= INDEX_LIMIT);
+    MOZ_ASSERT(length() == array->length);
+    for (uint32_t i = 0; i < length(); i++)
+        array->vector[i].init(vector[i]);
+}
+
+bool
+CGTryNoteList::append(JSTryNoteKind kind, uint32_t stackDepth, size_t start, size_t end)
+{
+    MOZ_ASSERT(start <= end);
+    MOZ_ASSERT(size_t(uint32_t(start)) == start);
+    MOZ_ASSERT(size_t(uint32_t(end)) == end);
+
+    JSTryNote note;
+    note.kind = kind;
+    note.stackDepth = stackDepth;
+    note.start = uint32_t(start);
+    note.length = uint32_t(end - start);
+
+    return list.append(note);
+}
+
+void
+CGTryNoteList::finish(TryNoteArray* array)
+{
+    MOZ_ASSERT(length() == array->length);
+
+    for (unsigned i = 0; i < length(); i++)
+        array->vector[i] = list[i];
+}
+
+bool
+CGScopeNoteList::append(uint32_t scopeIndex, uint32_t offset, bool inPrologue,
+                        uint32_t parent)
+{
+    CGScopeNote note;
+    mozilla::PodZero(&note);
+
+    note.index = scopeIndex;
+    note.start = offset;
+    note.parent = parent;
+    note.startInPrologue = inPrologue;
+
+    return list.append(note);
+}
+
+void
+CGScopeNoteList::recordEnd(uint32_t index, uint32_t offset, bool inPrologue)
+{
+    MOZ_ASSERT(index < length());
+    MOZ_ASSERT(list[index].length == 0);
+    list[index].end = offset;
+    list[index].endInPrologue = inPrologue;
+}
+
+void
+CGScopeNoteList::finish(ScopeNoteArray* array, uint32_t prologueLength)
+{
+    MOZ_ASSERT(length() == array->length);
+
+    for (unsigned i = 0; i < length(); i++) {
+        if (!list[i].startInPrologue)
+            list[i].start += prologueLength;
+        if (!list[i].endInPrologue && list[i].end != UINT32_MAX)
+            list[i].end += prologueLength;
+        MOZ_ASSERT(list[i].end >= list[i].start);
+        list[i].length = list[i].end - list[i].start;
+        array->vector[i] = list[i];
+    }
+}
+
+void
+CGYieldOffsetList::finish(YieldOffsetArray& array, uint32_t prologueLength)
+{
+    MOZ_ASSERT(length() == array.length());
+
+    for (unsigned i = 0; i < length(); i++)
+        array[i] = prologueLength + list[i];
+}
+
+/*
+ * We should try to get rid of offsetBias (always 0 or 1, where 1 is
+ * JSOP_{NOP,POP}_LENGTH), which is used only by SRC_FOR.
+ */
+const JSSrcNoteSpec js_SrcNoteSpec[] = {
+#define DEFINE_SRC_NOTE_SPEC(sym, name, arity) { name, arity },
+    FOR_EACH_SRC_NOTE_TYPE(DEFINE_SRC_NOTE_SPEC)
+#undef DEFINE_SRC_NOTE_SPEC
+};
+
+static int
+SrcNoteArity(jssrcnote* sn)
+{
+    MOZ_ASSERT(SN_TYPE(sn) < SRC_LAST);
+    return js_SrcNoteSpec[SN_TYPE(sn)].arity;
+}
+
+JS_FRIEND_API(unsigned)
+js::SrcNoteLength(jssrcnote* sn)
+{
+    unsigned arity;
+    jssrcnote* base;
+
+    arity = SrcNoteArity(sn);
+    for (base = sn++; arity; sn++, arity--) {
+        if (*sn & SN_4BYTE_OFFSET_FLAG)
+            sn += 3;
+    }
+    return sn - base;
+}
+
+JS_FRIEND_API(ptrdiff_t)
+js::GetSrcNoteOffset(jssrcnote* sn, unsigned which)
+{
+    /* Find the offset numbered which (i.e., skip exactly which offsets). */
+    MOZ_ASSERT(SN_TYPE(sn) != SRC_XDELTA);
+    MOZ_ASSERT((int) which < SrcNoteArity(sn));
+    for (sn++; which; sn++, which--) {
+        if (*sn & SN_4BYTE_OFFSET_FLAG)
+            sn += 3;
+    }
+    if (*sn & SN_4BYTE_OFFSET_FLAG) {
+        return (ptrdiff_t)(((uint32_t)(sn[0] & SN_4BYTE_OFFSET_MASK) << 24)
+                           | (sn[1] << 16)
+                           | (sn[2] << 8)
+                           | sn[3]);
+    }
+    return (ptrdiff_t)*sn;
+}
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
new file mode 100644
index 0000000000..1bb4191ee1
--- /dev/null
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -0,0 +1,763 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* JS bytecode generation. */
+
+#ifndef frontend_BytecodeEmitter_h
+#define frontend_BytecodeEmitter_h
+
+#include "jscntxt.h"
+#include "jsopcode.h"
+#include "jsscript.h"
+
+#include "ds/InlineTable.h"
+#include "frontend/Parser.h"
+#include "frontend/SharedContext.h"
+#include "frontend/SourceNotes.h"
+#include "vm/Interpreter.h"
+
+namespace js {
+namespace frontend {
+
+class FullParseHandler;
+class ObjectBox;
+class ParseNode;
+template <typename ParseHandler> class Parser;
+class SharedContext;
+class TokenStream;
+
+class CGConstList {
+    Vector<Value> list;
+  public:
+    explicit CGConstList(ExclusiveContext* cx) : list(cx) {}
+    MOZ_MUST_USE bool append(const Value& v) {
+        MOZ_ASSERT_IF(v.isString(), v.toString()->isAtom());
+        return list.append(v);
+    }
+    size_t length() const { return list.length(); }
+    void finish(ConstArray* array);
+};
+
+struct CGObjectList {
+    uint32_t            length;     /* number of emitted so far objects */
+    ObjectBox*          firstbox;  /* first emitted object */
+    ObjectBox*          lastbox;   /* last emitted object */
+
+    CGObjectList() : length(0), firstbox(nullptr), lastbox(nullptr) {}
+
+    bool isAdded(ObjectBox* objbox);
+    unsigned add(ObjectBox* objbox);
+    unsigned indexOf(JSObject* obj);
+    void finish(ObjectArray* array);
+    ObjectBox* find(uint32_t index);
+};
+
+struct MOZ_STACK_CLASS CGScopeList {
+    Rooted<GCVector<Scope*>> vector;
+
+    explicit CGScopeList(ExclusiveContext* cx)
+      : vector(cx, GCVector<Scope*>(cx))
+    { }
+
+    bool append(Scope* scope) { return vector.append(scope); }
+    uint32_t length() const { return vector.length(); }
+    void finish(ScopeArray* array);
+};
+
+struct CGTryNoteList {
+    Vector<JSTryNote> list;
+    explicit CGTryNoteList(ExclusiveContext* cx) : list(cx) {}
+
+    MOZ_MUST_USE bool append(JSTryNoteKind kind, uint32_t stackDepth, size_t start, size_t end);
+    size_t length() const { return list.length(); }
+    void finish(TryNoteArray* array);
+};
+
+struct CGScopeNote : public ScopeNote
+{
+    // The end offset. Used to compute the length; may need adjusting first if
+    // in the prologue.
+    uint32_t end;
+
+    // Is the start offset in the prologue?
+    bool startInPrologue;
+
+    // Is the end offset in the prologue?
+    bool endInPrologue;
+};
+
+struct CGScopeNoteList {
+    Vector<CGScopeNote> list;
+    explicit CGScopeNoteList(ExclusiveContext* cx) : list(cx) {}
+
+    MOZ_MUST_USE bool append(uint32_t scopeIndex, uint32_t offset, bool inPrologue,
+                             uint32_t parent);
+    void recordEnd(uint32_t index, uint32_t offset, bool inPrologue);
+    size_t length() const { return list.length(); }
+    void finish(ScopeNoteArray* array, uint32_t prologueLength);
+};
+
+struct CGYieldOffsetList {
+    Vector<uint32_t> list;
+    explicit CGYieldOffsetList(ExclusiveContext* cx) : list(cx) {}
+
+    MOZ_MUST_USE bool append(uint32_t offset) { return list.append(offset); }
+    size_t length() const { return list.length(); }
+    void finish(YieldOffsetArray& array, uint32_t prologueLength);
+};
+
+// Use zero inline elements because these go on the stack and affect how many
+// nested functions are possible.
+typedef Vector<jsbytecode, 0> BytecodeVector;
+typedef Vector<jssrcnote, 0> SrcNotesVector;
+
+// Linked list of jump instructions that need to be patched. The linked list is
+// stored in the bytes of the incomplete bytecode that will be patched, so no
+// extra memory is needed, and patching the instructions destroys the list.
+//
+// Example:
+//
+//     JumpList brList;
+//     if (!emitJump(JSOP_IFEQ, &brList))
+//         return false;
+//     ...
+//     JumpTarget label;
+//     if (!emitJumpTarget(&label))
+//         return false;
+//     ...
+//     if (!emitJump(JSOP_GOTO, &brList))
+//         return false;
+//     ...
+//     patchJumpsToTarget(brList, label);
+//
+//                 +-> -1
+//                 |
+//                 |
+//    ifeq ..   <+ +                +-+   ifeq ..
+//    ..         |                  |     ..
+//  label:       |                  +-> label:
+//    jumptarget |                  |     jumptarget
+//    ..         |                  |     ..
+//    goto .. <+ +                  +-+   goto .. <+
+//             |                                   |
+//             |                                   |
+//             +                                   +
+//           brList                              brList
+//
+//       |                                  ^
+//       +------- patchJumpsToTarget -------+
+//
+
+// Offset of a jump target instruction, used for patching jump instructions.
+struct JumpTarget {
+    ptrdiff_t offset;
+};
+
+struct JumpList {
+    // -1 is used to mark the end of jump lists.
+    JumpList() : offset(-1) {}
+    ptrdiff_t offset;
+
+    // Add a jump instruction to the list.
+    void push(jsbytecode* code, ptrdiff_t jumpOffset);
+
+    // Patch all jump instructions in this list to jump to `target`.  This
+    // clobbers the list.
+    void patchAll(jsbytecode* code, JumpTarget target);
+};
+
+struct MOZ_STACK_CLASS BytecodeEmitter
+{
+    class TDZCheckCache;
+    class NestableControl;
+    class EmitterScope;
+
+    SharedContext* const sc;      /* context shared between parsing and bytecode generation */
+
+    ExclusiveContext* const cx;
+
+    BytecodeEmitter* const parent;  /* enclosing function or global context */
+
+    Rooted<JSScript*> script;       /* the JSScript we're ultimately producing */
+
+    Rooted<LazyScript*> lazyScript; /* the lazy script if mode is LazyFunction,
+                                        nullptr otherwise. */
+
+    struct EmitSection {
+        BytecodeVector code;        /* bytecode */
+        SrcNotesVector notes;       /* source notes, see below */
+        ptrdiff_t   lastNoteOffset; /* code offset for last source note */
+        uint32_t    currentLine;    /* line number for tree-based srcnote gen */
+        uint32_t    lastColumn;     /* zero-based column index on currentLine of
+                                       last SRC_COLSPAN-annotated opcode */
+        JumpTarget lastTarget;      // Last jump target emitted.
+
+        EmitSection(ExclusiveContext* cx, uint32_t lineNum)
+          : code(cx), notes(cx), lastNoteOffset(0), currentLine(lineNum), lastColumn(0),
+            lastTarget{ -1 - ptrdiff_t(JSOP_JUMPTARGET_LENGTH) }
+        {}
+    };
+    EmitSection prologue, main, *current;
+
+    Parser<FullParseHandler>* const parser;
+
+    PooledMapPtr<AtomIndexMap> atomIndices; /* literals indexed for mapping */
+    unsigned        firstLine;      /* first line, for JSScript::initFromEmitter */
+
+    uint32_t        maxFixedSlots;  /* maximum number of fixed frame slots so far */
+    uint32_t        maxStackDepth;  /* maximum number of expression stack slots so far */
+
+    int32_t         stackDepth;     /* current stack depth in script frame */
+
+    uint32_t        arrayCompDepth; /* stack depth of array in comprehension */
+
+    unsigned        emitLevel;      /* emitTree recursion level */
+
+    uint32_t        bodyScopeIndex; /* index into scopeList of the body scope */
+
+    EmitterScope*    varEmitterScope;
+    NestableControl* innermostNestableControl;
+    EmitterScope*    innermostEmitterScope;
+    TDZCheckCache*   innermostTDZCheckCache;
+
+    CGConstList      constList;      /* constants to be included with the script */
+    CGObjectList     objectList;     /* list of emitted objects */
+    CGScopeList      scopeList;      /* list of emitted scopes */
+    CGTryNoteList    tryNoteList;    /* list of emitted try notes */
+    CGScopeNoteList  scopeNoteList;  /* list of emitted block scope notes */
+
+    /*
+     * For each yield op, map the yield index (stored as bytecode operand) to
+     * the offset of the next op.
+     */
+    CGYieldOffsetList yieldOffsetList;
+
+    uint16_t        typesetCount;   /* Number of JOF_TYPESET opcodes generated */
+
+    bool            hasSingletons:1;    /* script contains singleton initializer JSOP_OBJECT */
+
+    bool            hasTryFinally:1;    /* script contains finally block */
+
+    bool            emittingRunOnceLambda:1; /* true while emitting a lambda which is only
+                                                expected to run once. */
+
+    bool isRunOnceLambda();
+
+    enum EmitterMode {
+        Normal,
+
+        /*
+         * Emit JSOP_GETINTRINSIC instead of JSOP_GETNAME and assert that
+         * JSOP_GETNAME and JSOP_*GNAME don't ever get emitted. See the comment
+         * for the field |selfHostingMode| in Parser.h for details.
+         */
+        SelfHosting,
+
+        /*
+         * Check the static scope chain of the root function for resolving free
+         * variable accesses in the script.
+         */
+        LazyFunction
+    };
+
+    const EmitterMode emitterMode;
+
+    // The end location of a function body that is being emitted.
+    uint32_t functionBodyEndPos;
+    // Whether functionBodyEndPos was set.
+    bool functionBodyEndPosSet;
+
+    /*
+     * Note that BytecodeEmitters are magic: they own the arena "top-of-stack"
+     * space above their tempMark points. This means that you cannot alloc from
+     * tempLifoAlloc and save the pointer beyond the next BytecodeEmitter
+     * destruction.
+     */
+    BytecodeEmitter(BytecodeEmitter* parent, Parser<FullParseHandler>* parser, SharedContext* sc,
+                    HandleScript script, Handle<LazyScript*> lazyScript, uint32_t lineNum,
+                    EmitterMode emitterMode = Normal);
+
+    // An alternate constructor that uses a TokenPos for the starting
+    // line and that sets functionBodyEndPos as well.
+    BytecodeEmitter(BytecodeEmitter* parent, Parser<FullParseHandler>* parser, SharedContext* sc,
+                    HandleScript script, Handle<LazyScript*> lazyScript,
+                    TokenPos bodyPosition, EmitterMode emitterMode = Normal);
+
+    MOZ_MUST_USE bool init();
+
+    template <typename Predicate /* (NestableControl*) -> bool */>
+    NestableControl* findInnermostNestableControl(Predicate predicate) const;
+
+    template <typename T>
+    T* findInnermostNestableControl() const;
+
+    template <typename T, typename Predicate /* (T*) -> bool */>
+    T* findInnermostNestableControl(Predicate predicate) const;
+
+    NameLocation lookupName(JSAtom* name);
+
+    // To implement Annex B and the formal parameter defaults scope semantics
+    // requires accessing names that would otherwise be shadowed. This method
+    // returns the access location of a name that is known to be bound in a
+    // target scope.
+    mozilla::Maybe<NameLocation> locationOfNameBoundInScope(JSAtom* name, EmitterScope* target);
+
+    // Get the location of a name known to be bound in the function scope,
+    // starting at the source scope.
+    mozilla::Maybe<NameLocation> locationOfNameBoundInFunctionScope(JSAtom* name,
+                                                                    EmitterScope* source);
+
+    mozilla::Maybe<NameLocation> locationOfNameBoundInFunctionScope(JSAtom* name) {
+        return locationOfNameBoundInFunctionScope(name, innermostEmitterScope);
+    }
+
+    void setVarEmitterScope(EmitterScope* emitterScope) {
+        MOZ_ASSERT(emitterScope);
+        MOZ_ASSERT(!varEmitterScope);
+        varEmitterScope = emitterScope;
+    }
+
+    Scope* bodyScope() const { return scopeList.vector[bodyScopeIndex]; }
+    Scope* outermostScope() const { return scopeList.vector[0]; }
+    Scope* innermostScope() const;
+
+    MOZ_ALWAYS_INLINE
+    MOZ_MUST_USE bool makeAtomIndex(JSAtom* atom, uint32_t* indexp) {
+        MOZ_ASSERT(atomIndices);
+        AtomIndexMap::AddPtr p = atomIndices->lookupForAdd(atom);
+        if (p) {
+            *indexp = p->value();
+            return true;
+        }
+
+        uint32_t index = atomIndices->count();
+        if (!atomIndices->add(p, atom, index))
+            return false;
+
+        *indexp = index;
+        return true;
+    }
+
+    bool isInLoop();
+    MOZ_MUST_USE bool checkSingletonContext();
+
+    // Check whether our function is in a run-once context (a toplevel
+    // run-one script or a run-once lambda).
+    MOZ_MUST_USE bool checkRunOnceContext();
+
+    bool needsImplicitThis();
+
+    MOZ_MUST_USE bool maybeSetDisplayURL();
+    MOZ_MUST_USE bool maybeSetSourceMap();
+    void tellDebuggerAboutCompiledScript(ExclusiveContext* cx);
+
+    inline TokenStream* tokenStream();
+
+    BytecodeVector& code() const { return current->code; }
+    jsbytecode* code(ptrdiff_t offset) const { return current->code.begin() + offset; }
+    ptrdiff_t offset() const { return current->code.end() - current->code.begin(); }
+    ptrdiff_t prologueOffset() const { return prologue.code.end() - prologue.code.begin(); }
+    void switchToMain() { current = &main; }
+    void switchToPrologue() { current = &prologue; }
+    bool inPrologue() const { return current == &prologue; }
+
+    SrcNotesVector& notes() const { return current->notes; }
+    ptrdiff_t lastNoteOffset() const { return current->lastNoteOffset; }
+    unsigned currentLine() const { return current->currentLine; }
+    unsigned lastColumn() const { return current->lastColumn; }
+
+    // Check if the last emitted opcode is a jump target.
+    bool lastOpcodeIsJumpTarget() const {
+        return offset() - current->lastTarget.offset == ptrdiff_t(JSOP_JUMPTARGET_LENGTH);
+    }
+
+    // JumpTarget should not be part of the emitted statement, as they can be
+    // aliased by multiple statements. If we included the jump target as part of
+    // the statement we might have issues where the enclosing statement might
+    // not contain all the opcodes of the enclosed statements.
+    ptrdiff_t lastNonJumpTargetOffset() const {
+        return lastOpcodeIsJumpTarget() ? current->lastTarget.offset : offset();
+    }
+
+    void setFunctionBodyEndPos(TokenPos pos) {
+        functionBodyEndPos = pos.end;
+        functionBodyEndPosSet = true;
+    }
+
+    bool reportError(ParseNode* pn, unsigned errorNumber, ...);
+    bool reportStrictWarning(ParseNode* pn, unsigned errorNumber, ...);
+    bool reportStrictModeError(ParseNode* pn, unsigned errorNumber, ...);
+
+    // If pn contains a useful expression, return true with *answer set to true.
+    // If pn contains a useless expression, return true with *answer set to
+    // false. Return false on error.
+    //
+    // The caller should initialize *answer to false and invoke this function on
+    // an expression statement or similar subtree to decide whether the tree
+    // could produce code that has any side effects.  For an expression
+    // statement, we define useless code as code with no side effects, because
+    // the main effect, the value left on the stack after the code executes,
+    // will be discarded by a pop bytecode.
+    MOZ_MUST_USE bool checkSideEffects(ParseNode* pn, bool* answer);
+
+#ifdef DEBUG
+    MOZ_MUST_USE bool checkStrictOrSloppy(JSOp op);
+#endif
+
+    // Append a new source note of the given type (and therefore size) to the
+    // notes dynamic array, updating noteCount. Return the new note's index
+    // within the array pointed at by current->notes as outparam.
+    MOZ_MUST_USE bool newSrcNote(SrcNoteType type, unsigned* indexp = nullptr);
+    MOZ_MUST_USE bool newSrcNote2(SrcNoteType type, ptrdiff_t offset, unsigned* indexp = nullptr);
+    MOZ_MUST_USE bool newSrcNote3(SrcNoteType type, ptrdiff_t offset1, ptrdiff_t offset2,
+                                  unsigned* indexp = nullptr);
+
+    void copySrcNotes(jssrcnote* destination, uint32_t nsrcnotes);
+    MOZ_MUST_USE bool setSrcNoteOffset(unsigned index, unsigned which, ptrdiff_t offset);
+
+    // NB: this function can add at most one extra extended delta note.
+    MOZ_MUST_USE bool addToSrcNoteDelta(jssrcnote* sn, ptrdiff_t delta);
+
+    // Finish taking source notes in cx's notePool. If successful, the final
+    // source note count is stored in the out outparam.
+    MOZ_MUST_USE bool finishTakingSrcNotes(uint32_t* out);
+
+    // Control whether emitTree emits a line number note.
+    enum EmitLineNumberNote {
+        EMIT_LINENOTE,
+        SUPPRESS_LINENOTE
+    };
+
+    // Emit code for the tree rooted at pn.
+    MOZ_MUST_USE bool emitTree(ParseNode* pn, EmitLineNumberNote emitLineNote = EMIT_LINENOTE);
+
+    // Emit code for the tree rooted at pn with its own TDZ cache.
+    MOZ_MUST_USE bool emitConditionallyExecutedTree(ParseNode* pn);
+
+    // Emit global, eval, or module code for tree rooted at body. Always
+    // encompasses the entire source.
+    MOZ_MUST_USE bool emitScript(ParseNode* body);
+
+    // Emit function code for the tree rooted at body.
+    MOZ_MUST_USE bool emitFunctionScript(ParseNode* body);
+
+    // If op is JOF_TYPESET (see the type barriers comment in TypeInference.h),
+    // reserve a type set to store its result.
+    void checkTypeSet(JSOp op);
+
+    void updateDepth(ptrdiff_t target);
+    MOZ_MUST_USE bool updateLineNumberNotes(uint32_t offset);
+    MOZ_MUST_USE bool updateSourceCoordNotes(uint32_t offset);
+
+    JSOp strictifySetNameOp(JSOp op);
+
+    MOZ_MUST_USE bool flushPops(int* npops);
+
+    MOZ_MUST_USE bool emitCheck(ptrdiff_t delta, ptrdiff_t* offset);
+
+    // Emit one bytecode.
+    MOZ_MUST_USE bool emit1(JSOp op);
+
+    // Emit two bytecodes, an opcode (op) with a byte of immediate operand
+    // (op1).
+    MOZ_MUST_USE bool emit2(JSOp op, uint8_t op1);
+
+    // Emit three bytecodes, an opcode with two bytes of immediate operands.
+    MOZ_MUST_USE bool emit3(JSOp op, jsbytecode op1, jsbytecode op2);
+
+    // Helper to emit JSOP_DUPAT. The argument is the value's depth on the
+    // JS stack, as measured from the top.
+    MOZ_MUST_USE bool emitDupAt(unsigned slotFromTop);
+
+    // Helper to emit JSOP_CHECKISOBJ.
+    MOZ_MUST_USE bool emitCheckIsObj(CheckIsObjectKind kind);
+
+    // Emit a bytecode followed by an uint16 immediate operand stored in
+    // big-endian order.
+    MOZ_MUST_USE bool emitUint16Operand(JSOp op, uint32_t operand);
+
+    // Emit a bytecode followed by an uint32 immediate operand.
+    MOZ_MUST_USE bool emitUint32Operand(JSOp op, uint32_t operand);
+
+    // Emit (1 + extra) bytecodes, for N bytes of op and its immediate operand.
+    MOZ_MUST_USE bool emitN(JSOp op, size_t extra, ptrdiff_t* offset = nullptr);
+
+    MOZ_MUST_USE bool emitNumberOp(double dval);
+
+    MOZ_MUST_USE bool emitThisLiteral(ParseNode* pn);
+    MOZ_MUST_USE bool emitGetFunctionThis(ParseNode* pn);
+    MOZ_MUST_USE bool emitGetThisForSuperBase(ParseNode* pn);
+    MOZ_MUST_USE bool emitSetThis(ParseNode* pn);
+    MOZ_MUST_USE bool emitCheckDerivedClassConstructorReturn();
+
+    // Handle jump opcodes and jump targets.
+    MOZ_MUST_USE bool emitJumpTarget(JumpTarget* target);
+    MOZ_MUST_USE bool emitJumpNoFallthrough(JSOp op, JumpList* jump);
+    MOZ_MUST_USE bool emitJump(JSOp op, JumpList* jump);
+    MOZ_MUST_USE bool emitBackwardJump(JSOp op, JumpTarget target, JumpList* jump,
+                                       JumpTarget* fallthrough);
+    void patchJumpsToTarget(JumpList jump, JumpTarget target);
+    MOZ_MUST_USE bool emitJumpTargetAndPatch(JumpList jump);
+
+    MOZ_MUST_USE bool emitCall(JSOp op, uint16_t argc, ParseNode* pn = nullptr);
+    MOZ_MUST_USE bool emitCallIncDec(ParseNode* incDec);
+
+    MOZ_MUST_USE bool emitLoopHead(ParseNode* nextpn, JumpTarget* top);
+    MOZ_MUST_USE bool emitLoopEntry(ParseNode* nextpn, JumpList entryJump);
+
+    MOZ_MUST_USE bool emitGoto(NestableControl* target, JumpList* jumplist,
+                               SrcNoteType noteType = SRC_NULL);
+
+    MOZ_MUST_USE bool emitIndex32(JSOp op, uint32_t index);
+    MOZ_MUST_USE bool emitIndexOp(JSOp op, uint32_t index);
+
+    MOZ_MUST_USE bool emitAtomOp(JSAtom* atom, JSOp op);
+    MOZ_MUST_USE bool emitAtomOp(ParseNode* pn, JSOp op);
+
+    MOZ_MUST_USE bool emitArrayLiteral(ParseNode* pn);
+    MOZ_MUST_USE bool emitArray(ParseNode* pn, uint32_t count, JSOp op);
+    MOZ_MUST_USE bool emitArrayComp(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitInternedScopeOp(uint32_t index, JSOp op);
+    MOZ_MUST_USE bool emitInternedObjectOp(uint32_t index, JSOp op);
+    MOZ_MUST_USE bool emitObjectOp(ObjectBox* objbox, JSOp op);
+    MOZ_MUST_USE bool emitObjectPairOp(ObjectBox* objbox1, ObjectBox* objbox2, JSOp op);
+    MOZ_MUST_USE bool emitRegExp(uint32_t index);
+
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitFunction(ParseNode* pn, bool needsProto = false);
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitObject(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitHoistedFunctionsInList(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitPropertyList(ParseNode* pn, MutableHandlePlainObject objp,
+                                       PropListType type);
+
+    // To catch accidental misuse, emitUint16Operand/emit3 assert that they are
+    // not used to unconditionally emit JSOP_GETLOCAL. Variable access should
+    // instead be emitted using EmitVarOp. In special cases, when the caller
+    // definitely knows that a given local slot is unaliased, this function may be
+    // used as a non-asserting version of emitUint16Operand.
+    MOZ_MUST_USE bool emitLocalOp(JSOp op, uint32_t slot);
+
+    MOZ_MUST_USE bool emitArgOp(JSOp op, uint16_t slot);
+    MOZ_MUST_USE bool emitEnvCoordOp(JSOp op, EnvironmentCoordinate ec);
+
+    MOZ_MUST_USE bool emitGetNameAtLocation(JSAtom* name, const NameLocation& loc,
+                                            bool callContext = false);
+    MOZ_MUST_USE bool emitGetName(JSAtom* name, bool callContext = false) {
+        return emitGetNameAtLocation(name, lookupName(name), callContext);
+    }
+    MOZ_MUST_USE bool emitGetName(ParseNode* pn, bool callContext = false);
+
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitSetOrInitializeNameAtLocation(HandleAtom name, const NameLocation& loc,
+                                                        RHSEmitter emitRhs, bool initialize);
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitSetOrInitializeName(HandleAtom name, RHSEmitter emitRhs,
+                                              bool initialize)
+    {
+        return emitSetOrInitializeNameAtLocation(name, lookupName(name), emitRhs, initialize);
+    }
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitSetName(ParseNode* pn, RHSEmitter emitRhs) {
+        RootedAtom name(cx, pn->name());
+        return emitSetName(name, emitRhs);
+    }
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitSetName(HandleAtom name, RHSEmitter emitRhs) {
+        return emitSetOrInitializeName(name, emitRhs, false);
+    }
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitInitializeName(ParseNode* pn, RHSEmitter emitRhs) {
+        RootedAtom name(cx, pn->name());
+        return emitInitializeName(name, emitRhs);
+    }
+    template <typename RHSEmitter>
+    MOZ_MUST_USE bool emitInitializeName(HandleAtom name, RHSEmitter emitRhs) {
+        return emitSetOrInitializeName(name, emitRhs, true);
+    }
+
+    MOZ_MUST_USE bool emitTDZCheckIfNeeded(JSAtom* name, const NameLocation& loc);
+
+    MOZ_MUST_USE bool emitNameIncDec(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitDeclarationList(ParseNode* decls);
+    MOZ_MUST_USE bool emitSingleDeclaration(ParseNode* decls, ParseNode* decl,
+                                            ParseNode* initializer);
+
+    MOZ_MUST_USE bool emitNewInit(JSProtoKey key);
+    MOZ_MUST_USE bool emitSingletonInitialiser(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitPrepareIteratorResult();
+    MOZ_MUST_USE bool emitFinishIteratorResult(bool done);
+    MOZ_MUST_USE bool iteratorResultShape(unsigned* shape);
+
+    MOZ_MUST_USE bool emitYield(ParseNode* pn);
+    MOZ_MUST_USE bool emitYieldOp(JSOp op);
+    MOZ_MUST_USE bool emitYieldStar(ParseNode* iter, ParseNode* gen);
+
+    MOZ_MUST_USE bool emitPropLHS(ParseNode* pn);
+    MOZ_MUST_USE bool emitPropOp(ParseNode* pn, JSOp op);
+    MOZ_MUST_USE bool emitPropIncDec(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitAsyncWrapperLambda(unsigned index, bool isArrow);
+    MOZ_MUST_USE bool emitAsyncWrapper(unsigned index, bool needsHomeObject, bool isArrow);
+
+    MOZ_MUST_USE bool emitComputedPropertyName(ParseNode* computedPropName);
+
+    // Emit bytecode to put operands for a JSOP_GETELEM/CALLELEM/SETELEM/DELELEM
+    // opcode onto the stack in the right order. In the case of SETELEM, the
+    // value to be assigned must already be pushed.
+    enum class EmitElemOption { Get, Set, Call, IncDec, CompoundAssign };
+    MOZ_MUST_USE bool emitElemOperands(ParseNode* pn, EmitElemOption opts);
+
+    MOZ_MUST_USE bool emitElemOpBase(JSOp op);
+    MOZ_MUST_USE bool emitElemOp(ParseNode* pn, JSOp op);
+    MOZ_MUST_USE bool emitElemIncDec(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitCatch(ParseNode* pn);
+    MOZ_MUST_USE bool emitIf(ParseNode* pn);
+    MOZ_MUST_USE bool emitWith(ParseNode* pn);
+
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitLabeledStatement(const LabeledStatement* pn);
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitLexicalScope(ParseNode* pn);
+    MOZ_MUST_USE bool emitLexicalScopeBody(ParseNode* body,
+                                           EmitLineNumberNote emitLineNote = EMIT_LINENOTE);
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitSwitch(ParseNode* pn);
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitTry(ParseNode* pn);
+
+    enum DestructuringFlavor {
+        // Destructuring into a declaration.
+        DestructuringDeclaration,
+
+        // Destructuring into a formal parameter, when the formal parameters
+        // contain an expression that might be evaluated, and thus require
+        // this destructuring to assign not into the innermost scope that
+        // contains the function body's vars, but into its enclosing scope for
+        // parameter expressions.
+        DestructuringFormalParameterInVarScope,
+
+        // Destructuring as part of an AssignmentExpression.
+        DestructuringAssignment
+    };
+
+    // emitDestructuringLHS assumes the to-be-destructured value has been pushed on
+    // the stack and emits code to destructure a single lhs expression (either a
+    // name or a compound []/{} expression).
+    MOZ_MUST_USE bool emitDestructuringLHS(ParseNode* target, DestructuringFlavor flav);
+    MOZ_MUST_USE bool emitConditionallyExecutedDestructuringLHS(ParseNode* target,
+                                                                DestructuringFlavor flav);
+
+    // emitDestructuringOps assumes the to-be-destructured value has been
+    // pushed on the stack and emits code to destructure each part of a [] or
+    // {} lhs expression.
+    MOZ_MUST_USE bool emitDestructuringOps(ParseNode* pattern, DestructuringFlavor flav);
+    MOZ_MUST_USE bool emitDestructuringOpsArray(ParseNode* pattern, DestructuringFlavor flav);
+    MOZ_MUST_USE bool emitDestructuringOpsObject(ParseNode* pattern, DestructuringFlavor flav);
+
+    typedef bool
+    (*DestructuringDeclEmitter)(BytecodeEmitter* bce, ParseNode* pn);
+
+    template <typename NameEmitter>
+    MOZ_MUST_USE bool emitDestructuringDeclsWithEmitter(ParseNode* pattern, NameEmitter emitName);
+
+    // Throw a TypeError if the value atop the stack isn't convertible to an
+    // object, with no overall effect on the stack.
+    MOZ_MUST_USE bool emitRequireObjectCoercible();
+
+    // emitIterator expects the iterable to already be on the stack.
+    // It will replace that stack value with the corresponding iterator
+    MOZ_MUST_USE bool emitIterator();
+
+    // Pops iterator from the top of the stack. Pushes the result of |.next()|
+    // onto the stack.
+    MOZ_MUST_USE bool emitIteratorNext(ParseNode* pn, bool allowSelfHosted = false);
+
+    // Check if the value on top of the stack is "undefined". If so, replace
+    // that value on the stack with the value defined by |defaultExpr|.
+    MOZ_MUST_USE bool emitDefault(ParseNode* defaultExpr);
+
+    MOZ_MUST_USE bool emitCallSiteObject(ParseNode* pn);
+    MOZ_MUST_USE bool emitTemplateString(ParseNode* pn);
+    MOZ_MUST_USE bool emitAssignment(ParseNode* lhs, JSOp op, ParseNode* rhs);
+
+    MOZ_MUST_USE bool emitReturn(ParseNode* pn);
+    MOZ_MUST_USE bool emitStatement(ParseNode* pn);
+    MOZ_MUST_USE bool emitStatementList(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitDeleteName(ParseNode* pn);
+    MOZ_MUST_USE bool emitDeleteProperty(ParseNode* pn);
+    MOZ_MUST_USE bool emitDeleteElement(ParseNode* pn);
+    MOZ_MUST_USE bool emitDeleteExpression(ParseNode* pn);
+
+    // |op| must be JSOP_TYPEOF or JSOP_TYPEOFEXPR.
+    MOZ_MUST_USE bool emitTypeof(ParseNode* node, JSOp op);
+
+    MOZ_MUST_USE bool emitUnary(ParseNode* pn);
+    MOZ_MUST_USE bool emitRightAssociative(ParseNode* pn);
+    MOZ_MUST_USE bool emitLeftAssociative(ParseNode* pn);
+    MOZ_MUST_USE bool emitLogical(ParseNode* pn);
+    MOZ_MUST_USE bool emitSequenceExpr(ParseNode* pn);
+
+    MOZ_NEVER_INLINE MOZ_MUST_USE bool emitIncOrDec(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitConditionalExpression(ConditionalExpression& conditional);
+
+    MOZ_MUST_USE bool isRestParameter(ParseNode* pn, bool* result);
+    MOZ_MUST_USE bool emitOptimizeSpread(ParseNode* arg0, JumpList* jmp, bool* emitted);
+
+    MOZ_MUST_USE bool emitCallOrNew(ParseNode* pn);
+    MOZ_MUST_USE bool emitSelfHostedCallFunction(ParseNode* pn);
+    MOZ_MUST_USE bool emitSelfHostedResumeGenerator(ParseNode* pn);
+    MOZ_MUST_USE bool emitSelfHostedForceInterpreter(ParseNode* pn);
+    MOZ_MUST_USE bool emitSelfHostedAllowContentSpread(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitComprehensionFor(ParseNode* compFor);
+    MOZ_MUST_USE bool emitComprehensionForIn(ParseNode* pn);
+    MOZ_MUST_USE bool emitComprehensionForInOrOfVariables(ParseNode* pn, bool* lexicalScope);
+    MOZ_MUST_USE bool emitComprehensionForOf(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitDo(ParseNode* pn);
+    MOZ_MUST_USE bool emitWhile(ParseNode* pn);
+
+    MOZ_MUST_USE bool emitFor(ParseNode* pn, EmitterScope* headLexicalEmitterScope = nullptr);
+    MOZ_MUST_USE bool emitCStyleFor(ParseNode* pn, EmitterScope* headLexicalEmitterScope);
+    MOZ_MUST_USE bool emitForIn(ParseNode* pn, EmitterScope* headLexicalEmitterScope);
+    MOZ_MUST_USE bool emitForOf(ParseNode* pn, EmitterScope* headLexicalEmitterScope);
+
+    MOZ_MUST_USE bool emitInitializeForInOrOfTarget(ParseNode* forHead);
+
+    MOZ_MUST_USE bool emitBreak(PropertyName* label);
+    MOZ_MUST_USE bool emitContinue(PropertyName* label);
+
+    MOZ_MUST_USE bool emitFunctionFormalParametersAndBody(ParseNode* pn);
+    MOZ_MUST_USE bool emitFunctionFormalParameters(ParseNode* pn);
+    MOZ_MUST_USE bool emitInitializeFunctionSpecialNames();
+    MOZ_MUST_USE bool emitFunctionBody(ParseNode* pn);
+    MOZ_MUST_USE bool emitLexicalInitialization(ParseNode* pn);
+
+    // Emit bytecode for the spread operator.
+    //
+    // emitSpread expects the current index (I) of the array, the array itself
+    // and the iterator to be on the stack in that order (iterator on the bottom).
+    // It will pop the iterator and I, then iterate over the iterator by calling
+    // |.next()| and put the results into the I-th element of array with
+    // incrementing I, then push the result I (it will be original I +
+    // iteration count). The stack after iteration will look like |ARRAY INDEX|.
+    MOZ_MUST_USE bool emitSpread(bool allowSelfHosted = false);
+
+    MOZ_MUST_USE bool emitClass(ParseNode* pn);
+    MOZ_MUST_USE bool emitSuperPropLHS(ParseNode* superBase, bool isCall = false);
+    MOZ_MUST_USE bool emitSuperPropOp(ParseNode* pn, JSOp op, bool isCall = false);
+    MOZ_MUST_USE bool emitSuperElemOperands(ParseNode* pn,
+                                            EmitElemOption opts = EmitElemOption::Get);
+    MOZ_MUST_USE bool emitSuperElemOp(ParseNode* pn, JSOp op, bool isCall = false);
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_BytecodeEmitter_h */
diff --git a/js/src/frontend/FoldConstants.cpp b/js/src/frontend/FoldConstants.cpp
new file mode 100644
index 0000000000..6f62ffac68
--- /dev/null
+++ b/js/src/frontend/FoldConstants.cpp
@@ -0,0 +1,1928 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "frontend/FoldConstants.h"
+
+#include "mozilla/FloatingPoint.h"
+
+#include "jslibmath.h"
+
+#include "frontend/ParseNode.h"
+#include "frontend/Parser.h"
+#include "js/Conversions.h"
+
+#include "jscntxtinlines.h"
+#include "jsobjinlines.h"
+
+using namespace js;
+using namespace js::frontend;
+
+using mozilla::IsNaN;
+using mozilla::IsNegative;
+using mozilla::NegativeInfinity;
+using mozilla::PositiveInfinity;
+using JS::GenericNaN;
+using JS::ToInt32;
+using JS::ToUint32;
+
+static bool
+ContainsHoistedDeclaration(ExclusiveContext* cx, ParseNode* node, bool* result);
+
+static bool
+ListContainsHoistedDeclaration(ExclusiveContext* cx, ListNode* list, bool* result)
+{
+    for (ParseNode* node = list->pn_head; node; node = node->pn_next) {
+        if (!ContainsHoistedDeclaration(cx, node, result))
+            return false;
+        if (*result)
+            return true;
+    }
+
+    *result = false;
+    return true;
+}
+
+// Determines whether the given ParseNode contains any declarations whose
+// visibility will extend outside the node itself -- that is, whether the
+// ParseNode contains any var statements.
+//
+// THIS IS NOT A GENERAL-PURPOSE FUNCTION.  It is only written to work in the
+// specific context of deciding that |node|, as one arm of a PNK_IF controlled
+// by a constant condition, contains a declaration that forbids |node| being
+// completely eliminated as dead.
+static bool
+ContainsHoistedDeclaration(ExclusiveContext* cx, ParseNode* node, bool* result)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+  restart:
+
+    // With a better-typed AST, we would have distinct parse node classes for
+    // expressions and for statements and would characterize expressions with
+    // ExpressionKind and statements with StatementKind.  Perhaps someday.  In
+    // the meantime we must characterize every ParseNodeKind, even the
+    // expression/sub-expression ones that, if we handle all statement kinds
+    // correctly, we'll never see.
+    switch (node->getKind()) {
+      // Base case.
+      case PNK_VAR:
+        *result = true;
+        return true;
+
+      // Non-global lexical declarations are block-scoped (ergo not hoistable).
+      case PNK_LET:
+      case PNK_CONST:
+        MOZ_ASSERT(node->isArity(PN_LIST));
+        *result = false;
+        return true;
+
+      // Similarly to the lexical declarations above, classes cannot add hoisted
+      // declarations
+      case PNK_CLASS:
+        MOZ_ASSERT(node->isArity(PN_TERNARY));
+        *result = false;
+        return true;
+
+      // Function declarations *can* be hoisted declarations.  But in the
+      // magical world of the rewritten frontend, the declaration necessitated
+      // by a nested function statement, not at body level, doesn't require
+      // that we preserve an unreachable function declaration node against
+      // dead-code removal.
+      case PNK_FUNCTION:
+        MOZ_ASSERT(node->isArity(PN_CODE));
+        *result = false;
+        return true;
+
+      case PNK_MODULE:
+        *result = false;
+        return true;
+
+      // Statements with no sub-components at all.
+      case PNK_NOP: // induced by function f() {} function f() {}
+      case PNK_DEBUGGER:
+        MOZ_ASSERT(node->isArity(PN_NULLARY));
+        *result = false;
+        return true;
+
+      // Statements containing only an expression have no declarations.
+      case PNK_SEMI:
+      case PNK_THROW:
+      case PNK_RETURN:
+        MOZ_ASSERT(node->isArity(PN_UNARY));
+        *result = false;
+        return true;
+
+      // These two aren't statements in the spec, but we sometimes insert them
+      // in statement lists anyway.
+      case PNK_YIELD_STAR:
+      case PNK_YIELD:
+        MOZ_ASSERT(node->isArity(PN_BINARY));
+        *result = false;
+        return true;
+
+      // Other statements with no sub-statement components.
+      case PNK_BREAK:
+      case PNK_CONTINUE:
+      case PNK_IMPORT:
+      case PNK_IMPORT_SPEC_LIST:
+      case PNK_IMPORT_SPEC:
+      case PNK_EXPORT_FROM:
+      case PNK_EXPORT_DEFAULT:
+      case PNK_EXPORT_SPEC_LIST:
+      case PNK_EXPORT_SPEC:
+      case PNK_EXPORT:
+      case PNK_EXPORT_BATCH_SPEC:
+        *result = false;
+        return true;
+
+      // Statements possibly containing hoistable declarations only in the left
+      // half, in ParseNode terms -- the loop body in AST terms.
+      case PNK_DOWHILE:
+        return ContainsHoistedDeclaration(cx, node->pn_left, result);
+
+      // Statements possibly containing hoistable declarations only in the
+      // right half, in ParseNode terms -- the loop body or nested statement
+      // (usually a block statement), in AST terms.
+      case PNK_WHILE:
+      case PNK_WITH:
+        return ContainsHoistedDeclaration(cx, node->pn_right, result);
+
+      case PNK_LABEL:
+        return ContainsHoistedDeclaration(cx, node->pn_expr, result);
+
+      // Statements with more complicated structures.
+
+      // if-statement nodes may have hoisted declarations in their consequent
+      // and alternative components.
+      case PNK_IF: {
+        MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+        ParseNode* consequent = node->pn_kid2;
+        if (!ContainsHoistedDeclaration(cx, consequent, result))
+            return false;
+        if (*result)
+            return true;
+
+        if ((node = node->pn_kid3))
+            goto restart;
+
+        *result = false;
+        return true;
+      }
+
+      // Legacy array and generator comprehensions use PNK_IF to represent
+      // conditions specified in the comprehension tail: for example,
+      // [x for (x in obj) if (x)].  The consequent of such PNK_IF nodes is
+      // either PNK_YIELD in a PNK_SEMI statement (generator comprehensions) or
+      // PNK_ARRAYPUSH (array comprehensions) .  The first case is consistent
+      // with normal if-statement structure with consequent/alternative as
+      // statements.  The second case is abnormal and requires that we not
+      // banish PNK_ARRAYPUSH to the unreachable list, handling it explicitly.
+      //
+      // We could require that this one weird PNK_ARRAYPUSH case be packaged in
+      // a PNK_SEMI, for consistency.  That requires careful bytecode emitter
+      // adjustment that seems unwarranted for a deprecated feature.
+      case PNK_ARRAYPUSH:
+        *result = false;
+        return true;
+
+      // try-statements have statements to execute, and one or both of a
+      // catch-list and a finally-block.
+      case PNK_TRY: {
+        MOZ_ASSERT(node->isArity(PN_TERNARY));
+        MOZ_ASSERT(node->pn_kid2 || node->pn_kid3,
+                   "must have either catch(es) or finally");
+
+        ParseNode* tryBlock = node->pn_kid1;
+        if (!ContainsHoistedDeclaration(cx, tryBlock, result))
+            return false;
+        if (*result)
+            return true;
+
+        if (ParseNode* catchList = node->pn_kid2) {
+            for (ParseNode* lexicalScope = catchList->pn_head;
+                 lexicalScope;
+                 lexicalScope = lexicalScope->pn_next)
+            {
+                MOZ_ASSERT(lexicalScope->isKind(PNK_LEXICALSCOPE));
+
+                ParseNode* catchNode = lexicalScope->pn_expr;
+                MOZ_ASSERT(catchNode->isKind(PNK_CATCH));
+
+                ParseNode* catchStatements = catchNode->pn_kid3;
+                if (!ContainsHoistedDeclaration(cx, catchStatements, result))
+                    return false;
+                if (*result)
+                    return true;
+            }
+        }
+
+        if (ParseNode* finallyBlock = node->pn_kid3)
+            return ContainsHoistedDeclaration(cx, finallyBlock, result);
+
+        *result = false;
+        return true;
+      }
+
+      // A switch node's left half is an expression; only its right half (a
+      // list of cases/defaults, or a block node) could contain hoisted
+      // declarations.
+      case PNK_SWITCH:
+        MOZ_ASSERT(node->isArity(PN_BINARY));
+        return ContainsHoistedDeclaration(cx, node->pn_right, result);
+
+      case PNK_CASE:
+        return ContainsHoistedDeclaration(cx, node->as<CaseClause>().statementList(), result);
+
+      case PNK_FOR:
+      case PNK_COMPREHENSIONFOR: {
+        MOZ_ASSERT(node->isArity(PN_BINARY));
+
+        ParseNode* loopHead = node->pn_left;
+        MOZ_ASSERT(loopHead->isKind(PNK_FORHEAD) ||
+                   loopHead->isKind(PNK_FORIN) ||
+                   loopHead->isKind(PNK_FOROF));
+
+        if (loopHead->isKind(PNK_FORHEAD)) {
+            // for (init?; cond?; update?), with only init possibly containing
+            // a hoisted declaration.  (Note: a lexical-declaration |init| is
+            // (at present) hoisted in SpiderMonkey parlance -- but such
+            // hoisting doesn't extend outside of this statement, so it is not
+            // hoisting in the sense meant by ContainsHoistedDeclaration.)
+            MOZ_ASSERT(loopHead->isArity(PN_TERNARY));
+
+            ParseNode* init = loopHead->pn_kid1;
+            if (init && init->isKind(PNK_VAR)) {
+                *result = true;
+                return true;
+            }
+        } else {
+            MOZ_ASSERT(loopHead->isKind(PNK_FORIN) || loopHead->isKind(PNK_FOROF));
+
+            // for each? (target in ...), where only target may introduce
+            // hoisted declarations.
+            //
+            //   -- or --
+            //
+            // for (target of ...), where only target may introduce hoisted
+            // declarations.
+            //
+            // Either way, if |target| contains a declaration, it's |loopHead|'s
+            // first kid.
+            MOZ_ASSERT(loopHead->isArity(PN_TERNARY));
+
+            ParseNode* decl = loopHead->pn_kid1;
+            if (decl && decl->isKind(PNK_VAR)) {
+                *result = true;
+                return true;
+            }
+        }
+
+        ParseNode* loopBody = node->pn_right;
+        return ContainsHoistedDeclaration(cx, loopBody, result);
+      }
+
+      case PNK_LEXICALSCOPE: {
+        MOZ_ASSERT(node->isArity(PN_SCOPE));
+        ParseNode* expr = node->pn_expr;
+
+        if (expr->isKind(PNK_FOR) || expr->isKind(PNK_FUNCTION))
+            return ContainsHoistedDeclaration(cx, expr, result);
+
+        MOZ_ASSERT(expr->isKind(PNK_STATEMENTLIST));
+        return ListContainsHoistedDeclaration(cx, &node->pn_expr->as<ListNode>(), result);
+      }
+
+      // List nodes with all non-null children.
+      case PNK_STATEMENTLIST:
+        return ListContainsHoistedDeclaration(cx, &node->as<ListNode>(), result);
+
+      // Grammar sub-components that should never be reached directly by this
+      // method, because some parent component should have asserted itself.
+      case PNK_OBJECT_PROPERTY_NAME:
+      case PNK_COMPUTED_NAME:
+      case PNK_SPREAD:
+      case PNK_MUTATEPROTO:
+      case PNK_COLON:
+      case PNK_SHORTHAND:
+      case PNK_CONDITIONAL:
+      case PNK_TYPEOFNAME:
+      case PNK_TYPEOFEXPR:
+      case PNK_AWAIT:
+      case PNK_VOID:
+      case PNK_NOT:
+      case PNK_BITNOT:
+      case PNK_DELETENAME:
+      case PNK_DELETEPROP:
+      case PNK_DELETEELEM:
+      case PNK_DELETEEXPR:
+      case PNK_POS:
+      case PNK_NEG:
+      case PNK_PREINCREMENT:
+      case PNK_POSTINCREMENT:
+      case PNK_PREDECREMENT:
+      case PNK_POSTDECREMENT:
+      case PNK_OR:
+      case PNK_AND:
+      case PNK_BITOR:
+      case PNK_BITXOR:
+      case PNK_BITAND:
+      case PNK_STRICTEQ:
+      case PNK_EQ:
+      case PNK_STRICTNE:
+      case PNK_NE:
+      case PNK_LT:
+      case PNK_LE:
+      case PNK_GT:
+      case PNK_GE:
+      case PNK_INSTANCEOF:
+      case PNK_IN:
+      case PNK_LSH:
+      case PNK_RSH:
+      case PNK_URSH:
+      case PNK_ADD:
+      case PNK_SUB:
+      case PNK_STAR:
+      case PNK_DIV:
+      case PNK_MOD:
+      case PNK_POW:
+      case PNK_ASSIGN:
+      case PNK_ADDASSIGN:
+      case PNK_SUBASSIGN:
+      case PNK_BITORASSIGN:
+      case PNK_BITXORASSIGN:
+      case PNK_BITANDASSIGN:
+      case PNK_LSHASSIGN:
+      case PNK_RSHASSIGN:
+      case PNK_URSHASSIGN:
+      case PNK_MULASSIGN:
+      case PNK_DIVASSIGN:
+      case PNK_MODASSIGN:
+      case PNK_POWASSIGN:
+      case PNK_COMMA:
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+      case PNK_DOT:
+      case PNK_ELEM:
+      case PNK_CALL:
+      case PNK_NAME:
+      case PNK_TEMPLATE_STRING:
+      case PNK_TEMPLATE_STRING_LIST:
+      case PNK_TAGGED_TEMPLATE:
+      case PNK_CALLSITEOBJ:
+      case PNK_STRING:
+      case PNK_REGEXP:
+      case PNK_TRUE:
+      case PNK_FALSE:
+      case PNK_NULL:
+      case PNK_THIS:
+      case PNK_ELISION:
+      case PNK_NUMBER:
+      case PNK_NEW:
+      case PNK_GENERATOR:
+      case PNK_GENEXP:
+      case PNK_ARRAYCOMP:
+      case PNK_PARAMSBODY:
+      case PNK_CATCHLIST:
+      case PNK_CATCH:
+      case PNK_FORIN:
+      case PNK_FOROF:
+      case PNK_FORHEAD:
+      case PNK_CLASSMETHOD:
+      case PNK_CLASSMETHODLIST:
+      case PNK_CLASSNAMES:
+      case PNK_NEWTARGET:
+      case PNK_POSHOLDER:
+      case PNK_SUPERCALL:
+      case PNK_SUPERBASE:
+      case PNK_SETTHIS:
+        MOZ_CRASH("ContainsHoistedDeclaration should have indicated false on "
+                  "some parent node without recurring to test this node");
+
+      case PNK_LIMIT: // invalid sentinel value
+        MOZ_CRASH("unexpected PNK_LIMIT in node");
+    }
+
+    MOZ_CRASH("invalid node kind");
+}
+
+/*
+ * Fold from one constant type to another.
+ * XXX handles only strings and numbers for now
+ */
+static bool
+FoldType(ExclusiveContext* cx, ParseNode* pn, ParseNodeKind kind)
+{
+    if (!pn->isKind(kind)) {
+        switch (kind) {
+          case PNK_NUMBER:
+            if (pn->isKind(PNK_STRING)) {
+                double d;
+                if (!StringToNumber(cx, pn->pn_atom, &d))
+                    return false;
+                pn->pn_dval = d;
+                pn->setKind(PNK_NUMBER);
+                pn->setOp(JSOP_DOUBLE);
+            }
+            break;
+
+          case PNK_STRING:
+            if (pn->isKind(PNK_NUMBER)) {
+                pn->pn_atom = NumberToAtom(cx, pn->pn_dval);
+                if (!pn->pn_atom)
+                    return false;
+                pn->setKind(PNK_STRING);
+                pn->setOp(JSOP_STRING);
+            }
+            break;
+
+          default:;
+        }
+    }
+    return true;
+}
+
+// Remove a ParseNode, **pnp, from a parse tree, putting another ParseNode,
+// *pn, in its place.
+//
+// pnp points to a ParseNode pointer. This must be the only pointer that points
+// to the parse node being replaced. The replacement, *pn, is unchanged except
+// for its pn_next pointer; updating that is necessary if *pn's new parent is a
+// list node.
+static void
+ReplaceNode(ParseNode** pnp, ParseNode* pn)
+{
+    pn->pn_next = (*pnp)->pn_next;
+    *pnp = pn;
+}
+
+static bool
+IsEffectless(ParseNode* node)
+{
+    return node->isKind(PNK_TRUE) ||
+           node->isKind(PNK_FALSE) ||
+           node->isKind(PNK_STRING) ||
+           node->isKind(PNK_TEMPLATE_STRING) ||
+           node->isKind(PNK_NUMBER) ||
+           node->isKind(PNK_NULL) ||
+           node->isKind(PNK_FUNCTION) ||
+           node->isKind(PNK_GENEXP);
+}
+
+enum Truthiness { Truthy, Falsy, Unknown };
+
+static Truthiness
+Boolish(ParseNode* pn)
+{
+    switch (pn->getKind()) {
+      case PNK_NUMBER:
+        return (pn->pn_dval != 0 && !IsNaN(pn->pn_dval)) ? Truthy : Falsy;
+
+      case PNK_STRING:
+      case PNK_TEMPLATE_STRING:
+        return (pn->pn_atom->length() > 0) ? Truthy : Falsy;
+
+      case PNK_TRUE:
+      case PNK_FUNCTION:
+      case PNK_GENEXP:
+        return Truthy;
+
+      case PNK_FALSE:
+      case PNK_NULL:
+        return Falsy;
+
+      case PNK_VOID: {
+        // |void <foo>| evaluates to |undefined| which isn't truthy.  But the
+        // sense of this method requires that the expression be literally
+        // replaceable with true/false: not the case if the nested expression
+        // is effectful, might throw, &c.  Walk past the |void| (and nested
+        // |void| expressions, for good measure) and check that the nested
+        // expression doesn't break this requirement before indicating falsity.
+        do {
+            pn = pn->pn_kid;
+        } while (pn->isKind(PNK_VOID));
+
+        return IsEffectless(pn) ? Falsy : Unknown;
+      }
+
+      default:
+        return Unknown;
+    }
+}
+
+static bool
+Fold(ExclusiveContext* cx, ParseNode** pnp, Parser<FullParseHandler>& parser, bool inGenexpLambda);
+
+static bool
+FoldCondition(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+              bool inGenexpLambda)
+{
+    // Conditions fold like any other expression...
+    if (!Fold(cx, nodePtr, parser, inGenexpLambda))
+        return false;
+
+    // ...but then they sometimes can be further folded to constants.
+    ParseNode* node = *nodePtr;
+    Truthiness t = Boolish(node);
+    if (t != Unknown) {
+        // We can turn function nodes into constant nodes here, but mutating
+        // function nodes is tricky --- in particular, mutating a function node
+        // that appears on a method list corrupts the method list. However,
+        // methods are M's in statements of the form 'this.foo = M;', which we
+        // never fold, so we're okay.
+        parser.prepareNodeForMutation(node);
+        if (t == Truthy) {
+            node->setKind(PNK_TRUE);
+            node->setOp(JSOP_TRUE);
+        } else {
+            node->setKind(PNK_FALSE);
+            node->setOp(JSOP_FALSE);
+        }
+        node->setArity(PN_NULLARY);
+    }
+
+    return true;
+}
+
+static bool
+FoldTypeOfExpr(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+               bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_TYPEOFEXPR));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode*& expr = node->pn_kid;
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    // Constant-fold the entire |typeof| if given a constant with known type.
+    RootedPropertyName result(cx);
+    if (expr->isKind(PNK_STRING) || expr->isKind(PNK_TEMPLATE_STRING))
+        result = cx->names().string;
+    else if (expr->isKind(PNK_NUMBER))
+        result = cx->names().number;
+    else if (expr->isKind(PNK_NULL))
+        result = cx->names().object;
+    else if (expr->isKind(PNK_TRUE) || expr->isKind(PNK_FALSE))
+        result = cx->names().boolean;
+    else if (expr->isKind(PNK_FUNCTION))
+        result = cx->names().function;
+
+    if (result) {
+        parser.prepareNodeForMutation(node);
+
+        node->setKind(PNK_STRING);
+        node->setArity(PN_NULLARY);
+        node->setOp(JSOP_NOP);
+        node->pn_atom = result;
+    }
+
+    return true;
+}
+
+static bool
+FoldDeleteExpr(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+               bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEEXPR));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode*& expr = node->pn_kid;
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    // Expression deletion evaluates the expression, then evaluates to true.
+    // For effectless expressions, eliminate the expression evaluation.
+    if (IsEffectless(expr)) {
+        parser.prepareNodeForMutation(node);
+        node->setKind(PNK_TRUE);
+        node->setArity(PN_NULLARY);
+        node->setOp(JSOP_TRUE);
+    }
+
+    return true;
+}
+
+static bool
+FoldDeleteElement(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                  bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEELEM));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+    MOZ_ASSERT(node->pn_kid->isKind(PNK_ELEM));
+
+    ParseNode*& expr = node->pn_kid;
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    // If we're deleting an element, but constant-folding converted our
+    // element reference into a dotted property access, we must *also*
+    // morph the node's kind.
+    //
+    // In principle this also applies to |super["foo"] -> super.foo|,
+    // but we don't constant-fold |super["foo"]| yet.
+    MOZ_ASSERT(expr->isKind(PNK_ELEM) || expr->isKind(PNK_DOT));
+    if (expr->isKind(PNK_DOT))
+        node->setKind(PNK_DELETEPROP);
+
+    return true;
+}
+
+static bool
+FoldDeleteProperty(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                   bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_DELETEPROP));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+    MOZ_ASSERT(node->pn_kid->isKind(PNK_DOT));
+
+    ParseNode*& expr = node->pn_kid;
+#ifdef DEBUG
+    ParseNodeKind oldKind = expr->getKind();
+#endif
+
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    MOZ_ASSERT(expr->isKind(oldKind),
+               "kind should have remained invariant under folding");
+
+    return true;
+}
+
+static bool
+FoldNot(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+        bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_NOT));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode*& expr = node->pn_kid;
+    if (!FoldCondition(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    if (expr->isKind(PNK_NUMBER)) {
+        double d = expr->pn_dval;
+
+        parser.prepareNodeForMutation(node);
+        if (d == 0 || IsNaN(d)) {
+            node->setKind(PNK_TRUE);
+            node->setOp(JSOP_TRUE);
+        } else {
+            node->setKind(PNK_FALSE);
+            node->setOp(JSOP_FALSE);
+        }
+        node->setArity(PN_NULLARY);
+    } else if (expr->isKind(PNK_TRUE) || expr->isKind(PNK_FALSE)) {
+        bool newval = !expr->isKind(PNK_TRUE);
+
+        parser.prepareNodeForMutation(node);
+        node->setKind(newval ? PNK_TRUE : PNK_FALSE);
+        node->setArity(PN_NULLARY);
+        node->setOp(newval ? JSOP_TRUE : JSOP_FALSE);
+    }
+
+    return true;
+}
+
+static bool
+FoldUnaryArithmetic(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                    bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_BITNOT) || node->isKind(PNK_POS) || node->isKind(PNK_NEG),
+               "need a different method for this node kind");
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode*& expr = node->pn_kid;
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    if (expr->isKind(PNK_NUMBER) || expr->isKind(PNK_TRUE) || expr->isKind(PNK_FALSE)) {
+        double d = expr->isKind(PNK_NUMBER)
+                   ? expr->pn_dval
+                   : double(expr->isKind(PNK_TRUE));
+
+        if (node->isKind(PNK_BITNOT))
+            d = ~ToInt32(d);
+        else if (node->isKind(PNK_NEG))
+            d = -d;
+        else
+            MOZ_ASSERT(node->isKind(PNK_POS)); // nothing to do
+
+        parser.prepareNodeForMutation(node);
+        node->setKind(PNK_NUMBER);
+        node->setOp(JSOP_DOUBLE);
+        node->setArity(PN_NULLARY);
+        node->pn_dval = d;
+    }
+
+    return true;
+}
+
+static bool
+FoldIncrementDecrement(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                       bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_PREINCREMENT) ||
+               node->isKind(PNK_POSTINCREMENT) ||
+               node->isKind(PNK_PREDECREMENT) ||
+               node->isKind(PNK_POSTDECREMENT));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    ParseNode*& target = node->pn_kid;
+    MOZ_ASSERT(parser.isValidSimpleAssignmentTarget(target, Parser<FullParseHandler>::PermitAssignmentToFunctionCalls));
+
+    if (!Fold(cx, &target, parser, inGenexpLambda))
+        return false;
+
+    MOZ_ASSERT(parser.isValidSimpleAssignmentTarget(target, Parser<FullParseHandler>::PermitAssignmentToFunctionCalls));
+
+    return true;
+}
+
+static bool
+FoldAndOr(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+          bool inGenexpLambda)
+{
+    ParseNode* node = *nodePtr;
+
+    MOZ_ASSERT(node->isKind(PNK_AND) || node->isKind(PNK_OR));
+    MOZ_ASSERT(node->isArity(PN_LIST));
+
+    bool isOrNode = node->isKind(PNK_OR);
+    ParseNode** elem = &node->pn_head;
+    do {
+        if (!Fold(cx, elem, parser, inGenexpLambda))
+            return false;
+
+        Truthiness t = Boolish(*elem);
+
+        // If we don't know the constant-folded node's truthiness, we can't
+        // reduce this node with its surroundings.  Continue folding any
+        // remaining nodes.
+        if (t == Unknown) {
+            elem = &(*elem)->pn_next;
+            continue;
+        }
+
+        // If the constant-folded node's truthiness will terminate the
+        // condition -- `a || true || expr` or |b && false && expr| -- then
+        // trailing nodes will never be evaluated.  Truncate the list after
+        // the known-truthiness node, as it's the overall result.
+        if ((t == Truthy) == isOrNode) {
+            ParseNode* afterNext;
+            for (ParseNode* next = (*elem)->pn_next; next; next = afterNext) {
+                afterNext = next->pn_next;
+                parser.handler.freeTree(next);
+                --node->pn_count;
+            }
+
+            // Terminate the original and/or list at the known-truthiness
+            // node.
+            (*elem)->pn_next = nullptr;
+            elem = &(*elem)->pn_next;
+            break;
+        }
+
+        MOZ_ASSERT((t == Truthy) == !isOrNode);
+
+        // We've encountered a vacuous node that'll never short- circuit
+        // evaluation.
+        if ((*elem)->pn_next) {
+            // This node is never the overall result when there are
+            // subsequent nodes.  Remove it.
+            ParseNode* elt = *elem;
+            *elem = elt->pn_next;
+            parser.handler.freeTree(elt);
+            --node->pn_count;
+        } else {
+            // Otherwise this node is the result of the overall expression,
+            // so leave it alone.  And we're done.
+            elem = &(*elem)->pn_next;
+            break;
+        }
+    } while (*elem);
+
+    // If the last node in the list was replaced, we need to update the
+    // tail pointer in the original and/or node.
+    node->pn_tail = elem;
+
+    node->checkListConsistency();
+
+    // If we removed nodes, we may have to replace a one-element list with
+    // its element.
+    if (node->pn_count == 1) {
+        ParseNode* first = node->pn_head;
+        ReplaceNode(nodePtr, first);
+
+        node->setKind(PNK_NULL);
+        node->setArity(PN_NULLARY);
+        parser.freeTree(node);
+    }
+
+    return true;
+}
+
+static bool
+FoldConditional(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+                bool inGenexpLambda)
+{
+    ParseNode** nextNode = nodePtr;
+
+    do {
+        // |nextNode| on entry points to the C?T:F expression to be folded.
+        // Reset it to exit the loop in the common case where F isn't another
+        // ?: expression.
+        nodePtr = nextNode;
+        nextNode = nullptr;
+
+        ParseNode* node = *nodePtr;
+        MOZ_ASSERT(node->isKind(PNK_CONDITIONAL));
+        MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+        ParseNode*& expr = node->pn_kid1;
+        if (!FoldCondition(cx, &expr, parser, inGenexpLambda))
+            return false;
+
+        ParseNode*& ifTruthy = node->pn_kid2;
+        if (!Fold(cx, &ifTruthy, parser, inGenexpLambda))
+            return false;
+
+        ParseNode*& ifFalsy = node->pn_kid3;
+
+        // If our C?T:F node has F as another ?: node, *iteratively* constant-
+        // fold F *after* folding C and T (and possibly eliminating C and one
+        // of T/F entirely); otherwise fold F normally.  Making |nextNode| non-
+        // null causes this loop to run again to fold F.
+        //
+        // Conceivably we could instead/also iteratively constant-fold T, if T
+        // were more complex than F.  Such an optimization is unimplemented.
+        if (ifFalsy->isKind(PNK_CONDITIONAL)) {
+            nextNode = &ifFalsy;
+        } else {
+            if (!Fold(cx, &ifFalsy, parser, inGenexpLambda))
+                return false;
+        }
+
+        // Try to constant-fold based on the condition expression.
+        Truthiness t = Boolish(expr);
+        if (t == Unknown)
+            continue;
+
+        // Otherwise reduce 'C ? T : F' to T or F as directed by C.
+        ParseNode* replacement;
+        ParseNode* discarded;
+        if (t == Truthy) {
+            replacement = ifTruthy;
+            discarded = ifFalsy;
+        } else {
+            replacement = ifFalsy;
+            discarded = ifTruthy;
+        }
+
+        // Otherwise perform a replacement.  This invalidates |nextNode|, so
+        // reset it (if the replacement requires folding) or clear it (if
+        // |ifFalsy| is dead code) as needed.
+        if (nextNode)
+            nextNode = (*nextNode == replacement) ? nodePtr : nullptr;
+        ReplaceNode(nodePtr, replacement);
+
+        parser.freeTree(discarded);
+    } while (nextNode);
+
+    return true;
+}
+
+static bool
+FoldIf(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+       bool inGenexpLambda)
+{
+    ParseNode** nextNode = nodePtr;
+
+    do {
+        // |nextNode| on entry points to the initial |if| to be folded.  Reset
+        // it to exit the loop when the |else| arm isn't another |if|.
+        nodePtr = nextNode;
+        nextNode = nullptr;
+
+        ParseNode* node = *nodePtr;
+        MOZ_ASSERT(node->isKind(PNK_IF));
+        MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+        ParseNode*& expr = node->pn_kid1;
+        if (!FoldCondition(cx, &expr, parser, inGenexpLambda))
+            return false;
+
+        ParseNode*& consequent = node->pn_kid2;
+        if (!Fold(cx, &consequent, parser, inGenexpLambda))
+            return false;
+
+        ParseNode*& alternative = node->pn_kid3;
+        if (alternative) {
+            // If in |if (C) T; else F;| we have |F| as another |if|,
+            // *iteratively* constant-fold |F| *after* folding |C| and |T| (and
+            // possibly completely replacing the whole thing with |T| or |F|);
+            // otherwise fold F normally.  Making |nextNode| non-null causes
+            // this loop to run again to fold F.
+            if (alternative->isKind(PNK_IF)) {
+                nextNode = &alternative;
+            } else {
+                if (!Fold(cx, &alternative, parser, inGenexpLambda))
+                    return false;
+            }
+        }
+
+        // Eliminate the consequent or alternative if the condition has
+        // constant truthiness.  Don't eliminate if we have an |if (0)| in
+        // trailing position in a generator expression, as this is a special
+        // form we can't fold away.
+        Truthiness t = Boolish(expr);
+        if (t == Unknown || inGenexpLambda)
+            continue;
+
+        // Careful!  Either of these can be null: |replacement| in |if (0) T;|,
+        // and |discarded| in |if (true) T;|.
+        ParseNode* replacement;
+        ParseNode* discarded;
+        if (t == Truthy) {
+            replacement = consequent;
+            discarded = alternative;
+        } else {
+            replacement = alternative;
+            discarded = consequent;
+        }
+
+        bool performReplacement = true;
+        if (discarded) {
+            // A declaration that hoists outside the discarded arm prevents the
+            // |if| from being folded away.
+            bool containsHoistedDecls;
+            if (!ContainsHoistedDeclaration(cx, discarded, &containsHoistedDecls))
+                return false;
+
+            performReplacement = !containsHoistedDecls;
+        }
+
+        if (!performReplacement)
+            continue;
+
+        if (!replacement) {
+            // If there's no replacement node, we have a constantly-false |if|
+            // with no |else|.  Replace the entire thing with an empty
+            // statement list.
+            parser.prepareNodeForMutation(node);
+            node->setKind(PNK_STATEMENTLIST);
+            node->setArity(PN_LIST);
+            node->makeEmpty();
+        } else {
+            // Replacement invalidates |nextNode|, so reset it (if the
+            // replacement requires folding) or clear it (if |alternative|
+            // is dead code) as needed.
+            if (nextNode)
+                nextNode = (*nextNode == replacement) ? nodePtr : nullptr;
+            ReplaceNode(nodePtr, replacement);
+
+            // Morph the original node into a discardable node, then
+            // aggressively free it and the discarded arm (if any) to suss out
+            // any bugs in the preceding logic.
+            node->setKind(PNK_STATEMENTLIST);
+            node->setArity(PN_LIST);
+            node->makeEmpty();
+            if (discarded)
+                node->append(discarded);
+            parser.freeTree(node);
+        }
+    } while (nextNode);
+
+    return true;
+}
+
+static bool
+FoldFunction(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+             bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_FUNCTION));
+    MOZ_ASSERT(node->isArity(PN_CODE));
+
+    // Don't constant-fold inside "use asm" code, as this could create a parse
+    // tree that doesn't type-check as asm.js.
+    if (node->pn_funbox->useAsmOrInsideUseAsm())
+        return true;
+
+    // Note: pn_body is null for lazily-parsed functions.
+    if (ParseNode*& functionBody = node->pn_body) {
+        if (!Fold(cx, &functionBody, parser, node->pn_funbox->isGenexpLambda))
+            return false;
+    }
+
+    return true;
+}
+
+static double
+ComputeBinary(ParseNodeKind kind, double left, double right)
+{
+    if (kind == PNK_ADD)
+        return left + right;
+
+    if (kind == PNK_SUB)
+        return left - right;
+
+    if (kind == PNK_STAR)
+        return left * right;
+
+    if (kind == PNK_MOD)
+        return right == 0 ? GenericNaN() : js_fmod(left, right);
+
+    if (kind == PNK_URSH)
+        return ToUint32(left) >> (ToUint32(right) & 31);
+
+    if (kind == PNK_DIV) {
+        if (right == 0) {
+#if defined(XP_WIN)
+            /* XXX MSVC miscompiles such that (NaN == 0) */
+            if (IsNaN(right))
+                return GenericNaN();
+#endif
+            if (left == 0 || IsNaN(left))
+                return GenericNaN();
+            if (IsNegative(left) != IsNegative(right))
+                return NegativeInfinity<double>();
+            return PositiveInfinity<double>();
+        }
+
+        return left / right;
+    }
+
+    MOZ_ASSERT(kind == PNK_LSH || kind == PNK_RSH);
+
+    int32_t i = ToInt32(left);
+    uint32_t j = ToUint32(right) & 31;
+    return int32_t((kind == PNK_LSH) ? uint32_t(i) << j : i >> j);
+}
+
+static bool
+FoldModule(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser)
+{
+    MOZ_ASSERT(node->isKind(PNK_MODULE));
+    MOZ_ASSERT(node->isArity(PN_CODE));
+
+    ParseNode*& moduleBody = node->pn_body;
+    MOZ_ASSERT(moduleBody);
+    return Fold(cx, &moduleBody, parser, false);
+}
+
+static bool
+FoldBinaryArithmetic(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                     bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_SUB) ||
+               node->isKind(PNK_STAR) ||
+               node->isKind(PNK_LSH) ||
+               node->isKind(PNK_RSH) ||
+               node->isKind(PNK_URSH) ||
+               node->isKind(PNK_DIV) ||
+               node->isKind(PNK_MOD));
+    MOZ_ASSERT(node->isArity(PN_LIST));
+    MOZ_ASSERT(node->pn_count >= 2);
+
+    // Fold each operand, ideally into a number.
+    ParseNode** listp = &node->pn_head;
+    for (; *listp; listp = &(*listp)->pn_next) {
+        if (!Fold(cx, listp, parser, inGenexpLambda))
+            return false;
+
+        if (!FoldType(cx, *listp, PNK_NUMBER))
+            return false;
+    }
+
+    // Repoint the list's tail pointer.
+    node->pn_tail = listp;
+
+    // Now fold all leading numeric terms together into a single number.
+    // (Trailing terms for the non-shift operations can't be folded together
+    // due to floating point imprecision.  For example, if |x === -2**53|,
+    // |x - 1 - 1 === -2**53| but |x - 2 === -2**53 - 2|.  Shifts could be
+    // folded, but it doesn't seem worth the effort.)
+    ParseNode* elem = node->pn_head;
+    ParseNode* next = elem->pn_next;
+    if (elem->isKind(PNK_NUMBER)) {
+        ParseNodeKind kind = node->getKind();
+        while (true) {
+            if (!next || !next->isKind(PNK_NUMBER))
+                break;
+
+            double d = ComputeBinary(kind, elem->pn_dval, next->pn_dval);
+
+            ParseNode* afterNext = next->pn_next;
+            parser.freeTree(next);
+            next = afterNext;
+            elem->pn_next = next;
+
+            elem->setKind(PNK_NUMBER);
+            elem->setOp(JSOP_DOUBLE);
+            elem->setArity(PN_NULLARY);
+            elem->pn_dval = d;
+
+            node->pn_count--;
+        }
+
+        if (node->pn_count == 1) {
+            MOZ_ASSERT(node->pn_head == elem);
+            MOZ_ASSERT(elem->isKind(PNK_NUMBER));
+
+            double d = elem->pn_dval;
+            node->setKind(PNK_NUMBER);
+            node->setArity(PN_NULLARY);
+            node->setOp(JSOP_DOUBLE);
+            node->pn_dval = d;
+
+            parser.freeTree(elem);
+        }
+    }
+
+    return true;
+}
+
+static bool
+FoldExponentiation(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                   bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_POW));
+    MOZ_ASSERT(node->isArity(PN_LIST));
+    MOZ_ASSERT(node->pn_count >= 2);
+
+    // Fold each operand, ideally into a number.
+    ParseNode** listp = &node->pn_head;
+    for (; *listp; listp = &(*listp)->pn_next) {
+        if (!Fold(cx, listp, parser, inGenexpLambda))
+            return false;
+
+        if (!FoldType(cx, *listp, PNK_NUMBER))
+            return false;
+    }
+
+    // Repoint the list's tail pointer.
+    node->pn_tail = listp;
+
+    // Unlike all other binary arithmetic operators, ** is right-associative:
+    // 2**3**5 is 2**(3**5), not (2**3)**5.  As list nodes singly-link their
+    // children, full constant-folding requires either linear space or dodgy
+    // in-place linked list reversal.  So we only fold one exponentiation: it's
+    // easy and addresses common cases like |2**32|.
+    if (node->pn_count > 2)
+        return true;
+
+    ParseNode* base = node->pn_head;
+    ParseNode* exponent = base->pn_next;
+    if (!base->isKind(PNK_NUMBER) || !exponent->isKind(PNK_NUMBER))
+        return true;
+
+    double d1 = base->pn_dval, d2 = exponent->pn_dval;
+
+    parser.prepareNodeForMutation(node);
+    node->setKind(PNK_NUMBER);
+    node->setArity(PN_NULLARY);
+    node->setOp(JSOP_DOUBLE);
+    node->pn_dval = ecmaPow(d1, d2);
+    return true;
+}
+
+static bool
+FoldList(ExclusiveContext* cx, ParseNode* list, Parser<FullParseHandler>& parser,
+         bool inGenexpLambda)
+{
+    MOZ_ASSERT(list->isArity(PN_LIST));
+
+    ParseNode** elem = &list->pn_head;
+    for (; *elem; elem = &(*elem)->pn_next) {
+        if (!Fold(cx, elem, parser, inGenexpLambda))
+            return false;
+    }
+
+    // Repoint the list's tail pointer if the final element was replaced.
+    list->pn_tail = elem;
+
+    list->checkListConsistency();
+
+    return true;
+}
+
+static bool
+FoldReturn(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+           bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_RETURN));
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    if (ParseNode*& expr = node->pn_kid) {
+        if (!Fold(cx, &expr, parser, inGenexpLambda))
+            return false;
+    }
+
+    return true;
+}
+
+static bool
+FoldTry(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+        bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_TRY));
+    MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+    ParseNode*& statements = node->pn_kid1;
+    if (!Fold(cx, &statements, parser, inGenexpLambda))
+        return false;
+
+    if (ParseNode*& catchList = node->pn_kid2) {
+        if (!Fold(cx, &catchList, parser, inGenexpLambda))
+            return false;
+    }
+
+    if (ParseNode*& finally = node->pn_kid3) {
+        if (!Fold(cx, &finally, parser, inGenexpLambda))
+            return false;
+    }
+
+    return true;
+}
+
+static bool
+FoldCatch(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+          bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_CATCH));
+    MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+    ParseNode*& declPattern = node->pn_kid1;
+    if (!Fold(cx, &declPattern, parser, inGenexpLambda))
+        return false;
+
+    if (ParseNode*& cond = node->pn_kid2) {
+        if (!FoldCondition(cx, &cond, parser, inGenexpLambda))
+            return false;
+    }
+
+    if (ParseNode*& statements = node->pn_kid3) {
+        if (!Fold(cx, &statements, parser, inGenexpLambda))
+            return false;
+    }
+
+    return true;
+}
+
+static bool
+FoldClass(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+          bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_CLASS));
+    MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+    if (ParseNode*& classNames = node->pn_kid1) {
+        if (!Fold(cx, &classNames, parser, inGenexpLambda))
+            return false;
+    }
+
+    if (ParseNode*& heritage = node->pn_kid2) {
+        if (!Fold(cx, &heritage, parser, inGenexpLambda))
+            return false;
+    }
+
+    ParseNode*& body = node->pn_kid3;
+    return Fold(cx, &body, parser, inGenexpLambda);
+}
+
+static bool
+FoldElement(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+            bool inGenexpLambda)
+{
+    ParseNode* node = *nodePtr;
+
+    MOZ_ASSERT(node->isKind(PNK_ELEM));
+    MOZ_ASSERT(node->isArity(PN_BINARY));
+
+    ParseNode*& expr = node->pn_left;
+    if (!Fold(cx, &expr, parser, inGenexpLambda))
+        return false;
+
+    ParseNode*& key = node->pn_right;
+    if (!Fold(cx, &key, parser, inGenexpLambda))
+        return false;
+
+    PropertyName* name = nullptr;
+    if (key->isKind(PNK_STRING)) {
+        JSAtom* atom = key->pn_atom;
+        uint32_t index;
+
+        if (atom->isIndex(&index)) {
+            // Optimization 1: We have something like expr["100"]. This is
+            // equivalent to expr[100] which is faster.
+            key->setKind(PNK_NUMBER);
+            key->setOp(JSOP_DOUBLE);
+            key->pn_dval = index;
+        } else {
+            name = atom->asPropertyName();
+        }
+    } else if (key->isKind(PNK_NUMBER)) {
+        double number = key->pn_dval;
+        if (number != ToUint32(number)) {
+            // Optimization 2: We have something like expr[3.14]. The number
+            // isn't an array index, so it converts to a string ("3.14"),
+            // enabling optimization 3 below.
+            JSAtom* atom = ToAtom<NoGC>(cx, DoubleValue(number));
+            if (!atom)
+                return false;
+            name = atom->asPropertyName();
+        }
+    }
+
+    // If we don't have a name, we can't optimize to getprop.
+    if (!name)
+        return true;
+
+    // Also don't optimize if the name doesn't map directly to its id for TI's
+    // purposes.
+    if (NameToId(name) != IdToTypeId(NameToId(name)))
+        return true;
+
+    // Optimization 3: We have expr["foo"] where foo is not an index.  Convert
+    // to a property access (like expr.foo) that optimizes better downstream.
+    // Don't bother with this for names that TI considers to be indexes, to
+    // simplify downstream analysis.
+    ParseNode* dottedAccess = parser.handler.newPropertyAccess(expr, name, node->pn_pos.end);
+    if (!dottedAccess)
+        return false;
+    dottedAccess->setInParens(node->isInParens());
+    ReplaceNode(nodePtr, dottedAccess);
+
+    // If we've replaced |expr["prop"]| with |expr.prop|, we can now free the
+    // |"prop"| and |expr["prop"]| nodes -- but not the |expr| node that we're
+    // now using as a sub-node of |dottedAccess|.  Munge |expr["prop"]| into a
+    // node with |"prop"| as its only child, that'll pass AST sanity-checking
+    // assertions during freeing, then free it.
+    node->setKind(PNK_TYPEOFEXPR);
+    node->setArity(PN_UNARY);
+    node->pn_kid = key;
+    parser.freeTree(node);
+
+    return true;
+}
+
+static bool
+FoldAdd(ExclusiveContext* cx, ParseNode** nodePtr, Parser<FullParseHandler>& parser,
+        bool inGenexpLambda)
+{
+    ParseNode* node = *nodePtr;
+
+    MOZ_ASSERT(node->isKind(PNK_ADD));
+    MOZ_ASSERT(node->isArity(PN_LIST));
+    MOZ_ASSERT(node->pn_count >= 2);
+
+    // Generically fold all operands first.
+    if (!FoldList(cx, node, parser, inGenexpLambda))
+        return false;
+
+    // Fold leading numeric operands together:
+    //
+    //   (1 + 2 + x)  becomes  (3 + x)
+    //
+    // Don't go past the leading operands: additions after a string are
+    // string concatenations, not additions: ("1" + 2 + 3 === "123").
+    ParseNode* current = node->pn_head;
+    ParseNode* next = current->pn_next;
+    if (current->isKind(PNK_NUMBER)) {
+        do {
+            if (!next->isKind(PNK_NUMBER))
+                break;
+
+            current->pn_dval += next->pn_dval;
+            current->pn_next = next->pn_next;
+            parser.freeTree(next);
+            next = current->pn_next;
+
+            MOZ_ASSERT(node->pn_count > 1);
+            node->pn_count--;
+        } while (next);
+    }
+
+    // If any operands remain, attempt string concatenation folding.
+    do {
+        // If no operands remain, we're done.
+        if (!next)
+            break;
+
+        // (number + string) is string concatenation *only* at the start of
+        // the list: (x + 1 + "2" !== x + "12") when x is a number.
+        if (current->isKind(PNK_NUMBER) && next->isKind(PNK_STRING)) {
+            if (!FoldType(cx, current, PNK_STRING))
+                return false;
+            next = current->pn_next;
+        }
+
+        // The first string forces all subsequent additions to be
+        // string concatenations.
+        do {
+            if (current->isKind(PNK_STRING))
+                break;
+
+            current = next;
+            next = next->pn_next;
+        } while (next);
+
+        // If there's nothing left to fold, we're done.
+        if (!next)
+            break;
+
+        RootedString combination(cx);
+        RootedString tmp(cx);
+        do {
+            // Create a rope of the current string and all succeeding
+            // constants that we can convert to strings, then atomize it
+            // and replace them all with that fresh string.
+            MOZ_ASSERT(current->isKind(PNK_STRING));
+
+            combination = current->pn_atom;
+
+            do {
+                // Try folding the next operand to a string.
+                if (!FoldType(cx, next, PNK_STRING))
+                    return false;
+
+                // Stop glomming once folding doesn't produce a string.
+                if (!next->isKind(PNK_STRING))
+                    break;
+
+                // Add this string to the combination and remove the node.
+                tmp = next->pn_atom;
+                combination = ConcatStrings<CanGC>(cx, combination, tmp);
+                if (!combination)
+                    return false;
+
+                current->pn_next = next->pn_next;
+                parser.freeTree(next);
+                next = current->pn_next;
+
+                MOZ_ASSERT(node->pn_count > 1);
+                node->pn_count--;
+            } while (next);
+
+            // Replace |current|'s string with the entire combination.
+            MOZ_ASSERT(current->isKind(PNK_STRING));
+            combination = AtomizeString(cx, combination);
+            if (!combination)
+                return false;
+            current->pn_atom = &combination->asAtom();
+
+
+            // If we're out of nodes, we're done.
+            if (!next)
+                break;
+
+            current = next;
+            next = current->pn_next;
+
+            // If we're out of nodes *after* the non-foldable-to-string
+            // node, we're done.
+            if (!next)
+                break;
+
+            // Otherwise find the next node foldable to a string, and loop.
+            do {
+                current = next;
+                next = current->pn_next;
+
+                if (!FoldType(cx, current, PNK_STRING))
+                    return false;
+                next = current->pn_next;
+            } while (!current->isKind(PNK_STRING) && next);
+        } while (next);
+    } while (false);
+
+    MOZ_ASSERT(!next, "must have considered all nodes here");
+    MOZ_ASSERT(!current->pn_next, "current node must be the last node");
+
+    node->pn_tail = &current->pn_next;
+    node->checkListConsistency();
+
+    if (node->pn_count == 1) {
+        // We reduced the list to a constant.  Replace the PNK_ADD node
+        // with that constant.
+        ReplaceNode(nodePtr, current);
+
+        // Free the old node to aggressively verify nothing uses it.
+        node->setKind(PNK_TRUE);
+        node->setArity(PN_NULLARY);
+        node->setOp(JSOP_TRUE);
+        parser.freeTree(node);
+    }
+
+    return true;
+}
+
+static bool
+FoldCall(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+         bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_CALL) || node->isKind(PNK_SUPERCALL) ||
+               node->isKind(PNK_TAGGED_TEMPLATE));
+    MOZ_ASSERT(node->isArity(PN_LIST));
+
+    // Don't fold a parenthesized callable component in an invocation, as this
+    // might cause a different |this| value to be used, changing semantics:
+    //
+    //   var prop = "global";
+    //   var obj = { prop: "obj", f: function() { return this.prop; } };
+    //   assertEq((true ? obj.f : null)(), "global");
+    //   assertEq(obj.f(), "obj");
+    //   assertEq((true ? obj.f : null)``, "global");
+    //   assertEq(obj.f``, "obj");
+    //
+    // See bug 537673 and bug 1182373.
+    ParseNode** listp = &node->pn_head;
+    if ((*listp)->isInParens())
+        listp = &(*listp)->pn_next;
+
+    for (; *listp; listp = &(*listp)->pn_next) {
+        if (!Fold(cx, listp, parser, inGenexpLambda))
+            return false;
+    }
+
+    // If the last node in the list was replaced, pn_tail points into the wrong node.
+    node->pn_tail = listp;
+
+    node->checkListConsistency();
+    return true;
+}
+
+static bool
+FoldForInOrOf(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+              bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_FORIN) || node->isKind(PNK_FOROF));
+    MOZ_ASSERT(node->isArity(PN_TERNARY));
+    MOZ_ASSERT(!node->pn_kid2);
+
+    return Fold(cx, &node->pn_kid1, parser, inGenexpLambda) &&
+           Fold(cx, &node->pn_kid3, parser, inGenexpLambda);
+}
+
+static bool
+FoldForHead(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+            bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_FORHEAD));
+    MOZ_ASSERT(node->isArity(PN_TERNARY));
+
+    if (ParseNode*& init = node->pn_kid1) {
+        if (!Fold(cx, &init, parser, inGenexpLambda))
+            return false;
+    }
+
+    if (ParseNode*& test = node->pn_kid2) {
+        if (!FoldCondition(cx, &test, parser, inGenexpLambda))
+            return false;
+
+        if (test->isKind(PNK_TRUE)) {
+            parser.freeTree(test);
+            test = nullptr;
+        }
+    }
+
+    if (ParseNode*& update = node->pn_kid3) {
+        if (!Fold(cx, &update, parser, inGenexpLambda))
+            return false;
+    }
+
+    return true;
+}
+
+static bool
+FoldDottedProperty(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+                   bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_DOT));
+    MOZ_ASSERT(node->isArity(PN_NAME));
+
+    // Iterate through a long chain of dotted property accesses to find the
+    // most-nested non-dotted property node, then fold that.
+    ParseNode** nested = &node->pn_expr;
+    while ((*nested)->isKind(PNK_DOT)) {
+        MOZ_ASSERT((*nested)->isArity(PN_NAME));
+        nested = &(*nested)->pn_expr;
+    }
+
+    return Fold(cx, nested, parser, inGenexpLambda);
+}
+
+static bool
+FoldName(ExclusiveContext* cx, ParseNode* node, Parser<FullParseHandler>& parser,
+         bool inGenexpLambda)
+{
+    MOZ_ASSERT(node->isKind(PNK_NAME));
+    MOZ_ASSERT(node->isArity(PN_NAME));
+
+    if (!node->pn_expr)
+        return true;
+
+    return Fold(cx, &node->pn_expr, parser, inGenexpLambda);
+}
+
+bool
+Fold(ExclusiveContext* cx, ParseNode** pnp, Parser<FullParseHandler>& parser, bool inGenexpLambda)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    ParseNode* pn = *pnp;
+
+    switch (pn->getKind()) {
+      case PNK_NOP:
+      case PNK_REGEXP:
+      case PNK_STRING:
+      case PNK_TRUE:
+      case PNK_FALSE:
+      case PNK_NULL:
+      case PNK_ELISION:
+      case PNK_NUMBER:
+      case PNK_DEBUGGER:
+      case PNK_BREAK:
+      case PNK_CONTINUE:
+      case PNK_TEMPLATE_STRING:
+      case PNK_GENERATOR:
+      case PNK_EXPORT_BATCH_SPEC:
+      case PNK_OBJECT_PROPERTY_NAME:
+      case PNK_POSHOLDER:
+        MOZ_ASSERT(pn->isArity(PN_NULLARY));
+        return true;
+
+      case PNK_SUPERBASE:
+      case PNK_TYPEOFNAME:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        MOZ_ASSERT(pn->pn_kid->isKind(PNK_NAME));
+        MOZ_ASSERT(!pn->pn_kid->expr());
+        return true;
+
+      case PNK_TYPEOFEXPR:
+        return FoldTypeOfExpr(cx, pn, parser, inGenexpLambda);
+
+      case PNK_DELETENAME: {
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        MOZ_ASSERT(pn->pn_kid->isKind(PNK_NAME));
+        return true;
+      }
+
+      case PNK_DELETEEXPR:
+        return FoldDeleteExpr(cx, pn, parser, inGenexpLambda);
+
+      case PNK_DELETEELEM:
+        return FoldDeleteElement(cx, pn, parser, inGenexpLambda);
+
+      case PNK_DELETEPROP:
+        return FoldDeleteProperty(cx, pn, parser, inGenexpLambda);
+
+      case PNK_CONDITIONAL:
+        return FoldConditional(cx, pnp, parser, inGenexpLambda);
+
+      case PNK_IF:
+        return FoldIf(cx, pnp, parser, inGenexpLambda);
+
+      case PNK_NOT:
+        return FoldNot(cx, pn, parser, inGenexpLambda);
+
+      case PNK_BITNOT:
+      case PNK_POS:
+      case PNK_NEG:
+        return FoldUnaryArithmetic(cx, pn, parser, inGenexpLambda);
+
+      case PNK_PREINCREMENT:
+      case PNK_POSTINCREMENT:
+      case PNK_PREDECREMENT:
+      case PNK_POSTDECREMENT:
+        return FoldIncrementDecrement(cx, pn, parser, inGenexpLambda);
+
+      case PNK_THROW:
+      case PNK_ARRAYPUSH:
+      case PNK_MUTATEPROTO:
+      case PNK_COMPUTED_NAME:
+      case PNK_SPREAD:
+      case PNK_EXPORT:
+      case PNK_VOID:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        return Fold(cx, &pn->pn_kid, parser, inGenexpLambda);
+
+      case PNK_EXPORT_DEFAULT:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda);
+
+      case PNK_SEMI:
+      case PNK_THIS:
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        if (ParseNode*& expr = pn->pn_kid)
+            return Fold(cx, &expr, parser, inGenexpLambda);
+        return true;
+
+      case PNK_AND:
+      case PNK_OR:
+        return FoldAndOr(cx, pnp, parser, inGenexpLambda);
+
+      case PNK_FUNCTION:
+        return FoldFunction(cx, pn, parser, inGenexpLambda);
+
+      case PNK_MODULE:
+        return FoldModule(cx, pn, parser);
+
+      case PNK_SUB:
+      case PNK_STAR:
+      case PNK_LSH:
+      case PNK_RSH:
+      case PNK_URSH:
+      case PNK_DIV:
+      case PNK_MOD:
+        return FoldBinaryArithmetic(cx, pn, parser, inGenexpLambda);
+
+      case PNK_POW:
+        return FoldExponentiation(cx, pn, parser, inGenexpLambda);
+
+      // Various list nodes not requiring care to minimally fold.  Some of
+      // these could be further folded/optimized, but we don't make the effort.
+      case PNK_BITOR:
+      case PNK_BITXOR:
+      case PNK_BITAND:
+      case PNK_STRICTEQ:
+      case PNK_EQ:
+      case PNK_STRICTNE:
+      case PNK_NE:
+      case PNK_LT:
+      case PNK_LE:
+      case PNK_GT:
+      case PNK_GE:
+      case PNK_INSTANCEOF:
+      case PNK_IN:
+      case PNK_COMMA:
+      case PNK_NEW:
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+      case PNK_ARRAYCOMP:
+      case PNK_STATEMENTLIST:
+      case PNK_CLASSMETHODLIST:
+      case PNK_CATCHLIST:
+      case PNK_TEMPLATE_STRING_LIST:
+      case PNK_VAR:
+      case PNK_CONST:
+      case PNK_LET:
+      case PNK_PARAMSBODY:
+      case PNK_CALLSITEOBJ:
+      case PNK_EXPORT_SPEC_LIST:
+      case PNK_IMPORT_SPEC_LIST:
+      case PNK_GENEXP:
+        return FoldList(cx, pn, parser, inGenexpLambda);
+
+      case PNK_YIELD_STAR:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_NAME));
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda);
+
+      case PNK_YIELD:
+      case PNK_AWAIT:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_NAME) ||
+                   (pn->pn_right->isKind(PNK_ASSIGN) &&
+                    pn->pn_right->pn_left->isKind(PNK_NAME) &&
+                    pn->pn_right->pn_right->isKind(PNK_GENERATOR)));
+        if (!pn->pn_left)
+            return true;
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda);
+
+      case PNK_RETURN:
+        return FoldReturn(cx, pn, parser, inGenexpLambda);
+
+      case PNK_TRY:
+        return FoldTry(cx, pn, parser, inGenexpLambda);
+
+      case PNK_CATCH:
+        return FoldCatch(cx, pn, parser, inGenexpLambda);
+
+      case PNK_CLASS:
+        return FoldClass(cx, pn, parser, inGenexpLambda);
+
+      case PNK_ELEM:
+        return FoldElement(cx, pnp, parser, inGenexpLambda);
+
+      case PNK_ADD:
+        return FoldAdd(cx, pnp, parser, inGenexpLambda);
+
+      case PNK_CALL:
+      case PNK_SUPERCALL:
+      case PNK_TAGGED_TEMPLATE:
+        return FoldCall(cx, pn, parser, inGenexpLambda);
+
+      case PNK_SWITCH:
+      case PNK_COLON:
+      case PNK_ASSIGN:
+      case PNK_ADDASSIGN:
+      case PNK_SUBASSIGN:
+      case PNK_BITORASSIGN:
+      case PNK_BITANDASSIGN:
+      case PNK_BITXORASSIGN:
+      case PNK_LSHASSIGN:
+      case PNK_RSHASSIGN:
+      case PNK_URSHASSIGN:
+      case PNK_DIVASSIGN:
+      case PNK_MODASSIGN:
+      case PNK_MULASSIGN:
+      case PNK_POWASSIGN:
+      case PNK_IMPORT:
+      case PNK_EXPORT_FROM:
+      case PNK_SHORTHAND:
+      case PNK_FOR:
+      case PNK_COMPREHENSIONFOR:
+      case PNK_CLASSMETHOD:
+      case PNK_IMPORT_SPEC:
+      case PNK_EXPORT_SPEC:
+      case PNK_SETTHIS:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda) &&
+               Fold(cx, &pn->pn_right, parser, inGenexpLambda);
+
+      case PNK_NEWTARGET:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT(pn->pn_left->isKind(PNK_POSHOLDER));
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_POSHOLDER));
+        return true;
+
+      case PNK_CLASSNAMES:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        if (ParseNode*& outerBinding = pn->pn_left) {
+            if (!Fold(cx, &outerBinding, parser, inGenexpLambda))
+                return false;
+        }
+        return Fold(cx, &pn->pn_right, parser, inGenexpLambda);
+
+      case PNK_DOWHILE:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda) &&
+               FoldCondition(cx, &pn->pn_right, parser, inGenexpLambda);
+
+      case PNK_WHILE:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        return FoldCondition(cx, &pn->pn_left, parser, inGenexpLambda) &&
+               Fold(cx, &pn->pn_right, parser, inGenexpLambda);
+
+      case PNK_CASE: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+
+        // pn_left is null for DefaultClauses.
+        if (pn->pn_left) {
+            if (!Fold(cx, &pn->pn_left, parser, inGenexpLambda))
+                return false;
+        }
+        return Fold(cx, &pn->pn_right, parser, inGenexpLambda);
+      }
+
+      case PNK_WITH:
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        return Fold(cx, &pn->pn_left, parser, inGenexpLambda) &&
+               Fold(cx, &pn->pn_right, parser, inGenexpLambda);
+
+      case PNK_FORIN:
+      case PNK_FOROF:
+        return FoldForInOrOf(cx, pn, parser, inGenexpLambda);
+
+      case PNK_FORHEAD:
+        return FoldForHead(cx, pn, parser, inGenexpLambda);
+
+      case PNK_LABEL:
+        MOZ_ASSERT(pn->isArity(PN_NAME));
+        return Fold(cx, &pn->pn_expr, parser, inGenexpLambda);
+
+      case PNK_DOT:
+        return FoldDottedProperty(cx, pn, parser, inGenexpLambda);
+
+      case PNK_LEXICALSCOPE:
+        MOZ_ASSERT(pn->isArity(PN_SCOPE));
+        if (!pn->scopeBody())
+            return true;
+        return Fold(cx, &pn->pn_u.scope.body, parser, inGenexpLambda);
+
+      case PNK_NAME:
+        return FoldName(cx, pn, parser, inGenexpLambda);
+
+      case PNK_LIMIT: // invalid sentinel value
+        MOZ_CRASH("invalid node kind");
+    }
+
+    MOZ_CRASH("shouldn't reach here");
+    return false;
+}
+
+bool
+frontend::FoldConstants(ExclusiveContext* cx, ParseNode** pnp, Parser<FullParseHandler>* parser)
+{
+    // Don't constant-fold inside "use asm" code, as this could create a parse
+    // tree that doesn't type-check as asm.js.
+    if (parser->pc->useAsmOrInsideUseAsm())
+        return true;
+
+    return Fold(cx, pnp, *parser, false);
+}
diff --git a/js/src/frontend/FoldConstants.h b/js/src/frontend/FoldConstants.h
new file mode 100644
index 0000000000..274daaaaef
--- /dev/null
+++ b/js/src/frontend/FoldConstants.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_FoldConstants_h
+#define frontend_FoldConstants_h
+
+#include "frontend/SyntaxParseHandler.h"
+
+namespace js {
+namespace frontend {
+
+// Perform constant folding on the given AST. For example, the program
+// `print(2 + 2)` would become `print(4)`.
+//
+// pnp is the address of a pointer variable that points to the root node of the
+// AST. On success, *pnp points to the root node of the new tree, which may be
+// the same node (unchanged or modified in place) or a new node.
+//
+// Usage:
+//    pn = parser->statement();
+//    if (!pn)
+//        return false;
+//    if (!FoldConstants(cx, &pn, parser))
+//        return false;
+MOZ_MUST_USE bool
+FoldConstants(ExclusiveContext* cx, ParseNode** pnp, Parser<FullParseHandler>* parser);
+
+inline MOZ_MUST_USE bool
+FoldConstants(ExclusiveContext* cx, SyntaxParseHandler::Node* pnp,
+              Parser<SyntaxParseHandler>* parser)
+{
+    return true;
+}
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_FoldConstants_h */
diff --git a/js/src/frontend/FullParseHandler.h b/js/src/frontend/FullParseHandler.h
new file mode 100644
index 0000000000..add881900a
--- /dev/null
+++ b/js/src/frontend/FullParseHandler.h
@@ -0,0 +1,977 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_FullParseHandler_h
+#define frontend_FullParseHandler_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/PodOperations.h"
+
+#include "frontend/ParseNode.h"
+#include "frontend/SharedContext.h"
+
+namespace js {
+namespace frontend {
+
+template <typename ParseHandler>
+class Parser;
+
+class SyntaxParseHandler;
+
+// Parse handler used when generating a full parse tree for all code which the
+// parser encounters.
+class FullParseHandler
+{
+    ParseNodeAllocator allocator;
+    TokenStream& tokenStream;
+
+    ParseNode* allocParseNode(size_t size) {
+        MOZ_ASSERT(size == sizeof(ParseNode));
+        return static_cast<ParseNode*>(allocator.allocNode());
+    }
+
+    ParseNode* cloneNode(const ParseNode& other) {
+        ParseNode* node = allocParseNode(sizeof(ParseNode));
+        if (!node)
+            return nullptr;
+        mozilla::PodAssign(node, &other);
+        return node;
+    }
+
+    /*
+     * If this is a full parse to construct the bytecode for a function that
+     * was previously lazily parsed, that lazy function and the current index
+     * into its inner functions. We do not want to reparse the inner functions.
+     */
+    const Rooted<LazyScript*> lazyOuterFunction_;
+    size_t lazyInnerFunctionIndex;
+    size_t lazyClosedOverBindingIndex;
+
+    const TokenPos& pos() {
+        return tokenStream.currentToken().pos;
+    }
+
+  public:
+
+    /*
+     * If non-nullptr, points to a syntax parser which can be used for inner
+     * functions. Cleared if language features not handled by the syntax parser
+     * are encountered, in which case all future activity will use the full
+     * parser.
+     */
+    Parser<SyntaxParseHandler>* syntaxParser;
+
+    /* new_ methods for creating parse nodes. These report OOM on context. */
+    JS_DECLARE_NEW_METHODS(new_, allocParseNode, inline)
+
+    typedef ParseNode* Node;
+
+    bool isPropertyAccess(ParseNode* node) {
+        return node->isKind(PNK_DOT) || node->isKind(PNK_ELEM);
+    }
+
+    bool isFunctionCall(ParseNode* node) {
+        // Note: super() is a special form, *not* a function call.
+        return node->isKind(PNK_CALL);
+    }
+
+    static bool isUnparenthesizedDestructuringPattern(ParseNode* node) {
+        return !node->isInParens() && (node->isKind(PNK_OBJECT) || node->isKind(PNK_ARRAY));
+    }
+
+    static bool isParenthesizedDestructuringPattern(ParseNode* node) {
+        // Technically this isn't a destructuring pattern at all -- the grammar
+        // doesn't treat it as such.  But we need to know when this happens to
+        // consider it a SyntaxError rather than an invalid-left-hand-side
+        // ReferenceError.
+        return node->isInParens() && (node->isKind(PNK_OBJECT) || node->isKind(PNK_ARRAY));
+    }
+
+    static bool isDestructuringPatternAnyParentheses(ParseNode* node) {
+        return isUnparenthesizedDestructuringPattern(node) ||
+               isParenthesizedDestructuringPattern(node);
+    }
+
+    FullParseHandler(ExclusiveContext* cx, LifoAlloc& alloc,
+                     TokenStream& tokenStream, Parser<SyntaxParseHandler>* syntaxParser,
+                     LazyScript* lazyOuterFunction)
+      : allocator(cx, alloc),
+        tokenStream(tokenStream),
+        lazyOuterFunction_(cx, lazyOuterFunction),
+        lazyInnerFunctionIndex(0),
+        lazyClosedOverBindingIndex(0),
+        syntaxParser(syntaxParser)
+    {}
+
+    static ParseNode* null() { return nullptr; }
+
+    ParseNode* freeTree(ParseNode* pn) { return allocator.freeTree(pn); }
+    void prepareNodeForMutation(ParseNode* pn) { return allocator.prepareNodeForMutation(pn); }
+    const Token& currentToken() { return tokenStream.currentToken(); }
+
+    ParseNode* newName(PropertyName* name, const TokenPos& pos, ExclusiveContext* cx)
+    {
+        return new_<NameNode>(PNK_NAME, JSOP_GETNAME, name, pos);
+    }
+
+    ParseNode* newComputedName(ParseNode* expr, uint32_t begin, uint32_t end) {
+        TokenPos pos(begin, end);
+        return new_<UnaryNode>(PNK_COMPUTED_NAME, JSOP_NOP, pos, expr);
+    }
+
+    ParseNode* newObjectLiteralPropertyName(JSAtom* atom, const TokenPos& pos) {
+        return new_<NullaryNode>(PNK_OBJECT_PROPERTY_NAME, JSOP_NOP, pos, atom);
+    }
+
+    ParseNode* newNumber(double value, DecimalPoint decimalPoint, const TokenPos& pos) {
+        ParseNode* pn = new_<NullaryNode>(PNK_NUMBER, pos);
+        if (!pn)
+            return nullptr;
+        pn->initNumber(value, decimalPoint);
+        return pn;
+    }
+
+    ParseNode* newBooleanLiteral(bool cond, const TokenPos& pos) {
+        return new_<BooleanLiteral>(cond, pos);
+    }
+
+    ParseNode* newStringLiteral(JSAtom* atom, const TokenPos& pos) {
+        return new_<NullaryNode>(PNK_STRING, JSOP_NOP, pos, atom);
+    }
+
+    ParseNode* newTemplateStringLiteral(JSAtom* atom, const TokenPos& pos) {
+        return new_<NullaryNode>(PNK_TEMPLATE_STRING, JSOP_NOP, pos, atom);
+    }
+
+    ParseNode* newCallSiteObject(uint32_t begin) {
+        ParseNode* callSite = new_<CallSiteNode>(begin);
+        if (!callSite)
+            return null();
+
+        Node propExpr = newArrayLiteral(getPosition(callSite).begin);
+        if (!propExpr)
+            return null();
+
+        addArrayElement(callSite, propExpr);
+
+        return callSite;
+    }
+
+    void addToCallSiteObject(ParseNode* callSiteObj, ParseNode* rawNode, ParseNode* cookedNode) {
+        MOZ_ASSERT(callSiteObj->isKind(PNK_CALLSITEOBJ));
+
+        addArrayElement(callSiteObj, cookedNode);
+        addArrayElement(callSiteObj->pn_head, rawNode);
+
+        /*
+         * We don't know when the last noSubstTemplate will come in, and we
+         * don't want to deal with this outside this method
+         */
+        setEndPosition(callSiteObj, callSiteObj->pn_head);
+    }
+
+    ParseNode* newThisLiteral(const TokenPos& pos, ParseNode* thisName) {
+        return new_<ThisLiteral>(pos, thisName);
+    }
+
+    ParseNode* newNullLiteral(const TokenPos& pos) {
+        return new_<NullLiteral>(pos);
+    }
+
+    // The Boxer object here is any object that can allocate ObjectBoxes.
+    // Specifically, a Boxer has a .newObjectBox(T) method that accepts a
+    // Rooted<RegExpObject*> argument and returns an ObjectBox*.
+    template <class Boxer>
+    ParseNode* newRegExp(RegExpObject* reobj, const TokenPos& pos, Boxer& boxer) {
+        ObjectBox* objbox = boxer.newObjectBox(reobj);
+        if (!objbox)
+            return null();
+        return new_<RegExpLiteral>(objbox, pos);
+    }
+
+    ParseNode* newConditional(ParseNode* cond, ParseNode* thenExpr, ParseNode* elseExpr) {
+        return new_<ConditionalExpression>(cond, thenExpr, elseExpr);
+    }
+
+    ParseNode* newDelete(uint32_t begin, ParseNode* expr) {
+        if (expr->isKind(PNK_NAME)) {
+            expr->setOp(JSOP_DELNAME);
+            return newUnary(PNK_DELETENAME, JSOP_NOP, begin, expr);
+        }
+
+        if (expr->isKind(PNK_DOT))
+            return newUnary(PNK_DELETEPROP, JSOP_NOP, begin, expr);
+
+        if (expr->isKind(PNK_ELEM))
+            return newUnary(PNK_DELETEELEM, JSOP_NOP, begin, expr);
+
+        return newUnary(PNK_DELETEEXPR, JSOP_NOP, begin, expr);
+    }
+
+    ParseNode* newTypeof(uint32_t begin, ParseNode* kid) {
+        TokenPos pos(begin, kid->pn_pos.end);
+        ParseNodeKind kind = kid->isKind(PNK_NAME) ? PNK_TYPEOFNAME : PNK_TYPEOFEXPR;
+        return new_<UnaryNode>(kind, JSOP_NOP, pos, kid);
+    }
+
+    ParseNode* newNullary(ParseNodeKind kind, JSOp op, const TokenPos& pos) {
+        return new_<NullaryNode>(kind, op, pos);
+    }
+
+    ParseNode* newUnary(ParseNodeKind kind, JSOp op, uint32_t begin, ParseNode* kid) {
+        TokenPos pos(begin, kid ? kid->pn_pos.end : begin + 1);
+        return new_<UnaryNode>(kind, op, pos, kid);
+    }
+
+    ParseNode* newUpdate(ParseNodeKind kind, uint32_t begin, ParseNode* kid) {
+        TokenPos pos(begin, kid->pn_pos.end);
+        return new_<UnaryNode>(kind, JSOP_NOP, pos, kid);
+    }
+
+    ParseNode* newSpread(uint32_t begin, ParseNode* kid) {
+        TokenPos pos(begin, kid->pn_pos.end);
+        return new_<UnaryNode>(PNK_SPREAD, JSOP_NOP, pos, kid);
+    }
+
+    ParseNode* newArrayPush(uint32_t begin, ParseNode* kid) {
+        TokenPos pos(begin, kid->pn_pos.end);
+        return new_<UnaryNode>(PNK_ARRAYPUSH, JSOP_ARRAYPUSH, pos, kid);
+    }
+
+    ParseNode* newBinary(ParseNodeKind kind, JSOp op = JSOP_NOP) {
+        return new_<BinaryNode>(kind, op, pos(), (ParseNode*) nullptr, (ParseNode*) nullptr);
+    }
+    ParseNode* newBinary(ParseNodeKind kind, ParseNode* left,
+                         JSOp op = JSOP_NOP) {
+        return new_<BinaryNode>(kind, op, left->pn_pos, left, (ParseNode*) nullptr);
+    }
+    ParseNode* newBinary(ParseNodeKind kind, ParseNode* left, ParseNode* right,
+                         JSOp op = JSOP_NOP) {
+        TokenPos pos(left->pn_pos.begin, right->pn_pos.end);
+        return new_<BinaryNode>(kind, op, pos, left, right);
+    }
+    ParseNode* appendOrCreateList(ParseNodeKind kind, ParseNode* left, ParseNode* right,
+                                  ParseContext* pc, JSOp op = JSOP_NOP)
+    {
+        return ParseNode::appendOrCreateList(kind, op, left, right, this, pc);
+    }
+
+    ParseNode* newTernary(ParseNodeKind kind,
+                          ParseNode* first, ParseNode* second, ParseNode* third,
+                          JSOp op = JSOP_NOP)
+    {
+        return new_<TernaryNode>(kind, op, first, second, third);
+    }
+
+    // Expressions
+
+    ParseNode* newArrayComprehension(ParseNode* body, const TokenPos& pos) {
+        MOZ_ASSERT(pos.begin <= body->pn_pos.begin);
+        MOZ_ASSERT(body->pn_pos.end <= pos.end);
+        ParseNode* pn = new_<ListNode>(PNK_ARRAYCOMP, pos);
+        if (!pn)
+            return nullptr;
+        pn->append(body);
+        return pn;
+    }
+
+    ParseNode* newArrayLiteral(uint32_t begin) {
+        ParseNode* literal = new_<ListNode>(PNK_ARRAY, TokenPos(begin, begin + 1));
+        // Later in this stack: remove dependency on this opcode.
+        if (literal)
+            literal->setOp(JSOP_NEWINIT);
+        return literal;
+    }
+
+    MOZ_MUST_USE bool addElision(ParseNode* literal, const TokenPos& pos) {
+        ParseNode* elision = new_<NullaryNode>(PNK_ELISION, pos);
+        if (!elision)
+            return false;
+        literal->append(elision);
+        literal->pn_xflags |= PNX_ARRAYHOLESPREAD | PNX_NONCONST;
+        return true;
+    }
+
+    MOZ_MUST_USE bool addSpreadElement(ParseNode* literal, uint32_t begin, ParseNode* inner) {
+        TokenPos pos(begin, inner->pn_pos.end);
+        ParseNode* spread = new_<UnaryNode>(PNK_SPREAD, JSOP_NOP, pos, inner);
+        if (!spread)
+            return null();
+        literal->append(spread);
+        literal->pn_xflags |= PNX_ARRAYHOLESPREAD | PNX_NONCONST;
+        return true;
+    }
+
+    void addArrayElement(ParseNode* literal, ParseNode* element) {
+        if (!element->isConstant())
+            literal->pn_xflags |= PNX_NONCONST;
+        literal->append(element);
+    }
+
+    ParseNode* newCall() {
+        return newList(PNK_CALL, JSOP_CALL);
+    }
+
+    ParseNode* newTaggedTemplate() {
+        return newList(PNK_TAGGED_TEMPLATE, JSOP_CALL);
+    }
+
+    ParseNode* newObjectLiteral(uint32_t begin) {
+        ParseNode* literal = new_<ListNode>(PNK_OBJECT, TokenPos(begin, begin + 1));
+        // Later in this stack: remove dependency on this opcode.
+        if (literal)
+            literal->setOp(JSOP_NEWINIT);
+        return literal;
+    }
+
+    ParseNode* newClass(ParseNode* name, ParseNode* heritage, ParseNode* methodBlock) {
+        return new_<ClassNode>(name, heritage, methodBlock);
+    }
+    ParseNode* newClassMethodList(uint32_t begin) {
+        return new_<ListNode>(PNK_CLASSMETHODLIST, TokenPos(begin, begin + 1));
+    }
+    ParseNode* newClassNames(ParseNode* outer, ParseNode* inner, const TokenPos& pos) {
+        return new_<ClassNames>(outer, inner, pos);
+    }
+    ParseNode* newNewTarget(ParseNode* newHolder, ParseNode* targetHolder) {
+        return new_<BinaryNode>(PNK_NEWTARGET, JSOP_NOP, newHolder, targetHolder);
+    }
+    ParseNode* newPosHolder(const TokenPos& pos) {
+        return new_<NullaryNode>(PNK_POSHOLDER, pos);
+    }
+    ParseNode* newSuperBase(ParseNode* thisName, const TokenPos& pos) {
+        return new_<UnaryNode>(PNK_SUPERBASE, JSOP_NOP, pos, thisName);
+    }
+
+    MOZ_MUST_USE bool addPrototypeMutation(ParseNode* literal, uint32_t begin, ParseNode* expr) {
+        // Object literals with mutated [[Prototype]] are non-constant so that
+        // singleton objects will have Object.prototype as their [[Prototype]].
+        setListFlag(literal, PNX_NONCONST);
+
+        ParseNode* mutation = newUnary(PNK_MUTATEPROTO, JSOP_NOP, begin, expr);
+        if (!mutation)
+            return false;
+        literal->append(mutation);
+        return true;
+    }
+
+    MOZ_MUST_USE bool addPropertyDefinition(ParseNode* literal, ParseNode* key, ParseNode* val) {
+        MOZ_ASSERT(literal->isKind(PNK_OBJECT));
+        MOZ_ASSERT(literal->isArity(PN_LIST));
+        MOZ_ASSERT(key->isKind(PNK_NUMBER) ||
+                   key->isKind(PNK_OBJECT_PROPERTY_NAME) ||
+                   key->isKind(PNK_STRING) ||
+                   key->isKind(PNK_COMPUTED_NAME));
+
+        ParseNode* propdef = newBinary(PNK_COLON, key, val, JSOP_INITPROP);
+        if (!propdef)
+            return false;
+        literal->append(propdef);
+        return true;
+    }
+
+    MOZ_MUST_USE bool addShorthand(ParseNode* literal, ParseNode* name, ParseNode* expr) {
+        MOZ_ASSERT(literal->isKind(PNK_OBJECT));
+        MOZ_ASSERT(literal->isArity(PN_LIST));
+        MOZ_ASSERT(name->isKind(PNK_OBJECT_PROPERTY_NAME));
+        MOZ_ASSERT(expr->isKind(PNK_NAME));
+        MOZ_ASSERT(name->pn_atom == expr->pn_atom);
+
+        setListFlag(literal, PNX_NONCONST);
+        ParseNode* propdef = newBinary(PNK_SHORTHAND, name, expr, JSOP_INITPROP);
+        if (!propdef)
+            return false;
+        literal->append(propdef);
+        return true;
+    }
+
+    MOZ_MUST_USE bool addObjectMethodDefinition(ParseNode* literal, ParseNode* key, ParseNode* fn,
+                                                JSOp op)
+    {
+        MOZ_ASSERT(literal->isArity(PN_LIST));
+        MOZ_ASSERT(key->isKind(PNK_NUMBER) ||
+                   key->isKind(PNK_OBJECT_PROPERTY_NAME) ||
+                   key->isKind(PNK_STRING) ||
+                   key->isKind(PNK_COMPUTED_NAME));
+        literal->pn_xflags |= PNX_NONCONST;
+
+        ParseNode* propdef = newBinary(PNK_COLON, key, fn, op);
+        if (!propdef)
+            return false;
+        literal->append(propdef);
+        return true;
+    }
+
+    MOZ_MUST_USE bool addClassMethodDefinition(ParseNode* methodList, ParseNode* key, ParseNode* fn,
+                                               JSOp op, bool isStatic)
+    {
+        MOZ_ASSERT(methodList->isKind(PNK_CLASSMETHODLIST));
+        MOZ_ASSERT(key->isKind(PNK_NUMBER) ||
+                   key->isKind(PNK_OBJECT_PROPERTY_NAME) ||
+                   key->isKind(PNK_STRING) ||
+                   key->isKind(PNK_COMPUTED_NAME));
+
+        ParseNode* classMethod = new_<ClassMethod>(key, fn, op, isStatic);
+        if (!classMethod)
+            return false;
+        methodList->append(classMethod);
+        return true;
+    }
+
+    ParseNode* newYieldExpression(uint32_t begin, ParseNode* value, ParseNode* gen,
+                                  JSOp op = JSOP_YIELD) {
+        TokenPos pos(begin, value ? value->pn_pos.end : begin + 1);
+        return new_<BinaryNode>(PNK_YIELD, op, pos, value, gen);
+    }
+
+    ParseNode* newYieldStarExpression(uint32_t begin, ParseNode* value, ParseNode* gen) {
+        TokenPos pos(begin, value->pn_pos.end);
+        return new_<BinaryNode>(PNK_YIELD_STAR, JSOP_NOP, pos, value, gen);
+    }
+
+    ParseNode* newAwaitExpression(uint32_t begin, ParseNode* value, ParseNode* gen) {
+        TokenPos pos(begin, value ? value->pn_pos.end : begin + 1);
+        return new_<BinaryNode>(PNK_AWAIT, JSOP_YIELD, pos, value, gen);
+    }
+
+    // Statements
+
+    ParseNode* newStatementList(const TokenPos& pos) {
+        return new_<ListNode>(PNK_STATEMENTLIST, pos);
+    }
+
+    MOZ_MUST_USE bool isFunctionStmt(ParseNode* stmt) {
+        while (stmt->isKind(PNK_LABEL))
+            stmt = stmt->as<LabeledStatement>().statement();
+        return stmt->isKind(PNK_FUNCTION);
+    }
+
+    void addStatementToList(ParseNode* list, ParseNode* stmt) {
+        MOZ_ASSERT(list->isKind(PNK_STATEMENTLIST));
+
+        list->append(stmt);
+
+        if (isFunctionStmt(stmt)) {
+            // PNX_FUNCDEFS notifies the emitter that the block contains
+            // body-level function definitions that should be processed
+            // before the rest of nodes.
+            list->pn_xflags |= PNX_FUNCDEFS;
+        }
+    }
+
+    void addCaseStatementToList(ParseNode* list, ParseNode* casepn) {
+        MOZ_ASSERT(list->isKind(PNK_STATEMENTLIST));
+        MOZ_ASSERT(casepn->isKind(PNK_CASE));
+        MOZ_ASSERT(casepn->pn_right->isKind(PNK_STATEMENTLIST));
+
+        list->append(casepn);
+
+        if (casepn->pn_right->pn_xflags & PNX_FUNCDEFS)
+            list->pn_xflags |= PNX_FUNCDEFS;
+    }
+
+    MOZ_MUST_USE bool prependInitialYield(ParseNode* stmtList, ParseNode* genName) {
+        MOZ_ASSERT(stmtList->isKind(PNK_STATEMENTLIST));
+
+        TokenPos yieldPos(stmtList->pn_pos.begin, stmtList->pn_pos.begin + 1);
+        ParseNode* makeGen = new_<NullaryNode>(PNK_GENERATOR, yieldPos);
+        if (!makeGen)
+            return false;
+
+        MOZ_ASSERT(genName->getOp() == JSOP_GETNAME);
+        genName->setOp(JSOP_SETNAME);
+        ParseNode* genInit = newBinary(PNK_ASSIGN, genName, makeGen);
+        if (!genInit)
+            return false;
+
+        ParseNode* initialYield = newYieldExpression(yieldPos.begin, nullptr, genInit,
+                                                     JSOP_INITIALYIELD);
+        if (!initialYield)
+            return false;
+
+        stmtList->prepend(initialYield);
+        return true;
+    }
+
+    ParseNode* newSetThis(ParseNode* thisName, ParseNode* val) {
+        MOZ_ASSERT(thisName->getOp() == JSOP_GETNAME);
+        thisName->setOp(JSOP_SETNAME);
+        return newBinary(PNK_SETTHIS, thisName, val);
+    }
+
+    ParseNode* newEmptyStatement(const TokenPos& pos) {
+        return new_<UnaryNode>(PNK_SEMI, JSOP_NOP, pos, (ParseNode*) nullptr);
+    }
+
+    ParseNode* newImportDeclaration(ParseNode* importSpecSet,
+                                    ParseNode* moduleSpec, const TokenPos& pos)
+    {
+        ParseNode* pn = new_<BinaryNode>(PNK_IMPORT, JSOP_NOP, pos,
+                                         importSpecSet, moduleSpec);
+        if (!pn)
+            return null();
+        return pn;
+    }
+
+    ParseNode* newExportDeclaration(ParseNode* kid, const TokenPos& pos) {
+        return new_<UnaryNode>(PNK_EXPORT, JSOP_NOP, pos, kid);
+    }
+
+    ParseNode* newExportFromDeclaration(uint32_t begin, ParseNode* exportSpecSet,
+                                        ParseNode* moduleSpec)
+    {
+        ParseNode* pn = new_<BinaryNode>(PNK_EXPORT_FROM, JSOP_NOP, exportSpecSet, moduleSpec);
+        if (!pn)
+            return null();
+        pn->pn_pos.begin = begin;
+        return pn;
+    }
+
+    ParseNode* newExportDefaultDeclaration(ParseNode* kid, ParseNode* maybeBinding,
+                                           const TokenPos& pos) {
+        return new_<BinaryNode>(PNK_EXPORT_DEFAULT, JSOP_NOP, pos, kid, maybeBinding);
+    }
+
+    ParseNode* newExprStatement(ParseNode* expr, uint32_t end) {
+        MOZ_ASSERT(expr->pn_pos.end <= end);
+        return new_<UnaryNode>(PNK_SEMI, JSOP_NOP, TokenPos(expr->pn_pos.begin, end), expr);
+    }
+
+    ParseNode* newIfStatement(uint32_t begin, ParseNode* cond, ParseNode* thenBranch,
+                              ParseNode* elseBranch)
+    {
+        ParseNode* pn = new_<TernaryNode>(PNK_IF, JSOP_NOP, cond, thenBranch, elseBranch);
+        if (!pn)
+            return null();
+        pn->pn_pos.begin = begin;
+        return pn;
+    }
+
+    ParseNode* newDoWhileStatement(ParseNode* body, ParseNode* cond, const TokenPos& pos) {
+        return new_<BinaryNode>(PNK_DOWHILE, JSOP_NOP, pos, body, cond);
+    }
+
+    ParseNode* newWhileStatement(uint32_t begin, ParseNode* cond, ParseNode* body) {
+        TokenPos pos(begin, body->pn_pos.end);
+        return new_<BinaryNode>(PNK_WHILE, JSOP_NOP, pos, cond, body);
+    }
+
+    ParseNode* newForStatement(uint32_t begin, ParseNode* forHead, ParseNode* body,
+                               unsigned iflags)
+    {
+        /* A FOR node is binary, left is loop control and right is the body. */
+        JSOp op = forHead->isKind(PNK_FORIN) ? JSOP_ITER : JSOP_NOP;
+        BinaryNode* pn = new_<BinaryNode>(PNK_FOR, op, TokenPos(begin, body->pn_pos.end),
+                                          forHead, body);
+        if (!pn)
+            return null();
+        pn->pn_iflags = iflags;
+        return pn;
+    }
+
+    ParseNode* newComprehensionFor(uint32_t begin, ParseNode* forHead, ParseNode* body) {
+        // A PNK_COMPREHENSIONFOR node is binary: left is loop control, right
+        // is the body.
+        MOZ_ASSERT(forHead->isKind(PNK_FORIN) || forHead->isKind(PNK_FOROF));
+        JSOp op = forHead->isKind(PNK_FORIN) ? JSOP_ITER : JSOP_NOP;
+        BinaryNode* pn = new_<BinaryNode>(PNK_COMPREHENSIONFOR, op,
+                                          TokenPos(begin, body->pn_pos.end), forHead, body);
+        if (!pn)
+            return null();
+        pn->pn_iflags = JSOP_ITER;
+        return pn;
+    }
+
+    ParseNode* newComprehensionBinding(ParseNode* kid) {
+        MOZ_ASSERT(kid->isKind(PNK_NAME));
+        return new_<ListNode>(PNK_LET, JSOP_NOP, kid);
+    }
+
+    ParseNode* newForHead(ParseNode* init, ParseNode* test, ParseNode* update,
+                          const TokenPos& pos)
+    {
+        return new_<TernaryNode>(PNK_FORHEAD, JSOP_NOP, init, test, update, pos);
+    }
+
+    ParseNode* newForInOrOfHead(ParseNodeKind kind, ParseNode* target, ParseNode* iteratedExpr,
+                                const TokenPos& pos)
+    {
+        MOZ_ASSERT(kind == PNK_FORIN || kind == PNK_FOROF);
+        return new_<TernaryNode>(kind, JSOP_NOP, target, nullptr, iteratedExpr, pos);
+    }
+
+    ParseNode* newSwitchStatement(uint32_t begin, ParseNode* discriminant, ParseNode* caseList) {
+        TokenPos pos(begin, caseList->pn_pos.end);
+        return new_<BinaryNode>(PNK_SWITCH, JSOP_NOP, pos, discriminant, caseList);
+    }
+
+    ParseNode* newCaseOrDefault(uint32_t begin, ParseNode* expr, ParseNode* body) {
+        return new_<CaseClause>(expr, body, begin);
+    }
+
+    ParseNode* newContinueStatement(PropertyName* label, const TokenPos& pos) {
+        return new_<ContinueStatement>(label, pos);
+    }
+
+    ParseNode* newBreakStatement(PropertyName* label, const TokenPos& pos) {
+        return new_<BreakStatement>(label, pos);
+    }
+
+    ParseNode* newReturnStatement(ParseNode* expr, const TokenPos& pos) {
+        MOZ_ASSERT_IF(expr, pos.encloses(expr->pn_pos));
+        return new_<UnaryNode>(PNK_RETURN, JSOP_RETURN, pos, expr);
+    }
+
+    ParseNode* newWithStatement(uint32_t begin, ParseNode* expr, ParseNode* body) {
+        return new_<BinaryNode>(PNK_WITH, JSOP_NOP, TokenPos(begin, body->pn_pos.end),
+                                expr, body);
+    }
+
+    ParseNode* newLabeledStatement(PropertyName* label, ParseNode* stmt, uint32_t begin) {
+        return new_<LabeledStatement>(label, stmt, begin);
+    }
+
+    ParseNode* newThrowStatement(ParseNode* expr, const TokenPos& pos) {
+        MOZ_ASSERT(pos.encloses(expr->pn_pos));
+        return new_<UnaryNode>(PNK_THROW, JSOP_THROW, pos, expr);
+    }
+
+    ParseNode* newTryStatement(uint32_t begin, ParseNode* body, ParseNode* catchList,
+                               ParseNode* finallyBlock) {
+        TokenPos pos(begin, (finallyBlock ? finallyBlock : catchList)->pn_pos.end);
+        return new_<TernaryNode>(PNK_TRY, JSOP_NOP, body, catchList, finallyBlock, pos);
+    }
+
+    ParseNode* newDebuggerStatement(const TokenPos& pos) {
+        return new_<DebuggerStatement>(pos);
+    }
+
+    ParseNode* newPropertyAccess(ParseNode* pn, PropertyName* name, uint32_t end) {
+        return new_<PropertyAccess>(pn, name, pn->pn_pos.begin, end);
+    }
+
+    ParseNode* newPropertyByValue(ParseNode* lhs, ParseNode* index, uint32_t end) {
+        return new_<PropertyByValue>(lhs, index, lhs->pn_pos.begin, end);
+    }
+
+    inline MOZ_MUST_USE bool addCatchBlock(ParseNode* catchList, ParseNode* lexicalScope,
+                                           ParseNode* catchName, ParseNode* catchGuard,
+                                           ParseNode* catchBody);
+
+    inline MOZ_MUST_USE bool setLastFunctionFormalParameterDefault(ParseNode* funcpn,
+                                                                   ParseNode* pn);
+    inline void setLastFunctionFormalParameterDestructuring(ParseNode* funcpn, ParseNode* pn);
+
+    ParseNode* newFunctionDefinition() {
+        return new_<CodeNode>(PNK_FUNCTION, pos());
+    }
+    bool setComprehensionLambdaBody(ParseNode* pn, ParseNode* body) {
+        MOZ_ASSERT(body->isKind(PNK_STATEMENTLIST));
+        ParseNode* paramsBody = newList(PNK_PARAMSBODY, body);
+        if (!paramsBody)
+            return false;
+        setFunctionFormalParametersAndBody(pn, paramsBody);
+        return true;
+    }
+    void setFunctionFormalParametersAndBody(ParseNode* pn, ParseNode* kid) {
+        MOZ_ASSERT_IF(kid, kid->isKind(PNK_PARAMSBODY));
+        pn->pn_body = kid;
+    }
+    void setFunctionBox(ParseNode* pn, FunctionBox* funbox) {
+        MOZ_ASSERT(pn->isKind(PNK_FUNCTION));
+        pn->pn_funbox = funbox;
+        funbox->functionNode = pn;
+    }
+    void addFunctionFormalParameter(ParseNode* pn, ParseNode* argpn) {
+        pn->pn_body->append(argpn);
+    }
+    void setFunctionBody(ParseNode* fn, ParseNode* body) {
+        MOZ_ASSERT(fn->pn_body->isKind(PNK_PARAMSBODY));
+        fn->pn_body->append(body);
+    }
+
+    ParseNode* newModule() {
+        return new_<CodeNode>(PNK_MODULE, pos());
+    }
+
+    ParseNode* newLexicalScope(LexicalScope::Data* bindings, ParseNode* body) {
+        return new_<LexicalScopeNode>(bindings, body);
+    }
+
+    ParseNode* newAssignment(ParseNodeKind kind, ParseNode* lhs, ParseNode* rhs,
+                             JSOp op)
+    {
+        return newBinary(kind, lhs, rhs, op);
+    }
+
+    bool isUnparenthesizedYieldExpression(ParseNode* node) {
+        return node->isKind(PNK_YIELD) && !node->isInParens();
+    }
+
+    bool isUnparenthesizedCommaExpression(ParseNode* node) {
+        return node->isKind(PNK_COMMA) && !node->isInParens();
+    }
+
+    bool isUnparenthesizedAssignment(Node node) {
+        if (node->isKind(PNK_ASSIGN) && !node->isInParens()) {
+            // PNK_ASSIGN is also (mis)used for things like |var name = expr;|.
+            // But this method is only called on actual expressions, so we can
+            // just assert the node's op is the one used for plain assignment.
+            MOZ_ASSERT(node->isOp(JSOP_NOP));
+            return true;
+        }
+
+        return false;
+    }
+
+    bool isUnparenthesizedUnaryExpression(ParseNode* node) {
+        if (!node->isInParens()) {
+            ParseNodeKind kind = node->getKind();
+            return kind == PNK_VOID || kind == PNK_NOT || kind == PNK_BITNOT || kind == PNK_POS ||
+                   kind == PNK_NEG || IsTypeofKind(kind) || IsDeleteKind(kind);
+        }
+        return false;
+    }
+
+    bool isReturnStatement(ParseNode* node) {
+        return node->isKind(PNK_RETURN);
+    }
+
+    bool isStatementPermittedAfterReturnStatement(ParseNode *node) {
+        ParseNodeKind kind = node->getKind();
+        return kind == PNK_FUNCTION || kind == PNK_VAR || kind == PNK_BREAK || kind == PNK_THROW ||
+               (kind == PNK_SEMI && !node->pn_kid);
+    }
+
+    bool isSuperBase(ParseNode* node) {
+        return node->isKind(PNK_SUPERBASE);
+    }
+
+    inline MOZ_MUST_USE bool finishInitializerAssignment(ParseNode* pn, ParseNode* init);
+
+    void setBeginPosition(ParseNode* pn, ParseNode* oth) {
+        setBeginPosition(pn, oth->pn_pos.begin);
+    }
+    void setBeginPosition(ParseNode* pn, uint32_t begin) {
+        pn->pn_pos.begin = begin;
+        MOZ_ASSERT(pn->pn_pos.begin <= pn->pn_pos.end);
+    }
+
+    void setEndPosition(ParseNode* pn, ParseNode* oth) {
+        setEndPosition(pn, oth->pn_pos.end);
+    }
+    void setEndPosition(ParseNode* pn, uint32_t end) {
+        pn->pn_pos.end = end;
+        MOZ_ASSERT(pn->pn_pos.begin <= pn->pn_pos.end);
+    }
+
+    void setPosition(ParseNode* pn, const TokenPos& pos) {
+        pn->pn_pos = pos;
+    }
+    TokenPos getPosition(ParseNode* pn) {
+        return pn->pn_pos;
+    }
+
+    bool isDeclarationKind(ParseNodeKind kind) {
+        return kind == PNK_VAR || kind == PNK_LET || kind == PNK_CONST;
+    }
+
+    ParseNode* newList(ParseNodeKind kind, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(!isDeclarationKind(kind));
+        return new_<ListNode>(kind, op, pos());
+    }
+
+    ParseNode* newList(ParseNodeKind kind, uint32_t begin, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(!isDeclarationKind(kind));
+        return new_<ListNode>(kind, op, TokenPos(begin, begin + 1));
+    }
+
+    ParseNode* newList(ParseNodeKind kind, ParseNode* kid, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(!isDeclarationKind(kind));
+        return new_<ListNode>(kind, op, kid);
+    }
+
+    ParseNode* newDeclarationList(ParseNodeKind kind, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(isDeclarationKind(kind));
+        return new_<ListNode>(kind, op, pos());
+    }
+
+    ParseNode* newDeclarationList(ParseNodeKind kind, ParseNode* kid, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(isDeclarationKind(kind));
+        return new_<ListNode>(kind, op, kid);
+    }
+
+    bool isDeclarationList(ParseNode* node) {
+        return isDeclarationKind(node->getKind());
+    }
+
+    ParseNode* singleBindingFromDeclaration(ParseNode* decl) {
+        MOZ_ASSERT(isDeclarationList(decl));
+        MOZ_ASSERT(decl->pn_count == 1);
+        return decl->pn_head;
+    }
+
+    ParseNode* newCatchList() {
+        return new_<ListNode>(PNK_CATCHLIST, JSOP_NOP, pos());
+    }
+
+    ParseNode* newCommaExpressionList(ParseNode* kid) {
+        return newList(PNK_COMMA, kid, JSOP_NOP);
+    }
+
+    void addList(ParseNode* list, ParseNode* kid) {
+        list->append(kid);
+    }
+
+    void setOp(ParseNode* pn, JSOp op) {
+        pn->setOp(op);
+    }
+    void setListFlag(ParseNode* pn, unsigned flag) {
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        pn->pn_xflags |= flag;
+    }
+    MOZ_MUST_USE ParseNode* parenthesize(ParseNode* pn) {
+        pn->setInParens(true);
+        return pn;
+    }
+    MOZ_MUST_USE ParseNode* setLikelyIIFE(ParseNode* pn) {
+        return parenthesize(pn);
+    }
+    void setPrologue(ParseNode* pn) {
+        pn->pn_prologue = true;
+    }
+
+    bool isConstant(ParseNode* pn) {
+        return pn->isConstant();
+    }
+
+    bool isUnparenthesizedName(ParseNode* node) {
+        return node->isKind(PNK_NAME) && !node->isInParens();
+    }
+
+    bool isNameAnyParentheses(ParseNode* node) {
+        return node->isKind(PNK_NAME);
+    }
+
+    bool nameIsEvalAnyParentheses(ParseNode* node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this function on known names");
+
+        return node->pn_atom == cx->names().eval;
+    }
+
+    const char* nameIsArgumentsEvalAnyParentheses(ParseNode* node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this function on known names");
+
+        if (nameIsEvalAnyParentheses(node, cx))
+            return js_eval_str;
+        if (node->pn_atom == cx->names().arguments)
+            return js_arguments_str;
+        return nullptr;
+    }
+
+    bool nameIsUnparenthesizedAsync(ParseNode* node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this function on known names");
+
+        return node->pn_atom == cx->names().async;
+    }
+
+    bool isCall(ParseNode* pn) {
+        return pn->isKind(PNK_CALL);
+    }
+    PropertyName* maybeDottedProperty(ParseNode* pn) {
+        return pn->is<PropertyAccess>() ? &pn->as<PropertyAccess>().name() : nullptr;
+    }
+    JSAtom* isStringExprStatement(ParseNode* pn, TokenPos* pos) {
+        if (JSAtom* atom = pn->isStringExprStatement()) {
+            *pos = pn->pn_kid->pn_pos;
+            return atom;
+        }
+        return nullptr;
+    }
+
+    void adjustGetToSet(ParseNode* node) {
+        node->setOp(node->isOp(JSOP_GETLOCAL) ? JSOP_SETLOCAL : JSOP_SETNAME);
+    }
+
+    void disableSyntaxParser() {
+        syntaxParser = nullptr;
+    }
+
+    bool canSkipLazyInnerFunctions() {
+        return !!lazyOuterFunction_;
+    }
+    bool canSkipLazyClosedOverBindings() {
+        return !!lazyOuterFunction_;
+    }
+    LazyScript* lazyOuterFunction() {
+        return lazyOuterFunction_;
+    }
+    JSFunction* nextLazyInnerFunction() {
+        MOZ_ASSERT(lazyInnerFunctionIndex < lazyOuterFunction()->numInnerFunctions());
+        return lazyOuterFunction()->innerFunctions()[lazyInnerFunctionIndex++];
+    }
+    JSAtom* nextLazyClosedOverBinding() {
+        MOZ_ASSERT(lazyClosedOverBindingIndex < lazyOuterFunction()->numClosedOverBindings());
+        return lazyOuterFunction()->closedOverBindings()[lazyClosedOverBindingIndex++];
+    }
+};
+
+inline bool
+FullParseHandler::addCatchBlock(ParseNode* catchList, ParseNode* lexicalScope,
+                                ParseNode* catchName, ParseNode* catchGuard, ParseNode* catchBody)
+{
+    ParseNode* catchpn = newTernary(PNK_CATCH, catchName, catchGuard, catchBody);
+    if (!catchpn)
+        return false;
+    catchList->append(lexicalScope);
+    lexicalScope->setScopeBody(catchpn);
+    return true;
+}
+
+inline bool
+FullParseHandler::setLastFunctionFormalParameterDefault(ParseNode* funcpn, ParseNode* defaultValue)
+{
+    ParseNode* arg = funcpn->pn_body->last();
+    ParseNode* pn = newBinary(PNK_ASSIGN, arg, defaultValue, JSOP_NOP);
+    if (!pn)
+        return false;
+
+    funcpn->pn_body->pn_pos.end = pn->pn_pos.end;
+    ParseNode* pnchild = funcpn->pn_body->pn_head;
+    ParseNode* pnlast = funcpn->pn_body->last();
+    MOZ_ASSERT(pnchild);
+    if (pnchild == pnlast) {
+        funcpn->pn_body->pn_head = pn;
+    } else {
+        while (pnchild->pn_next != pnlast) {
+            MOZ_ASSERT(pnchild->pn_next);
+            pnchild = pnchild->pn_next;
+        }
+        pnchild->pn_next = pn;
+    }
+    funcpn->pn_body->pn_tail = &pn->pn_next;
+
+    return true;
+}
+
+inline bool
+FullParseHandler::finishInitializerAssignment(ParseNode* pn, ParseNode* init)
+{
+    pn->pn_expr = init;
+    pn->setOp(JSOP_SETNAME);
+
+    /* The declarator's position must include the initializer. */
+    pn->pn_pos.end = init->pn_pos.end;
+    return true;
+}
+
+} // namespace frontend
+} // namespace js
+
+#endif /* frontend_FullParseHandler_h */
diff --git a/js/src/frontend/NameAnalysisTypes.h b/js/src/frontend/NameAnalysisTypes.h
new file mode 100644
index 0000000000..d39e177fba
--- /dev/null
+++ b/js/src/frontend/NameAnalysisTypes.h
@@ -0,0 +1,366 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_NameAnalysis_h
+#define frontend_NameAnalysis_h
+
+#include "jsopcode.h"
+
+#include "vm/Scope.h"
+
+namespace js {
+
+// An "environment coordinate" describes how to get from head of the
+// environment chain to a given lexically-enclosing variable. An environment
+// coordinate has two dimensions:
+//  - hops: the number of environment objects on the scope chain to skip
+//  - slot: the slot on the environment object holding the variable's value
+class EnvironmentCoordinate
+{
+    uint32_t hops_;
+    uint32_t slot_;
+
+    // Technically, hops_/slot_ are ENVCOORD_(HOPS|SLOT)_BITS wide.  Since
+    // EnvironmentCoordinate is a temporary value, don't bother with a bitfield as
+    // this only adds overhead.
+    static_assert(ENVCOORD_HOPS_BITS <= 32, "We have enough bits below");
+    static_assert(ENVCOORD_SLOT_BITS <= 32, "We have enough bits below");
+
+  public:
+    explicit inline EnvironmentCoordinate(jsbytecode* pc)
+      : hops_(GET_ENVCOORD_HOPS(pc)), slot_(GET_ENVCOORD_SLOT(pc + ENVCOORD_HOPS_LEN))
+    {
+        MOZ_ASSERT(JOF_OPTYPE(JSOp(*pc)) == JOF_ENVCOORD);
+    }
+
+    EnvironmentCoordinate() {}
+
+    void setHops(uint32_t hops) {
+        MOZ_ASSERT(hops < ENVCOORD_HOPS_LIMIT);
+        hops_ = hops;
+    }
+
+    void setSlot(uint32_t slot) {
+        MOZ_ASSERT(slot < ENVCOORD_SLOT_LIMIT);
+        slot_ = slot;
+    }
+
+    uint32_t hops() const {
+        MOZ_ASSERT(hops_ < ENVCOORD_HOPS_LIMIT);
+        return hops_;
+    }
+
+    uint32_t slot() const {
+        MOZ_ASSERT(slot_ < ENVCOORD_SLOT_LIMIT);
+        return slot_;
+    }
+
+    bool operator==(const EnvironmentCoordinate& rhs) const {
+        return hops() == rhs.hops() && slot() == rhs.slot();
+    }
+};
+
+namespace frontend {
+
+// A detailed kind used for tracking declarations in the Parser. Used for
+// specific early error semantics and better error messages.
+enum class DeclarationKind : uint8_t
+{
+    PositionalFormalParameter,
+    FormalParameter,
+    CoverArrowParameter,
+    Var,
+    ForOfVar,
+    Let,
+    Const,
+    Import,
+    BodyLevelFunction,
+    LexicalFunction,
+    VarForAnnexBLexicalFunction,
+    SimpleCatchParameter,
+    CatchParameter
+};
+
+static inline BindingKind
+DeclarationKindToBindingKind(DeclarationKind kind)
+{
+    switch (kind) {
+      case DeclarationKind::PositionalFormalParameter:
+      case DeclarationKind::FormalParameter:
+      case DeclarationKind::CoverArrowParameter:
+        return BindingKind::FormalParameter;
+
+      case DeclarationKind::Var:
+      case DeclarationKind::BodyLevelFunction:
+      case DeclarationKind::VarForAnnexBLexicalFunction:
+      case DeclarationKind::ForOfVar:
+        return BindingKind::Var;
+
+      case DeclarationKind::Let:
+      case DeclarationKind::LexicalFunction:
+      case DeclarationKind::SimpleCatchParameter:
+      case DeclarationKind::CatchParameter:
+        return BindingKind::Let;
+
+      case DeclarationKind::Const:
+        return BindingKind::Const;
+
+      case DeclarationKind::Import:
+        return BindingKind::Import;
+    }
+
+    MOZ_CRASH("Bad DeclarationKind");
+}
+
+static inline bool
+DeclarationKindIsLexical(DeclarationKind kind)
+{
+    return BindingKindIsLexical(DeclarationKindToBindingKind(kind));
+}
+
+// Used in Parser to track declared names.
+class DeclaredNameInfo
+{
+    DeclarationKind kind_;
+
+    // If the declared name is a binding, whether the binding is closed
+    // over. Its value is meaningless if the declared name is not a binding
+    // (i.e., a 'var' declared name in a non-var scope).
+    bool closedOver_;
+
+  public:
+    explicit DeclaredNameInfo(DeclarationKind kind)
+      : kind_(kind),
+        closedOver_(false)
+    { }
+
+    // Needed for InlineMap.
+    DeclaredNameInfo() = default;
+
+    DeclarationKind kind() const {
+        return kind_;
+    }
+
+    void alterKind(DeclarationKind kind) {
+        kind_ = kind;
+    }
+
+    void setClosedOver() {
+        closedOver_ = true;
+    }
+
+    bool closedOver() const {
+        return closedOver_;
+    }
+};
+
+// Used in BytecodeEmitter to map names to locations.
+class NameLocation
+{
+  public:
+    enum class Kind : uint8_t
+    {
+        // Cannot statically determine where the name lives. Needs to walk the
+        // environment chain to search for the name.
+        Dynamic,
+
+        // The name lives on the global or is a global lexical binding. Search
+        // for the name on the global scope.
+        Global,
+
+        // Special mode used only when emitting self-hosted scripts. See
+        // BytecodeEmitter::lookupName.
+        Intrinsic,
+
+        // In a named lambda, the name is the callee itself.
+        NamedLambdaCallee,
+
+        // The name is a positional formal parameter name and can be retrieved
+        // directly from the stack using slot_.
+        ArgumentSlot,
+
+        // The name is not closed over and lives on the frame in slot_.
+        FrameSlot,
+
+        // The name is closed over and lives on an environment hops_ away in slot_.
+        EnvironmentCoordinate,
+
+        // An imported name in a module.
+        Import,
+
+        // Cannot statically determine where the synthesized var for Annex
+        // B.3.3 lives.
+        DynamicAnnexBVar
+    };
+
+  private:
+    // Where the name lives.
+    Kind kind_;
+
+    // If the name is not Dynamic or DynamicAnnexBVar, the kind of the
+    // binding.
+    BindingKind bindingKind_;
+
+    // If the name is closed over and accessed via EnvironmentCoordinate, the
+    // number of dynamic environments to skip.
+    //
+    // Otherwise UINT8_MAX.
+    uint8_t hops_;
+
+    // If the name lives on the frame, the slot frame.
+    //
+    // If the name is closed over and accessed via EnvironmentCoordinate, the
+    // slot on the environment.
+    //
+    // Otherwise LOCALNO_LIMIT/ENVCOORD_SLOT_LIMIT.
+    uint32_t slot_ : ENVCOORD_SLOT_BITS;
+
+    static_assert(LOCALNO_BITS == ENVCOORD_SLOT_BITS,
+                  "Frame and environment slots must be same sized.");
+
+    NameLocation(Kind kind, BindingKind bindingKind,
+                 uint8_t hops = UINT8_MAX, uint32_t slot = ENVCOORD_SLOT_LIMIT)
+      : kind_(kind),
+        bindingKind_(bindingKind),
+        hops_(hops),
+        slot_(slot)
+    { }
+
+  public:
+    // Default constructor for InlineMap.
+    NameLocation() = default;
+
+    static NameLocation Dynamic() {
+        return NameLocation();
+    }
+
+    static NameLocation Global(BindingKind bindKind) {
+        MOZ_ASSERT(bindKind != BindingKind::FormalParameter);
+        return NameLocation(Kind::Global, bindKind);
+    }
+
+    static NameLocation Intrinsic() {
+        return NameLocation(Kind::Intrinsic, BindingKind::Var);
+    }
+
+    static NameLocation NamedLambdaCallee() {
+        return NameLocation(Kind::NamedLambdaCallee, BindingKind::NamedLambdaCallee);
+    }
+
+    static NameLocation ArgumentSlot(uint16_t slot) {
+        return NameLocation(Kind::ArgumentSlot, BindingKind::FormalParameter, 0, slot);
+    }
+
+    static NameLocation FrameSlot(BindingKind bindKind, uint32_t slot) {
+        MOZ_ASSERT(slot < LOCALNO_LIMIT);
+        return NameLocation(Kind::FrameSlot, bindKind, 0, slot);
+    }
+
+    static NameLocation EnvironmentCoordinate(BindingKind bindKind, uint8_t hops, uint32_t slot) {
+        MOZ_ASSERT(slot < ENVCOORD_SLOT_LIMIT);
+        return NameLocation(Kind::EnvironmentCoordinate, bindKind, hops, slot);
+    }
+
+    static NameLocation Import() {
+        return NameLocation(Kind::Import, BindingKind::Import);
+    }
+
+    static NameLocation DynamicAnnexBVar() {
+        return NameLocation(Kind::DynamicAnnexBVar, BindingKind::Var);
+    }
+
+    static NameLocation fromBinding(BindingKind bindKind, const BindingLocation& bl) {
+        switch (bl.kind()) {
+          case BindingLocation::Kind::Global:
+            return Global(bindKind);
+          case BindingLocation::Kind::Argument:
+            return ArgumentSlot(bl.argumentSlot());
+          case BindingLocation::Kind::Frame:
+            return FrameSlot(bindKind, bl.slot());
+          case BindingLocation::Kind::Environment:
+            return EnvironmentCoordinate(bindKind, 0, bl.slot());
+          case BindingLocation::Kind::Import:
+            return Import();
+          case BindingLocation::Kind::NamedLambdaCallee:
+            return NamedLambdaCallee();
+        }
+        MOZ_CRASH("Bad BindingKind");
+    }
+
+    bool operator==(const NameLocation& other) const {
+        return kind_ == other.kind_ && bindingKind_ == other.bindingKind_ &&
+               hops_ == other.hops_ && slot_ == other.slot_;
+    }
+
+    bool operator!=(const NameLocation& other) const {
+        return !(*this == other);
+    }
+
+    Kind kind() const {
+        return kind_;
+    }
+
+    uint16_t argumentSlot() const {
+        MOZ_ASSERT(kind_ == Kind::ArgumentSlot);
+        return mozilla::AssertedCast<uint16_t>(slot_);
+    }
+
+    uint32_t frameSlot() const {
+        MOZ_ASSERT(kind_ == Kind::FrameSlot);
+        return slot_;
+    }
+
+    NameLocation addHops(uint8_t more) {
+        MOZ_ASSERT(hops_ < ENVCOORD_HOPS_LIMIT - more);
+        MOZ_ASSERT(kind_ == Kind::EnvironmentCoordinate);
+        return NameLocation(kind_, bindingKind_, hops_ + more, slot_);
+    }
+
+    class EnvironmentCoordinate environmentCoordinate() const {
+        MOZ_ASSERT(kind_ == Kind::EnvironmentCoordinate);
+        class EnvironmentCoordinate coord;
+        coord.setHops(hops_);
+        coord.setSlot(slot_);
+        return coord;
+    }
+
+    BindingKind bindingKind() const {
+        MOZ_ASSERT(kind_ != Kind::Dynamic);
+        return bindingKind_;
+    }
+
+    bool isLexical() const {
+        return BindingKindIsLexical(bindingKind());
+    }
+
+    bool isConst() const {
+        return bindingKind() == BindingKind::Const;
+    }
+
+    bool hasKnownSlot() const {
+        return kind_ == Kind::ArgumentSlot ||
+               kind_ == Kind::FrameSlot ||
+               kind_ == Kind::EnvironmentCoordinate;
+    }
+};
+
+// This type is declared here for LazyScript::Create.
+using AtomVector = Vector<JSAtom*, 24, SystemAllocPolicy>;
+
+} // namespace frontend
+} // namespace js
+
+namespace mozilla {
+
+template <>
+struct IsPod<js::frontend::DeclaredNameInfo> : TrueType {};
+
+template <>
+struct IsPod<js::frontend::NameLocation> : TrueType {};
+
+} // namespace mozilla
+
+#endif // frontend_NameAnalysis_h
diff --git a/js/src/frontend/NameCollections.h b/js/src/frontend/NameCollections.h
new file mode 100644
index 0000000000..58c5d0ac04
--- /dev/null
+++ b/js/src/frontend/NameCollections.h
@@ -0,0 +1,338 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_NameCollections_h
+#define frontend_NameCollections_h
+
+#include "ds/InlineTable.h"
+#include "frontend/NameAnalysisTypes.h"
+#include "js/Vector.h"
+#include "vm/Stack.h"
+
+namespace js {
+namespace frontend {
+
+// A pool of recyclable containers for use in the frontend. The Parser and
+// BytecodeEmitter create many maps for name analysis that are short-lived
+// (i.e., for the duration of parsing or emitting a lexical scope). Making
+// them recyclable cuts down significantly on allocator churn.
+template <typename RepresentativeCollection, typename ConcreteCollectionPool>
+class CollectionPool
+{
+    using RecyclableCollections = Vector<void*, 32, SystemAllocPolicy>;
+
+    RecyclableCollections all_;
+    RecyclableCollections recyclable_;
+
+    static RepresentativeCollection* asRepresentative(void* p) {
+        return reinterpret_cast<RepresentativeCollection*>(p);
+    }
+
+    RepresentativeCollection* allocate() {
+        size_t newAllLength = all_.length() + 1;
+        if (!all_.reserve(newAllLength) || !recyclable_.reserve(newAllLength))
+            return nullptr;
+
+        RepresentativeCollection* collection = js_new<RepresentativeCollection>();
+        if (collection)
+            all_.infallibleAppend(collection);
+        return collection;
+    }
+
+  public:
+    ~CollectionPool() {
+        purgeAll();
+    }
+
+    bool empty() const {
+        return all_.empty();
+    }
+
+    void purgeAll() {
+        void** end = all_.end();
+        for (void** it = all_.begin(); it != end; ++it)
+            js_delete(asRepresentative(*it));
+
+        all_.clearAndFree();
+        recyclable_.clearAndFree();
+    }
+
+    // Fallibly aquire one of the supported collection types from the pool.
+    template <typename Collection>
+    Collection* acquire(ExclusiveContext* cx) {
+        ConcreteCollectionPool::template assertInvariants<Collection>();
+
+        RepresentativeCollection* collection;
+        if (recyclable_.empty()) {
+            collection = allocate();
+            if (!collection)
+                ReportOutOfMemory(cx);
+        } else {
+            collection = asRepresentative(recyclable_.popCopy());
+            collection->clear();
+        }
+        return reinterpret_cast<Collection*>(collection);
+    }
+
+    // Release a collection back to the pool.
+    template <typename Collection>
+    void release(Collection** collection) {
+        ConcreteCollectionPool::template assertInvariants<Collection>();
+        MOZ_ASSERT(*collection);
+
+#ifdef DEBUG
+        bool ok = false;
+        // Make sure the collection is in |all_| but not already in |recyclable_|.
+        for (void** it = all_.begin(); it != all_.end(); ++it) {
+            if (*it == *collection) {
+                ok = true;
+                break;
+            }
+        }
+        MOZ_ASSERT(ok);
+        for (void** it = recyclable_.begin(); it != recyclable_.end(); ++it)
+            MOZ_ASSERT(*it != *collection);
+#endif
+
+        MOZ_ASSERT(recyclable_.length() < all_.length());
+        // Reserved in allocateFresh.
+        recyclable_.infallibleAppend(*collection);
+        *collection = nullptr;
+    }
+};
+
+template <typename Wrapped>
+struct RecyclableAtomMapValueWrapper
+{
+    union {
+        Wrapped wrapped;
+        uint64_t dummy;
+    };
+
+    static void assertInvariant() {
+        static_assert(sizeof(Wrapped) <= sizeof(uint64_t),
+                      "Can only recycle atom maps with values smaller than uint64");
+    }
+
+    RecyclableAtomMapValueWrapper() {
+        assertInvariant();
+    }
+
+    MOZ_IMPLICIT RecyclableAtomMapValueWrapper(Wrapped w)
+      : wrapped(w)
+    {
+        assertInvariant();
+    }
+
+    MOZ_IMPLICIT operator Wrapped&() {
+        return wrapped;
+    }
+
+    MOZ_IMPLICIT operator Wrapped&() const {
+        return wrapped;
+    }
+
+    Wrapped* operator->() {
+        return &wrapped;
+    }
+
+    const Wrapped* operator->() const {
+        return &wrapped;
+    }
+};
+
+template <typename MapValue>
+using RecyclableNameMap = InlineMap<JSAtom*,
+                                    RecyclableAtomMapValueWrapper<MapValue>,
+                                    24,
+                                    DefaultHasher<JSAtom*>,
+                                    SystemAllocPolicy>;
+
+using DeclaredNameMap = RecyclableNameMap<DeclaredNameInfo>;
+using CheckTDZMap = RecyclableNameMap<MaybeCheckTDZ>;
+using NameLocationMap = RecyclableNameMap<NameLocation>;
+using AtomIndexMap = RecyclableNameMap<uint32_t>;
+
+#undef RECYCLABLE_NAME_MAP_TYPE
+
+template <typename RepresentativeTable>
+class InlineTablePool
+  : public CollectionPool<RepresentativeTable, InlineTablePool<RepresentativeTable>>
+{
+  public:
+    template <typename Table>
+    static void assertInvariants() {
+        static_assert(Table::SizeOfInlineEntries == RepresentativeTable::SizeOfInlineEntries,
+                      "Only tables with the same size for inline entries are usable in the pool.");
+        static_assert(mozilla::IsPod<typename Table::Table::Entry>::value,
+                      "Only tables with POD values are usable in the pool.");
+    }
+};
+
+using FunctionBoxVector = Vector<FunctionBox*, 24, SystemAllocPolicy>;
+
+template <typename RepresentativeVector>
+class VectorPool : public CollectionPool<RepresentativeVector, VectorPool<RepresentativeVector>>
+{
+  public:
+    template <typename Vector>
+    static void assertInvariants() {
+        static_assert(Vector::sMaxInlineStorage == RepresentativeVector::sMaxInlineStorage,
+                      "Only vectors with the same size for inline entries are usable in the pool.");
+        static_assert(mozilla::IsPod<typename Vector::ElementType>::value,
+                      "Only vectors of POD values are usable in the pool.");
+        static_assert(sizeof(typename Vector::ElementType) ==
+                      sizeof(typename RepresentativeVector::ElementType),
+                      "Only vectors with same-sized elements are usable in the pool.");
+    }
+};
+
+class NameCollectionPool
+{
+    InlineTablePool<AtomIndexMap> mapPool_;
+    VectorPool<AtomVector> vectorPool_;
+    uint32_t activeCompilations_;
+
+  public:
+    NameCollectionPool()
+      : activeCompilations_(0)
+    { }
+
+    bool hasActiveCompilation() const {
+        return activeCompilations_ != 0;
+    }
+
+    void addActiveCompilation() {
+        activeCompilations_++;
+    }
+
+    void removeActiveCompilation() {
+        MOZ_ASSERT(hasActiveCompilation());
+        activeCompilations_--;
+    }
+
+    template <typename Map>
+    Map* acquireMap(ExclusiveContext* cx) {
+        MOZ_ASSERT(hasActiveCompilation());
+        return mapPool_.acquire<Map>(cx);
+    }
+
+    template <typename Map>
+    void releaseMap(Map** map) {
+        MOZ_ASSERT(hasActiveCompilation());
+        MOZ_ASSERT(map);
+        if (*map)
+            mapPool_.release(map);
+    }
+
+    template <typename Vector>
+    Vector* acquireVector(ExclusiveContext* cx) {
+        MOZ_ASSERT(hasActiveCompilation());
+        return vectorPool_.acquire<Vector>(cx);
+    }
+
+    template <typename Vector>
+    void releaseVector(Vector** vec) {
+        MOZ_ASSERT(hasActiveCompilation());
+        MOZ_ASSERT(vec);
+        if (*vec)
+            vectorPool_.release(vec);
+    }
+
+    void purge() {
+        if (!hasActiveCompilation()) {
+            mapPool_.purgeAll();
+            vectorPool_.purgeAll();
+        }
+    }
+};
+
+#define POOLED_COLLECTION_PTR_METHODS(N, T)                       \
+    NameCollectionPool& pool_;                                    \
+    T* collection_;                                               \
+                                                                  \
+    T& collection() {                                             \
+        MOZ_ASSERT(collection_);                                  \
+        return *collection_;                                      \
+    }                                                             \
+                                                                  \
+    const T& collection() const {                                 \
+        MOZ_ASSERT(collection_);                                  \
+        return *collection_;                                      \
+    }                                                             \
+                                                                  \
+  public:                                                         \
+    explicit N(NameCollectionPool& pool)                          \
+      : pool_(pool),                                              \
+        collection_(nullptr)                                      \
+    { }                                                           \
+                                                                  \
+    ~N() {                                                        \
+        pool_.release##T(&collection_);                           \
+    }                                                             \
+                                                                  \
+    bool acquire(ExclusiveContext* cx) {                          \
+        MOZ_ASSERT(!collection_);                                 \
+        collection_ = pool_.acquire##T<T>(cx);                    \
+        return !!collection_;                                     \
+    }                                                             \
+                                                                  \
+    explicit operator bool() const {                              \
+        return !!collection_;                                     \
+    }                                                             \
+                                                                  \
+    T* operator->() {                                             \
+        return &collection();                                     \
+    }                                                             \
+                                                                  \
+    const T* operator->() const {                                 \
+        return &collection();                                     \
+    }                                                             \
+                                                                  \
+    T& operator*() {                                              \
+        return collection();                                      \
+    }                                                             \
+                                                                  \
+    const T& operator*() const {                                  \
+        return collection();                                      \
+    }
+
+template <typename Map>
+class PooledMapPtr
+{
+    POOLED_COLLECTION_PTR_METHODS(PooledMapPtr, Map)
+};
+
+template <typename Vector>
+class PooledVectorPtr
+{
+    POOLED_COLLECTION_PTR_METHODS(PooledVectorPtr, Vector)
+
+    typename Vector::ElementType& operator[](size_t index) {
+        return collection()[index];
+    }
+
+    const typename Vector::ElementType& operator[](size_t index) const {
+        return collection()[index];
+    }
+};
+
+#undef POOLED_COLLECTION_PTR_METHODS
+
+} // namespace frontend
+} // namespace js
+
+namespace mozilla {
+
+template <>
+struct IsPod<js::MaybeCheckTDZ> : TrueType {};
+
+template <typename T>
+struct IsPod<js::frontend::RecyclableAtomMapValueWrapper<T>> : IsPod<T> {};
+
+} // namespace mozilla
+
+#endif // frontend_NameCollections_h
diff --git a/js/src/frontend/NameFunctions.cpp b/js/src/frontend/NameFunctions.cpp
new file mode 100644
index 0000000000..ce1318f0b1
--- /dev/null
+++ b/js/src/frontend/NameFunctions.cpp
@@ -0,0 +1,838 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "frontend/NameFunctions.h"
+
+#include "mozilla/Sprintf.h"
+
+#include "jsfun.h"
+#include "jsprf.h"
+
+#include "frontend/BytecodeCompiler.h"
+#include "frontend/ParseNode.h"
+#include "frontend/SharedContext.h"
+#include "vm/StringBuffer.h"
+
+using namespace js;
+using namespace js::frontend;
+
+namespace {
+
+class NameResolver
+{
+    static const size_t MaxParents = 100;
+
+    ExclusiveContext* cx;
+    size_t nparents;                /* number of parents in the parents array */
+    ParseNode* parents[MaxParents]; /* history of ParseNodes we've been looking at */
+    StringBuffer* buf;              /* when resolving, buffer to append to */
+
+    /* Test whether a ParseNode represents a function invocation */
+    bool call(ParseNode* pn) {
+        return pn && pn->isKind(PNK_CALL);
+    }
+
+    /*
+     * Append a reference to a property named |name| to |buf|. If |name| is
+     * a proper identifier name, then we append '.name'; otherwise, we
+     * append '["name"]'.
+     *
+     * Note that we need the IsIdentifier check for atoms from both
+     * PNK_NAME nodes and PNK_STRING nodes: given code like a["b c"], the
+     * front end will produce a PNK_DOT with a PNK_NAME child whose name
+     * contains spaces.
+     */
+    bool appendPropertyReference(JSAtom* name) {
+        if (IsIdentifier(name))
+            return buf->append('.') && buf->append(name);
+
+        /* Quote the string as needed. */
+        JSString* source = QuoteString(cx, name, '"');
+        return source && buf->append('[') && buf->append(source) && buf->append(']');
+    }
+
+    /* Append a number to buf. */
+    bool appendNumber(double n) {
+        char number[30];
+        int digits = SprintfLiteral(number, "%g", n);
+        return buf->append(number, digits);
+    }
+
+    /* Append "[<n>]" to buf, referencing a property named by a numeric literal. */
+    bool appendNumericPropertyReference(double n) {
+        return buf->append("[") && appendNumber(n) && buf->append(']');
+    }
+
+    /*
+     * Walk over the given ParseNode, attempting to convert it to a stringified
+     * name that respresents where the function is being assigned to.
+     *
+     * |*foundName| is set to true if a name is found for the expression.
+     */
+    bool nameExpression(ParseNode* n, bool* foundName) {
+        switch (n->getKind()) {
+          case PNK_DOT:
+            if (!nameExpression(n->expr(), foundName))
+                return false;
+            if (!*foundName)
+                return true;
+            return appendPropertyReference(n->pn_atom);
+
+          case PNK_NAME:
+            *foundName = true;
+            return buf->append(n->pn_atom);
+
+          case PNK_THIS:
+            *foundName = true;
+            return buf->append("this");
+
+          case PNK_ELEM:
+            if (!nameExpression(n->pn_left, foundName))
+                return false;
+            if (!*foundName)
+                return true;
+            if (!buf->append('[') || !nameExpression(n->pn_right, foundName))
+                return false;
+            if (!*foundName)
+                return true;
+            return buf->append(']');
+
+          case PNK_NUMBER:
+            *foundName = true;
+            return appendNumber(n->pn_dval);
+
+          default:
+            /* We're confused as to what to call this function. */
+            *foundName = false;
+            return true;
+        }
+    }
+
+    /*
+     * When naming an anonymous function, the process works loosely by walking
+     * up the AST and then translating that to a string. The stringification
+     * happens from some far-up assignment and then going back down the parse
+     * tree to the function definition point.
+     *
+     * This function will walk up the parse tree, gathering relevant nodes used
+     * for naming, and return the assignment node if there is one. The provided
+     * array and size will be filled in, and the returned node could be nullptr
+     * if no assignment is found. The first element of the array will be the
+     * innermost node relevant to naming, and the last element will be the
+     * outermost node.
+     */
+    ParseNode* gatherNameable(ParseNode** nameable, size_t* size) {
+        *size = 0;
+
+        for (int pos = nparents - 1; pos >= 0; pos--) {
+            ParseNode* cur = parents[pos];
+            if (cur->isAssignment())
+                return cur;
+
+            switch (cur->getKind()) {
+              case PNK_NAME:     return cur;  /* found the initialized declaration */
+              case PNK_THIS:     return cur;  /* Setting a property of 'this'. */
+              case PNK_FUNCTION: return nullptr; /* won't find an assignment or declaration */
+
+              case PNK_RETURN:
+                /*
+                 * Normally the relevant parent of a node is its direct parent, but
+                 * sometimes with code like:
+                 *
+                 *    var foo = (function() { return function() {}; })();
+                 *
+                 * the outer function is just a helper to create a scope for the
+                 * returned function. Hence the name of the returned function should
+                 * actually be 'foo'.  This loop sees if the current node is a
+                 * PNK_RETURN, and if there is a direct function call we skip to
+                 * that.
+                 */
+                for (int tmp = pos - 1; tmp > 0; tmp--) {
+                    if (isDirectCall(tmp, cur)) {
+                        pos = tmp;
+                        break;
+                    } else if (call(cur)) {
+                        /* Don't skip too high in the tree */
+                        break;
+                    }
+                    cur = parents[tmp];
+                }
+                break;
+
+              case PNK_COLON:
+              case PNK_SHORTHAND:
+                /*
+                 * Record the PNK_COLON/SHORTHAND but skip the PNK_OBJECT so we're not
+                 * flagged as a contributor.
+                 */
+                pos--;
+                MOZ_FALLTHROUGH;
+
+              default:
+                /* Save any other nodes we encounter on the way up. */
+                MOZ_ASSERT(*size < MaxParents);
+                nameable[(*size)++] = cur;
+                break;
+            }
+        }
+
+        return nullptr;
+    }
+
+    /*
+     * Resolve the name of a function. If the function already has a name
+     * listed, then it is skipped. Otherwise an intelligent name is guessed to
+     * assign to the function's displayAtom field.
+     */
+    bool resolveFun(ParseNode* pn, HandleAtom prefix, MutableHandleAtom retAtom) {
+        MOZ_ASSERT(pn != nullptr);
+        MOZ_ASSERT(pn->isKind(PNK_FUNCTION));
+        MOZ_ASSERT(pn->isArity(PN_CODE));
+        RootedFunction fun(cx, pn->pn_funbox->function());
+
+        StringBuffer buf(cx);
+        this->buf = &buf;
+
+        retAtom.set(nullptr);
+
+        /* If the function already has a name, use that */
+        if (fun->displayAtom() != nullptr) {
+            if (prefix == nullptr) {
+                retAtom.set(fun->displayAtom());
+                return true;
+            }
+            if (!buf.append(prefix) ||
+                !buf.append('/') ||
+                !buf.append(fun->displayAtom()))
+                return false;
+            retAtom.set(buf.finishAtom());
+            return !!retAtom;
+        }
+
+        /* If a prefix is specified, then it is a form of namespace */
+        if (prefix != nullptr && (!buf.append(prefix) || !buf.append('/')))
+            return false;
+
+        /* Gather all nodes relevant to naming */
+        ParseNode* toName[MaxParents];
+        size_t size;
+        ParseNode* assignment = gatherNameable(toName, &size);
+
+        /* If the function is assigned to something, then that is very relevant */
+        if (assignment) {
+            if (assignment->isAssignment())
+                assignment = assignment->pn_left;
+            bool foundName = false;
+            if (!nameExpression(assignment, &foundName))
+                return false;
+            if (!foundName)
+                return true;
+        }
+
+        /*
+         * Other than the actual assignment, other relevant nodes to naming are
+         * those in object initializers and then particular nodes marking a
+         * contribution.
+         */
+        for (int pos = size - 1; pos >= 0; pos--) {
+            ParseNode* node = toName[pos];
+
+            if (node->isKind(PNK_COLON) || node->isKind(PNK_SHORTHAND)) {
+                ParseNode* left = node->pn_left;
+                if (left->isKind(PNK_OBJECT_PROPERTY_NAME) || left->isKind(PNK_STRING)) {
+                    if (!appendPropertyReference(left->pn_atom))
+                        return false;
+                } else if (left->isKind(PNK_NUMBER)) {
+                    if (!appendNumericPropertyReference(left->pn_dval))
+                        return false;
+                } else {
+                    MOZ_ASSERT(left->isKind(PNK_COMPUTED_NAME));
+                }
+            } else {
+                /*
+                 * Don't have consecutive '<' characters, and also don't start
+                 * with a '<' character.
+                 */
+                if (!buf.empty() && buf.getChar(buf.length() - 1) != '<' && !buf.append('<'))
+                    return false;
+            }
+        }
+
+        /*
+         * functions which are "genuinely anonymous" but are contained in some
+         * other namespace are rather considered as "contributing" to the outer
+         * function, so give them a contribution symbol here.
+         */
+        if (!buf.empty() && buf.getChar(buf.length() - 1) == '/' && !buf.append('<'))
+            return false;
+
+        if (buf.empty())
+            return true;
+
+        retAtom.set(buf.finishAtom());
+        if (!retAtom)
+            return false;
+        fun->setGuessedAtom(retAtom);
+        return true;
+    }
+
+    /*
+     * Tests whether parents[pos] is a function call whose callee is cur.
+     * This is the case for functions which do things like simply create a scope
+     * for new variables and then return an anonymous function using this scope.
+     */
+    bool isDirectCall(int pos, ParseNode* cur) {
+        return pos >= 0 && call(parents[pos]) && parents[pos]->pn_head == cur;
+    }
+
+    bool resolveTemplateLiteral(ParseNode* node, HandleAtom prefix) {
+        MOZ_ASSERT(node->isKind(PNK_TEMPLATE_STRING_LIST));
+        ParseNode* element = node->pn_head;
+        while (true) {
+            MOZ_ASSERT(element->isKind(PNK_TEMPLATE_STRING));
+
+            element = element->pn_next;
+            if (!element)
+                return true;
+
+            if (!resolve(element, prefix))
+                return false;
+
+            element = element->pn_next;
+        }
+    }
+
+    bool resolveTaggedTemplate(ParseNode* node, HandleAtom prefix) {
+        MOZ_ASSERT(node->isKind(PNK_TAGGED_TEMPLATE));
+
+        ParseNode* element = node->pn_head;
+
+        // The list head is a leading expression, e.g. |tag| in |tag`foo`|,
+        // that might contain functions.
+        if (!resolve(element, prefix))
+            return false;
+
+        // Next is the callsite object node.  This node only contains
+        // internal strings and an array -- no user-controlled expressions.
+        element = element->pn_next;
+#ifdef DEBUG
+        {
+            MOZ_ASSERT(element->isKind(PNK_CALLSITEOBJ));
+            ParseNode* array = element->pn_head;
+            MOZ_ASSERT(array->isKind(PNK_ARRAY));
+            for (ParseNode* kid = array->pn_head; kid; kid = kid->pn_next)
+                MOZ_ASSERT(kid->isKind(PNK_TEMPLATE_STRING));
+            for (ParseNode* next = array->pn_next; next; next = next->pn_next)
+                MOZ_ASSERT(next->isKind(PNK_TEMPLATE_STRING));
+        }
+#endif
+
+        // Next come any interpolated expressions in the tagged template.
+        ParseNode* interpolated = element->pn_next;
+        for (; interpolated; interpolated = interpolated->pn_next) {
+            if (!resolve(interpolated, prefix))
+                return false;
+        }
+
+        return true;
+    }
+
+  public:
+    explicit NameResolver(ExclusiveContext* cx) : cx(cx), nparents(0), buf(nullptr) {}
+
+    /*
+     * Resolve all names for anonymous functions recursively within the
+     * ParseNode instance given. The prefix is for each subsequent name, and
+     * should initially be nullptr.
+     */
+    bool resolve(ParseNode* cur, HandleAtom prefixArg = nullptr) {
+        RootedAtom prefix(cx, prefixArg);
+        if (cur == nullptr)
+            return true;
+
+        MOZ_ASSERT((cur->isKind(PNK_FUNCTION) || cur->isKind(PNK_MODULE)) == cur->isArity(PN_CODE));
+        if (cur->isKind(PNK_FUNCTION)) {
+            RootedAtom prefix2(cx);
+            if (!resolveFun(cur, prefix, &prefix2))
+                return false;
+
+            /*
+             * If a function looks like (function(){})() where the parent node
+             * of the definition of the function is a call, then it shouldn't
+             * contribute anything to the namespace, so don't bother updating
+             * the prefix to whatever was returned.
+             */
+            if (!isDirectCall(nparents - 1, cur))
+                prefix = prefix2;
+        }
+        if (nparents >= MaxParents)
+            return true;
+        parents[nparents++] = cur;
+
+        switch (cur->getKind()) {
+          // Nodes with no children that might require name resolution need no
+          // further work.
+          case PNK_NOP:
+          case PNK_STRING:
+          case PNK_TEMPLATE_STRING:
+          case PNK_REGEXP:
+          case PNK_TRUE:
+          case PNK_FALSE:
+          case PNK_NULL:
+          case PNK_ELISION:
+          case PNK_GENERATOR:
+          case PNK_NUMBER:
+          case PNK_BREAK:
+          case PNK_CONTINUE:
+          case PNK_DEBUGGER:
+          case PNK_EXPORT_BATCH_SPEC:
+          case PNK_OBJECT_PROPERTY_NAME:
+          case PNK_POSHOLDER:
+            MOZ_ASSERT(cur->isArity(PN_NULLARY));
+            break;
+
+          case PNK_TYPEOFNAME:
+          case PNK_SUPERBASE:
+            MOZ_ASSERT(cur->isArity(PN_UNARY));
+            MOZ_ASSERT(cur->pn_kid->isKind(PNK_NAME));
+            MOZ_ASSERT(!cur->pn_kid->expr());
+            break;
+
+          case PNK_NEWTARGET:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            MOZ_ASSERT(cur->pn_left->isKind(PNK_POSHOLDER));
+            MOZ_ASSERT(cur->pn_right->isKind(PNK_POSHOLDER));
+            break;
+
+          // Nodes with a single non-null child requiring name resolution.
+          case PNK_TYPEOFEXPR:
+          case PNK_VOID:
+          case PNK_NOT:
+          case PNK_BITNOT:
+          case PNK_THROW:
+          case PNK_DELETENAME:
+          case PNK_DELETEPROP:
+          case PNK_DELETEELEM:
+          case PNK_DELETEEXPR:
+          case PNK_NEG:
+          case PNK_POS:
+          case PNK_PREINCREMENT:
+          case PNK_POSTINCREMENT:
+          case PNK_PREDECREMENT:
+          case PNK_POSTDECREMENT:
+          case PNK_COMPUTED_NAME:
+          case PNK_ARRAYPUSH:
+          case PNK_SPREAD:
+          case PNK_MUTATEPROTO:
+          case PNK_EXPORT:
+            MOZ_ASSERT(cur->isArity(PN_UNARY));
+            if (!resolve(cur->pn_kid, prefix))
+                return false;
+            break;
+
+          // Nodes with a single nullable child.
+          case PNK_SEMI:
+          case PNK_THIS:
+            MOZ_ASSERT(cur->isArity(PN_UNARY));
+            if (ParseNode* expr = cur->pn_kid) {
+                if (!resolve(expr, prefix))
+                    return false;
+            }
+            break;
+
+          // Binary nodes with two non-null children.
+          case PNK_ASSIGN:
+          case PNK_ADDASSIGN:
+          case PNK_SUBASSIGN:
+          case PNK_BITORASSIGN:
+          case PNK_BITXORASSIGN:
+          case PNK_BITANDASSIGN:
+          case PNK_LSHASSIGN:
+          case PNK_RSHASSIGN:
+          case PNK_URSHASSIGN:
+          case PNK_MULASSIGN:
+          case PNK_DIVASSIGN:
+          case PNK_MODASSIGN:
+          case PNK_POWASSIGN:
+          case PNK_COLON:
+          case PNK_SHORTHAND:
+          case PNK_DOWHILE:
+          case PNK_WHILE:
+          case PNK_SWITCH:
+          case PNK_FOR:
+          case PNK_COMPREHENSIONFOR:
+          case PNK_CLASSMETHOD:
+          case PNK_SETTHIS:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            if (!resolve(cur->pn_left, prefix))
+                return false;
+            if (!resolve(cur->pn_right, prefix))
+                return false;
+            break;
+
+          case PNK_ELEM:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            if (!cur->as<PropertyByValue>().isSuper() && !resolve(cur->pn_left, prefix))
+                return false;
+            if (!resolve(cur->pn_right, prefix))
+                return false;
+            break;
+
+          case PNK_WITH:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            if (!resolve(cur->pn_left, prefix))
+                return false;
+            if (!resolve(cur->pn_right, prefix))
+                return false;
+            break;
+
+          case PNK_CASE:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            if (ParseNode* caseExpr = cur->pn_left) {
+                if (!resolve(caseExpr, prefix))
+                    return false;
+            }
+            if (!resolve(cur->pn_right, prefix))
+                return false;
+            break;
+
+          case PNK_YIELD_STAR:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            MOZ_ASSERT(cur->pn_right->isKind(PNK_NAME));
+            if (!resolve(cur->pn_left, prefix))
+                return false;
+            break;
+
+          case PNK_YIELD:
+          case PNK_AWAIT:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            if (cur->pn_left) {
+                if (!resolve(cur->pn_left, prefix))
+                    return false;
+            }
+            MOZ_ASSERT(cur->pn_right->isKind(PNK_NAME) ||
+                       (cur->pn_right->isKind(PNK_ASSIGN) &&
+                        cur->pn_right->pn_left->isKind(PNK_NAME) &&
+                        cur->pn_right->pn_right->isKind(PNK_GENERATOR)));
+            break;
+
+          case PNK_RETURN:
+            MOZ_ASSERT(cur->isArity(PN_UNARY));
+            if (ParseNode* returnValue = cur->pn_kid) {
+                if (!resolve(returnValue, prefix))
+                    return false;
+            }
+            break;
+
+          case PNK_IMPORT:
+          case PNK_EXPORT_FROM:
+          case PNK_EXPORT_DEFAULT:
+            MOZ_ASSERT(cur->isArity(PN_BINARY));
+            // The left halves of these nodes don't contain any unconstrained
+            // expressions, but it's very hard to assert this to safely rely on
+            // it.  So recur anyway.
+            if (!resolve(cur->pn_left, prefix))
+                return false;
+            MOZ_ASSERT_IF(!cur->isKind(PNK_EXPORT_DEFAULT),
+                          cur->pn_right->isKind(PNK_STRING));
+            break;
+
+          // Ternary nodes with three expression children.
+          case PNK_CONDITIONAL:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (!resolve(cur->pn_kid1, prefix))
+                return false;
+            if (!resolve(cur->pn_kid2, prefix))
+                return false;
+            if (!resolve(cur->pn_kid3, prefix))
+                return false;
+            break;
+
+          // The first part of a for-in/of is the declaration in the loop (or
+          // null if no declaration).  The latter two parts are the location
+          // assigned each loop and the value being looped over; obviously,
+          // either might contain functions to name.  Declarations may (through
+          // computed property names, and possibly through [deprecated!]
+          // initializers) also contain functions to name.
+          case PNK_FORIN:
+          case PNK_FOROF:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (ParseNode* decl = cur->pn_kid1) {
+                if (!resolve(decl, prefix))
+                    return false;
+            }
+            if (!resolve(cur->pn_kid2, prefix))
+                return false;
+            if (!resolve(cur->pn_kid3, prefix))
+                return false;
+            break;
+
+          // Every part of a for(;;) head may contain a function needing name
+          // resolution.
+          case PNK_FORHEAD:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (ParseNode* init = cur->pn_kid1) {
+                if (!resolve(init, prefix))
+                    return false;
+            }
+            if (ParseNode* cond = cur->pn_kid2) {
+                if (!resolve(cond, prefix))
+                    return false;
+            }
+            if (ParseNode* step = cur->pn_kid3) {
+                if (!resolve(step, prefix))
+                    return false;
+            }
+            break;
+
+          // The first child of a class is a pair of names referring to it,
+          // inside and outside the class.  The second is the class's heritage,
+          // if any.  The third is the class body.
+          case PNK_CLASS:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            MOZ_ASSERT_IF(cur->pn_kid1, cur->pn_kid1->isKind(PNK_CLASSNAMES));
+            MOZ_ASSERT_IF(cur->pn_kid1, cur->pn_kid1->isArity(PN_BINARY));
+            MOZ_ASSERT_IF(cur->pn_kid1 && cur->pn_kid1->pn_left,
+                          cur->pn_kid1->pn_left->isKind(PNK_NAME));
+            MOZ_ASSERT_IF(cur->pn_kid1 && cur->pn_kid1->pn_left,
+                          !cur->pn_kid1->pn_left->expr());
+            MOZ_ASSERT_IF(cur->pn_kid1, cur->pn_kid1->pn_right->isKind(PNK_NAME));
+            MOZ_ASSERT_IF(cur->pn_kid1, !cur->pn_kid1->pn_right->expr());
+            if (cur->pn_kid2) {
+                if (!resolve(cur->pn_kid2, prefix))
+                    return false;
+            }
+            if (!resolve(cur->pn_kid3, prefix))
+                return false;
+            break;
+
+          // The condition and consequent are non-optional, but the alternative
+          // might be omitted.
+          case PNK_IF:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (!resolve(cur->pn_kid1, prefix))
+                return false;
+            if (!resolve(cur->pn_kid2, prefix))
+                return false;
+            if (cur->pn_kid3) {
+                if (!resolve(cur->pn_kid3, prefix))
+                    return false;
+            }
+            break;
+
+          // The statements in the try-block are mandatory.  The catch-blocks
+          // and finally block are optional (but at least one or the other must
+          // be present).
+          case PNK_TRY:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (!resolve(cur->pn_kid1, prefix))
+                return false;
+            MOZ_ASSERT(cur->pn_kid2 || cur->pn_kid3);
+            if (ParseNode* catchList = cur->pn_kid2) {
+                MOZ_ASSERT(catchList->isKind(PNK_CATCHLIST));
+                if (!resolve(catchList, prefix))
+                    return false;
+            }
+            if (ParseNode* finallyBlock = cur->pn_kid3) {
+                if (!resolve(finallyBlock, prefix))
+                    return false;
+            }
+            break;
+
+          // The first child, the catch-pattern, may contain functions via
+          // computed property names.  The optional catch-conditions may
+          // contain any expression.  The catch statements, of course, may
+          // contain arbitrary expressions.
+          case PNK_CATCH:
+            MOZ_ASSERT(cur->isArity(PN_TERNARY));
+            if (!resolve(cur->pn_kid1, prefix))
+                return false;
+            if (cur->pn_kid2) {
+                if (!resolve(cur->pn_kid2, prefix))
+                    return false;
+            }
+            if (!resolve(cur->pn_kid3, prefix))
+                return false;
+            break;
+
+          // Nodes with arbitrary-expression children.
+          case PNK_OR:
+          case PNK_AND:
+          case PNK_BITOR:
+          case PNK_BITXOR:
+          case PNK_BITAND:
+          case PNK_STRICTEQ:
+          case PNK_EQ:
+          case PNK_STRICTNE:
+          case PNK_NE:
+          case PNK_LT:
+          case PNK_LE:
+          case PNK_GT:
+          case PNK_GE:
+          case PNK_INSTANCEOF:
+          case PNK_IN:
+          case PNK_LSH:
+          case PNK_RSH:
+          case PNK_URSH:
+          case PNK_ADD:
+          case PNK_SUB:
+          case PNK_STAR:
+          case PNK_DIV:
+          case PNK_MOD:
+          case PNK_POW:
+          case PNK_COMMA:
+          case PNK_NEW:
+          case PNK_CALL:
+          case PNK_SUPERCALL:
+          case PNK_GENEXP:
+          case PNK_ARRAY:
+          case PNK_STATEMENTLIST:
+          case PNK_PARAMSBODY:
+          // Initializers for individual variables, and computed property names
+          // within destructuring patterns, may contain unnamed functions.
+          case PNK_VAR:
+          case PNK_CONST:
+          case PNK_LET:
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            for (ParseNode* element = cur->pn_head; element; element = element->pn_next) {
+                if (!resolve(element, prefix))
+                    return false;
+            }
+            break;
+
+          // Array comprehension nodes are lists with a single child:
+          // PNK_COMPREHENSIONFOR for comprehensions, PNK_LEXICALSCOPE for
+          // legacy comprehensions.  Probably this should be a non-list
+          // eventually.
+          case PNK_ARRAYCOMP:
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            MOZ_ASSERT(cur->pn_count == 1);
+            MOZ_ASSERT(cur->pn_head->isKind(PNK_LEXICALSCOPE) ||
+                       cur->pn_head->isKind(PNK_COMPREHENSIONFOR));
+            if (!resolve(cur->pn_head, prefix))
+                return false;
+            break;
+
+          case PNK_OBJECT:
+          case PNK_CLASSMETHODLIST:
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            for (ParseNode* element = cur->pn_head; element; element = element->pn_next) {
+                if (!resolve(element, prefix))
+                    return false;
+            }
+            break;
+
+          // A template string list's contents alternate raw template string
+          // contents with expressions interpolated into the overall literal.
+          case PNK_TEMPLATE_STRING_LIST:
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            if (!resolveTemplateLiteral(cur, prefix))
+                return false;
+            break;
+
+          case PNK_TAGGED_TEMPLATE:
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            if (!resolveTaggedTemplate(cur, prefix))
+                return false;
+            break;
+
+          // Import/export spec lists contain import/export specs containing
+          // only pairs of names. Alternatively, an export spec lists may
+          // contain a single export batch specifier.
+          case PNK_EXPORT_SPEC_LIST:
+          case PNK_IMPORT_SPEC_LIST: {
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+#ifdef DEBUG
+            bool isImport = cur->isKind(PNK_IMPORT_SPEC_LIST);
+            ParseNode* item = cur->pn_head;
+            if (!isImport && item && item->isKind(PNK_EXPORT_BATCH_SPEC)) {
+                MOZ_ASSERT(item->isArity(PN_NULLARY));
+                break;
+            }
+            for (; item; item = item->pn_next) {
+                MOZ_ASSERT(item->isKind(isImport ? PNK_IMPORT_SPEC : PNK_EXPORT_SPEC));
+                MOZ_ASSERT(item->isArity(PN_BINARY));
+                MOZ_ASSERT(item->pn_left->isKind(PNK_NAME));
+                MOZ_ASSERT(!item->pn_left->expr());
+                MOZ_ASSERT(item->pn_right->isKind(PNK_NAME));
+                MOZ_ASSERT(!item->pn_right->expr());
+            }
+#endif
+            break;
+          }
+
+          case PNK_CATCHLIST: {
+            MOZ_ASSERT(cur->isArity(PN_LIST));
+            for (ParseNode* catchNode = cur->pn_head; catchNode; catchNode = catchNode->pn_next) {
+                MOZ_ASSERT(catchNode->isKind(PNK_LEXICALSCOPE));
+                MOZ_ASSERT(catchNode->scopeBody()->isKind(PNK_CATCH));
+                MOZ_ASSERT(catchNode->scopeBody()->isArity(PN_TERNARY));
+                if (!resolve(catchNode->scopeBody(), prefix))
+                    return false;
+            }
+            break;
+          }
+
+          case PNK_DOT:
+            MOZ_ASSERT(cur->isArity(PN_NAME));
+
+            // Super prop nodes do not have a meaningful LHS
+            if (cur->as<PropertyAccess>().isSuper())
+                break;
+            if (!resolve(cur->expr(), prefix))
+                return false;
+            break;
+
+          case PNK_LABEL:
+            MOZ_ASSERT(cur->isArity(PN_NAME));
+            if (!resolve(cur->expr(), prefix))
+                return false;
+            break;
+
+          case PNK_NAME:
+            MOZ_ASSERT(cur->isArity(PN_NAME));
+            if (!resolve(cur->expr(), prefix))
+                return false;
+            break;
+
+          case PNK_LEXICALSCOPE:
+            MOZ_ASSERT(cur->isArity(PN_SCOPE));
+            if (!resolve(cur->scopeBody(), prefix))
+                return false;
+            break;
+
+          case PNK_FUNCTION:
+          case PNK_MODULE:
+            MOZ_ASSERT(cur->isArity(PN_CODE));
+            if (!resolve(cur->pn_body, prefix))
+                return false;
+            break;
+
+          // Kinds that should be handled by parent node resolution.
+
+          case PNK_IMPORT_SPEC: // by PNK_IMPORT_SPEC_LIST
+          case PNK_EXPORT_SPEC: // by PNK_EXPORT_SPEC_LIST
+          case PNK_CALLSITEOBJ: // by PNK_TAGGED_TEMPLATE
+          case PNK_CLASSNAMES:  // by PNK_CLASS
+            MOZ_CRASH("should have been handled by a parent node");
+
+          case PNK_LIMIT: // invalid sentinel value
+            MOZ_CRASH("invalid node kind");
+        }
+
+        nparents--;
+        return true;
+    }
+};
+
+} /* anonymous namespace */
+
+bool
+frontend::NameFunctions(ExclusiveContext* cx, ParseNode* pn)
+{
+    NameResolver nr(cx);
+    return nr.resolve(pn);
+}
diff --git a/js/src/frontend/NameFunctions.h b/js/src/frontend/NameFunctions.h
new file mode 100644
index 0000000000..a04e7040ec
--- /dev/null
+++ b/js/src/frontend/NameFunctions.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_NameFunctions_h
+#define frontend_NameFunctions_h
+
+#include "mozilla/Attributes.h"
+
+#include "js/TypeDecls.h"
+
+namespace js {
+
+class ExclusiveContext;
+
+namespace frontend {
+
+class ParseNode;
+
+MOZ_MUST_USE bool
+NameFunctions(ExclusiveContext* cx, ParseNode* pn);
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_NameFunctions_h */
diff --git a/js/src/frontend/ParseNode-inl.h b/js/src/frontend/ParseNode-inl.h
new file mode 100644
index 0000000000..395d09b5b9
--- /dev/null
+++ b/js/src/frontend/ParseNode-inl.h
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_ParseNode_inl_h
+#define frontend_ParseNode_inl_h
+
+#include "frontend/ParseNode.h"
+
+#include "frontend/SharedContext.h"
+
+namespace js {
+namespace frontend {
+
+inline PropertyName*
+ParseNode::name() const
+{
+    MOZ_ASSERT(isKind(PNK_FUNCTION) || isKind(PNK_NAME));
+    JSAtom* atom = isKind(PNK_FUNCTION) ? pn_funbox->function()->name() : pn_atom;
+    return atom->asPropertyName();
+}
+
+inline JSAtom*
+ParseNode::atom() const
+{
+    MOZ_ASSERT(isKind(PNK_STRING));
+    return pn_atom;
+}
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_ParseNode_inl_h */
diff --git a/js/src/frontend/ParseNode.cpp b/js/src/frontend/ParseNode.cpp
new file mode 100644
index 0000000000..f79baba9ef
--- /dev/null
+++ b/js/src/frontend/ParseNode.cpp
@@ -0,0 +1,904 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "frontend/ParseNode-inl.h"
+
+#include "frontend/Parser.h"
+
+#include "jscntxtinlines.h"
+
+using namespace js;
+using namespace js::frontend;
+
+using mozilla::ArrayLength;
+using mozilla::IsFinite;
+
+#ifdef DEBUG
+void
+ParseNode::checkListConsistency()
+{
+    MOZ_ASSERT(isArity(PN_LIST));
+    ParseNode** tail;
+    uint32_t count = 0;
+    if (pn_head) {
+        ParseNode* last = pn_head;
+        ParseNode* pn = last;
+        while (pn) {
+            last = pn;
+            pn = pn->pn_next;
+            count++;
+        }
+
+        tail = &last->pn_next;
+    } else {
+        tail = &pn_head;
+    }
+    MOZ_ASSERT(pn_tail == tail);
+    MOZ_ASSERT(pn_count == count);
+}
+#endif
+
+/* Add |node| to |parser|'s free node list. */
+void
+ParseNodeAllocator::freeNode(ParseNode* pn)
+{
+    /* Catch back-to-back dup recycles. */
+    MOZ_ASSERT(pn != freelist);
+
+#ifdef DEBUG
+    /* Poison the node, to catch attempts to use it without initializing it. */
+    memset(pn, 0xab, sizeof(*pn));
+#endif
+
+    pn->pn_next = freelist;
+    freelist = pn;
+}
+
+namespace {
+
+/*
+ * A work pool of ParseNodes. The work pool is a stack, chained together
+ * by nodes' pn_next fields. We use this to avoid creating deep C++ stacks
+ * when recycling deep parse trees.
+ *
+ * Since parse nodes are probably allocated in something close to the order
+ * they appear in a depth-first traversal of the tree, making the work pool
+ * a stack should give us pretty good locality.
+ */
+class NodeStack {
+  public:
+    NodeStack() : top(nullptr) { }
+    bool empty() { return top == nullptr; }
+    void push(ParseNode* pn) {
+        pn->pn_next = top;
+        top = pn;
+    }
+    /* Push the children of the PN_LIST node |pn| on the stack. */
+    void pushList(ParseNode* pn) {
+        /* This clobbers pn->pn_head if the list is empty; should be okay. */
+        *pn->pn_tail = top;
+        top = pn->pn_head;
+    }
+    ParseNode* pop() {
+        MOZ_ASSERT(!empty());
+        ParseNode* hold = top; /* my kingdom for a prog1 */
+        top = top->pn_next;
+        return hold;
+    }
+  private:
+    ParseNode* top;
+};
+
+} /* anonymous namespace */
+
+enum class PushResult { Recyclable, CleanUpLater };
+
+static PushResult
+PushCodeNodeChildren(ParseNode* node, NodeStack* stack)
+{
+    MOZ_ASSERT(node->isArity(PN_CODE));
+
+    /*
+     * Function nodes are linked into the function box tree, and may appear
+     * on method lists. Both of those lists are singly-linked, so trying to
+     * update them now could result in quadratic behavior when recycling
+     * trees containing many functions; and the lists can be very long. So
+     * we put off cleaning the lists up until just before function
+     * analysis, when we call CleanFunctionList.
+     *
+     * In fact, we can't recycle the parse node yet, either: it may appear
+     * on a method list, and reusing the node would corrupt that. Instead,
+     * we clear its pn_funbox pointer to mark it as deleted;
+     * CleanFunctionList recycles it as well.
+     *
+     * We do recycle the nodes around it, though, so we must clear pointers
+     * to them to avoid leaving dangling references where someone can find
+     * them.
+     */
+    node->pn_funbox = nullptr;
+    if (node->pn_body)
+        stack->push(node->pn_body);
+    node->pn_body = nullptr;
+
+    return PushResult::CleanUpLater;
+}
+
+static PushResult
+PushNameNodeChildren(ParseNode* node, NodeStack* stack)
+{
+    MOZ_ASSERT(node->isArity(PN_NAME));
+
+    if (node->pn_expr)
+        stack->push(node->pn_expr);
+    node->pn_expr = nullptr;
+    return PushResult::Recyclable;
+}
+
+static PushResult
+PushScopeNodeChildren(ParseNode* node, NodeStack* stack)
+{
+    MOZ_ASSERT(node->isArity(PN_SCOPE));
+
+    if (node->scopeBody())
+        stack->push(node->scopeBody());
+    node->setScopeBody(nullptr);
+    return PushResult::Recyclable;
+}
+
+static PushResult
+PushListNodeChildren(ParseNode* node, NodeStack* stack)
+{
+    MOZ_ASSERT(node->isArity(PN_LIST));
+    node->checkListConsistency();
+
+    stack->pushList(node);
+
+    return PushResult::Recyclable;
+}
+
+static PushResult
+PushUnaryNodeChild(ParseNode* node, NodeStack* stack)
+{
+    MOZ_ASSERT(node->isArity(PN_UNARY));
+
+    stack->push(node->pn_kid);
+
+    return PushResult::Recyclable;
+}
+
+/*
+ * Push the children of |pn| on |stack|. Return true if |pn| itself could be
+ * safely recycled, or false if it must be cleaned later (pn_used and pn_defn
+ * nodes, and all function nodes; see comments for CleanFunctionList in
+ * SemanticAnalysis.cpp). Some callers want to free |pn|; others
+ * (js::ParseNodeAllocator::prepareNodeForMutation) don't care about |pn|, and
+ * just need to take care of its children.
+ */
+static PushResult
+PushNodeChildren(ParseNode* pn, NodeStack* stack)
+{
+    switch (pn->getKind()) {
+      // Trivial nodes that refer to no nodes, are referred to by nothing
+      // but their parents, are never used, and are never a definition.
+      case PNK_NOP:
+      case PNK_STRING:
+      case PNK_TEMPLATE_STRING:
+      case PNK_REGEXP:
+      case PNK_TRUE:
+      case PNK_FALSE:
+      case PNK_NULL:
+      case PNK_ELISION:
+      case PNK_GENERATOR:
+      case PNK_NUMBER:
+      case PNK_BREAK:
+      case PNK_CONTINUE:
+      case PNK_DEBUGGER:
+      case PNK_EXPORT_BATCH_SPEC:
+      case PNK_OBJECT_PROPERTY_NAME:
+      case PNK_POSHOLDER:
+        MOZ_ASSERT(pn->isArity(PN_NULLARY));
+        return PushResult::Recyclable;
+
+      // Nodes with a single non-null child.
+      case PNK_TYPEOFNAME:
+      case PNK_TYPEOFEXPR:
+      case PNK_VOID:
+      case PNK_NOT:
+      case PNK_BITNOT:
+      case PNK_THROW:
+      case PNK_DELETENAME:
+      case PNK_DELETEPROP:
+      case PNK_DELETEELEM:
+      case PNK_DELETEEXPR:
+      case PNK_POS:
+      case PNK_NEG:
+      case PNK_PREINCREMENT:
+      case PNK_POSTINCREMENT:
+      case PNK_PREDECREMENT:
+      case PNK_POSTDECREMENT:
+      case PNK_COMPUTED_NAME:
+      case PNK_ARRAYPUSH:
+      case PNK_SPREAD:
+      case PNK_MUTATEPROTO:
+      case PNK_EXPORT:
+      case PNK_SUPERBASE:
+        return PushUnaryNodeChild(pn, stack);
+
+      // Nodes with a single nullable child.
+      case PNK_THIS:
+      case PNK_SEMI: {
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        if (pn->pn_kid)
+            stack->push(pn->pn_kid);
+        return PushResult::Recyclable;
+      }
+
+      // Binary nodes with two non-null children.
+
+      // All assignment and compound assignment nodes qualify.
+      case PNK_ASSIGN:
+      case PNK_ADDASSIGN:
+      case PNK_SUBASSIGN:
+      case PNK_BITORASSIGN:
+      case PNK_BITXORASSIGN:
+      case PNK_BITANDASSIGN:
+      case PNK_LSHASSIGN:
+      case PNK_RSHASSIGN:
+      case PNK_URSHASSIGN:
+      case PNK_MULASSIGN:
+      case PNK_DIVASSIGN:
+      case PNK_MODASSIGN:
+      case PNK_POWASSIGN:
+      // ...and a few others.
+      case PNK_ELEM:
+      case PNK_IMPORT_SPEC:
+      case PNK_EXPORT_SPEC:
+      case PNK_COLON:
+      case PNK_SHORTHAND:
+      case PNK_DOWHILE:
+      case PNK_WHILE:
+      case PNK_SWITCH:
+      case PNK_CLASSMETHOD:
+      case PNK_NEWTARGET:
+      case PNK_SETTHIS:
+      case PNK_FOR:
+      case PNK_COMPREHENSIONFOR:
+      case PNK_WITH: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        stack->push(pn->pn_left);
+        stack->push(pn->pn_right);
+        return PushResult::Recyclable;
+      }
+
+      // Default clauses are PNK_CASE but do not have case expressions.
+      // Named class expressions do not have outer binding nodes.
+      // So both are binary nodes with a possibly-null pn_left.
+      case PNK_CASE:
+      case PNK_CLASSNAMES: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        if (pn->pn_left)
+            stack->push(pn->pn_left);
+        stack->push(pn->pn_right);
+        return PushResult::Recyclable;
+      }
+
+      // The left half is the expression being yielded.  The right half is
+      // internal goop: a name reference to the invisible '.generator' local
+      // variable, or an assignment of a PNK_GENERATOR node to the '.generator'
+      // local, for a synthesized, prepended initial yield.  Yum!
+      case PNK_YIELD_STAR:
+      case PNK_YIELD:
+      case PNK_AWAIT: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT(pn->pn_right);
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_NAME) ||
+                   (pn->pn_right->isKind(PNK_ASSIGN) &&
+                    pn->pn_right->pn_left->isKind(PNK_NAME) &&
+                    pn->pn_right->pn_right->isKind(PNK_GENERATOR)));
+        if (pn->pn_left)
+            stack->push(pn->pn_left);
+        stack->push(pn->pn_right);
+        return PushResult::Recyclable;
+      }
+
+      // A return node's child is what you'd expect: the return expression,
+      // if any.
+      case PNK_RETURN: {
+        MOZ_ASSERT(pn->isArity(PN_UNARY));
+        if (pn->pn_kid)
+            stack->push(pn->pn_kid);
+        return PushResult::Recyclable;
+      }
+
+      // Import and export-from nodes have a list of specifiers on the left
+      // and a module string on the right.
+      case PNK_IMPORT:
+      case PNK_EXPORT_FROM: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT_IF(pn->isKind(PNK_IMPORT), pn->pn_left->isKind(PNK_IMPORT_SPEC_LIST));
+        MOZ_ASSERT_IF(pn->isKind(PNK_EXPORT_FROM), pn->pn_left->isKind(PNK_EXPORT_SPEC_LIST));
+        MOZ_ASSERT(pn->pn_left->isArity(PN_LIST));
+        MOZ_ASSERT(pn->pn_right->isKind(PNK_STRING));
+        stack->pushList(pn->pn_left);
+        stack->push(pn->pn_right);
+        return PushResult::Recyclable;
+      }
+
+      case PNK_EXPORT_DEFAULT: {
+        MOZ_ASSERT(pn->isArity(PN_BINARY));
+        MOZ_ASSERT_IF(pn->pn_right, pn->pn_right->isKind(PNK_NAME));
+        stack->push(pn->pn_left);
+        if (pn->pn_right)
+            stack->push(pn->pn_right);
+        return PushResult::Recyclable;
+      }
+
+      // Ternary nodes with all children non-null.
+      case PNK_CONDITIONAL: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        stack->push(pn->pn_kid1);
+        stack->push(pn->pn_kid2);
+        stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // For for-in and for-of, the first child is the left-hand side of the
+      // 'in' or 'of' (a declaration or an assignment target). The second
+      // child is always null, and the third child is the expression looped
+      // over.  For example, in |for (var p in obj)|, the first child is |var
+      // p|, the second child is null, and the third child is |obj|.
+      case PNK_FORIN:
+      case PNK_FOROF: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        MOZ_ASSERT(!pn->pn_kid2);
+        stack->push(pn->pn_kid1);
+        stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // for (;;) nodes have one child per optional component of the loop head.
+      case PNK_FORHEAD: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        if (pn->pn_kid1)
+            stack->push(pn->pn_kid1);
+        if (pn->pn_kid2)
+            stack->push(pn->pn_kid2);
+        if (pn->pn_kid3)
+            stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // classes might have an optional node for the heritage, as well as the names
+      case PNK_CLASS: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        if (pn->pn_kid1)
+            stack->push(pn->pn_kid1);
+        if (pn->pn_kid2)
+            stack->push(pn->pn_kid2);
+        stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // if-statement nodes have condition and consequent children and a
+      // possibly-null alternative.
+      case PNK_IF: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        stack->push(pn->pn_kid1);
+        stack->push(pn->pn_kid2);
+        if (pn->pn_kid3)
+            stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // try-statements have statements to execute, and one or both of a
+      // catch-list and a finally-block.
+      case PNK_TRY: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        MOZ_ASSERT(pn->pn_kid2 || pn->pn_kid3);
+        stack->push(pn->pn_kid1);
+        if (pn->pn_kid2)
+            stack->push(pn->pn_kid2);
+        if (pn->pn_kid3)
+            stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // A catch node has first kid as catch-variable pattern, the second kid
+      // as catch condition (which, if non-null, records the |<cond>| in
+      // SpiderMonkey's |catch (e if <cond>)| extension), and third kid as the
+      // statements in the catch block.
+      case PNK_CATCH: {
+        MOZ_ASSERT(pn->isArity(PN_TERNARY));
+        stack->push(pn->pn_kid1);
+        if (pn->pn_kid2)
+            stack->push(pn->pn_kid2);
+        stack->push(pn->pn_kid3);
+        return PushResult::Recyclable;
+      }
+
+      // List nodes with all non-null children.
+      case PNK_OR:
+      case PNK_AND:
+      case PNK_BITOR:
+      case PNK_BITXOR:
+      case PNK_BITAND:
+      case PNK_STRICTEQ:
+      case PNK_EQ:
+      case PNK_STRICTNE:
+      case PNK_NE:
+      case PNK_LT:
+      case PNK_LE:
+      case PNK_GT:
+      case PNK_GE:
+      case PNK_INSTANCEOF:
+      case PNK_IN:
+      case PNK_LSH:
+      case PNK_RSH:
+      case PNK_URSH:
+      case PNK_ADD:
+      case PNK_SUB:
+      case PNK_STAR:
+      case PNK_DIV:
+      case PNK_MOD:
+      case PNK_POW:
+      case PNK_COMMA:
+      case PNK_NEW:
+      case PNK_CALL:
+      case PNK_SUPERCALL:
+      case PNK_GENEXP:
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+      case PNK_TEMPLATE_STRING_LIST:
+      case PNK_TAGGED_TEMPLATE:
+      case PNK_CALLSITEOBJ:
+      case PNK_VAR:
+      case PNK_CONST:
+      case PNK_LET:
+      case PNK_CATCHLIST:
+      case PNK_STATEMENTLIST:
+      case PNK_IMPORT_SPEC_LIST:
+      case PNK_EXPORT_SPEC_LIST:
+      case PNK_PARAMSBODY:
+      case PNK_CLASSMETHODLIST:
+        return PushListNodeChildren(pn, stack);
+
+      // Array comprehension nodes are lists with a single child:
+      // PNK_COMPREHENSIONFOR for comprehensions, PNK_LEXICALSCOPE for legacy
+      // comprehensions.  Probably this should be a non-list eventually.
+      case PNK_ARRAYCOMP: {
+#ifdef DEBUG
+        MOZ_ASSERT(pn->isKind(PNK_ARRAYCOMP));
+        MOZ_ASSERT(pn->isArity(PN_LIST));
+        MOZ_ASSERT(pn->pn_count == 1);
+        MOZ_ASSERT(pn->pn_head->isKind(PNK_LEXICALSCOPE) ||
+                   pn->pn_head->isKind(PNK_COMPREHENSIONFOR));
+#endif
+        return PushListNodeChildren(pn, stack);
+      }
+
+      case PNK_LABEL:
+      case PNK_DOT:
+      case PNK_NAME:
+        return PushNameNodeChildren(pn, stack);
+
+      case PNK_LEXICALSCOPE:
+        return PushScopeNodeChildren(pn, stack);
+
+      case PNK_FUNCTION:
+      case PNK_MODULE:
+        return PushCodeNodeChildren(pn, stack);
+
+      case PNK_LIMIT: // invalid sentinel value
+        MOZ_CRASH("invalid node kind");
+    }
+
+    MOZ_CRASH("bad ParseNodeKind");
+    return PushResult::CleanUpLater;
+}
+
+/*
+ * Prepare |pn| to be mutated in place into a new kind of node. Recycle all
+ * |pn|'s recyclable children (but not |pn| itself!), and disconnect it from
+ * metadata structures (the function box tree).
+ */
+void
+ParseNodeAllocator::prepareNodeForMutation(ParseNode* pn)
+{
+    // Nothing to do for nullary nodes.
+    if (pn->isArity(PN_NULLARY))
+        return;
+
+    // Put |pn|'s children (but not |pn| itself) on a work stack.
+    NodeStack stack;
+    PushNodeChildren(pn, &stack);
+
+    // For each node on the work stack, push its children on the work stack,
+    // and free the node if we can.
+    while (!stack.empty()) {
+        pn = stack.pop();
+        if (PushNodeChildren(pn, &stack) == PushResult::Recyclable)
+            freeNode(pn);
+    }
+}
+
+/*
+ * Return the nodes in the subtree |pn| to the parser's free node list, for
+ * reallocation.
+ */
+ParseNode*
+ParseNodeAllocator::freeTree(ParseNode* pn)
+{
+    if (!pn)
+        return nullptr;
+
+    ParseNode* savedNext = pn->pn_next;
+
+    NodeStack stack;
+    for (;;) {
+        if (PushNodeChildren(pn, &stack) == PushResult::Recyclable)
+            freeNode(pn);
+        if (stack.empty())
+            break;
+        pn = stack.pop();
+    }
+
+    return savedNext;
+}
+
+/*
+ * Allocate a ParseNode from parser's node freelist or, failing that, from
+ * cx's temporary arena.
+ */
+void*
+ParseNodeAllocator::allocNode()
+{
+    if (ParseNode* pn = freelist) {
+        freelist = pn->pn_next;
+        return pn;
+    }
+
+    LifoAlloc::AutoFallibleScope fallibleAllocator(&alloc);
+    void* p = alloc.alloc(sizeof (ParseNode));
+    if (!p)
+        ReportOutOfMemory(cx);
+    return p;
+}
+
+ParseNode*
+ParseNode::appendOrCreateList(ParseNodeKind kind, JSOp op, ParseNode* left, ParseNode* right,
+                              FullParseHandler* handler, ParseContext* pc)
+{
+    // The asm.js specification is written in ECMAScript grammar terms that
+    // specify *only* a binary tree.  It's a royal pain to implement the asm.js
+    // spec to act upon n-ary lists as created below.  So for asm.js, form a
+    // binary tree of lists exactly as ECMAScript would by skipping the
+    // following optimization.
+    if (!pc->useAsmOrInsideUseAsm()) {
+        // Left-associative trees of a given operator (e.g. |a + b + c|) are
+        // binary trees in the spec: (+ (+ a b) c) in Lisp terms.  Recursively
+        // processing such a tree, exactly implemented that way, would blow the
+        // the stack.  We use a list node that uses O(1) stack to represent
+        // such operations: (+ a b c).
+        //
+        // (**) is right-associative; per spec |a ** b ** c| parses as
+        // (** a (** b c)). But we treat this the same way, creating a list
+        // node: (** a b c). All consumers must understand that this must be
+        // processed with a right fold, whereas the list (+ a b c) must be
+        // processed with a left fold because (+) is left-associative.
+        //
+        if (left->isKind(kind) &&
+            left->isOp(op) &&
+            (CodeSpec[op].format & JOF_LEFTASSOC ||
+             (kind == PNK_POW && !left->pn_parens)))
+        {
+            ListNode* list = &left->as<ListNode>();
+
+            list->append(right);
+            list->pn_pos.end = right->pn_pos.end;
+
+            return list;
+        }
+    }
+
+    ParseNode* list = handler->new_<ListNode>(kind, op, left);
+    if (!list)
+        return nullptr;
+
+    list->append(right);
+    return list;
+}
+
+#ifdef DEBUG
+
+static const char * const parseNodeNames[] = {
+#define STRINGIFY(name) #name,
+    FOR_EACH_PARSE_NODE_KIND(STRINGIFY)
+#undef STRINGIFY
+};
+
+void
+frontend::DumpParseTree(ParseNode* pn, int indent)
+{
+    if (pn == nullptr)
+        fprintf(stderr, "#NULL");
+    else
+        pn->dump(indent);
+}
+
+static void
+IndentNewLine(int indent)
+{
+    fputc('\n', stderr);
+    for (int i = 0; i < indent; ++i)
+        fputc(' ', stderr);
+}
+
+void
+ParseNode::dump()
+{
+    dump(0);
+    fputc('\n', stderr);
+}
+
+void
+ParseNode::dump(int indent)
+{
+    switch (pn_arity) {
+      case PN_NULLARY:
+        ((NullaryNode*) this)->dump();
+        break;
+      case PN_UNARY:
+        ((UnaryNode*) this)->dump(indent);
+        break;
+      case PN_BINARY:
+        ((BinaryNode*) this)->dump(indent);
+        break;
+      case PN_TERNARY:
+        ((TernaryNode*) this)->dump(indent);
+        break;
+      case PN_CODE:
+        ((CodeNode*) this)->dump(indent);
+        break;
+      case PN_LIST:
+        ((ListNode*) this)->dump(indent);
+        break;
+      case PN_NAME:
+        ((NameNode*) this)->dump(indent);
+        break;
+      case PN_SCOPE:
+        ((LexicalScopeNode*) this)->dump(indent);
+        break;
+      default:
+        fprintf(stderr, "#<BAD NODE %p, kind=%u, arity=%u>",
+                (void*) this, unsigned(getKind()), unsigned(pn_arity));
+        break;
+    }
+}
+
+void
+NullaryNode::dump()
+{
+    switch (getKind()) {
+      case PNK_TRUE:  fprintf(stderr, "#true");  break;
+      case PNK_FALSE: fprintf(stderr, "#false"); break;
+      case PNK_NULL:  fprintf(stderr, "#null");  break;
+
+      case PNK_NUMBER: {
+        ToCStringBuf cbuf;
+        const char* cstr = NumberToCString(nullptr, &cbuf, pn_dval);
+        if (!IsFinite(pn_dval))
+            fputc('#', stderr);
+        if (cstr)
+            fprintf(stderr, "%s", cstr);
+        else
+            fprintf(stderr, "%g", pn_dval);
+        break;
+      }
+
+      case PNK_STRING:
+        pn_atom->dumpCharsNoNewline();
+        break;
+
+      default:
+        fprintf(stderr, "(%s)", parseNodeNames[getKind()]);
+    }
+}
+
+void
+UnaryNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s ", name);
+    indent += strlen(name) + 2;
+    DumpParseTree(pn_kid, indent);
+    fprintf(stderr, ")");
+}
+
+void
+BinaryNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s ", name);
+    indent += strlen(name) + 2;
+    DumpParseTree(pn_left, indent);
+    IndentNewLine(indent);
+    DumpParseTree(pn_right, indent);
+    fprintf(stderr, ")");
+}
+
+void
+TernaryNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s ", name);
+    indent += strlen(name) + 2;
+    DumpParseTree(pn_kid1, indent);
+    IndentNewLine(indent);
+    DumpParseTree(pn_kid2, indent);
+    IndentNewLine(indent);
+    DumpParseTree(pn_kid3, indent);
+    fprintf(stderr, ")");
+}
+
+void
+CodeNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s ", name);
+    indent += strlen(name) + 2;
+    DumpParseTree(pn_body, indent);
+    fprintf(stderr, ")");
+}
+
+void
+ListNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s [", name);
+    if (pn_head != nullptr) {
+        indent += strlen(name) + 3;
+        DumpParseTree(pn_head, indent);
+        ParseNode* pn = pn_head->pn_next;
+        while (pn != nullptr) {
+            IndentNewLine(indent);
+            DumpParseTree(pn, indent);
+            pn = pn->pn_next;
+        }
+    }
+    fprintf(stderr, "])");
+}
+
+template <typename CharT>
+static void
+DumpName(const CharT* s, size_t len)
+{
+    if (len == 0)
+        fprintf(stderr, "#<zero-length name>");
+
+    for (size_t i = 0; i < len; i++) {
+        char16_t c = s[i];
+        if (c > 32 && c < 127)
+            fputc(c, stderr);
+        else if (c <= 255)
+            fprintf(stderr, "\\x%02x", unsigned(c));
+        else
+            fprintf(stderr, "\\u%04x", unsigned(c));
+    }
+}
+
+void
+NameNode::dump(int indent)
+{
+    if (isKind(PNK_NAME) || isKind(PNK_DOT)) {
+        if (isKind(PNK_DOT))
+            fprintf(stderr, "(.");
+
+        if (!pn_atom) {
+            fprintf(stderr, "#<null name>");
+        } else if (getOp() == JSOP_GETARG && pn_atom->length() == 0) {
+            // Dump destructuring parameter.
+            fprintf(stderr, "(#<zero-length name> ");
+            DumpParseTree(expr(), indent + 21);
+            fputc(')', stderr);
+        } else {
+            JS::AutoCheckCannotGC nogc;
+            if (pn_atom->hasLatin1Chars())
+                DumpName(pn_atom->latin1Chars(nogc), pn_atom->length());
+            else
+                DumpName(pn_atom->twoByteChars(nogc), pn_atom->length());
+        }
+
+        if (isKind(PNK_DOT)) {
+            fputc(' ', stderr);
+            if (as<PropertyAccess>().isSuper())
+                fprintf(stderr, "super");
+            else
+                DumpParseTree(expr(), indent + 2);
+            fputc(')', stderr);
+        }
+        return;
+    }
+
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s ", name);
+    indent += strlen(name) + 2;
+    DumpParseTree(expr(), indent);
+    fprintf(stderr, ")");
+}
+
+void
+LexicalScopeNode::dump(int indent)
+{
+    const char* name = parseNodeNames[getKind()];
+    fprintf(stderr, "(%s [", name);
+    int nameIndent = indent + strlen(name) + 3;
+    if (!isEmptyScope()) {
+        LexicalScope::Data* bindings = scopeBindings();
+        for (uint32_t i = 0; i < bindings->length; i++) {
+            JSAtom* name = bindings->names[i].name();
+            JS::AutoCheckCannotGC nogc;
+            if (name->hasLatin1Chars())
+                DumpName(name->latin1Chars(nogc), name->length());
+            else
+                DumpName(name->twoByteChars(nogc), name->length());
+            if (i < bindings->length - 1)
+                IndentNewLine(nameIndent);
+        }
+    }
+    fprintf(stderr, "]");
+    indent += 2;
+    IndentNewLine(indent);
+    DumpParseTree(scopeBody(), indent);
+    fprintf(stderr, ")");
+}
+#endif
+
+ObjectBox::ObjectBox(JSObject* object, ObjectBox* traceLink)
+  : object(object),
+    traceLink(traceLink),
+    emitLink(nullptr)
+{
+    MOZ_ASSERT(!object->is<JSFunction>());
+    MOZ_ASSERT(object->isTenured());
+}
+
+ObjectBox::ObjectBox(JSFunction* function, ObjectBox* traceLink)
+  : object(function),
+    traceLink(traceLink),
+    emitLink(nullptr)
+{
+    MOZ_ASSERT(object->is<JSFunction>());
+    MOZ_ASSERT(asFunctionBox()->function() == function);
+    MOZ_ASSERT(object->isTenured());
+}
+
+FunctionBox*
+ObjectBox::asFunctionBox()
+{
+    MOZ_ASSERT(isFunctionBox());
+    return static_cast<FunctionBox*>(this);
+}
+
+/* static */ void
+ObjectBox::TraceList(JSTracer* trc, ObjectBox* listHead)
+{
+    for (ObjectBox* box = listHead; box; box = box->traceLink)
+        box->trace(trc);
+}
+
+void
+ObjectBox::trace(JSTracer* trc)
+{
+    TraceRoot(trc, &object, "parser.object");
+}
+
+void
+FunctionBox::trace(JSTracer* trc)
+{
+    ObjectBox::trace(trc);
+    if (enclosingScope_)
+        TraceRoot(trc, &enclosingScope_, "funbox-enclosingScope");
+}
diff --git a/js/src/frontend/ParseNode.h b/js/src/frontend/ParseNode.h
new file mode 100644
index 0000000000..d37aaaae08
--- /dev/null
+++ b/js/src/frontend/ParseNode.h
@@ -0,0 +1,1450 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_ParseNode_h
+#define frontend_ParseNode_h
+
+#include "mozilla/Attributes.h"
+
+#include "builtin/ModuleObject.h"
+#include "frontend/TokenStream.h"
+
+namespace js {
+namespace frontend {
+
+class ParseContext;
+class FullParseHandler;
+class FunctionBox;
+class ObjectBox;
+
+#define FOR_EACH_PARSE_NODE_KIND(F) \
+    F(NOP) \
+    F(SEMI) \
+    F(COMMA) \
+    F(CONDITIONAL) \
+    F(COLON) \
+    F(SHORTHAND) \
+    F(POS) \
+    F(NEG) \
+    F(PREINCREMENT) \
+    F(POSTINCREMENT) \
+    F(PREDECREMENT) \
+    F(POSTDECREMENT) \
+    F(DOT) \
+    F(ELEM) \
+    F(ARRAY) \
+    F(ELISION) \
+    F(STATEMENTLIST) \
+    F(LABEL) \
+    F(OBJECT) \
+    F(CALL) \
+    F(NAME) \
+    F(OBJECT_PROPERTY_NAME) \
+    F(COMPUTED_NAME) \
+    F(NUMBER) \
+    F(STRING) \
+    F(TEMPLATE_STRING_LIST) \
+    F(TEMPLATE_STRING) \
+    F(TAGGED_TEMPLATE) \
+    F(CALLSITEOBJ) \
+    F(REGEXP) \
+    F(TRUE) \
+    F(FALSE) \
+    F(NULL) \
+    F(THIS) \
+    F(FUNCTION) \
+    F(MODULE) \
+    F(IF) \
+    F(SWITCH) \
+    F(CASE) \
+    F(WHILE) \
+    F(DOWHILE) \
+    F(FOR) \
+    F(COMPREHENSIONFOR) \
+    F(BREAK) \
+    F(CONTINUE) \
+    F(VAR) \
+    F(CONST) \
+    F(WITH) \
+    F(RETURN) \
+    F(NEW) \
+    /* Delete operations.  These must be sequential. */ \
+    F(DELETENAME) \
+    F(DELETEPROP) \
+    F(DELETEELEM) \
+    F(DELETEEXPR) \
+    F(TRY) \
+    F(CATCH) \
+    F(CATCHLIST) \
+    F(THROW) \
+    F(DEBUGGER) \
+    F(GENERATOR) \
+    F(YIELD) \
+    F(YIELD_STAR) \
+    F(GENEXP) \
+    F(ARRAYCOMP) \
+    F(ARRAYPUSH) \
+    F(LEXICALSCOPE) \
+    F(LET) \
+    F(IMPORT) \
+    F(IMPORT_SPEC_LIST) \
+    F(IMPORT_SPEC) \
+    F(EXPORT) \
+    F(EXPORT_FROM) \
+    F(EXPORT_DEFAULT) \
+    F(EXPORT_SPEC_LIST) \
+    F(EXPORT_SPEC) \
+    F(EXPORT_BATCH_SPEC) \
+    F(FORIN) \
+    F(FOROF) \
+    F(FORHEAD) \
+    F(PARAMSBODY) \
+    F(SPREAD) \
+    F(MUTATEPROTO) \
+    F(CLASS) \
+    F(CLASSMETHOD) \
+    F(CLASSMETHODLIST) \
+    F(CLASSNAMES) \
+    F(NEWTARGET) \
+    F(POSHOLDER) \
+    F(SUPERBASE) \
+    F(SUPERCALL) \
+    F(SETTHIS) \
+    \
+    /* Unary operators. */ \
+    F(TYPEOFNAME) \
+    F(TYPEOFEXPR) \
+    F(VOID) \
+    F(NOT) \
+    F(BITNOT) \
+    F(AWAIT) \
+    \
+    /* \
+     * Binary operators. \
+     * These must be in the same order as TOK_OR and friends in TokenStream.h. \
+     */ \
+    F(OR) \
+    F(AND) \
+    F(BITOR) \
+    F(BITXOR) \
+    F(BITAND) \
+    F(STRICTEQ) \
+    F(EQ) \
+    F(STRICTNE) \
+    F(NE) \
+    F(LT) \
+    F(LE) \
+    F(GT) \
+    F(GE) \
+    F(INSTANCEOF) \
+    F(IN) \
+    F(LSH) \
+    F(RSH) \
+    F(URSH) \
+    F(ADD) \
+    F(SUB) \
+    F(STAR) \
+    F(DIV) \
+    F(MOD) \
+    F(POW) \
+    \
+    /* Assignment operators (= += -= etc.). */ \
+    /* ParseNode::isAssignment assumes all these are consecutive. */ \
+    F(ASSIGN) \
+    F(ADDASSIGN) \
+    F(SUBASSIGN) \
+    F(BITORASSIGN) \
+    F(BITXORASSIGN) \
+    F(BITANDASSIGN) \
+    F(LSHASSIGN) \
+    F(RSHASSIGN) \
+    F(URSHASSIGN) \
+    F(MULASSIGN) \
+    F(DIVASSIGN) \
+    F(MODASSIGN) \
+    F(POWASSIGN)
+
+/*
+ * Parsing builds a tree of nodes that directs code generation.  This tree is
+ * not a concrete syntax tree in all respects (for example, || and && are left
+ * associative, but (A && B && C) translates into the right-associated tree
+ * <A && <B && C>> so that code generation can emit a left-associative branch
+ * around <B && C> when A is false).  Nodes are labeled by kind, with a
+ * secondary JSOp label when needed.
+ *
+ * The long comment after this enum block describes the kinds in detail.
+ */
+enum ParseNodeKind
+{
+#define EMIT_ENUM(name) PNK_##name,
+    FOR_EACH_PARSE_NODE_KIND(EMIT_ENUM)
+#undef EMIT_ENUM
+    PNK_LIMIT, /* domain size */
+    PNK_BINOP_FIRST = PNK_OR,
+    PNK_BINOP_LAST = PNK_POW,
+    PNK_ASSIGNMENT_START = PNK_ASSIGN,
+    PNK_ASSIGNMENT_LAST = PNK_POWASSIGN
+};
+
+inline bool
+IsDeleteKind(ParseNodeKind kind)
+{
+    return PNK_DELETENAME <= kind && kind <= PNK_DELETEEXPR;
+}
+
+inline bool
+IsTypeofKind(ParseNodeKind kind)
+{
+    return PNK_TYPEOFNAME <= kind && kind <= PNK_TYPEOFEXPR;
+}
+
+/*
+ * Label        Variant     Members
+ * -----        -------     -------
+ * <Definitions>
+ * PNK_FUNCTION name        pn_funbox: ptr to js::FunctionBox holding function
+ *                            object containing arg and var properties.  We
+ *                            create the function object at parse (not emit)
+ *                            time to specialize arg and var bytecodes early.
+ *                          pn_body: PNK_PARAMSBODY, ordinarily;
+ *                            PNK_LEXICALSCOPE for implicit function in genexpr
+ * PNK_PARAMSBODY list      list of formal parameters with
+ *                              PNK_NAME node with non-empty name for
+ *                                SingleNameBinding without Initializer
+ *                              PNK_ASSIGN node for SingleNameBinding with
+ *                                Initializer
+ *                              PNK_NAME node with empty name for destructuring
+ *                                pn_expr: PNK_ARRAY, PNK_OBJECT, or PNK_ASSIGN
+ *                                  PNK_ARRAY or PNK_OBJECT for BindingPattern
+ *                                    without Initializer
+ *                                  PNK_ASSIGN for BindingPattern with
+ *                                    Initializer
+ *                          followed by:
+ *                              PNK_STATEMENTLIST node for function body
+ *                                statements,
+ *                              PNK_RETURN for expression closure
+ *                          pn_count: 1 + number of formal parameters
+ *                          pn_tree: PNK_PARAMSBODY or PNK_STATEMENTLIST node
+ * PNK_SPREAD   unary       pn_kid: expression being spread
+ *
+ * <Statements>
+ * PNK_STATEMENTLIST list   pn_head: list of pn_count statements
+ * PNK_IF       ternary     pn_kid1: cond, pn_kid2: then, pn_kid3: else or null.
+ *                            In body of a comprehension or desugared generator
+ *                            expression, pn_kid2 is PNK_YIELD, PNK_ARRAYPUSH,
+ *                            or (if the push was optimized away) empty
+ *                            PNK_STATEMENTLIST.
+ * PNK_SWITCH   binary      pn_left: discriminant
+ *                          pn_right: list of PNK_CASE nodes, with at most one
+ *                            default node, or if there are let bindings
+ *                            in the top level of the switch body's cases, a
+ *                            PNK_LEXICALSCOPE node that contains the list of
+ *                            PNK_CASE nodes.
+ * PNK_CASE     binary      pn_left: case-expression if CaseClause, or
+ *                            null if DefaultClause
+ *                          pn_right: PNK_STATEMENTLIST node for this case's
+ *                            statements
+ *                          pn_u.binary.offset: scratch space for the emitter
+ * PNK_WHILE    binary      pn_left: cond, pn_right: body
+ * PNK_DOWHILE  binary      pn_left: body, pn_right: cond
+ * PNK_FOR      binary      pn_left: either PNK_FORIN (for-in statement),
+ *                            PNK_FOROF (for-of) or PNK_FORHEAD (for(;;))
+ *                          pn_right: body
+ * PNK_COMPREHENSIONFOR     pn_left: either PNK_FORIN or PNK_FOROF
+ *              binary      pn_right: body
+ * PNK_FORIN    ternary     pn_kid1: declaration or expression to left of 'in'
+ *                          pn_kid2: null
+ *                          pn_kid3: object expr to right of 'in'
+ * PNK_FOROF    ternary     pn_kid1: declaration or expression to left of 'of'
+ *                          pn_kid2: null
+ *                          pn_kid3: expr to right of 'of'
+ * PNK_FORHEAD  ternary     pn_kid1:  init expr before first ';' or nullptr
+ *                          pn_kid2:  cond expr before second ';' or nullptr
+ *                          pn_kid3:  update expr after second ';' or nullptr
+ * PNK_THROW    unary       pn_op: JSOP_THROW, pn_kid: exception
+ * PNK_TRY      ternary     pn_kid1: try block
+ *                          pn_kid2: null or PNK_CATCHLIST list
+ *                          pn_kid3: null or finally block
+ * PNK_CATCHLIST list       pn_head: list of PNK_LEXICALSCOPE nodes, one per
+ *                                   catch-block, each with pn_expr pointing
+ *                                   to a PNK_CATCH node
+ * PNK_CATCH    ternary     pn_kid1: PNK_NAME, PNK_ARRAY, or PNK_OBJECT catch var node
+ *                                   (PNK_ARRAY or PNK_OBJECT if destructuring)
+ *                          pn_kid2: null or the catch guard expression
+ *                          pn_kid3: catch block statements
+ * PNK_BREAK    name        pn_atom: label or null
+ * PNK_CONTINUE name        pn_atom: label or null
+ * PNK_WITH     binary      pn_left: head expr; pn_right: body;
+ * PNK_VAR,     list        pn_head: list of PNK_NAME or PNK_ASSIGN nodes
+ * PNK_LET,                          each name node has either
+ * PNK_CONST                           pn_used: false
+ *                                     pn_atom: variable name
+ *                                     pn_expr: initializer or null
+ *                                   or
+ *                                     pn_used: true
+ *                                     pn_atom: variable name
+ *                                     pn_lexdef: def node
+ *                                   each assignment node has
+ *                                     pn_left: PNK_NAME with pn_used true and
+ *                                              pn_lexdef (NOT pn_expr) set
+ *                                     pn_right: initializer
+ * PNK_RETURN   unary       pn_kid: return expr or null
+ * PNK_SEMI     unary       pn_kid: expr or null statement
+ *                          pn_prologue: true if Directive Prologue member
+ *                              in original source, not introduced via
+ *                              constant folding or other tree rewriting
+ * PNK_LABEL    name        pn_atom: label, pn_expr: labeled statement
+ * PNK_IMPORT   binary      pn_left: PNK_IMPORT_SPEC_LIST import specifiers
+ *                          pn_right: PNK_STRING module specifier
+ * PNK_EXPORT   unary       pn_kid: declaration expression
+ * PNK_EXPORT_FROM binary   pn_left: PNK_EXPORT_SPEC_LIST export specifiers
+ *                          pn_right: PNK_STRING module specifier
+ * PNK_EXPORT_DEFAULT unary pn_kid: export default declaration or expression
+ *
+ * <Expressions>
+ * All left-associated binary trees of the same type are optimized into lists
+ * to avoid recursion when processing expression chains.
+ * PNK_COMMA    list        pn_head: list of pn_count comma-separated exprs
+ * PNK_ASSIGN   binary      pn_left: lvalue, pn_right: rvalue
+ * PNK_ADDASSIGN,   binary  pn_left: lvalue, pn_right: rvalue
+ * PNK_SUBASSIGN,           pn_op: JSOP_ADD for +=, etc.
+ * PNK_BITORASSIGN,
+ * PNK_BITXORASSIGN,
+ * PNK_BITANDASSIGN,
+ * PNK_LSHASSIGN,
+ * PNK_RSHASSIGN,
+ * PNK_URSHASSIGN,
+ * PNK_MULASSIGN,
+ * PNK_DIVASSIGN,
+ * PNK_MODASSIGN,
+ * PNK_POWASSIGN
+ * PNK_CONDITIONAL ternary  (cond ? trueExpr : falseExpr)
+ *                          pn_kid1: cond, pn_kid2: then, pn_kid3: else
+ * PNK_OR,      list        pn_head; list of pn_count subexpressions
+ * PNK_AND,                 All of these operators are left-associative except (**).
+ * PNK_BITOR,
+ * PNK_BITXOR,
+ * PNK_BITAND,
+ * PNK_EQ,
+ * PNK_NE,
+ * PNK_STRICTEQ,
+ * PNK_STRICTNE,
+ * PNK_LT,
+ * PNK_LE,
+ * PNK_GT,
+ * PNK_GE,
+ * PNK_LSH,
+ * PNK_RSH,
+ * PNK_URSH,
+ * PNK_ADD,
+ * PNK_SUB,
+ * PNK_STAR,
+ * PNK_DIV,
+ * PNK_MOD,
+ * PNK_POW                  (**) is right-associative, but forms a list
+ *                          nonetheless. Special hacks everywhere.
+ *
+ * PNK_POS,     unary       pn_kid: UNARY expr
+ * PNK_NEG
+ * PNK_VOID,    unary       pn_kid: UNARY expr
+ * PNK_NOT,
+ * PNK_BITNOT,
+ * PNK_AWAIT
+ * PNK_TYPEOFNAME, unary    pn_kid: UNARY expr
+ * PNK_TYPEOFEXPR
+ * PNK_PREINCREMENT, unary  pn_kid: MEMBER expr
+ * PNK_POSTINCREMENT,
+ * PNK_PREDECREMENT,
+ * PNK_POSTDECREMENT
+ * PNK_NEW      list        pn_head: list of ctor, arg1, arg2, ... argN
+ *                          pn_count: 1 + N (where N is number of args)
+ *                          ctor is a MEMBER expr
+ * PNK_DELETENAME unary     pn_kid: PNK_NAME expr
+ * PNK_DELETEPROP unary     pn_kid: PNK_DOT expr
+ * PNK_DELETEELEM unary     pn_kid: PNK_ELEM expr
+ * PNK_DELETEEXPR unary     pn_kid: MEMBER expr that's evaluated, then the
+ *                          overall delete evaluates to true; can't be a kind
+ *                          for a more-specific PNK_DELETE* unless constant
+ *                          folding (or a similar parse tree manipulation) has
+ *                          occurred
+ * PNK_DOT      name        pn_expr: MEMBER expr to left of .
+ *                          pn_atom: name to right of .
+ * PNK_ELEM     binary      pn_left: MEMBER expr to left of [
+ *                          pn_right: expr between [ and ]
+ * PNK_CALL     list        pn_head: list of call, arg1, arg2, ... argN
+ *                          pn_count: 1 + N (where N is number of args)
+ *                          call is a MEMBER expr naming a callable object
+ * PNK_GENEXP   list        Exactly like PNK_CALL, used for the implicit call
+ *                          in the desugaring of a generator-expression.
+ * PNK_ARRAY    list        pn_head: list of pn_count array element exprs
+ *                          [,,] holes are represented by PNK_ELISION nodes
+ *                          pn_xflags: PN_ENDCOMMA if extra comma at end
+ * PNK_OBJECT   list        pn_head: list of pn_count binary PNK_COLON nodes
+ * PNK_COLON    binary      key-value pair in object initializer or
+ *                          destructuring lhs
+ *                          pn_left: property id, pn_right: value
+ * PNK_SHORTHAND binary     Same fields as PNK_COLON. This is used for object
+ *                          literal properties using shorthand ({x}).
+ * PNK_COMPUTED_NAME unary  ES6 ComputedPropertyName.
+ *                          pn_kid: the AssignmentExpression inside the square brackets
+ * PNK_NAME,    name        pn_atom: name, string, or object atom
+ * PNK_STRING               pn_op: JSOP_GETNAME, JSOP_STRING, or JSOP_OBJECT
+ *                          If JSOP_GETNAME, pn_op may be JSOP_*ARG or JSOP_*VAR
+ *                          telling const-ness and static analysis results
+ * PNK_TEMPLATE_STRING_LIST pn_head: list of alternating expr and template strings
+ *              list
+ * PNK_TEMPLATE_STRING      pn_atom: template string atom
+                nullary     pn_op: JSOP_NOP
+ * PNK_TAGGED_TEMPLATE      pn_head: list of call, call site object, arg1, arg2, ... argN
+ *              list        pn_count: 2 + N (N is the number of substitutions)
+ * PNK_CALLSITEOBJ list     pn_head: a PNK_ARRAY node followed by
+ *                          list of pn_count - 1 PNK_TEMPLATE_STRING nodes
+ * PNK_REGEXP   nullary     pn_objbox: RegExp model object
+ * PNK_NUMBER   dval        pn_dval: double value of numeric literal
+ * PNK_TRUE,    nullary     pn_op: JSOp bytecode
+ * PNK_FALSE,
+ * PNK_NULL
+ *
+ * PNK_THIS,        unary   pn_kid: '.this' Name if function `this`, else nullptr
+ * PNK_SUPERBASE    unary   pn_kid: '.this' Name
+ *
+ * PNK_SETTHIS      binary  pn_left: '.this' Name, pn_right: SuperCall
+ *
+ * PNK_LEXICALSCOPE scope   pn_u.scope.bindings: scope bindings
+ *                          pn_u.scope.body: scope body
+ * PNK_GENERATOR    nullary
+ * PNK_YIELD,       binary  pn_left: expr or null; pn_right: generator object
+ * PNK_YIELD_STAR
+ * PNK_ARRAYCOMP    list    pn_count: 1
+ *                          pn_head: list of 1 element, which is block
+ *                          enclosing for loop(s) and optionally
+ *                          if-guarded PNK_ARRAYPUSH
+ * PNK_ARRAYPUSH    unary   pn_op: JSOP_ARRAYCOMP
+ *                          pn_kid: array comprehension expression
+ * PNK_NOP          nullary
+ */
+enum ParseNodeArity
+{
+    PN_NULLARY,                         /* 0 kids, only pn_atom/pn_dval/etc. */
+    PN_UNARY,                           /* one kid, plus a couple of scalars */
+    PN_BINARY,                          /* two kids, plus a couple of scalars */
+    PN_TERNARY,                         /* three kids */
+    PN_CODE,                            /* module or function definition node */
+    PN_LIST,                            /* generic singly linked list */
+    PN_NAME,                            /* name, label, or regexp */
+    PN_SCOPE                            /* lexical scope */
+};
+
+class LoopControlStatement;
+class BreakStatement;
+class ContinueStatement;
+class ConditionalExpression;
+class PropertyAccess;
+
+class ParseNode
+{
+    uint16_t pn_type;   /* PNK_* type */
+    uint8_t pn_op;      /* see JSOp enum and jsopcode.tbl */
+    uint8_t pn_arity:4; /* see ParseNodeArity enum */
+    bool pn_parens:1;   /* this expr was enclosed in parens */
+
+    ParseNode(const ParseNode& other) = delete;
+    void operator=(const ParseNode& other) = delete;
+
+  public:
+    ParseNode(ParseNodeKind kind, JSOp op, ParseNodeArity arity)
+      : pn_type(kind),
+        pn_op(op),
+        pn_arity(arity),
+        pn_parens(false),
+        pn_pos(0, 0),
+        pn_next(nullptr)
+    {
+        MOZ_ASSERT(kind < PNK_LIMIT);
+        memset(&pn_u, 0, sizeof pn_u);
+    }
+
+    ParseNode(ParseNodeKind kind, JSOp op, ParseNodeArity arity, const TokenPos& pos)
+      : pn_type(kind),
+        pn_op(op),
+        pn_arity(arity),
+        pn_parens(false),
+        pn_pos(pos),
+        pn_next(nullptr)
+    {
+        MOZ_ASSERT(kind < PNK_LIMIT);
+        memset(&pn_u, 0, sizeof pn_u);
+    }
+
+    JSOp getOp() const                     { return JSOp(pn_op); }
+    void setOp(JSOp op)                    { pn_op = op; }
+    bool isOp(JSOp op) const               { return getOp() == op; }
+
+    ParseNodeKind getKind() const {
+        MOZ_ASSERT(pn_type < PNK_LIMIT);
+        return ParseNodeKind(pn_type);
+    }
+    void setKind(ParseNodeKind kind) {
+        MOZ_ASSERT(kind < PNK_LIMIT);
+        pn_type = kind;
+    }
+    bool isKind(ParseNodeKind kind) const  { return getKind() == kind; }
+
+    ParseNodeArity getArity() const        { return ParseNodeArity(pn_arity); }
+    bool isArity(ParseNodeArity a) const   { return getArity() == a; }
+    void setArity(ParseNodeArity a)        { pn_arity = a; }
+
+    bool isAssignment() const {
+        ParseNodeKind kind = getKind();
+        return PNK_ASSIGNMENT_START <= kind && kind <= PNK_ASSIGNMENT_LAST;
+    }
+
+    bool isBinaryOperation() const {
+        ParseNodeKind kind = getKind();
+        return PNK_BINOP_FIRST <= kind && kind <= PNK_BINOP_LAST;
+    }
+
+    /* Boolean attributes. */
+    bool isInParens() const                { return pn_parens; }
+    bool isLikelyIIFE() const              { return isInParens(); }
+    void setInParens(bool enabled)         { pn_parens = enabled; }
+
+    TokenPos            pn_pos;         /* two 16-bit pairs here, for 64 bits */
+    ParseNode*          pn_next;        /* intrinsic link in parent PN_LIST */
+
+    union {
+        struct {                        /* list of next-linked nodes */
+            ParseNode*  head;           /* first node in list */
+            ParseNode** tail;           /* ptr to ptr to last node in list */
+            uint32_t    count;          /* number of nodes in list */
+            uint32_t    xflags;         /* see PNX_* below */
+        } list;
+        struct {                        /* ternary: if, for(;;), ?: */
+            ParseNode*  kid1;           /* condition, discriminant, etc. */
+            ParseNode*  kid2;           /* then-part, case list, etc. */
+            ParseNode*  kid3;           /* else-part, default case, etc. */
+        } ternary;
+        struct {                        /* two kids if binary */
+            ParseNode*  left;
+            ParseNode*  right;
+            union {
+                unsigned iflags;        /* JSITER_* flags for PNK_{COMPREHENSION,}FOR node */
+                bool isStatic;          /* only for PNK_CLASSMETHOD */
+                uint32_t offset;        /* for the emitter's use on PNK_CASE nodes */
+            };
+        } binary;
+        struct {                        /* one kid if unary */
+            ParseNode*  kid;
+            bool        prologue;       /* directive prologue member (as
+                                           pn_prologue) */
+        } unary;
+        struct {                        /* name, labeled statement, etc. */
+            union {
+                JSAtom*      atom;      /* lexical name or label atom */
+                ObjectBox*   objbox;    /* regexp object */
+                FunctionBox* funbox;    /* function object */
+            };
+            ParseNode*  expr;           /* module or function body, var
+                                           initializer, argument default, or
+                                           base object of PNK_DOT */
+        } name;
+        struct {
+            LexicalScope::Data* bindings;
+            ParseNode*          body;
+        } scope;
+        struct {
+            double       value;         /* aligned numeric literal value */
+            DecimalPoint decimalPoint;  /* Whether the number has a decimal point */
+        } number;
+        class {
+            friend class LoopControlStatement;
+            PropertyName*    label;    /* target of break/continue statement */
+        } loopControl;
+    } pn_u;
+
+#define pn_objbox       pn_u.name.objbox
+#define pn_funbox       pn_u.name.funbox
+#define pn_body         pn_u.name.expr
+#define pn_head         pn_u.list.head
+#define pn_tail         pn_u.list.tail
+#define pn_count        pn_u.list.count
+#define pn_xflags       pn_u.list.xflags
+#define pn_kid1         pn_u.ternary.kid1
+#define pn_kid2         pn_u.ternary.kid2
+#define pn_kid3         pn_u.ternary.kid3
+#define pn_left         pn_u.binary.left
+#define pn_right        pn_u.binary.right
+#define pn_pval         pn_u.binary.pval
+#define pn_iflags       pn_u.binary.iflags
+#define pn_kid          pn_u.unary.kid
+#define pn_prologue     pn_u.unary.prologue
+#define pn_atom         pn_u.name.atom
+#define pn_objbox       pn_u.name.objbox
+#define pn_expr         pn_u.name.expr
+#define pn_dval         pn_u.number.value
+
+
+  public:
+    /*
+     * If |left| is a list of the given kind/left-associative op, append
+     * |right| to it and return |left|.  Otherwise return a [left, right] list.
+     */
+    static ParseNode*
+    appendOrCreateList(ParseNodeKind kind, JSOp op, ParseNode* left, ParseNode* right,
+                       FullParseHandler* handler, ParseContext* pc);
+
+    inline PropertyName* name() const;
+    inline JSAtom* atom() const;
+
+    ParseNode* expr() const {
+        MOZ_ASSERT(pn_arity == PN_NAME || pn_arity == PN_CODE);
+        return pn_expr;
+    }
+
+    bool isEmptyScope() const {
+        MOZ_ASSERT(pn_arity == PN_SCOPE);
+        return !pn_u.scope.bindings;
+    }
+
+    Handle<LexicalScope::Data*> scopeBindings() const {
+        MOZ_ASSERT(!isEmptyScope());
+        // Bindings' GC safety depend on the presence of an AutoKeepAtoms that
+        // the rest of the frontend also depends on.
+        return Handle<LexicalScope::Data*>::fromMarkedLocation(&pn_u.scope.bindings);
+    }
+
+    ParseNode* scopeBody() const {
+        MOZ_ASSERT(pn_arity == PN_SCOPE);
+        return pn_u.scope.body;
+    }
+
+    void setScopeBody(ParseNode* body) {
+        MOZ_ASSERT(pn_arity == PN_SCOPE);
+        pn_u.scope.body = body;
+    }
+
+/* PN_LIST pn_xflags bits. */
+#define PNX_FUNCDEFS    0x01            /* contains top-level function statements */
+#define PNX_ARRAYHOLESPREAD 0x02        /* one or more of
+                                           1. array initialiser has holes
+                                           2. array initializer has spread node */
+#define PNX_NONCONST    0x04            /* initialiser has non-constants */
+
+    bool functionIsHoisted() const {
+        MOZ_ASSERT(pn_arity == PN_CODE && getKind() == PNK_FUNCTION);
+        MOZ_ASSERT(isOp(JSOP_LAMBDA) ||        // lambda, genexpr
+                   isOp(JSOP_LAMBDA_ARROW) ||  // arrow function
+                   isOp(JSOP_FUNWITHPROTO) ||  // already emitted lambda with needsProto
+                   isOp(JSOP_DEFFUN) ||        // non-body-level function statement
+                   isOp(JSOP_NOP) ||           // body-level function stmt in global code
+                   isOp(JSOP_GETLOCAL) ||      // body-level function stmt in function code
+                   isOp(JSOP_GETARG) ||        // body-level function redeclaring formal
+                   isOp(JSOP_INITLEXICAL));    // block-level function stmt
+        return !isOp(JSOP_LAMBDA) && !isOp(JSOP_LAMBDA_ARROW) &&
+               !isOp(JSOP_FUNWITHPROTO) && !isOp(JSOP_DEFFUN);
+    }
+
+    /*
+     * True if this statement node could be a member of a Directive Prologue: an
+     * expression statement consisting of a single string literal.
+     *
+     * This considers only the node and its children, not its context. After
+     * parsing, check the node's pn_prologue flag to see if it is indeed part of
+     * a directive prologue.
+     *
+     * Note that a Directive Prologue can contain statements that cannot
+     * themselves be directives (string literals that include escape sequences
+     * or escaped newlines, say). This member function returns true for such
+     * nodes; we use it to determine the extent of the prologue.
+     */
+    JSAtom* isStringExprStatement() const {
+        if (getKind() == PNK_SEMI) {
+            MOZ_ASSERT(pn_arity == PN_UNARY);
+            ParseNode* kid = pn_kid;
+            if (kid && kid->getKind() == PNK_STRING && !kid->pn_parens)
+                return kid->pn_atom;
+        }
+        return nullptr;
+    }
+
+    /* True if pn is a parsenode representing a literal constant. */
+    bool isLiteral() const {
+        return isKind(PNK_NUMBER) ||
+               isKind(PNK_STRING) ||
+               isKind(PNK_TRUE) ||
+               isKind(PNK_FALSE) ||
+               isKind(PNK_NULL);
+    }
+
+    /* Return true if this node appears in a Directive Prologue. */
+    bool isDirectivePrologueMember() const { return pn_prologue; }
+
+    // True iff this is a for-in/of loop variable declaration (var/let/const).
+    bool isForLoopDeclaration() const {
+        if (isKind(PNK_VAR) || isKind(PNK_LET) || isKind(PNK_CONST)) {
+            MOZ_ASSERT(isArity(PN_LIST));
+            MOZ_ASSERT(pn_count > 0);
+            return true;
+        }
+
+        return false;
+    }
+
+    ParseNode* generatorExpr() const {
+        MOZ_ASSERT(isKind(PNK_GENEXP));
+
+        ParseNode* callee = this->pn_head;
+        MOZ_ASSERT(callee->isKind(PNK_FUNCTION));
+
+        ParseNode* paramsBody = callee->pn_body;
+        MOZ_ASSERT(paramsBody->isKind(PNK_PARAMSBODY));
+
+        ParseNode* body = paramsBody->last();
+        MOZ_ASSERT(body->isKind(PNK_STATEMENTLIST));
+        MOZ_ASSERT(body->last()->isKind(PNK_LEXICALSCOPE) ||
+                   body->last()->isKind(PNK_COMPREHENSIONFOR));
+        return body->last();
+    }
+
+    /*
+     * Compute a pointer to the last element in a singly-linked list. NB: list
+     * must be non-empty for correct PN_LAST usage -- this is asserted!
+     */
+    ParseNode* last() const {
+        MOZ_ASSERT(pn_arity == PN_LIST);
+        MOZ_ASSERT(pn_count != 0);
+        return (ParseNode*)(uintptr_t(pn_tail) - offsetof(ParseNode, pn_next));
+    }
+
+    void initNumber(double value, DecimalPoint decimalPoint) {
+        MOZ_ASSERT(pn_arity == PN_NULLARY);
+        MOZ_ASSERT(getKind() == PNK_NUMBER);
+        pn_u.number.value = value;
+        pn_u.number.decimalPoint = decimalPoint;
+    }
+
+    void makeEmpty() {
+        MOZ_ASSERT(pn_arity == PN_LIST);
+        pn_head = nullptr;
+        pn_tail = &pn_head;
+        pn_count = 0;
+        pn_xflags = 0;
+    }
+
+    void initList(ParseNode* pn) {
+        MOZ_ASSERT(pn_arity == PN_LIST);
+        if (pn->pn_pos.begin < pn_pos.begin)
+            pn_pos.begin = pn->pn_pos.begin;
+        pn_pos.end = pn->pn_pos.end;
+        pn_head = pn;
+        pn_tail = &pn->pn_next;
+        pn_count = 1;
+        pn_xflags = 0;
+    }
+
+    void append(ParseNode* pn) {
+        MOZ_ASSERT(pn_arity == PN_LIST);
+        MOZ_ASSERT(pn->pn_pos.begin >= pn_pos.begin);
+        pn_pos.end = pn->pn_pos.end;
+        *pn_tail = pn;
+        pn_tail = &pn->pn_next;
+        pn_count++;
+    }
+
+    void prepend(ParseNode* pn) {
+        MOZ_ASSERT(pn_arity == PN_LIST);
+        pn->pn_next = pn_head;
+        pn_head = pn;
+        if (pn_tail == &pn_head)
+            pn_tail = &pn->pn_next;
+        pn_count++;
+    }
+
+    void checkListConsistency()
+#ifndef DEBUG
+    {}
+#endif
+    ;
+
+    enum AllowConstantObjects {
+        DontAllowObjects = 0,
+        AllowObjects,
+        ForCopyOnWriteArray
+    };
+
+    MOZ_MUST_USE bool getConstantValue(ExclusiveContext* cx, AllowConstantObjects allowObjects,
+                                       MutableHandleValue vp, Value* compare = nullptr,
+                                       size_t ncompare = 0, NewObjectKind newKind = TenuredObject);
+    inline bool isConstant();
+
+    template <class NodeType>
+    inline bool is() const {
+        return NodeType::test(*this);
+    }
+
+    /* Casting operations. */
+    template <class NodeType>
+    inline NodeType& as() {
+        MOZ_ASSERT(NodeType::test(*this));
+        return *static_cast<NodeType*>(this);
+    }
+
+    template <class NodeType>
+    inline const NodeType& as() const {
+        MOZ_ASSERT(NodeType::test(*this));
+        return *static_cast<const NodeType*>(this);
+    }
+
+#ifdef DEBUG
+    void dump();
+    void dump(int indent);
+#endif
+};
+
+struct NullaryNode : public ParseNode
+{
+    NullaryNode(ParseNodeKind kind, const TokenPos& pos)
+      : ParseNode(kind, JSOP_NOP, PN_NULLARY, pos) {}
+    NullaryNode(ParseNodeKind kind, JSOp op, const TokenPos& pos)
+      : ParseNode(kind, op, PN_NULLARY, pos) {}
+
+    // This constructor is for a few mad uses in the emitter. It populates
+    // the pn_atom field even though that field belongs to a branch in pn_u
+    // that nullary nodes shouldn't use -- bogus.
+    NullaryNode(ParseNodeKind kind, JSOp op, const TokenPos& pos, JSAtom* atom)
+      : ParseNode(kind, op, PN_NULLARY, pos)
+    {
+        pn_atom = atom;
+    }
+
+#ifdef DEBUG
+    void dump();
+#endif
+};
+
+struct UnaryNode : public ParseNode
+{
+    UnaryNode(ParseNodeKind kind, JSOp op, const TokenPos& pos, ParseNode* kid)
+      : ParseNode(kind, op, PN_UNARY, pos)
+    {
+        pn_kid = kid;
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct BinaryNode : public ParseNode
+{
+    BinaryNode(ParseNodeKind kind, JSOp op, const TokenPos& pos, ParseNode* left, ParseNode* right)
+      : ParseNode(kind, op, PN_BINARY, pos)
+    {
+        pn_left = left;
+        pn_right = right;
+    }
+
+    BinaryNode(ParseNodeKind kind, JSOp op, ParseNode* left, ParseNode* right)
+      : ParseNode(kind, op, PN_BINARY, TokenPos::box(left->pn_pos, right->pn_pos))
+    {
+        pn_left = left;
+        pn_right = right;
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct TernaryNode : public ParseNode
+{
+    TernaryNode(ParseNodeKind kind, JSOp op, ParseNode* kid1, ParseNode* kid2, ParseNode* kid3)
+      : ParseNode(kind, op, PN_TERNARY,
+                  TokenPos((kid1 ? kid1 : kid2 ? kid2 : kid3)->pn_pos.begin,
+                           (kid3 ? kid3 : kid2 ? kid2 : kid1)->pn_pos.end))
+    {
+        pn_kid1 = kid1;
+        pn_kid2 = kid2;
+        pn_kid3 = kid3;
+    }
+
+    TernaryNode(ParseNodeKind kind, JSOp op, ParseNode* kid1, ParseNode* kid2, ParseNode* kid3,
+                const TokenPos& pos)
+      : ParseNode(kind, op, PN_TERNARY, pos)
+    {
+        pn_kid1 = kid1;
+        pn_kid2 = kid2;
+        pn_kid3 = kid3;
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct ListNode : public ParseNode
+{
+    ListNode(ParseNodeKind kind, const TokenPos& pos)
+      : ParseNode(kind, JSOP_NOP, PN_LIST, pos)
+    {
+        makeEmpty();
+    }
+
+    ListNode(ParseNodeKind kind, JSOp op, const TokenPos& pos)
+      : ParseNode(kind, op, PN_LIST, pos)
+    {
+        makeEmpty();
+    }
+
+    ListNode(ParseNodeKind kind, JSOp op, ParseNode* kid)
+      : ParseNode(kind, op, PN_LIST, kid->pn_pos)
+    {
+        initList(kid);
+    }
+
+    static bool test(const ParseNode& node) {
+        return node.isArity(PN_LIST);
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct CodeNode : public ParseNode
+{
+    CodeNode(ParseNodeKind kind, const TokenPos& pos)
+      : ParseNode(kind, JSOP_NOP, PN_CODE, pos)
+    {
+        MOZ_ASSERT(kind == PNK_FUNCTION || kind == PNK_MODULE);
+        MOZ_ASSERT(!pn_body);
+        MOZ_ASSERT(!pn_objbox);
+    }
+
+  public:
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct NameNode : public ParseNode
+{
+    NameNode(ParseNodeKind kind, JSOp op, JSAtom* atom, const TokenPos& pos)
+      : ParseNode(kind, op, PN_NAME, pos)
+    {
+        pn_atom = atom;
+        pn_expr = nullptr;
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+struct LexicalScopeNode : public ParseNode
+{
+    LexicalScopeNode(LexicalScope::Data* bindings, ParseNode* body)
+      : ParseNode(PNK_LEXICALSCOPE, JSOP_NOP, PN_SCOPE, body->pn_pos)
+    {
+        pn_u.scope.bindings = bindings;
+        pn_u.scope.body = body;
+    }
+
+    static bool test(const ParseNode& node) {
+        return node.isKind(PNK_LEXICALSCOPE);
+    }
+
+#ifdef DEBUG
+    void dump(int indent);
+#endif
+};
+
+class LabeledStatement : public ParseNode
+{
+  public:
+    LabeledStatement(PropertyName* label, ParseNode* stmt, uint32_t begin)
+      : ParseNode(PNK_LABEL, JSOP_NOP, PN_NAME, TokenPos(begin, stmt->pn_pos.end))
+    {
+        pn_atom = label;
+        pn_expr = stmt;
+    }
+
+    PropertyName* label() const {
+        return pn_atom->asPropertyName();
+    }
+
+    ParseNode* statement() const {
+        return pn_expr;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_LABEL);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NAME));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+// Inside a switch statement, a CaseClause is a case-label and the subsequent
+// statements. The same node type is used for DefaultClauses. The only
+// difference is that their caseExpression() is null.
+class CaseClause : public BinaryNode
+{
+  public:
+    CaseClause(ParseNode* expr, ParseNode* stmts, uint32_t begin)
+      : BinaryNode(PNK_CASE, JSOP_NOP, TokenPos(begin, stmts->pn_pos.end), expr, stmts) {}
+
+    ParseNode* caseExpression() const { return pn_left; }
+    bool isDefault() const { return !caseExpression(); }
+    ParseNode* statementList() const { return pn_right; }
+
+    // The next CaseClause in the same switch statement.
+    CaseClause* next() const { return pn_next ? &pn_next->as<CaseClause>() : nullptr; }
+
+    // Scratch space used by the emitter.
+    uint32_t offset() const { return pn_u.binary.offset; }
+    void setOffset(uint32_t u) { pn_u.binary.offset = u; }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CASE);
+        MOZ_ASSERT_IF(match, node.isArity(PN_BINARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+class LoopControlStatement : public ParseNode
+{
+  protected:
+    LoopControlStatement(ParseNodeKind kind, PropertyName* label, const TokenPos& pos)
+      : ParseNode(kind, JSOP_NOP, PN_NULLARY, pos)
+    {
+        MOZ_ASSERT(kind == PNK_BREAK || kind == PNK_CONTINUE);
+        pn_u.loopControl.label = label;
+    }
+
+  public:
+    /* Label associated with this break/continue statement, if any. */
+    PropertyName* label() const {
+        return pn_u.loopControl.label;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_BREAK) || node.isKind(PNK_CONTINUE);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NULLARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+class BreakStatement : public LoopControlStatement
+{
+  public:
+    BreakStatement(PropertyName* label, const TokenPos& pos)
+      : LoopControlStatement(PNK_BREAK, label, pos)
+    { }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_BREAK);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NULLARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+class ContinueStatement : public LoopControlStatement
+{
+  public:
+    ContinueStatement(PropertyName* label, const TokenPos& pos)
+      : LoopControlStatement(PNK_CONTINUE, label, pos)
+    { }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CONTINUE);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NULLARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+class DebuggerStatement : public ParseNode
+{
+  public:
+    explicit DebuggerStatement(const TokenPos& pos)
+      : ParseNode(PNK_DEBUGGER, JSOP_NOP, PN_NULLARY, pos)
+    { }
+};
+
+class ConditionalExpression : public ParseNode
+{
+  public:
+    ConditionalExpression(ParseNode* condition, ParseNode* thenExpr, ParseNode* elseExpr)
+      : ParseNode(PNK_CONDITIONAL, JSOP_NOP, PN_TERNARY,
+                  TokenPos(condition->pn_pos.begin, elseExpr->pn_pos.end))
+    {
+        MOZ_ASSERT(condition);
+        MOZ_ASSERT(thenExpr);
+        MOZ_ASSERT(elseExpr);
+        pn_u.ternary.kid1 = condition;
+        pn_u.ternary.kid2 = thenExpr;
+        pn_u.ternary.kid3 = elseExpr;
+    }
+
+    ParseNode& condition() const {
+        return *pn_u.ternary.kid1;
+    }
+
+    ParseNode& thenExpression() const {
+        return *pn_u.ternary.kid2;
+    }
+
+    ParseNode& elseExpression() const {
+        return *pn_u.ternary.kid3;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CONDITIONAL);
+        MOZ_ASSERT_IF(match, node.isArity(PN_TERNARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_NOP));
+        return match;
+    }
+};
+
+class ThisLiteral : public UnaryNode
+{
+  public:
+    ThisLiteral(const TokenPos& pos, ParseNode* thisName)
+      : UnaryNode(PNK_THIS, JSOP_NOP, pos, thisName)
+    { }
+};
+
+class NullLiteral : public ParseNode
+{
+  public:
+    explicit NullLiteral(const TokenPos& pos) : ParseNode(PNK_NULL, JSOP_NULL, PN_NULLARY, pos) { }
+};
+
+class BooleanLiteral : public ParseNode
+{
+  public:
+    BooleanLiteral(bool b, const TokenPos& pos)
+      : ParseNode(b ? PNK_TRUE : PNK_FALSE, b ? JSOP_TRUE : JSOP_FALSE, PN_NULLARY, pos)
+    { }
+};
+
+class RegExpLiteral : public NullaryNode
+{
+  public:
+    RegExpLiteral(ObjectBox* reobj, const TokenPos& pos)
+      : NullaryNode(PNK_REGEXP, JSOP_REGEXP, pos)
+    {
+        pn_objbox = reobj;
+    }
+
+    ObjectBox* objbox() const { return pn_objbox; }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_REGEXP);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NULLARY));
+        MOZ_ASSERT_IF(match, node.isOp(JSOP_REGEXP));
+        return match;
+    }
+};
+
+class PropertyAccess : public ParseNode
+{
+  public:
+    PropertyAccess(ParseNode* lhs, PropertyName* name, uint32_t begin, uint32_t end)
+      : ParseNode(PNK_DOT, JSOP_NOP, PN_NAME, TokenPos(begin, end))
+    {
+        MOZ_ASSERT(lhs != nullptr);
+        MOZ_ASSERT(name != nullptr);
+        pn_u.name.expr = lhs;
+        pn_u.name.atom = name;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_DOT);
+        MOZ_ASSERT_IF(match, node.isArity(PN_NAME));
+        return match;
+    }
+
+    ParseNode& expression() const {
+        return *pn_u.name.expr;
+    }
+
+    PropertyName& name() const {
+        return *pn_u.name.atom->asPropertyName();
+    }
+
+    bool isSuper() const {
+        // PNK_SUPERBASE cannot result from any expression syntax.
+        return expression().isKind(PNK_SUPERBASE);
+    }
+};
+
+class PropertyByValue : public ParseNode
+{
+  public:
+    PropertyByValue(ParseNode* lhs, ParseNode* propExpr, uint32_t begin, uint32_t end)
+      : ParseNode(PNK_ELEM, JSOP_NOP, PN_BINARY, TokenPos(begin, end))
+    {
+        pn_u.binary.left = lhs;
+        pn_u.binary.right = propExpr;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_ELEM);
+        MOZ_ASSERT_IF(match, node.isArity(PN_BINARY));
+        return match;
+    }
+
+    bool isSuper() const {
+        return pn_left->isKind(PNK_SUPERBASE);
+    }
+};
+
+/*
+ * A CallSiteNode represents the implicit call site object argument in a TaggedTemplate.
+ */
+struct CallSiteNode : public ListNode {
+    explicit CallSiteNode(uint32_t begin): ListNode(PNK_CALLSITEOBJ, TokenPos(begin, begin + 1)) {}
+
+    static bool test(const ParseNode& node) {
+        return node.isKind(PNK_CALLSITEOBJ);
+    }
+
+    MOZ_MUST_USE bool getRawArrayValue(ExclusiveContext* cx, MutableHandleValue vp) {
+        return pn_head->getConstantValue(cx, AllowObjects, vp);
+    }
+};
+
+struct ClassMethod : public BinaryNode {
+    /*
+     * Method defintions often keep a name and function body that overlap,
+     * so explicitly define the beginning and end here.
+     */
+    ClassMethod(ParseNode* name, ParseNode* body, JSOp op, bool isStatic)
+      : BinaryNode(PNK_CLASSMETHOD, op, TokenPos(name->pn_pos.begin, body->pn_pos.end), name, body)
+    {
+        pn_u.binary.isStatic = isStatic;
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CLASSMETHOD);
+        MOZ_ASSERT_IF(match, node.isArity(PN_BINARY));
+        return match;
+    }
+
+    ParseNode& name() const {
+        return *pn_u.binary.left;
+    }
+    ParseNode& method() const {
+        return *pn_u.binary.right;
+    }
+    bool isStatic() const {
+        return pn_u.binary.isStatic;
+    }
+};
+
+struct ClassNames : public BinaryNode {
+    ClassNames(ParseNode* outerBinding, ParseNode* innerBinding, const TokenPos& pos)
+      : BinaryNode(PNK_CLASSNAMES, JSOP_NOP, pos, outerBinding, innerBinding)
+    {
+        MOZ_ASSERT_IF(outerBinding, outerBinding->isKind(PNK_NAME));
+        MOZ_ASSERT(innerBinding->isKind(PNK_NAME));
+        MOZ_ASSERT_IF(outerBinding, innerBinding->pn_atom == outerBinding->pn_atom);
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CLASSNAMES);
+        MOZ_ASSERT_IF(match, node.isArity(PN_BINARY));
+        return match;
+    }
+
+    /*
+     * Classes require two definitions: The first "outer" binding binds the
+     * class into the scope in which it was declared. the outer binding is a
+     * mutable lexial binding. The second "inner" binding binds the class by
+     * name inside a block in which the methods are evaulated. It is immutable,
+     * giving the methods access to the static members of the class even if
+     * the outer binding has been overwritten.
+     */
+    ParseNode* outerBinding() const {
+        return pn_u.binary.left;
+    }
+    ParseNode* innerBinding() const {
+        return pn_u.binary.right;
+    }
+};
+
+struct ClassNode : public TernaryNode {
+    ClassNode(ParseNode* names, ParseNode* heritage, ParseNode* methodsOrBlock)
+      : TernaryNode(PNK_CLASS, JSOP_NOP, names, heritage, methodsOrBlock)
+    {
+        MOZ_ASSERT_IF(names, names->is<ClassNames>());
+        MOZ_ASSERT(methodsOrBlock->is<LexicalScopeNode>() ||
+                   methodsOrBlock->isKind(PNK_CLASSMETHODLIST));
+    }
+
+    static bool test(const ParseNode& node) {
+        bool match = node.isKind(PNK_CLASS);
+        MOZ_ASSERT_IF(match, node.isArity(PN_TERNARY));
+        return match;
+    }
+
+    ClassNames* names() const {
+        return pn_kid1 ? &pn_kid1->as<ClassNames>() : nullptr;
+    }
+    ParseNode* heritage() const {
+        return pn_kid2;
+    }
+    ParseNode* methodList() const {
+        if (pn_kid3->isKind(PNK_CLASSMETHODLIST))
+            return pn_kid3;
+
+        MOZ_ASSERT(pn_kid3->is<LexicalScopeNode>());
+        ParseNode* list = pn_kid3->scopeBody();
+        MOZ_ASSERT(list->isKind(PNK_CLASSMETHODLIST));
+        return list;
+    }
+    Handle<LexicalScope::Data*> scopeBindings() const {
+        MOZ_ASSERT(pn_kid3->is<LexicalScopeNode>());
+        return pn_kid3->scopeBindings();
+    }
+};
+
+#ifdef DEBUG
+void DumpParseTree(ParseNode* pn, int indent = 0);
+#endif
+
+class ParseNodeAllocator
+{
+  public:
+    explicit ParseNodeAllocator(ExclusiveContext* cx, LifoAlloc& alloc)
+      : cx(cx), alloc(alloc), freelist(nullptr)
+    {}
+
+    void* allocNode();
+    void freeNode(ParseNode* pn);
+    ParseNode* freeTree(ParseNode* pn);
+    void prepareNodeForMutation(ParseNode* pn);
+
+  private:
+    ExclusiveContext* cx;
+    LifoAlloc& alloc;
+    ParseNode* freelist;
+};
+
+inline bool
+ParseNode::isConstant()
+{
+    switch (pn_type) {
+      case PNK_NUMBER:
+      case PNK_STRING:
+      case PNK_TEMPLATE_STRING:
+      case PNK_NULL:
+      case PNK_FALSE:
+      case PNK_TRUE:
+        return true;
+      case PNK_ARRAY:
+      case PNK_OBJECT:
+        MOZ_ASSERT(isOp(JSOP_NEWINIT));
+        return !(pn_xflags & PNX_NONCONST);
+      default:
+        return false;
+    }
+}
+
+class ObjectBox
+{
+  public:
+    JSObject* object;
+
+    ObjectBox(JSObject* object, ObjectBox* traceLink);
+    bool isFunctionBox() { return object->is<JSFunction>(); }
+    FunctionBox* asFunctionBox();
+    virtual void trace(JSTracer* trc);
+
+    static void TraceList(JSTracer* trc, ObjectBox* listHead);
+
+  protected:
+    friend struct CGObjectList;
+
+    ObjectBox* traceLink;
+    ObjectBox* emitLink;
+
+    ObjectBox(JSFunction* function, ObjectBox* traceLink);
+};
+
+enum ParseReportKind
+{
+    ParseError,
+    ParseWarning,
+    ParseExtraWarning,
+    ParseStrictError
+};
+
+enum FunctionSyntaxKind
+{
+    Expression,
+    Statement,
+    Arrow,
+    Method,
+    ClassConstructor,
+    DerivedClassConstructor,
+    Getter,
+    GetterNoExpressionClosure,
+    Setter,
+    SetterNoExpressionClosure
+};
+
+static inline bool
+IsConstructorKind(FunctionSyntaxKind kind)
+{
+    return kind == ClassConstructor || kind == DerivedClassConstructor;
+}
+
+static inline bool
+IsGetterKind(FunctionSyntaxKind kind)
+{
+    return kind == Getter || kind == GetterNoExpressionClosure;
+}
+
+static inline bool
+IsSetterKind(FunctionSyntaxKind kind)
+{
+    return kind == Setter || kind == SetterNoExpressionClosure;
+}
+
+static inline bool
+IsMethodDefinitionKind(FunctionSyntaxKind kind)
+{
+    return kind == Method || IsConstructorKind(kind) ||
+           IsGetterKind(kind) || IsSetterKind(kind);
+}
+
+static inline ParseNode*
+FunctionFormalParametersList(ParseNode* fn, unsigned* numFormals)
+{
+    MOZ_ASSERT(fn->isKind(PNK_FUNCTION));
+    ParseNode* argsBody = fn->pn_body;
+    MOZ_ASSERT(argsBody->isKind(PNK_PARAMSBODY));
+    *numFormals = argsBody->pn_count;
+    if (*numFormals > 0 &&
+        argsBody->last()->isKind(PNK_LEXICALSCOPE) &&
+        argsBody->last()->scopeBody()->isKind(PNK_STATEMENTLIST))
+    {
+        (*numFormals)--;
+    }
+    MOZ_ASSERT(argsBody->isArity(PN_LIST));
+    return argsBody->pn_head;
+}
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_ParseNode_h */
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
new file mode 100644
index 0000000000..49fef2bf95
--- /dev/null
+++ b/js/src/frontend/Parser.cpp
@@ -0,0 +1,9627 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * JS parser.
+ *
+ * This is a recursive-descent parser for the JavaScript language specified by
+ * "The ECMAScript Language Specification" (Standard ECMA-262).  It uses
+ * lexical and semantic feedback to disambiguate non-LL(1) structures.  It
+ * generates trees of nodes induced by the recursive parsing (not precise
+ * syntax trees, see Parser.h).  After tree construction, it rewrites trees to
+ * fold constants and evaluate compile-time expressions.
+ *
+ * This parser attempts no error recovery.
+ */
+
+#include "frontend/Parser.h"
+
+#include "jsapi.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsfun.h"
+#include "jsopcode.h"
+#include "jsscript.h"
+#include "jstypes.h"
+
+#include "builtin/ModuleObject.h"
+#include "builtin/SelfHostingDefines.h"
+#include "frontend/BytecodeCompiler.h"
+#include "frontend/FoldConstants.h"
+#include "frontend/TokenStream.h"
+#include "wasm/AsmJS.h"
+
+#include "jsatominlines.h"
+#include "jsscriptinlines.h"
+
+#include "frontend/ParseNode-inl.h"
+#include "vm/EnvironmentObject-inl.h"
+
+using namespace js;
+using namespace js::gc;
+
+using mozilla::Maybe;
+using mozilla::Move;
+using mozilla::Nothing;
+using mozilla::PodCopy;
+using mozilla::PodZero;
+using mozilla::Some;
+
+using JS::AutoGCRooter;
+
+namespace js {
+namespace frontend {
+
+using DeclaredNamePtr = ParseContext::Scope::DeclaredNamePtr;
+using AddDeclaredNamePtr = ParseContext::Scope::AddDeclaredNamePtr;
+using BindingIter = ParseContext::Scope::BindingIter;
+using UsedNamePtr = UsedNameTracker::UsedNameMap::Ptr;
+
+/* Read a token. Report an error and return null() if that token isn't of type tt. */
+#define MUST_MATCH_TOKEN_MOD(tt, modifier, errno)                                           \
+    JS_BEGIN_MACRO                                                                          \
+        TokenKind token;                                                                    \
+        if (!tokenStream.getToken(&token, modifier))                                        \
+            return null();                                                                  \
+        if (token != tt) {                                                                  \
+            report(ParseError, false, null(), errno);                                       \
+            return null();                                                                  \
+        }                                                                                   \
+    JS_END_MACRO
+
+#define MUST_MATCH_TOKEN(tt, errno) MUST_MATCH_TOKEN_MOD(tt, TokenStream::None, errno)
+
+template <class T, class U>
+static inline void
+PropagateTransitiveParseFlags(const T* inner, U* outer)
+{
+    if (inner->bindingsAccessedDynamically())
+        outer->setBindingsAccessedDynamically();
+    if (inner->hasDebuggerStatement())
+        outer->setHasDebuggerStatement();
+    if (inner->hasDirectEval())
+        outer->setHasDirectEval();
+}
+
+static const char*
+DeclarationKindString(DeclarationKind kind)
+{
+    switch (kind) {
+      case DeclarationKind::PositionalFormalParameter:
+      case DeclarationKind::FormalParameter:
+        return "formal parameter";
+      case DeclarationKind::CoverArrowParameter:
+        return "cover arrow parameter";
+      case DeclarationKind::Var:
+        return "var";
+      case DeclarationKind::Let:
+        return "let";
+      case DeclarationKind::Const:
+        return "const";
+      case DeclarationKind::Import:
+        return "import";
+      case DeclarationKind::BodyLevelFunction:
+      case DeclarationKind::LexicalFunction:
+        return "function";
+      case DeclarationKind::VarForAnnexBLexicalFunction:
+        return "annex b var";
+      case DeclarationKind::ForOfVar:
+        return "var in for-of";
+      case DeclarationKind::SimpleCatchParameter:
+      case DeclarationKind::CatchParameter:
+        return "catch parameter";
+    }
+
+    MOZ_CRASH("Bad DeclarationKind");
+}
+
+static bool
+StatementKindIsBraced(StatementKind kind)
+{
+    return kind == StatementKind::Block ||
+           kind == StatementKind::Switch ||
+           kind == StatementKind::Try ||
+           kind == StatementKind::Catch ||
+           kind == StatementKind::Finally;
+}
+
+void
+ParseContext::Scope::dump(ParseContext* pc)
+{
+    ExclusiveContext* cx = pc->sc()->context;
+
+    fprintf(stdout, "ParseScope %p", this);
+
+    fprintf(stdout, "\n  decls:\n");
+    for (DeclaredNameMap::Range r = declared_->all(); !r.empty(); r.popFront()) {
+        JSAutoByteString bytes;
+        if (!AtomToPrintableString(cx, r.front().key(), &bytes))
+            return;
+        DeclaredNameInfo& info = r.front().value().wrapped;
+        fprintf(stdout, "    %s %s%s\n",
+                DeclarationKindString(info.kind()),
+                bytes.ptr(),
+                info.closedOver() ? " (closed over)" : "");
+    }
+
+    fprintf(stdout, "\n");
+}
+
+/* static */ void
+ParseContext::Scope::removeVarForAnnexBLexicalFunction(ParseContext* pc, JSAtom* name)
+{
+    // Local strict mode is allowed, e.g., a class binding removing a
+    // synthesized Annex B binding.
+    MOZ_ASSERT(!pc->sc()->strictScript);
+
+    for (ParseContext::Scope* scope = pc->innermostScope();
+         scope != pc->varScope().enclosing();
+         scope = scope->enclosing())
+    {
+        if (DeclaredNamePtr p = scope->declared_->lookup(name)) {
+            if (p->value()->kind() == DeclarationKind::VarForAnnexBLexicalFunction)
+                scope->declared_->remove(p);
+        }
+    }
+
+    // Annex B semantics no longer applies to any functions with this name, as
+    // an early error would have occurred.
+    pc->removeInnerFunctionBoxesForAnnexB(name);
+}
+
+static bool
+DeclarationKindIsCatchParameter(DeclarationKind kind)
+{
+    return kind == DeclarationKind::SimpleCatchParameter ||
+           kind == DeclarationKind::CatchParameter;
+}
+
+bool
+ParseContext::Scope::addCatchParameters(ParseContext* pc, Scope& catchParamScope)
+{
+    if (pc->useAsmOrInsideUseAsm())
+        return true;
+
+    for (DeclaredNameMap::Range r = catchParamScope.declared_->all(); !r.empty(); r.popFront()) {
+        DeclarationKind kind = r.front().value()->kind();
+        MOZ_ASSERT(DeclarationKindIsCatchParameter(kind));
+        JSAtom* name = r.front().key();
+        AddDeclaredNamePtr p = lookupDeclaredNameForAdd(name);
+        MOZ_ASSERT(!p);
+        if (!addDeclaredName(pc, p, name, kind))
+            return false;
+    }
+
+    return true;
+}
+
+void
+ParseContext::Scope::removeCatchParameters(ParseContext* pc, Scope& catchParamScope)
+{
+    if (pc->useAsmOrInsideUseAsm())
+        return;
+
+    for (DeclaredNameMap::Range r = catchParamScope.declared_->all(); !r.empty(); r.popFront()) {
+        DeclaredNamePtr p = declared_->lookup(r.front().key());
+        MOZ_ASSERT(p);
+
+        // This check is needed because the catch body could have declared
+        // vars, which would have been added to catchParamScope.
+        if (DeclarationKindIsCatchParameter(r.front().value()->kind()))
+            declared_->remove(p);
+    }
+}
+
+void
+SharedContext::computeAllowSyntax(Scope* scope)
+{
+    for (ScopeIter si(scope); si; si++) {
+        if (si.kind() == ScopeKind::Function) {
+            JSFunction* fun = si.scope()->as<FunctionScope>().canonicalFunction();
+            if (fun->isArrow())
+                continue;
+            allowNewTarget_ = true;
+            allowSuperProperty_ = fun->allowSuperProperty();
+            allowSuperCall_ = fun->isDerivedClassConstructor();
+            return;
+        }
+    }
+}
+
+void
+SharedContext::computeThisBinding(Scope* scope)
+{
+    for (ScopeIter si(scope); si; si++) {
+        if (si.kind() == ScopeKind::Module) {
+            thisBinding_ = ThisBinding::Module;
+            return;
+        }
+
+        if (si.kind() == ScopeKind::Function) {
+            JSFunction* fun = si.scope()->as<FunctionScope>().canonicalFunction();
+
+            // Arrow functions and generator expression lambdas don't have
+            // their own `this` binding.
+            if (fun->isArrow() || fun->nonLazyScript()->isGeneratorExp())
+                continue;
+
+            // Derived class constructors (including nested arrow functions and
+            // eval) need TDZ checks when accessing |this|.
+            if (fun->isDerivedClassConstructor())
+                needsThisTDZChecks_ = true;
+
+            thisBinding_ = ThisBinding::Function;
+            return;
+        }
+    }
+
+    thisBinding_ = ThisBinding::Global;
+}
+
+void
+SharedContext::computeInWith(Scope* scope)
+{
+    for (ScopeIter si(scope); si; si++) {
+        if (si.kind() == ScopeKind::With) {
+            inWith_ = true;
+            break;
+        }
+    }
+}
+
+EvalSharedContext::EvalSharedContext(ExclusiveContext* cx, JSObject* enclosingEnv,
+                                     Scope* enclosingScope, Directives directives,
+                                     bool extraWarnings)
+  : SharedContext(cx, Kind::Eval, directives, extraWarnings),
+    enclosingScope_(cx, enclosingScope),
+    bindings(cx)
+{
+    computeAllowSyntax(enclosingScope);
+    computeInWith(enclosingScope);
+    computeThisBinding(enclosingScope);
+
+    // Like all things Debugger, Debugger.Frame.eval needs special
+    // handling. Since the environment chain of such evals are non-syntactic
+    // (DebuggerEnvironmentProxy is not an EnvironmentObject), computing the
+    // this binding with respect to enclosingScope is incorrect if the
+    // Debugger.Frame is a function frame. Recompute the this binding if we
+    // are such an eval.
+    if (enclosingEnv && enclosingScope->hasOnChain(ScopeKind::NonSyntactic)) {
+        // For Debugger.Frame.eval with bindings, the environment chain may
+        // have more than the DebugEnvironmentProxy.
+        JSObject* env = enclosingEnv;
+        while (env) {
+            if (env->is<DebugEnvironmentProxy>())
+                env = &env->as<DebugEnvironmentProxy>().environment();
+
+            if (env->is<CallObject>()) {
+                computeThisBinding(env->as<CallObject>().callee().nonLazyScript()->bodyScope());
+                break;
+            }
+
+            env = env->enclosingEnvironment();
+        }
+    }
+}
+
+bool
+ParseContext::init()
+{
+    if (scriptId_ == UINT32_MAX) {
+        tokenStream_.reportError(JSMSG_NEED_DIET, js_script_str);
+        return false;
+    }
+
+    ExclusiveContext* cx = sc()->context;
+
+    if (isFunctionBox()) {
+        // Named lambdas always need a binding for their own name. If this
+        // binding is closed over when we finish parsing the function in
+        // finishExtraFunctionScopes, the function box needs to be marked as
+        // needing a dynamic DeclEnv object.
+        RootedFunction fun(cx, functionBox()->function());
+        if (fun->isNamedLambda()) {
+            if (!namedLambdaScope_->init(this))
+                return false;
+            AddDeclaredNamePtr p = namedLambdaScope_->lookupDeclaredNameForAdd(fun->name());
+            MOZ_ASSERT(!p);
+            if (!namedLambdaScope_->addDeclaredName(this, p, fun->name(), DeclarationKind::Const))
+                return false;
+        }
+
+        if (!functionScope_->init(this))
+            return false;
+
+        if (!positionalFormalParameterNames_.acquire(cx))
+            return false;
+    }
+
+    if (!closedOverBindingsForLazy_.acquire(cx))
+        return false;
+
+    if (!sc()->strict()) {
+        if (!innerFunctionBoxesForAnnexB_.acquire(cx))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+ParseContext::addInnerFunctionBoxForAnnexB(FunctionBox* funbox)
+{
+    for (uint32_t i = 0; i < innerFunctionBoxesForAnnexB_->length(); i++) {
+        if (!innerFunctionBoxesForAnnexB_[i]) {
+            innerFunctionBoxesForAnnexB_[i] = funbox;
+            return true;
+        }
+    }
+    return innerFunctionBoxesForAnnexB_->append(funbox);
+}
+
+void
+ParseContext::removeInnerFunctionBoxesForAnnexB(JSAtom* name)
+{
+    for (uint32_t i = 0; i < innerFunctionBoxesForAnnexB_->length(); i++) {
+        if (FunctionBox* funbox = innerFunctionBoxesForAnnexB_[i]) {
+            if (funbox->function()->name() == name)
+                innerFunctionBoxesForAnnexB_[i] = nullptr;
+        }
+    }
+}
+
+void
+ParseContext::finishInnerFunctionBoxesForAnnexB()
+{
+    // Strict mode doesn't have wack Annex B function semantics. Or we
+    // could've failed to initialize ParseContext.
+    if (sc()->strict() || !innerFunctionBoxesForAnnexB_)
+        return;
+
+    for (uint32_t i = 0; i < innerFunctionBoxesForAnnexB_->length(); i++) {
+        if (FunctionBox* funbox = innerFunctionBoxesForAnnexB_[i])
+            funbox->isAnnexB = true;
+    }
+}
+
+ParseContext::~ParseContext()
+{
+    // Any funboxes still in the list at the end of parsing means no early
+    // error would have occurred for declaring a binding in the nearest var
+    // scope. Mark them as needing extra assignments to this var binding.
+    finishInnerFunctionBoxesForAnnexB();
+}
+
+bool
+UsedNameTracker::noteUse(ExclusiveContext* cx, JSAtom* name, uint32_t scriptId, uint32_t scopeId)
+{
+    if (UsedNameMap::AddPtr p = map_.lookupForAdd(name)) {
+        if (!p->value().noteUsedInScope(scriptId, scopeId))
+            return false;
+    } else {
+        UsedNameInfo info(cx);
+        if (!info.noteUsedInScope(scriptId, scopeId))
+            return false;
+        if (!map_.add(p, name, Move(info)))
+            return false;
+    }
+
+    return true;
+}
+
+void
+UsedNameTracker::UsedNameInfo::resetToScope(uint32_t scriptId, uint32_t scopeId)
+{
+    while (!uses_.empty()) {
+        Use& innermost = uses_.back();
+        if (innermost.scopeId < scopeId)
+            break;
+        MOZ_ASSERT(innermost.scriptId >= scriptId);
+        uses_.popBack();
+    }
+}
+
+void
+UsedNameTracker::rewind(RewindToken token)
+{
+    scriptCounter_ = token.scriptId;
+    scopeCounter_ = token.scopeId;
+
+    for (UsedNameMap::Range r = map_.all(); !r.empty(); r.popFront())
+        r.front().value().resetToScope(token.scriptId, token.scopeId);
+}
+
+FunctionBox::FunctionBox(ExclusiveContext* cx, LifoAlloc& alloc, ObjectBox* traceListHead,
+                         JSFunction* fun, Directives directives, bool extraWarnings,
+                         GeneratorKind generatorKind, FunctionAsyncKind asyncKind)
+  : ObjectBox(fun, traceListHead),
+    SharedContext(cx, Kind::ObjectBox, directives, extraWarnings),
+    enclosingScope_(nullptr),
+    namedLambdaBindings_(nullptr),
+    functionScopeBindings_(nullptr),
+    extraVarScopeBindings_(nullptr),
+    functionNode(nullptr),
+    bufStart(0),
+    bufEnd(0),
+    startLine(1),
+    startColumn(0),
+    length(0),
+    generatorKindBits_(GeneratorKindAsBits(generatorKind)),
+    asyncKindBits_(AsyncKindAsBits(asyncKind)),
+    isGenexpLambda(false),
+    hasDestructuringArgs(false),
+    hasParameterExprs(false),
+    hasDirectEvalInParameterExpr(false),
+    hasDuplicateParameters(false),
+    useAsm(false),
+    insideUseAsm(false),
+    isAnnexB(false),
+    wasEmitted(false),
+    declaredArguments(false),
+    usesArguments(false),
+    usesApply(false),
+    usesThis(false),
+    usesReturn(false),
+    funCxFlags()
+{
+    // Functions created at parse time may be set singleton after parsing and
+    // baked into JIT code, so they must be allocated tenured. They are held by
+    // the JSScript so cannot be collected during a minor GC anyway.
+    MOZ_ASSERT(fun->isTenured());
+}
+
+void
+FunctionBox::initFromLazyFunction()
+{
+    JSFunction* fun = function();
+    length = fun->nargs() - fun->hasRest();
+    if (fun->lazyScript()->isDerivedClassConstructor())
+        setDerivedClassConstructor();
+    if (fun->lazyScript()->needsHomeObject())
+        setNeedsHomeObject();
+    enclosingScope_ = fun->lazyScript()->enclosingScope();
+    initWithEnclosingScope(enclosingScope_);
+}
+
+void
+FunctionBox::initStandaloneFunction(Scope* enclosingScope)
+{
+    // Standalone functions are Function or Generator constructors and are
+    // always scoped to the global.
+    MOZ_ASSERT(enclosingScope->is<GlobalScope>());
+    JSFunction* fun = function();
+    length = fun->nargs() - fun->hasRest();
+    enclosingScope_ = enclosingScope;
+    allowNewTarget_ = true;
+    thisBinding_ = ThisBinding::Function;
+}
+
+void
+FunctionBox::initWithEnclosingParseContext(ParseContext* enclosing, FunctionSyntaxKind kind)
+{
+    SharedContext* sc = enclosing->sc();
+    useAsm = sc->isFunctionBox() && sc->asFunctionBox()->useAsmOrInsideUseAsm();
+
+    JSFunction* fun = function();
+
+    // Arrow functions and generator expression lambdas don't have
+    // their own `this` binding.
+    if (fun->isArrow()) {
+        allowNewTarget_ = sc->allowNewTarget();
+        allowSuperProperty_ = sc->allowSuperProperty();
+        allowSuperCall_ = sc->allowSuperCall();
+        needsThisTDZChecks_ = sc->needsThisTDZChecks();
+        thisBinding_ = sc->thisBinding();
+    } else {
+        allowNewTarget_ = true;
+        allowSuperProperty_ = fun->allowSuperProperty();
+
+        if (kind == DerivedClassConstructor) {
+            setDerivedClassConstructor();
+            allowSuperCall_ = true;
+            needsThisTDZChecks_ = true;
+        }
+
+        if (isGenexpLambda)
+            thisBinding_ = sc->thisBinding();
+        else
+            thisBinding_ = ThisBinding::Function;
+    }
+
+    if (sc->inWith()) {
+        inWith_ = true;
+    } else {
+        auto isWith = [](ParseContext::Statement* stmt) {
+            return stmt->kind() == StatementKind::With;
+        };
+
+        inWith_ = enclosing->findInnermostStatement(isWith);
+    }
+}
+
+void
+FunctionBox::initWithEnclosingScope(Scope* enclosingScope)
+{
+    if (!function()->isArrow()) {
+        allowNewTarget_ = true;
+        allowSuperProperty_ = function()->allowSuperProperty();
+
+        if (isDerivedClassConstructor()) {
+            setDerivedClassConstructor();
+            allowSuperCall_ = true;
+            needsThisTDZChecks_ = true;
+        }
+
+        thisBinding_ = ThisBinding::Function;
+    } else {
+        computeAllowSyntax(enclosingScope);
+        computeThisBinding(enclosingScope);
+    }
+
+    computeInWith(enclosingScope);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportHelper(ParseReportKind kind, bool strict, uint32_t offset,
+                                   unsigned errorNumber, va_list args)
+{
+    bool result = false;
+    switch (kind) {
+      case ParseError:
+        result = tokenStream.reportCompileErrorNumberVA(offset, JSREPORT_ERROR, errorNumber, args);
+        break;
+      case ParseWarning:
+        result =
+            tokenStream.reportCompileErrorNumberVA(offset, JSREPORT_WARNING, errorNumber, args);
+        break;
+      case ParseExtraWarning:
+        result = tokenStream.reportStrictWarningErrorNumberVA(offset, errorNumber, args);
+        break;
+      case ParseStrictError:
+        result = tokenStream.reportStrictModeErrorNumberVA(offset, strict, errorNumber, args);
+        break;
+    }
+    return result;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::report(ParseReportKind kind, bool strict, Node pn, unsigned errorNumber, ...)
+{
+    uint32_t offset = (pn ? handler.getPosition(pn) : pos()).begin;
+
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportHelper(kind, strict, offset, errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportNoOffset(ParseReportKind kind, bool strict, unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportHelper(kind, strict, TokenStream::NoOffset, errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportWithOffset(ParseReportKind kind, bool strict, uint32_t offset,
+                                       unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportHelper(kind, strict, offset, errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::abortIfSyntaxParser()
+{
+    handler.disableSyntaxParser();
+    return true;
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::abortIfSyntaxParser()
+{
+    abortedSyntaxParse = true;
+    return false;
+}
+
+template <typename ParseHandler>
+Parser<ParseHandler>::Parser(ExclusiveContext* cx, LifoAlloc& alloc,
+                             const ReadOnlyCompileOptions& options,
+                             const char16_t* chars, size_t length,
+                             bool foldConstants,
+                             UsedNameTracker& usedNames,
+                             Parser<SyntaxParseHandler>* syntaxParser,
+                             LazyScript* lazyOuterFunction)
+  : AutoGCRooter(cx, PARSER),
+    context(cx),
+    alloc(alloc),
+    tokenStream(cx, options, chars, length, thisForCtor()),
+    traceListHead(nullptr),
+    pc(nullptr),
+    usedNames(usedNames),
+    sct(nullptr),
+    ss(nullptr),
+    keepAtoms(cx->perThreadData),
+    foldConstants(foldConstants),
+#ifdef DEBUG
+    checkOptionsCalled(false),
+#endif
+    abortedSyntaxParse(false),
+    isUnexpectedEOF_(false),
+    handler(cx, alloc, tokenStream, syntaxParser, lazyOuterFunction)
+{
+    cx->perThreadData->frontendCollectionPool.addActiveCompilation();
+
+    // The Mozilla specific JSOPTION_EXTRA_WARNINGS option adds extra warnings
+    // which are not generated if functions are parsed lazily. Note that the
+    // standard "use strict" does not inhibit lazy parsing.
+    if (options.extraWarningsOption)
+        handler.disableSyntaxParser();
+
+    tempPoolMark = alloc.mark();
+}
+
+template<typename ParseHandler>
+bool
+Parser<ParseHandler>::checkOptions()
+{
+#ifdef DEBUG
+    checkOptionsCalled = true;
+#endif
+
+    if (!tokenStream.checkOptions())
+        return false;
+
+    return true;
+}
+
+template <typename ParseHandler>
+Parser<ParseHandler>::~Parser()
+{
+    MOZ_ASSERT(checkOptionsCalled);
+    alloc.release(tempPoolMark);
+
+    /*
+     * The parser can allocate enormous amounts of memory for large functions.
+     * Eagerly free the memory now (which otherwise won't be freed until the
+     * next GC) to avoid unnecessary OOMs.
+     */
+    alloc.freeAllIfHugeAndUnused();
+
+    context->perThreadData->frontendCollectionPool.removeActiveCompilation();
+}
+
+template <typename ParseHandler>
+ObjectBox*
+Parser<ParseHandler>::newObjectBox(JSObject* obj)
+{
+    MOZ_ASSERT(obj);
+
+    /*
+     * We use JSContext.tempLifoAlloc to allocate parsed objects and place them
+     * on a list in this Parser to ensure GC safety. Thus the tempLifoAlloc
+     * arenas containing the entries must be alive until we are done with
+     * scanning, parsing and code generation for the whole script or top-level
+     * function.
+     */
+
+    ObjectBox* objbox = alloc.new_<ObjectBox>(obj, traceListHead);
+    if (!objbox) {
+        ReportOutOfMemory(context);
+        return nullptr;
+    }
+
+    traceListHead = objbox;
+
+    return objbox;
+}
+
+template <typename ParseHandler>
+FunctionBox*
+Parser<ParseHandler>::newFunctionBox(Node fn, JSFunction* fun, Directives inheritedDirectives,
+                                     GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                     bool tryAnnexB)
+{
+    MOZ_ASSERT(fun);
+    MOZ_ASSERT_IF(tryAnnexB, !pc->sc()->strict());
+
+    /*
+     * We use JSContext.tempLifoAlloc to allocate parsed objects and place them
+     * on a list in this Parser to ensure GC safety. Thus the tempLifoAlloc
+     * arenas containing the entries must be alive until we are done with
+     * scanning, parsing and code generation for the whole script or top-level
+     * function.
+     */
+    FunctionBox* funbox =
+        alloc.new_<FunctionBox>(context, alloc, traceListHead, fun, inheritedDirectives,
+                                options().extraWarningsOption, generatorKind, asyncKind);
+    if (!funbox) {
+        ReportOutOfMemory(context);
+        return nullptr;
+    }
+
+    traceListHead = funbox;
+    if (fn)
+        handler.setFunctionBox(fn, funbox);
+
+    if (tryAnnexB && !pc->addInnerFunctionBoxForAnnexB(funbox))
+        return nullptr;
+
+    return funbox;
+}
+
+ModuleSharedContext::ModuleSharedContext(ExclusiveContext* cx, ModuleObject* module,
+                                         Scope* enclosingScope, ModuleBuilder& builder)
+  : SharedContext(cx, Kind::Module, Directives(true), false),
+    module_(cx, module),
+    enclosingScope_(cx, enclosingScope),
+    bindings(cx),
+    builder(builder)
+{
+    thisBinding_ = ThisBinding::Module;
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::trace(JSTracer* trc)
+{
+    ObjectBox::TraceList(trc, traceListHead);
+}
+
+void
+MarkParser(JSTracer* trc, AutoGCRooter* parser)
+{
+    static_cast<Parser<FullParseHandler>*>(parser)->trace(trc);
+}
+
+/*
+ * Parse a top-level JS script.
+ */
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::parse()
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    Directives directives(options().strictOption);
+    GlobalSharedContext globalsc(context, ScopeKind::Global,
+                                 directives, options().extraWarningsOption);
+    ParseContext globalpc(this, &globalsc, /* newDirectives = */ nullptr);
+    if (!globalpc.init())
+        return null();
+
+    ParseContext::VarScope varScope(this);
+    if (!varScope.init(pc))
+        return null();
+
+    Node pn = statementList(YieldIsName);
+    if (!pn)
+        return null();
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+    if (tt != TOK_EOF) {
+        report(ParseError, false, null(), JSMSG_GARBAGE_AFTER_INPUT,
+               "script", TokenKindToDesc(tt));
+        return null();
+    }
+    if (foldConstants) {
+        if (!FoldConstants(context, &pn, this))
+            return null();
+    }
+
+    return pn;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportBadReturn(Node pn, ParseReportKind kind,
+                                      unsigned errnum, unsigned anonerrnum)
+{
+    JSAutoByteString name;
+    if (JSAtom* atom = pc->functionBox()->function()->name()) {
+        if (!AtomToPrintableString(context, atom, &name))
+            return false;
+    } else {
+        errnum = anonerrnum;
+    }
+    return report(kind, pc->sc()->strict(), pn, errnum, name.ptr());
+}
+
+/*
+ * Strict mode forbids introducing new definitions for 'eval', 'arguments', or
+ * for any strict mode reserved keyword.
+ */
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::isValidStrictBinding(PropertyName* name)
+{
+    return name != context->names().eval &&
+           name != context->names().arguments &&
+           name != context->names().let &&
+           name != context->names().static_ &&
+           !(IsKeyword(name) && name != context->names().await);
+}
+
+/*
+ * Check that it is permitted to introduce a binding for |name|. Use |pos| for
+ * reporting error locations.
+ */
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkStrictBinding(PropertyName* name, TokenPos pos)
+{
+    if (!pc->sc()->needStrictChecks())
+        return true;
+
+    if (!isValidStrictBinding(name)) {
+        JSAutoByteString bytes;
+        if (!AtomToPrintableString(context, name, &bytes))
+            return false;
+        return reportWithOffset(ParseStrictError, pc->sc()->strict(), pos.begin,
+                                JSMSG_BAD_BINDING, bytes.ptr());
+    }
+
+    return true;
+}
+
+/*
+ * Returns true if all parameter names are valid strict mode binding names and
+ * no duplicate parameter names are present.
+ */
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::hasValidSimpleStrictParameterNames()
+{
+    MOZ_ASSERT(pc->isFunctionBox() && pc->functionBox()->hasSimpleParameterList());
+
+    if (pc->functionBox()->hasDuplicateParameters)
+        return false;
+
+    for (size_t i = 0; i < pc->positionalFormalParameterNames().length(); i++) {
+        JSAtom* name = pc->positionalFormalParameterNames()[i];
+        MOZ_ASSERT(name);
+        if (!isValidStrictBinding(name->asPropertyName()))
+            return false;
+    }
+    return true;
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::reportRedeclaration(HandlePropertyName name, DeclarationKind kind,
+                                          TokenPos pos)
+{
+    JSAutoByteString bytes;
+    if (!AtomToPrintableString(context, name, &bytes))
+        return;
+    reportWithOffset(ParseError, false, pos.begin, JSMSG_REDECLARED_VAR,
+                     DeclarationKindString(kind), bytes.ptr());
+}
+
+// notePositionalFormalParameter is called for both the arguments of a regular
+// function definition and the arguments specified by the Function
+// constructor.
+//
+// The 'disallowDuplicateParams' bool indicates whether the use of another
+// feature (destructuring or default arguments) disables duplicate arguments.
+// (ECMA-262 requires us to support duplicate parameter names, but, for newer
+// features, we consider the code to have "opted in" to higher standards and
+// forbid duplicates.)
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::notePositionalFormalParameter(Node fn, HandlePropertyName name,
+                                                    bool disallowDuplicateParams,
+                                                    bool* duplicatedParam)
+{
+    if (AddDeclaredNamePtr p = pc->functionScope().lookupDeclaredNameForAdd(name)) {
+        if (disallowDuplicateParams) {
+            report(ParseError, false, null(), JSMSG_BAD_DUP_ARGS);
+            return false;
+        }
+
+        // Strict-mode disallows duplicate args. We may not know whether we are
+        // in strict mode or not (since the function body hasn't been parsed).
+        // In such cases, report will queue up the potential error and return
+        // 'true'.
+        if (pc->sc()->needStrictChecks()) {
+            JSAutoByteString bytes;
+            if (!AtomToPrintableString(context, name, &bytes))
+                return false;
+            if (!report(ParseStrictError, pc->sc()->strict(), null(),
+                        JSMSG_DUPLICATE_FORMAL, bytes.ptr()))
+            {
+                return false;
+            }
+        }
+
+        *duplicatedParam = true;
+    } else {
+        DeclarationKind kind = DeclarationKind::PositionalFormalParameter;
+        if (!pc->functionScope().addDeclaredName(pc, p, name, kind))
+            return false;
+    }
+
+    if (!pc->positionalFormalParameterNames().append(name)) {
+        ReportOutOfMemory(context);
+        return false;
+    }
+
+    Node paramNode = newName(name);
+    if (!paramNode)
+        return false;
+
+    if (!checkStrictBinding(name, pos()))
+        return false;
+
+    handler.addFunctionFormalParameter(fn, paramNode);
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::noteDestructuredPositionalFormalParameter(Node fn, Node destruct)
+{
+    // Append an empty name to the positional formals vector to keep track of
+    // argument slots when making FunctionScope::Data.
+    if (!pc->positionalFormalParameterNames().append(nullptr)) {
+        ReportOutOfMemory(context);
+        return false;
+    }
+
+    handler.addFunctionFormalParameter(fn, destruct);
+    return true;
+}
+
+static bool
+DeclarationKindIsVar(DeclarationKind kind)
+{
+    return kind == DeclarationKind::Var ||
+           kind == DeclarationKind::BodyLevelFunction ||
+           kind == DeclarationKind::VarForAnnexBLexicalFunction ||
+           kind == DeclarationKind::ForOfVar;
+}
+
+template <typename ParseHandler>
+Maybe<DeclarationKind>
+Parser<ParseHandler>::isVarRedeclaredInEval(HandlePropertyName name, DeclarationKind kind)
+{
+    MOZ_ASSERT(DeclarationKindIsVar(kind));
+    MOZ_ASSERT(pc->sc()->isEvalContext());
+
+    // In the case of eval, we also need to check enclosing VM scopes to see
+    // if the var declaration is allowed in the context.
+    //
+    // This check is necessary in addition to
+    // js::CheckEvalDeclarationConflicts because we only know during parsing
+    // if a var is bound by for-of.
+    Scope* enclosingScope = pc->sc()->compilationEnclosingScope();
+    Scope* varScope = EvalScope::nearestVarScopeForDirectEval(enclosingScope);
+    MOZ_ASSERT(varScope);
+    for (ScopeIter si(enclosingScope); si; si++) {
+        for (js::BindingIter bi(si.scope()); bi; bi++) {
+            if (bi.name() != name)
+                continue;
+
+            switch (bi.kind()) {
+              case BindingKind::Let: {
+                  // Annex B.3.5 allows redeclaring simple (non-destructured)
+                  // catch parameters with var declarations, except when it
+                  // appears in a for-of.
+                  bool annexB35Allowance = si.kind() == ScopeKind::SimpleCatch &&
+                                           kind != DeclarationKind::ForOfVar;
+                  if (!annexB35Allowance) {
+                      return Some(ScopeKindIsCatch(si.kind())
+                                  ? DeclarationKind::CatchParameter
+                                  : DeclarationKind::Let);
+                  }
+                  break;
+              }
+
+              case BindingKind::Const:
+                return Some(DeclarationKind::Const);
+
+              case BindingKind::Import:
+              case BindingKind::FormalParameter:
+              case BindingKind::Var:
+              case BindingKind::NamedLambdaCallee:
+                break;
+            }
+        }
+
+        if (si.scope() == varScope)
+            break;
+    }
+
+    return Nothing();
+}
+
+static bool
+DeclarationKindIsParameter(DeclarationKind kind)
+{
+    return kind == DeclarationKind::PositionalFormalParameter ||
+           kind == DeclarationKind::FormalParameter;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::tryDeclareVar(HandlePropertyName name, DeclarationKind kind,
+                                    Maybe<DeclarationKind>* redeclaredKind)
+{
+    MOZ_ASSERT(DeclarationKindIsVar(kind));
+
+    // It is an early error if a 'var' declaration appears inside a
+    // scope contour that has a lexical declaration of the same name. For
+    // example, the following are early errors:
+    //
+    //   { let x; var x; }
+    //   { { var x; } let x; }
+    //
+    // And the following are not:
+    //
+    //   { var x; var x; }
+    //   { { let x; } var x; }
+
+    for (ParseContext::Scope* scope = pc->innermostScope();
+         scope != pc->varScope().enclosing();
+         scope = scope->enclosing())
+    {
+        if (AddDeclaredNamePtr p = scope->lookupDeclaredNameForAdd(name)) {
+            DeclarationKind declaredKind = p->value()->kind();
+            if (DeclarationKindIsVar(declaredKind)) {
+                // Any vars that are redeclared as body-level functions must
+                // be recorded as body-level functions.
+                //
+                // In the case of global and eval scripts, GlobalDeclaration-
+                // Instantiation [1] and EvalDeclarationInstantiation [2]
+                // check for the declarability of global var and function
+                // bindings via CanDeclareVar [3] and CanDeclareGlobal-
+                // Function [4]. CanDeclareGlobalFunction is strictly more
+                // restrictive than CanDeclareGlobalVar, so record the more
+                // restrictive kind. These semantics are implemented in
+                // CheckCanDeclareGlobalBinding.
+                //
+                // For a var previously declared as ForOfVar, this previous
+                // DeclarationKind is used only to check for if the
+                // 'arguments' binding should be declared. Since body-level
+                // functions shadow 'arguments' [5], it is correct to alter
+                // the kind to BodyLevelFunction. See
+                // declareFunctionArgumentsObject.
+                //
+                // For a var previously declared as
+                // VarForAnnexBLexicalFunction, this previous DeclarationKind
+                // is used so that vars synthesized solely for Annex B.3.3 may
+                // be removed if an early error would occur. If a synthesized
+                // Annex B.3.3 var has the same name as a body-level function,
+                // this is not a redeclaration, and indeed, because the
+                // body-level function binds the name, this name should not be
+                // removed should a redeclaration occur in the future. Thus it
+                // is also correct to alter the kind to BodyLevelFunction.
+                //
+                // [1] ES 15.1.11
+                // [2] ES 18.2.1.3
+                // [3] ES 8.1.1.4.15
+                // [4] ES 8.1.1.4.16
+                // [5] ES 9.2.12
+                if (kind == DeclarationKind::BodyLevelFunction)
+                    p->value()->alterKind(kind);
+            } else if (!DeclarationKindIsParameter(declaredKind)) {
+                // Annex B.3.5 allows redeclaring simple (non-destructured)
+                // catch parameters with var declarations, except when it
+                // appears in a for-of.
+                bool annexB35Allowance = declaredKind == DeclarationKind::SimpleCatchParameter &&
+                                         kind != DeclarationKind::ForOfVar;
+
+                // Annex B.3.3 allows redeclaring functions in the same block.
+                bool annexB33Allowance = declaredKind == DeclarationKind::LexicalFunction &&
+                                         kind == DeclarationKind::VarForAnnexBLexicalFunction &&
+                                         scope == pc->innermostScope();
+
+                if (!annexB35Allowance && !annexB33Allowance) {
+                    *redeclaredKind = Some(declaredKind);
+                    return true;
+                }
+            }
+        } else {
+            if (!scope->addDeclaredName(pc, p, name, kind))
+                return false;
+        }
+    }
+
+    if (!pc->sc()->strict() && pc->sc()->isEvalContext())
+        *redeclaredKind = isVarRedeclaredInEval(name, kind);
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::tryDeclareVarForAnnexBLexicalFunction(HandlePropertyName name,
+                                                            bool* tryAnnexB)
+{
+    Maybe<DeclarationKind> redeclaredKind;
+    if (!tryDeclareVar(name, DeclarationKind::VarForAnnexBLexicalFunction, &redeclaredKind))
+        return false;
+
+    if (redeclaredKind) {
+        // If an early error would have occurred, undo all the
+        // VarForAnnexBLexicalFunction declarations.
+        *tryAnnexB = false;
+        ParseContext::Scope::removeVarForAnnexBLexicalFunction(pc, name);
+    } else {
+        *tryAnnexB = true;
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkLexicalDeclarationDirectlyWithinBlock(ParseContext::Statement& stmt,
+                                                                 DeclarationKind kind,
+                                                                 TokenPos pos)
+{
+    MOZ_ASSERT(DeclarationKindIsLexical(kind));
+
+    // It is an early error to declare a lexical binding not directly
+    // within a block.
+    if (!StatementKindIsBraced(stmt.kind()) &&
+        stmt.kind() != StatementKind::ForLoopLexicalHead)
+    {
+        reportWithOffset(ParseError, false, pos.begin,
+                         stmt.kind() == StatementKind::Label
+                         ? JSMSG_LEXICAL_DECL_LABEL
+                         : JSMSG_LEXICAL_DECL_NOT_IN_BLOCK,
+                         DeclarationKindString(kind));
+        return false;
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::noteDeclaredName(HandlePropertyName name, DeclarationKind kind,
+                                       TokenPos pos)
+{
+    // The asm.js validator does all its own symbol-table management so, as an
+    // optimization, avoid doing any work here.
+    if (pc->useAsmOrInsideUseAsm())
+        return true;
+
+    if (!checkStrictBinding(name, pos))
+        return false;
+
+    switch (kind) {
+      case DeclarationKind::Var:
+      case DeclarationKind::BodyLevelFunction:
+      case DeclarationKind::ForOfVar: {
+        Maybe<DeclarationKind> redeclaredKind;
+        if (!tryDeclareVar(name, kind, &redeclaredKind))
+            return false;
+
+        if (redeclaredKind) {
+            reportRedeclaration(name, *redeclaredKind, pos);
+            return false;
+        }
+
+        break;
+      }
+
+      case DeclarationKind::FormalParameter: {
+        // It is an early error if any non-positional formal parameter name
+        // (e.g., destructuring formal parameter) is duplicated.
+
+        AddDeclaredNamePtr p = pc->functionScope().lookupDeclaredNameForAdd(name);
+        if (p) {
+            report(ParseError, false, null(), JSMSG_BAD_DUP_ARGS);
+            return false;
+        }
+
+        if (!pc->functionScope().addDeclaredName(pc, p, name, kind))
+            return false;
+
+        break;
+      }
+
+      case DeclarationKind::LexicalFunction: {
+        // Functions in block have complex allowances in sloppy mode for being
+        // labelled that other lexical declarations do not have. Those checks
+        // are more complex than calling checkLexicalDeclarationDirectlyWithin-
+        // Block and are done in checkFunctionDefinition.
+
+        ParseContext::Scope* scope = pc->innermostScope();
+        if (AddDeclaredNamePtr p = scope->lookupDeclaredNameForAdd(name)) {
+            // It is usually an early error if there is another declaration
+            // with the same name in the same scope.
+            //
+            // In sloppy mode, lexical functions may redeclare other lexical
+            // functions for web compatibility reasons.
+            if (pc->sc()->strict() ||
+                (p->value()->kind() != DeclarationKind::LexicalFunction &&
+                 p->value()->kind() != DeclarationKind::VarForAnnexBLexicalFunction))
+            {
+                reportRedeclaration(name, p->value()->kind(), pos);
+                return false;
+            }
+
+            // Update the DeclarationKind to make a LexicalFunction
+            // declaration that shadows the VarForAnnexBLexicalFunction.
+            p->value()->alterKind(kind);
+        } else {
+            if (!scope->addDeclaredName(pc, p, name, kind))
+                return false;
+        }
+
+        break;
+      }
+
+      case DeclarationKind::Let:
+      case DeclarationKind::Const:
+        // The BoundNames of LexicalDeclaration and ForDeclaration must not
+        // contain 'let'. (CatchParameter is the only lexical binding form
+        // without this restriction.)
+        if (name == context->names().let) {
+            reportWithOffset(ParseError, false, pos.begin, JSMSG_LEXICAL_DECL_DEFINES_LET);
+            return false;
+        }
+
+        MOZ_FALLTHROUGH;
+
+      case DeclarationKind::Import:
+        // Module code is always strict, so 'let' is always a keyword and never a name.
+        MOZ_ASSERT(name != context->names().let);
+        MOZ_FALLTHROUGH;
+
+      case DeclarationKind::SimpleCatchParameter:
+      case DeclarationKind::CatchParameter: {
+        if (ParseContext::Statement* stmt = pc->innermostStatement()) {
+            if (!checkLexicalDeclarationDirectlyWithinBlock(*stmt, kind, pos))
+                return false;
+        }
+
+        ParseContext::Scope* scope = pc->innermostScope();
+
+        // For body-level lexically declared names in a function, it is an
+        // early error if there is a formal parameter of the same name. This
+        // needs a special check if there is an extra var scope due to
+        // parameter expressions.
+        if (pc->isFunctionExtraBodyVarScopeInnermost()) {
+            DeclaredNamePtr p = pc->functionScope().lookupDeclaredName(name);
+            if (p && DeclarationKindIsParameter(p->value()->kind())) {
+                reportRedeclaration(name, p->value()->kind(), pos);
+                return false;
+            }
+        }
+
+        // It is an early error if there is another declaration with the same
+        // name in the same scope.
+        AddDeclaredNamePtr p = scope->lookupDeclaredNameForAdd(name);
+        if (p) {
+            // If the early error would have occurred due to Annex B.3.3
+            // semantics, remove the synthesized Annex B var declaration, do
+            // not report the redeclaration, and declare the lexical name.
+            if (p->value()->kind() == DeclarationKind::VarForAnnexBLexicalFunction) {
+                ParseContext::Scope::removeVarForAnnexBLexicalFunction(pc, name);
+                p = scope->lookupDeclaredNameForAdd(name);
+                MOZ_ASSERT(!p);
+            } else {
+                reportRedeclaration(name, p->value()->kind(), pos);
+                return false;
+            }
+        }
+
+        if (!p && !scope->addDeclaredName(pc, p, name, kind))
+            return false;
+
+        break;
+      }
+
+      case DeclarationKind::CoverArrowParameter:
+        // CoverArrowParameter is only used as a placeholder declaration kind.
+        break;
+
+      case DeclarationKind::PositionalFormalParameter:
+        MOZ_CRASH("Positional formal parameter names should use "
+                  "notePositionalFormalParameter");
+        break;
+
+      case DeclarationKind::VarForAnnexBLexicalFunction:
+        MOZ_CRASH("Synthesized Annex B vars should go through "
+                  "tryDeclareVarForAnnexBLexicalFunction");
+        break;
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::noteUsedName(HandlePropertyName name)
+{
+    // If the we are delazifying, the LazyScript already has all the
+    // closed-over info for bindings and there's no need to track used names.
+    if (handler.canSkipLazyClosedOverBindings())
+        return true;
+
+    // The asm.js validator does all its own symbol-table management so, as an
+    // optimization, avoid doing any work here.
+    if (pc->useAsmOrInsideUseAsm())
+        return true;
+
+    // Global bindings are properties and not actual bindings; we don't need
+    // to know if they are closed over. So no need to track used name at the
+    // global scope. It is not incorrect to track them, this is an
+    // optimization.
+    ParseContext::Scope* scope = pc->innermostScope();
+    if (pc->sc()->isGlobalContext() && scope == &pc->varScope())
+        return true;
+
+    return usedNames.noteUse(context, name, pc->scriptId(), scope->id());
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::hasUsedName(HandlePropertyName name)
+{
+    if (UsedNamePtr p = usedNames.lookup(name))
+        return p->value().isUsedInScript(pc->scriptId());
+    return false;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::propagateFreeNamesAndMarkClosedOverBindings(ParseContext::Scope& scope)
+{
+    if (handler.canSkipLazyClosedOverBindings()) {
+        // Scopes are nullptr-delimited in the LazyScript closed over bindings
+        // array.
+        while (JSAtom* name = handler.nextLazyClosedOverBinding())
+            scope.lookupDeclaredName(name)->value()->setClosedOver();
+        return true;
+    }
+
+    bool isSyntaxParser = mozilla::IsSame<ParseHandler, SyntaxParseHandler>::value;
+    uint32_t scriptId = pc->scriptId();
+    uint32_t scopeId = scope.id();
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        if (UsedNamePtr p = usedNames.lookup(bi.name())) {
+            bool closedOver;
+            p->value().noteBoundInScope(scriptId, scopeId, &closedOver);
+            if (closedOver) {
+                bi.setClosedOver();
+
+                if (isSyntaxParser && !pc->closedOverBindingsForLazy().append(bi.name())) {
+                    ReportOutOfMemory(context);
+                    return false;
+                }
+            }
+        }
+    }
+
+    // Append a nullptr to denote end-of-scope.
+    if (isSyntaxParser && !pc->closedOverBindingsForLazy().append(nullptr)) {
+        ReportOutOfMemory(context);
+        return false;
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::checkStatementsEOF()
+{
+    // This is designed to be paired with parsing a statement list at the top
+    // level.
+    //
+    // The statementList() call breaks on TOK_RC, so make sure we've
+    // reached EOF here.
+    TokenKind tt;
+    if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+        return false;
+    if (tt != TOK_EOF) {
+        report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+               "expression", TokenKindToDesc(tt));
+        return false;
+    }
+    return true;
+}
+
+template <typename Scope>
+static typename Scope::Data*
+NewEmptyBindingData(ExclusiveContext* cx, LifoAlloc& alloc, uint32_t numBindings)
+{
+    size_t allocSize = Scope::sizeOfData(numBindings);
+    typename Scope::Data* bindings = static_cast<typename Scope::Data*>(alloc.alloc(allocSize));
+    if (!bindings) {
+        ReportOutOfMemory(cx);
+        return nullptr;
+    }
+    PodZero(bindings);
+    return bindings;
+}
+
+template <>
+Maybe<GlobalScope::Data*>
+Parser<FullParseHandler>::newGlobalScopeData(ParseContext::Scope& scope)
+{
+    Vector<BindingName> funs(context);
+    Vector<BindingName> vars(context);
+    Vector<BindingName> lets(context);
+    Vector<BindingName> consts(context);
+
+    bool allBindingsClosedOver = pc->sc()->allBindingsClosedOver();
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        BindingName binding(bi.name(), allBindingsClosedOver || bi.closedOver());
+        switch (bi.kind()) {
+          case BindingKind::Var:
+            if (bi.declarationKind() == DeclarationKind::BodyLevelFunction) {
+                if (!funs.append(binding))
+                    return Nothing();
+            } else {
+                if (!vars.append(binding))
+                    return Nothing();
+            }
+            break;
+          case BindingKind::Let:
+            if (!lets.append(binding))
+                return Nothing();
+            break;
+          case BindingKind::Const:
+            if (!consts.append(binding))
+                return Nothing();
+            break;
+          default:
+            MOZ_CRASH("Bad global scope BindingKind");
+        }
+    }
+
+    GlobalScope::Data* bindings = nullptr;
+    uint32_t numBindings = funs.length() + vars.length() + lets.length() + consts.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<GlobalScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        // The ordering here is important. See comments in GlobalScope.
+        BindingName* start = bindings->names;
+        BindingName* cursor = start;
+
+        PodCopy(cursor, funs.begin(), funs.length());
+        cursor += funs.length();
+
+        bindings->varStart = cursor - start;
+        PodCopy(cursor, vars.begin(), vars.length());
+        cursor += vars.length();
+
+        bindings->letStart = cursor - start;
+        PodCopy(cursor, lets.begin(), lets.length());
+        cursor += lets.length();
+
+        bindings->constStart = cursor - start;
+        PodCopy(cursor, consts.begin(), consts.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+Maybe<ModuleScope::Data*>
+Parser<FullParseHandler>::newModuleScopeData(ParseContext::Scope& scope)
+{
+    Vector<BindingName> imports(context);
+    Vector<BindingName> vars(context);
+    Vector<BindingName> lets(context);
+    Vector<BindingName> consts(context);
+
+    bool allBindingsClosedOver = pc->sc()->allBindingsClosedOver();
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        // Imports are indirect bindings and must not be given known slots.
+        BindingName binding(bi.name(), (allBindingsClosedOver || bi.closedOver()) &&
+                                       bi.kind() != BindingKind::Import);
+        switch (bi.kind()) {
+          case BindingKind::Import:
+            if (!imports.append(binding))
+                return Nothing();
+            break;
+          case BindingKind::Var:
+            if (!vars.append(binding))
+                return Nothing();
+            break;
+          case BindingKind::Let:
+            if (!lets.append(binding))
+                return Nothing();
+            break;
+          case BindingKind::Const:
+            if (!consts.append(binding))
+                return Nothing();
+            break;
+          default:
+            MOZ_CRASH("Bad module scope BindingKind");
+        }
+    }
+
+    ModuleScope::Data* bindings = nullptr;
+    uint32_t numBindings = imports.length() + vars.length() + lets.length() + consts.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<ModuleScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        // The ordering here is important. See comments in ModuleScope.
+        BindingName* start = bindings->names;
+        BindingName* cursor = start;
+
+        PodCopy(cursor, imports.begin(), imports.length());
+        cursor += imports.length();
+
+        bindings->varStart = cursor - start;
+        PodCopy(cursor, vars.begin(), vars.length());
+        cursor += vars.length();
+
+        bindings->letStart = cursor - start;
+        PodCopy(cursor, lets.begin(), lets.length());
+        cursor += lets.length();
+
+        bindings->constStart = cursor - start;
+        PodCopy(cursor, consts.begin(), consts.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+Maybe<EvalScope::Data*>
+Parser<FullParseHandler>::newEvalScopeData(ParseContext::Scope& scope)
+{
+    Vector<BindingName> funs(context);
+    Vector<BindingName> vars(context);
+
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        // Eval scopes only contain 'var' bindings. Make all bindings aliased
+        // for now.
+        MOZ_ASSERT(bi.kind() == BindingKind::Var);
+        BindingName binding(bi.name(), true);
+        if (bi.declarationKind() == DeclarationKind::BodyLevelFunction) {
+            if (!funs.append(binding))
+                return Nothing();
+        } else {
+            if (!vars.append(binding))
+                return Nothing();
+        }
+    }
+
+    EvalScope::Data* bindings = nullptr;
+    uint32_t numBindings = funs.length() + vars.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<EvalScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        BindingName* start = bindings->names;
+        BindingName* cursor = start;
+
+        // Keep track of what vars are functions. This is only used in BCE to omit
+        // superfluous DEFVARs.
+        PodCopy(cursor, funs.begin(), funs.length());
+        cursor += funs.length();
+
+        bindings->varStart = cursor - start;
+        PodCopy(cursor, vars.begin(), vars.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+Maybe<FunctionScope::Data*>
+Parser<FullParseHandler>::newFunctionScopeData(ParseContext::Scope& scope, bool hasParameterExprs)
+{
+    Vector<BindingName> positionalFormals(context);
+    Vector<BindingName> formals(context);
+    Vector<BindingName> vars(context);
+
+    bool allBindingsClosedOver = pc->sc()->allBindingsClosedOver();
+    bool hasDuplicateParams = pc->functionBox()->hasDuplicateParameters;
+
+    // Positional parameter names must be added in order of appearance as they are
+    // referenced using argument slots.
+    for (size_t i = 0; i < pc->positionalFormalParameterNames().length(); i++) {
+        JSAtom* name = pc->positionalFormalParameterNames()[i];
+
+        BindingName bindName;
+        if (name) {
+            DeclaredNamePtr p = scope.lookupDeclaredName(name);
+
+            // Do not consider any positional formal parameters closed over if
+            // there are parameter defaults. It is the binding in the defaults
+            // scope that is closed over instead.
+            bool closedOver = allBindingsClosedOver ||
+                              (p && p->value()->closedOver());
+
+            // If the parameter name has duplicates, only the final parameter
+            // name should be on the environment, as otherwise the environment
+            // object would have multiple, same-named properties.
+            if (hasDuplicateParams) {
+                for (size_t j = pc->positionalFormalParameterNames().length() - 1; j > i; j--) {
+                    if (pc->positionalFormalParameterNames()[j] == name) {
+                        closedOver = false;
+                        break;
+                    }
+                }
+            }
+
+            bindName = BindingName(name, closedOver);
+        }
+
+        if (!positionalFormals.append(bindName))
+            return Nothing();
+    }
+
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        BindingName binding(bi.name(), allBindingsClosedOver || bi.closedOver());
+        switch (bi.kind()) {
+          case BindingKind::FormalParameter:
+            // Positional parameter names are already handled above.
+            if (bi.declarationKind() == DeclarationKind::FormalParameter) {
+                if (!formals.append(binding))
+                    return Nothing();
+            }
+            break;
+          case BindingKind::Var:
+            // The only vars in the function scope when there are parameter
+            // exprs, which induces a separate var environment, should be the
+            // special internal bindings.
+            MOZ_ASSERT_IF(hasParameterExprs,
+                          bi.name() == context->names().arguments ||
+                          bi.name() == context->names().dotThis ||
+                          bi.name() == context->names().dotGenerator);
+            if (!vars.append(binding))
+                return Nothing();
+            break;
+          default:
+            break;
+        }
+    }
+
+    FunctionScope::Data* bindings = nullptr;
+    uint32_t numBindings = positionalFormals.length() + formals.length() + vars.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<FunctionScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        // The ordering here is important. See comments in FunctionScope.
+        BindingName* start = bindings->names;
+        BindingName* cursor = start;
+
+        PodCopy(cursor, positionalFormals.begin(), positionalFormals.length());
+        cursor += positionalFormals.length();
+
+        bindings->nonPositionalFormalStart = cursor - start;
+        PodCopy(cursor, formals.begin(), formals.length());
+        cursor += formals.length();
+
+        bindings->varStart = cursor - start;
+        PodCopy(cursor, vars.begin(), vars.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+Maybe<VarScope::Data*>
+Parser<FullParseHandler>::newVarScopeData(ParseContext::Scope& scope)
+{
+    Vector<BindingName> vars(context);
+
+    bool allBindingsClosedOver = pc->sc()->allBindingsClosedOver();
+
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        BindingName binding(bi.name(), allBindingsClosedOver || bi.closedOver());
+        if (!vars.append(binding))
+            return Nothing();
+    }
+
+    VarScope::Data* bindings = nullptr;
+    uint32_t numBindings = vars.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<VarScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        // The ordering here is important. See comments in FunctionScope.
+        BindingName* start = bindings->names;
+        BindingName* cursor = start;
+
+        PodCopy(cursor, vars.begin(), vars.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+Maybe<LexicalScope::Data*>
+Parser<FullParseHandler>::newLexicalScopeData(ParseContext::Scope& scope)
+{
+    Vector<BindingName> lets(context);
+    Vector<BindingName> consts(context);
+
+    // Unlike other scopes with bindings which are body-level, it is unknown
+    // if pc->sc()->allBindingsClosedOver() is correct at the time of
+    // finishing parsing a lexical scope.
+    //
+    // Instead, pc->sc()->allBindingsClosedOver() is checked in
+    // EmitterScope::enterLexical. Also see comment there.
+    for (BindingIter bi = scope.bindings(pc); bi; bi++) {
+        BindingName binding(bi.name(), bi.closedOver());
+        switch (bi.kind()) {
+          case BindingKind::Let:
+            if (!lets.append(binding))
+                return Nothing();
+            break;
+          case BindingKind::Const:
+            if (!consts.append(binding))
+                return Nothing();
+            break;
+          default:
+            break;
+        }
+    }
+
+    LexicalScope::Data* bindings = nullptr;
+    uint32_t numBindings = lets.length() + consts.length();
+
+    if (numBindings > 0) {
+        bindings = NewEmptyBindingData<LexicalScope>(context, alloc, numBindings);
+        if (!bindings)
+            return Nothing();
+
+        // The ordering here is important. See comments in LexicalScope.
+        BindingName* cursor = bindings->names;
+        BindingName* start = cursor;
+
+        PodCopy(cursor, lets.begin(), lets.length());
+        cursor += lets.length();
+
+        bindings->constStart = cursor - start;
+        PodCopy(cursor, consts.begin(), consts.length());
+        bindings->length = numBindings;
+    }
+
+    return Some(bindings);
+}
+
+template <>
+SyntaxParseHandler::Node
+Parser<SyntaxParseHandler>::finishLexicalScope(ParseContext::Scope& scope, Node body)
+{
+    if (!propagateFreeNamesAndMarkClosedOverBindings(scope))
+        return null();
+    return body;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::finishLexicalScope(ParseContext::Scope& scope, ParseNode* body)
+{
+    if (!propagateFreeNamesAndMarkClosedOverBindings(scope))
+        return nullptr;
+    Maybe<LexicalScope::Data*> bindings = newLexicalScopeData(scope);
+    if (!bindings)
+        return nullptr;
+    return handler.newLexicalScope(*bindings, body);
+}
+
+static bool
+IsArgumentsUsedInLegacyGenerator(ExclusiveContext* cx, Scope* scope)
+{
+    JSAtom* argumentsName = cx->names().arguments;
+    for (ScopeIter si(scope); si; si++) {
+        if (si.scope()->is<LexicalScope>()) {
+            // Using a shadowed lexical 'arguments' is okay.
+            for (::BindingIter bi(si.scope()); bi; bi++) {
+                if (bi.name() == argumentsName)
+                    return false;
+            }
+        } else if (si.scope()->is<FunctionScope>()) {
+            // It's an error to use 'arguments' in a legacy generator expression.
+            JSScript* script = si.scope()->as<FunctionScope>().script();
+            return script->isGeneratorExp() && script->isLegacyGenerator();
+        }
+    }
+
+    return false;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::evalBody(EvalSharedContext* evalsc)
+{
+    ParseContext evalpc(this, evalsc, /* newDirectives = */ nullptr);
+    if (!evalpc.init())
+        return nullptr;
+
+    ParseContext::VarScope varScope(this);
+    if (!varScope.init(pc))
+        return nullptr;
+
+    // All evals have an implicit non-extensible lexical scope.
+    ParseContext::Scope lexicalScope(this);
+    if (!lexicalScope.init(pc))
+        return nullptr;
+
+    ParseNode* body = statementList(YieldIsName);
+    if (!body)
+        return nullptr;
+
+    if (!checkStatementsEOF())
+        return nullptr;
+
+    body = finishLexicalScope(lexicalScope, body);
+    if (!body)
+        return nullptr;
+
+    // It's an error to use 'arguments' in a legacy generator expression.
+    //
+    // If 'arguments' appears free (i.e. not a declared name) or if the
+    // declaration does not shadow the enclosing script's 'arguments'
+    // binding (i.e. not a lexical declaration), check the enclosing
+    // script.
+    if (hasUsedName(context->names().arguments)) {
+        if (IsArgumentsUsedInLegacyGenerator(context, pc->sc()->compilationEnclosingScope())) {
+            report(ParseError, false, nullptr, JSMSG_BAD_GENEXP_BODY, js_arguments_str);
+            return nullptr;
+        }
+    }
+
+#ifdef DEBUG
+    if (evalpc.superScopeNeedsHomeObject() && evalsc->compilationEnclosingScope()) {
+        // If superScopeNeedsHomeObject_ is set and we are an entry-point
+        // ParseContext, then we must be emitting an eval script, and the
+        // outer function must already be marked as needing a home object
+        // since it contains an eval.
+        ScopeIter si(evalsc->compilationEnclosingScope());
+        for (; si; si++) {
+            if (si.kind() == ScopeKind::Function) {
+                JSFunction* fun = si.scope()->as<FunctionScope>().canonicalFunction();
+                if (fun->isArrow())
+                    continue;
+                MOZ_ASSERT(fun->allowSuperProperty());
+                MOZ_ASSERT(fun->nonLazyScript()->needsHomeObject());
+                break;
+            }
+        }
+        MOZ_ASSERT(!si.done(),
+                   "Eval must have found an enclosing function box scope that allows super.property");
+    }
+#endif
+
+    if (!FoldConstants(context, &body, this))
+        return nullptr;
+
+    Maybe<EvalScope::Data*> bindings = newEvalScopeData(pc->varScope());
+    if (!bindings)
+        return nullptr;
+    evalsc->bindings = *bindings;
+
+    return body;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::globalBody(GlobalSharedContext* globalsc)
+{
+    ParseContext globalpc(this, globalsc, /* newDirectives = */ nullptr);
+    if (!globalpc.init())
+        return nullptr;
+
+    ParseContext::VarScope varScope(this);
+    if (!varScope.init(pc))
+        return nullptr;
+
+    ParseNode* body = statementList(YieldIsName);
+    if (!body)
+        return nullptr;
+
+    if (!checkStatementsEOF())
+        return nullptr;
+
+    if (!FoldConstants(context, &body, this))
+        return nullptr;
+
+    Maybe<GlobalScope::Data*> bindings = newGlobalScopeData(pc->varScope());
+    if (!bindings)
+        return nullptr;
+    globalsc->bindings = *bindings;
+
+    return body;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::moduleBody(ModuleSharedContext* modulesc)
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    ParseContext modulepc(this, modulesc, nullptr);
+    if (!modulepc.init())
+        return null();
+
+    ParseContext::VarScope varScope(this);
+    if (!varScope.init(pc))
+        return nullptr;
+
+    Node mn = handler.newModule();
+    if (!mn)
+        return null();
+
+    AutoAwaitIsKeyword awaitIsKeyword(&tokenStream, true);
+    ParseNode* pn = statementList(YieldIsKeyword);
+    if (!pn)
+        return null();
+
+    MOZ_ASSERT(pn->isKind(PNK_STATEMENTLIST));
+    mn->pn_body = pn;
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+    if (tt != TOK_EOF) {
+        report(ParseError, false, null(), JSMSG_GARBAGE_AFTER_INPUT, "module", TokenKindToDesc(tt));
+        return null();
+    }
+
+    if (!modulesc->builder.buildTables())
+        return null();
+
+    // Check exported local bindings exist and mark them as closed over.
+    for (auto entry : modulesc->builder.localExportEntries()) {
+        JSAtom* name = entry->localName();
+        MOZ_ASSERT(name);
+
+        DeclaredNamePtr p = modulepc.varScope().lookupDeclaredName(name);
+        if (!p) {
+            JSAutoByteString str;
+            if (!str.encodeLatin1(context, name))
+                return null();
+
+            JS_ReportErrorNumberLatin1(context->asJSContext(), GetErrorMessage, nullptr,
+                                       JSMSG_MISSING_EXPORT, str.ptr());
+            return null();
+        }
+
+        p->value()->setClosedOver();
+    }
+
+    if (!FoldConstants(context, &pn, this))
+        return null();
+
+    if (!propagateFreeNamesAndMarkClosedOverBindings(modulepc.varScope()))
+        return null();
+
+    Maybe<ModuleScope::Data*> bindings = newModuleScopeData(modulepc.varScope());
+    if (!bindings)
+        return nullptr;
+
+    modulesc->bindings = *bindings;
+    return mn;
+}
+
+template <>
+SyntaxParseHandler::Node
+Parser<SyntaxParseHandler>::moduleBody(ModuleSharedContext* modulesc)
+{
+    MOZ_ALWAYS_FALSE(abortIfSyntaxParser());
+    return SyntaxParseHandler::NodeFailure;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::hasUsedFunctionSpecialName(HandlePropertyName name)
+{
+    MOZ_ASSERT(name == context->names().arguments || name == context->names().dotThis);
+    return hasUsedName(name) || pc->functionBox()->bindingsAccessedDynamically();
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::declareFunctionThis()
+{
+    // The asm.js validator does all its own symbol-table management so, as an
+    // optimization, avoid doing any work here.
+    if (pc->useAsmOrInsideUseAsm())
+        return true;
+
+    // Derived class constructors emit JSOP_CHECKRETURN, which requires
+    // '.this' to be bound.
+    FunctionBox* funbox = pc->functionBox();
+    HandlePropertyName dotThis = context->names().dotThis;
+
+    bool declareThis;
+    if (handler.canSkipLazyClosedOverBindings())
+        declareThis = funbox->function()->lazyScript()->hasThisBinding();
+    else
+        declareThis = hasUsedFunctionSpecialName(dotThis) || funbox->isDerivedClassConstructor();
+
+    if (declareThis) {
+        ParseContext::Scope& funScope = pc->functionScope();
+        AddDeclaredNamePtr p = funScope.lookupDeclaredNameForAdd(dotThis);
+        MOZ_ASSERT(!p);
+        if (!funScope.addDeclaredName(pc, p, dotThis, DeclarationKind::Var))
+            return false;
+        funbox->setHasThisBinding();
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newInternalDotName(HandlePropertyName name)
+{
+    Node nameNode = newName(name);
+    if (!nameNode)
+        return null();
+    if (!noteUsedName(name))
+        return null();
+    return nameNode;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newThisName()
+{
+    return newInternalDotName(context->names().dotThis);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newDotGeneratorName()
+{
+    return newInternalDotName(context->names().dotGenerator);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::declareDotGeneratorName()
+{
+    // The special '.generator' binding must be on the function scope, as
+    // generators expect to find it on the CallObject.
+    ParseContext::Scope& funScope = pc->functionScope();
+    HandlePropertyName dotGenerator = context->names().dotGenerator;
+    AddDeclaredNamePtr p = funScope.lookupDeclaredNameForAdd(dotGenerator);
+    if (!p && !funScope.addDeclaredName(pc, p, dotGenerator, DeclarationKind::Var))
+        return false;
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::finishFunctionScopes()
+{
+    FunctionBox* funbox = pc->functionBox();
+
+    if (funbox->hasParameterExprs) {
+        if (!propagateFreeNamesAndMarkClosedOverBindings(pc->functionScope()))
+            return false;
+    }
+
+    if (funbox->function()->isNamedLambda()) {
+        if (!propagateFreeNamesAndMarkClosedOverBindings(pc->namedLambdaScope()))
+            return false;
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::finishFunction()
+{
+    if (!finishFunctionScopes())
+        return false;
+
+    FunctionBox* funbox = pc->functionBox();
+    bool hasParameterExprs = funbox->hasParameterExprs;
+
+    if (hasParameterExprs) {
+        Maybe<VarScope::Data*> bindings = newVarScopeData(pc->varScope());
+        if (!bindings)
+            return false;
+        funbox->extraVarScopeBindings().set(*bindings);
+    }
+
+    {
+        Maybe<FunctionScope::Data*> bindings = newFunctionScopeData(pc->functionScope(),
+                                                                    hasParameterExprs);
+        if (!bindings)
+            return false;
+        funbox->functionScopeBindings().set(*bindings);
+    }
+
+    if (funbox->function()->isNamedLambda()) {
+        Maybe<LexicalScope::Data*> bindings = newLexicalScopeData(pc->namedLambdaScope());
+        if (!bindings)
+            return false;
+        funbox->namedLambdaBindings().set(*bindings);
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::finishFunction()
+{
+    // The LazyScript for a lazily parsed function needs to know its set of
+    // free variables and inner functions so that when it is fully parsed, we
+    // can skip over any already syntax parsed inner functions and still
+    // retain correct scope information.
+
+    if (!finishFunctionScopes())
+        return false;
+
+    // There are too many bindings or inner functions to be saved into the
+    // LazyScript. Do a full parse.
+    if (pc->closedOverBindingsForLazy().length() >= LazyScript::NumClosedOverBindingsLimit ||
+        pc->innerFunctionsForLazy.length() >= LazyScript::NumInnerFunctionsLimit)
+    {
+        MOZ_ALWAYS_FALSE(abortIfSyntaxParser());
+        return false;
+    }
+
+    FunctionBox* funbox = pc->functionBox();
+    RootedFunction fun(context, funbox->function());
+    LazyScript* lazy = LazyScript::Create(context, fun, pc->closedOverBindingsForLazy(),
+                                          pc->innerFunctionsForLazy, versionNumber(),
+                                          funbox->bufStart, funbox->bufEnd,
+                                          funbox->startLine, funbox->startColumn);
+    if (!lazy)
+        return false;
+
+    // Flags that need to be copied into the JSScript when we do the full
+    // parse.
+    if (pc->sc()->strict())
+        lazy->setStrict();
+    lazy->setGeneratorKind(funbox->generatorKind());
+    lazy->setAsyncKind(funbox->asyncKind());
+    if (funbox->isLikelyConstructorWrapper())
+        lazy->setLikelyConstructorWrapper();
+    if (funbox->isDerivedClassConstructor())
+        lazy->setIsDerivedClassConstructor();
+    if (funbox->needsHomeObject())
+        lazy->setNeedsHomeObject();
+    if (funbox->declaredArguments)
+        lazy->setShouldDeclareArguments();
+    if (funbox->hasThisBinding())
+        lazy->setHasThisBinding();
+
+    // Flags that need to copied back into the parser when we do the full
+    // parse.
+    PropagateTransitiveParseFlags(funbox, lazy);
+
+    fun->initLazyScript(lazy);
+    return true;
+}
+
+static YieldHandling
+GetYieldHandling(GeneratorKind generatorKind, FunctionAsyncKind asyncKind)
+{
+    if (asyncKind == AsyncFunction)
+        return YieldIsName;
+    if (generatorKind == NotGenerator)
+        return YieldIsName;
+    return YieldIsKeyword;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::standaloneFunctionBody(HandleFunction fun,
+                                                 HandleScope enclosingScope,
+                                                 Handle<PropertyNameVector> formals,
+                                                 GeneratorKind generatorKind,
+                                                 FunctionAsyncKind asyncKind,
+                                                 Directives inheritedDirectives,
+                                                 Directives* newDirectives)
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    Node fn = handler.newFunctionDefinition();
+    if (!fn)
+        return null();
+
+    ParseNode* argsbody = handler.newList(PNK_PARAMSBODY);
+    if (!argsbody)
+        return null();
+    fn->pn_body = argsbody;
+
+    FunctionBox* funbox = newFunctionBox(fn, fun, inheritedDirectives, generatorKind,
+                                         asyncKind, /* tryAnnexB = */ false);
+    if (!funbox)
+        return null();
+    funbox->initStandaloneFunction(enclosingScope);
+
+    ParseContext funpc(this, funbox, newDirectives);
+    if (!funpc.init())
+        return null();
+    funpc.setIsStandaloneFunctionBody();
+    funpc.functionScope().useAsVarScope(&funpc);
+
+    if (formals.length() >= ARGNO_LIMIT) {
+        report(ParseError, false, null(), JSMSG_TOO_MANY_FUN_ARGS);
+        return null();
+    }
+
+    bool duplicatedParam = false;
+    for (uint32_t i = 0; i < formals.length(); i++) {
+        if (!notePositionalFormalParameter(fn, formals[i], false, &duplicatedParam))
+            return null();
+    }
+    funbox->hasDuplicateParameters = duplicatedParam;
+
+    YieldHandling yieldHandling = GetYieldHandling(generatorKind, asyncKind);
+    AutoAwaitIsKeyword awaitIsKeyword(&tokenStream, asyncKind == AsyncFunction);
+    ParseNode* pn = functionBody(InAllowed, yieldHandling, Statement, StatementListBody);
+    if (!pn)
+        return null();
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+    if (tt != TOK_EOF) {
+        report(ParseError, false, null(), JSMSG_GARBAGE_AFTER_INPUT,
+               "function body", TokenKindToDesc(tt));
+        return null();
+    }
+
+    if (!FoldConstants(context, &pn, this))
+        return null();
+
+    fn->pn_pos.end = pos().end;
+
+    MOZ_ASSERT(fn->pn_body->isKind(PNK_PARAMSBODY));
+    fn->pn_body->append(pn);
+
+    if (!finishFunction())
+        return null();
+
+    return fn;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::declareFunctionArgumentsObject()
+{
+    FunctionBox* funbox = pc->functionBox();
+    ParseContext::Scope& funScope = pc->functionScope();
+    ParseContext::Scope& varScope = pc->varScope();
+
+    bool hasExtraBodyVarScope = &funScope != &varScope;
+
+    // Time to implement the odd semantics of 'arguments'.
+    HandlePropertyName argumentsName = context->names().arguments;
+
+    bool tryDeclareArguments;
+    if (handler.canSkipLazyClosedOverBindings())
+        tryDeclareArguments = funbox->function()->lazyScript()->shouldDeclareArguments();
+    else
+        tryDeclareArguments = hasUsedFunctionSpecialName(argumentsName);
+
+    // ES 9.2.12 steps 19 and 20 say formal parameters, lexical bindings,
+    // and body-level functions named 'arguments' shadow the arguments
+    // object.
+    //
+    // So even if there wasn't a free use of 'arguments' but there is a var
+    // binding of 'arguments', we still might need the arguments object.
+    //
+    // If we have an extra var scope due to parameter expressions and the body
+    // declared 'var arguments', we still need to declare 'arguments' in the
+    // function scope.
+    DeclaredNamePtr p = varScope.lookupDeclaredName(argumentsName);
+    if (p && (p->value()->kind() == DeclarationKind::Var ||
+              p->value()->kind() == DeclarationKind::ForOfVar))
+    {
+        if (hasExtraBodyVarScope)
+            tryDeclareArguments = true;
+        else
+            funbox->usesArguments = true;
+    }
+
+    if (tryDeclareArguments) {
+        AddDeclaredNamePtr p = funScope.lookupDeclaredNameForAdd(argumentsName);
+        if (!p) {
+            if (!funScope.addDeclaredName(pc, p, argumentsName, DeclarationKind::Var))
+                return false;
+            funbox->declaredArguments = true;
+            funbox->usesArguments = true;
+        } else if (hasExtraBodyVarScope) {
+            // Formal parameters shadow the arguments object.
+            return true;
+        }
+    }
+
+    // Compute if we need an arguments object.
+    if (funbox->usesArguments) {
+        // There is an 'arguments' binding. Is the arguments object definitely
+        // needed?
+        //
+        // Also see the flags' comments in ContextFlags.
+        funbox->setArgumentsHasLocalBinding();
+
+        // Dynamic scope access destroys all hope of optimization.
+        if (pc->sc()->bindingsAccessedDynamically())
+            funbox->setDefinitelyNeedsArgsObj();
+
+        // If a script contains the debugger statement either directly or
+        // within an inner function, the arguments object should be created
+        // eagerly so the Debugger API may observe bindings.
+        if (pc->sc()->hasDebuggerStatement())
+            funbox->setDefinitelyNeedsArgsObj();
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::functionBody(InHandling inHandling, YieldHandling yieldHandling,
+                                   FunctionSyntaxKind kind, FunctionBodyType type)
+{
+    MOZ_ASSERT(pc->isFunctionBox());
+    MOZ_ASSERT(!pc->funHasReturnExpr && !pc->funHasReturnVoid);
+
+#ifdef DEBUG
+    uint32_t startYieldOffset = pc->lastYieldOffset;
+#endif
+
+    Node pn;
+    if (type == StatementListBody) {
+        bool inheritedStrict = pc->sc()->strict();
+        pn = statementList(yieldHandling);
+        if (!pn)
+            return null();
+
+        // When we transitioned from non-strict to strict mode, we need to
+        // validate that all parameter names are valid strict mode names.
+        if (!inheritedStrict && pc->sc()->strict()) {
+            MOZ_ASSERT(pc->sc()->hasExplicitUseStrict(),
+                       "strict mode should only change when a 'use strict' directive is present");
+            if (!hasValidSimpleStrictParameterNames()) {
+                // Request that this function be reparsed as strict to report
+                // the invalid parameter name at the correct source location.
+                pc->newDirectives->setStrict();
+                return null();
+            }
+        }
+    } else {
+        MOZ_ASSERT(type == ExpressionBody);
+
+        // Async functions are implemented as star generators, and star
+        // generators are assumed to be statement lists, to prepend initial
+        // `yield`.
+        Node stmtList = null();
+        if (pc->isAsync()) {
+            stmtList = handler.newStatementList(pos());
+            if (!stmtList)
+                return null();
+        }
+
+        Node kid = assignExpr(inHandling, yieldHandling, TripledotProhibited);
+        if (!kid)
+            return null();
+
+        pn = handler.newReturnStatement(kid, handler.getPosition(kid));
+        if (!pn)
+            return null();
+
+        if (pc->isAsync()) {
+            handler.addStatementToList(stmtList, pn);
+            pn = stmtList;
+        }
+    }
+
+    switch (pc->generatorKind()) {
+      case NotGenerator:
+        MOZ_ASSERT(pc->lastYieldOffset == startYieldOffset);
+        break;
+
+      case LegacyGenerator:
+        MOZ_ASSERT(pc->lastYieldOffset != startYieldOffset);
+
+        // These should throw while parsing the yield expression.
+        MOZ_ASSERT(kind != Arrow);
+        MOZ_ASSERT(!IsGetterKind(kind));
+        MOZ_ASSERT(!IsSetterKind(kind));
+        MOZ_ASSERT(!IsConstructorKind(kind));
+        MOZ_ASSERT(kind != Method);
+        MOZ_ASSERT(type != ExpressionBody);
+        break;
+
+      case StarGenerator:
+        MOZ_ASSERT_IF(!pc->isAsync(), kind != Arrow);
+        MOZ_ASSERT_IF(!pc->isAsync(), type == StatementListBody);
+        break;
+    }
+
+    if (pc->isGenerator()) {
+        MOZ_ASSERT_IF(!pc->isAsync(), type == StatementListBody);
+        if (!declareDotGeneratorName())
+            return null();
+        Node generator = newDotGeneratorName();
+        if (!generator)
+            return null();
+        if (!handler.prependInitialYield(pn, generator))
+            return null();
+    }
+
+    // Declare the 'arguments' and 'this' bindings if necessary before
+    // finishing up the scope so these special bindings get marked as closed
+    // over if necessary. Arrow functions don't have these bindings.
+    if (kind != Arrow) {
+        if (!declareFunctionArgumentsObject())
+            return null();
+        if (!declareFunctionThis())
+            return null();
+    }
+
+    return finishLexicalScope(pc->varScope(), pn);
+}
+
+template <typename ParseHandler>
+JSFunction*
+Parser<ParseHandler>::newFunction(HandleAtom atom, FunctionSyntaxKind kind,
+                                  GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                  HandleObject proto)
+{
+    MOZ_ASSERT_IF(kind == Statement, atom != nullptr);
+
+    RootedFunction fun(context);
+
+    gc::AllocKind allocKind = gc::AllocKind::FUNCTION;
+    JSFunction::Flags flags;
+#ifdef DEBUG
+    bool isGlobalSelfHostedBuiltin = false;
+#endif
+    switch (kind) {
+      case Expression:
+        flags = (generatorKind == NotGenerator
+                 ? JSFunction::INTERPRETED_LAMBDA
+                 : JSFunction::INTERPRETED_LAMBDA_GENERATOR);
+        break;
+      case Arrow:
+        flags = JSFunction::INTERPRETED_LAMBDA_ARROW;
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        break;
+      case Method:
+        MOZ_ASSERT(generatorKind == NotGenerator || generatorKind == StarGenerator);
+        flags = (generatorKind == NotGenerator
+                 ? JSFunction::INTERPRETED_METHOD
+                 : JSFunction::INTERPRETED_METHOD_GENERATOR);
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        break;
+      case ClassConstructor:
+      case DerivedClassConstructor:
+        flags = JSFunction::INTERPRETED_CLASS_CONSTRUCTOR;
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        break;
+      case Getter:
+      case GetterNoExpressionClosure:
+        flags = JSFunction::INTERPRETED_GETTER;
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        break;
+      case Setter:
+      case SetterNoExpressionClosure:
+        flags = JSFunction::INTERPRETED_SETTER;
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        break;
+      default:
+        MOZ_ASSERT(kind == Statement);
+#ifdef DEBUG
+        if (options().selfHostingMode && !pc->isFunctionBox()) {
+            isGlobalSelfHostedBuiltin = true;
+            allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+        }
+#endif
+        flags = (generatorKind == NotGenerator
+                 ? JSFunction::INTERPRETED_NORMAL
+                 : JSFunction::INTERPRETED_GENERATOR);
+    }
+
+    // We store the async wrapper in a slot for later access.
+    if (asyncKind == AsyncFunction)
+        allocKind = gc::AllocKind::FUNCTION_EXTENDED;
+
+    fun = NewFunctionWithProto(context, nullptr, 0, flags, nullptr, atom, proto,
+                               allocKind, TenuredObject);
+    if (!fun)
+        return nullptr;
+    if (options().selfHostingMode) {
+        fun->setIsSelfHostedBuiltin();
+#ifdef DEBUG
+        if (isGlobalSelfHostedBuiltin)
+            fun->setExtendedSlot(HAS_SELFHOSTED_CANONICAL_NAME_SLOT, BooleanValue(false));
+#endif
+    }
+    return fun;
+}
+
+/*
+ * WARNING: Do not call this function directly.
+ * Call either MatchOrInsertSemicolonAfterExpression or
+ * MatchOrInsertSemicolonAfterNonExpression instead, depending on context.
+ */
+static bool
+MatchOrInsertSemicolonHelper(TokenStream& ts, TokenStream::Modifier modifier)
+{
+    TokenKind tt = TOK_EOF;
+    if (!ts.peekTokenSameLine(&tt, modifier))
+        return false;
+    if (tt != TOK_EOF && tt != TOK_EOL && tt != TOK_SEMI && tt != TOK_RC) {
+        /* Advance the scanner for proper error location reporting. */
+        ts.consumeKnownToken(tt, modifier);
+        ts.reportError(JSMSG_SEMI_BEFORE_STMNT);
+        return false;
+    }
+    bool matched;
+    if (!ts.matchToken(&matched, TOK_SEMI, modifier))
+        return false;
+    if (!matched && modifier == TokenStream::None)
+        ts.addModifierException(TokenStream::OperandIsNone);
+    return true;
+}
+
+static bool
+MatchOrInsertSemicolonAfterExpression(TokenStream& ts)
+{
+    return MatchOrInsertSemicolonHelper(ts, TokenStream::None);
+}
+
+static bool
+MatchOrInsertSemicolonAfterNonExpression(TokenStream& ts)
+{
+    return MatchOrInsertSemicolonHelper(ts, TokenStream::Operand);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::leaveInnerFunction(ParseContext* outerpc)
+{
+    MOZ_ASSERT(pc != outerpc);
+
+    // If the current function allows super.property but cannot have a home
+    // object, i.e., it is an arrow function, we need to propagate the flag to
+    // the outer ParseContext.
+    if (pc->superScopeNeedsHomeObject()) {
+        if (!pc->isArrowFunction())
+            MOZ_ASSERT(pc->functionBox()->needsHomeObject());
+        else
+            outerpc->setSuperScopeNeedsHomeObject();
+    }
+
+    // Lazy functions inner to another lazy function need to be remembered by
+    // the inner function so that if the outer function is eventually parsed
+    // we do not need any further parsing or processing of the inner function.
+    //
+    // Append the inner function here unconditionally; the vector is only used
+    // if the Parser using outerpc is a syntax parsing. See
+    // Parser<SyntaxParseHandler>::finishFunction.
+    if (!outerpc->innerFunctionsForLazy.append(pc->functionBox()->function()))
+        return false;
+
+    PropagateTransitiveParseFlags(pc->functionBox(), outerpc->sc());
+
+    return true;
+}
+
+template <typename ParseHandler>
+JSAtom*
+Parser<ParseHandler>::prefixAccessorName(PropertyType propType, HandleAtom propAtom)
+{
+    RootedAtom prefix(context);
+    if (propType == PropertyType::Setter || propType == PropertyType::SetterNoExpressionClosure) {
+        prefix = context->names().setPrefix;
+    } else {
+        MOZ_ASSERT(propType == PropertyType::Getter || propType == PropertyType::GetterNoExpressionClosure);
+        prefix = context->names().getPrefix;
+    }
+
+    RootedString str(context, ConcatStrings<CanGC>(context, prefix, propAtom));
+    if (!str)
+        return nullptr;
+
+    return AtomizeString(context, str);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::functionArguments(YieldHandling yieldHandling, FunctionSyntaxKind kind,
+                                        Node funcpn)
+{
+    FunctionBox* funbox = pc->functionBox();
+
+    bool parenFreeArrow = false;
+    // Modifier for the following tokens.
+    // TokenStream::None for the following cases:
+    //   async a => 1
+    //         ^
+    //
+    //   (a) => 1
+    //   ^
+    //
+    //   async (a) => 1
+    //         ^
+    //
+    //   function f(a) {}
+    //             ^
+    //
+    // TokenStream::Operand for the following case:
+    //   a => 1
+    //   ^
+    TokenStream::Modifier firstTokenModifier = TokenStream::None;
+
+    // Modifier for the the first token in each argument.
+    // can be changed to TokenStream::None for the following case:
+    //   async a => 1
+    //         ^
+    TokenStream::Modifier argModifier = TokenStream::Operand;
+    if (kind == Arrow) {
+        TokenKind tt;
+        // In async function, the first token after `async` is already gotten
+        // with TokenStream::None.
+        // In sync function, the first token is already gotten with
+        // TokenStream::Operand.
+        firstTokenModifier = funbox->isAsync() ? TokenStream::None : TokenStream::Operand;
+        if (!tokenStream.peekToken(&tt, firstTokenModifier))
+            return false;
+        if (tt == TOK_NAME || tt == TOK_YIELD) {
+            parenFreeArrow = true;
+            argModifier = firstTokenModifier;
+        }
+    }
+    if (!parenFreeArrow) {
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt, firstTokenModifier))
+            return false;
+        if (tt != TOK_LP) {
+            report(ParseError, false, null(),
+                   kind == Arrow ? JSMSG_BAD_ARROW_ARGS : JSMSG_PAREN_BEFORE_FORMAL);
+            return false;
+        }
+
+        // Record the start of function source (for FunctionToString). If we
+        // are parenFreeArrow, we will set this below, after consuming the NAME.
+        funbox->setStart(tokenStream);
+    }
+
+    Node argsbody = handler.newList(PNK_PARAMSBODY);
+    if (!argsbody)
+        return false;
+    handler.setFunctionFormalParametersAndBody(funcpn, argsbody);
+
+    bool hasArguments = false;
+    if (parenFreeArrow) {
+        hasArguments = true;
+    } else {
+        bool matched;
+        if (!tokenStream.matchToken(&matched, TOK_RP, TokenStream::Operand))
+            return false;
+        if (!matched)
+            hasArguments = true;
+    }
+    if (hasArguments) {
+        bool hasRest = false;
+        bool hasDefault = false;
+        bool duplicatedParam = false;
+        bool disallowDuplicateParams = kind == Arrow || kind == Method || kind == ClassConstructor;
+        AtomVector& positionalFormals = pc->positionalFormalParameterNames();
+
+        if (IsGetterKind(kind)) {
+            report(ParseError, false, null(), JSMSG_ACCESSOR_WRONG_ARGS, "getter", "no", "s");
+            return false;
+        }
+
+        while (true) {
+            if (hasRest) {
+                report(ParseError, false, null(), JSMSG_PARAMETER_AFTER_REST);
+                return false;
+            }
+
+            TokenKind tt;
+            if (!tokenStream.getToken(&tt, argModifier))
+                return false;
+            argModifier = TokenStream::Operand;
+            MOZ_ASSERT_IF(parenFreeArrow, tt == TOK_NAME || tt == TOK_YIELD);
+
+            if (tt == TOK_TRIPLEDOT) {
+                if (IsSetterKind(kind)) {
+                    report(ParseError, false, null(),
+                           JSMSG_ACCESSOR_WRONG_ARGS, "setter", "one", "");
+                    return false;
+                }
+
+                disallowDuplicateParams = true;
+                if (duplicatedParam) {
+                    // Has duplicated args before the rest parameter.
+                    report(ParseError, false, null(), JSMSG_BAD_DUP_ARGS);
+                    return false;
+                }
+
+                hasRest = true;
+                funbox->function()->setHasRest();
+
+                if (!tokenStream.getToken(&tt))
+                    return false;
+
+                if (tt != TOK_NAME && tt != TOK_YIELD && tt != TOK_LB && tt != TOK_LC) {
+                    report(ParseError, false, null(), JSMSG_NO_REST_NAME);
+                    return false;
+                }
+            }
+
+            switch (tt) {
+              case TOK_LB:
+              case TOK_LC: {
+                disallowDuplicateParams = true;
+                if (duplicatedParam) {
+                    // Has duplicated args before the destructuring parameter.
+                    report(ParseError, false, null(), JSMSG_BAD_DUP_ARGS);
+                    return false;
+                }
+
+                funbox->hasDestructuringArgs = true;
+
+                Node destruct = destructuringDeclarationWithoutYieldOrAwait(
+                    DeclarationKind::FormalParameter,
+                    yieldHandling, tt);
+                if (!destruct)
+                    return false;
+
+                if (!noteDestructuredPositionalFormalParameter(funcpn, destruct))
+                    return false;
+
+                break;
+              }
+
+              case TOK_NAME:
+              case TOK_YIELD: {
+                if (parenFreeArrow)
+                    funbox->setStart(tokenStream);
+
+                if (funbox->isAsync() && tokenStream.currentName() == context->names().await) {
+                    // `await` is already gotten as TOK_NAME for the following
+                    // case:
+                    //
+                    //   async await => 1
+                    report(ParseError, false, null(), JSMSG_RESERVED_ID, "await");
+                    return false;
+                }
+
+                RootedPropertyName name(context, bindingIdentifier(yieldHandling));
+                if (!name)
+                    return false;
+
+                if (!notePositionalFormalParameter(funcpn, name, disallowDuplicateParams,
+                                                   &duplicatedParam))
+                {
+                    return false;
+                }
+                if (duplicatedParam)
+                    funbox->hasDuplicateParameters = true;
+
+                break;
+              }
+
+              default:
+                report(ParseError, false, null(), JSMSG_MISSING_FORMAL);
+                return false;
+            }
+
+            if (positionalFormals.length() >= ARGNO_LIMIT) {
+                report(ParseError, false, null(), JSMSG_TOO_MANY_FUN_ARGS);
+                return false;
+            }
+
+            bool matched;
+            if (!tokenStream.matchToken(&matched, TOK_ASSIGN))
+                return false;
+            if (matched) {
+                // A default argument without parentheses would look like:
+                // a = expr => body, but both operators are right-associative, so
+                // that would have been parsed as a = (expr => body) instead.
+                // Therefore it's impossible to get here with parenFreeArrow.
+                MOZ_ASSERT(!parenFreeArrow);
+
+                if (hasRest) {
+                    report(ParseError, false, null(), JSMSG_REST_WITH_DEFAULT);
+                    return false;
+                }
+                disallowDuplicateParams = true;
+                if (duplicatedParam) {
+                    report(ParseError, false, null(), JSMSG_BAD_DUP_ARGS);
+                    return false;
+                }
+
+                if (!hasDefault) {
+                    hasDefault = true;
+
+                    // The Function.length property is the number of formals
+                    // before the first default argument.
+                    funbox->length = positionalFormals.length() - 1;
+                }
+                funbox->hasParameterExprs = true;
+
+                Node def_expr = assignExprWithoutYieldOrAwait(yieldHandling);
+                if (!def_expr)
+                    return false;
+                if (!handler.setLastFunctionFormalParameterDefault(funcpn, def_expr))
+                    return false;
+            }
+
+            if (parenFreeArrow || IsSetterKind(kind))
+                break;
+
+            if (!tokenStream.matchToken(&matched, TOK_COMMA))
+                return false;
+            if (!matched)
+                break;
+
+            if (!hasRest) {
+                if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+                    return null();
+                if (tt == TOK_RP) {
+                    tokenStream.addModifierException(TokenStream::NoneIsOperand);
+                    break;
+                }
+            }
+        }
+
+        if (!parenFreeArrow) {
+            TokenKind tt;
+            if (!tokenStream.getToken(&tt))
+                return false;
+            if (tt != TOK_RP) {
+                if (IsSetterKind(kind)) {
+                    report(ParseError, false, null(),
+                           JSMSG_ACCESSOR_WRONG_ARGS, "setter", "one", "");
+                    return false;
+                }
+
+                report(ParseError, false, null(), JSMSG_PAREN_AFTER_FORMAL);
+                return false;
+            }
+        }
+
+        if (!hasDefault)
+            funbox->length = positionalFormals.length() - hasRest;
+
+        if (funbox->hasParameterExprs && funbox->hasDirectEval())
+            funbox->hasDirectEvalInParameterExpr = true;
+
+        funbox->function()->setArgCount(positionalFormals.length());
+    } else if (IsSetterKind(kind)) {
+        report(ParseError, false, null(), JSMSG_ACCESSOR_WRONG_ARGS, "setter", "one", "");
+        return false;
+    }
+
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkFunctionDefinition(HandleAtom funAtom, Node pn, FunctionSyntaxKind kind,
+                                              GeneratorKind generatorKind, bool* tryAnnexB)
+{
+    if (kind == Statement) {
+        TokenPos pos = handler.getPosition(pn);
+        RootedPropertyName funName(context, funAtom->asPropertyName());
+
+        // In sloppy mode, Annex B.3.2 allows labelled function
+        // declarations. Otherwise it is a parse error.
+        ParseContext::Statement* declaredInStmt = pc->innermostStatement();
+        if (declaredInStmt && declaredInStmt->kind() == StatementKind::Label) {
+            MOZ_ASSERT(!pc->sc()->strict(),
+                       "labeled functions shouldn't be parsed in strict mode");
+
+            // Find the innermost non-label statement.  Report an error if it's
+            // unbraced: functions can't appear in it.  Otherwise the statement
+            // (or its absence) determines the scope the function's bound in.
+            while (declaredInStmt && declaredInStmt->kind() == StatementKind::Label)
+                declaredInStmt = declaredInStmt->enclosing();
+
+            if (declaredInStmt && !StatementKindIsBraced(declaredInStmt->kind())) {
+                reportWithOffset(ParseError, false, pos.begin, JSMSG_SLOPPY_FUNCTION_LABEL);
+                return false;
+            }
+        }
+
+        if (declaredInStmt) {
+            MOZ_ASSERT(declaredInStmt->kind() != StatementKind::Label);
+            MOZ_ASSERT(StatementKindIsBraced(declaredInStmt->kind()));
+
+            if (!pc->sc()->strict() && generatorKind == NotGenerator) {
+                // Under sloppy mode, try Annex B.3.3 semantics. If making an
+                // additional 'var' binding of the same name does not throw an
+                // early error, do so. This 'var' binding would be assigned
+                // the function object when its declaration is reached, not at
+                // the start of the block.
+
+                if (!tryDeclareVarForAnnexBLexicalFunction(funName, tryAnnexB))
+                    return false;
+            }
+
+            if (!noteDeclaredName(funName, DeclarationKind::LexicalFunction, pos))
+                return false;
+        } else {
+            if (!noteDeclaredName(funName, DeclarationKind::BodyLevelFunction, pos))
+                return false;
+
+            // Body-level functions in modules are always closed over.
+            if (pc->atModuleLevel())
+                pc->varScope().lookupDeclaredName(funName)->value()->setClosedOver();
+        }
+    } else {
+        // A function expression does not introduce any binding.
+        handler.setOp(pn, kind == Arrow ? JSOP_LAMBDA_ARROW : JSOP_LAMBDA);
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::skipLazyInnerFunction(ParseNode* pn, FunctionSyntaxKind kind,
+                                                bool tryAnnexB)
+{
+    // When a lazily-parsed function is called, we only fully parse (and emit)
+    // that function, not any of its nested children. The initial syntax-only
+    // parse recorded the free variables of nested functions and their extents,
+    // so we can skip over them after accounting for their free variables.
+
+    RootedFunction fun(context, handler.nextLazyInnerFunction());
+    MOZ_ASSERT(!fun->isLegacyGenerator());
+    FunctionBox* funbox = newFunctionBox(pn, fun, Directives(/* strict = */ false),
+                                         fun->generatorKind(), fun->asyncKind(), tryAnnexB);
+    if (!funbox)
+        return false;
+
+    LazyScript* lazy = fun->lazyScript();
+    if (lazy->needsHomeObject())
+        funbox->setNeedsHomeObject();
+
+    PropagateTransitiveParseFlags(lazy, pc->sc());
+
+    // The position passed to tokenStream.advance() is an offset of the sort
+    // returned by userbuf.offset() and expected by userbuf.rawCharPtrAt(),
+    // while LazyScript::{begin,end} offsets are relative to the outermost
+    // script source.
+    Rooted<LazyScript*> lazyOuter(context, handler.lazyOuterFunction());
+    uint32_t userbufBase = lazyOuter->begin() - lazyOuter->column();
+    if (!tokenStream.advance(fun->lazyScript()->end() - userbufBase))
+        return false;
+
+    if (kind == Statement && fun->isExprBody()) {
+        if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+            return false;
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::skipLazyInnerFunction(Node pn, FunctionSyntaxKind kind,
+                                                  bool tryAnnexB)
+{
+    MOZ_CRASH("Cannot skip lazy inner functions when syntax parsing");
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::addExprAndGetNextTemplStrToken(YieldHandling yieldHandling, Node nodeList,
+                                                     TokenKind* ttp)
+{
+    Node pn = expr(InAllowed, yieldHandling, TripledotProhibited);
+    if (!pn)
+        return false;
+    handler.addList(nodeList, pn);
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return false;
+    if (tt != TOK_RC) {
+        report(ParseError, false, null(), JSMSG_TEMPLSTR_UNTERM_EXPR);
+        return false;
+    }
+
+    return tokenStream.getToken(ttp, TokenStream::TemplateTail);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::taggedTemplate(YieldHandling yieldHandling, Node nodeList, TokenKind tt)
+{
+    Node callSiteObjNode = handler.newCallSiteObject(pos().begin);
+    if (!callSiteObjNode)
+        return false;
+    handler.addList(nodeList, callSiteObjNode);
+
+    while (true) {
+        if (!appendToCallSiteObj(callSiteObjNode))
+            return false;
+        if (tt != TOK_TEMPLATE_HEAD)
+            break;
+
+        if (!addExprAndGetNextTemplStrToken(yieldHandling, nodeList, &tt))
+            return false;
+    }
+    handler.setEndPosition(nodeList, callSiteObjNode);
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::templateLiteral(YieldHandling yieldHandling)
+{
+    Node pn = noSubstitutionTemplate();
+    if (!pn)
+        return null();
+
+    Node nodeList = handler.newList(PNK_TEMPLATE_STRING_LIST, pn);
+    if (!nodeList)
+        return null();
+
+    TokenKind tt;
+    do {
+        if (!addExprAndGetNextTemplStrToken(yieldHandling, nodeList, &tt))
+            return null();
+
+        pn = noSubstitutionTemplate();
+        if (!pn)
+            return null();
+
+        handler.addList(nodeList, pn);
+    } while (tt == TOK_TEMPLATE_HEAD);
+    return nodeList;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::functionDefinition(InHandling inHandling, YieldHandling yieldHandling,
+                                         HandleAtom funName, FunctionSyntaxKind kind,
+                                         GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                         InvokedPrediction invoked)
+{
+    MOZ_ASSERT_IF(kind == Statement, funName);
+    MOZ_ASSERT_IF(asyncKind == AsyncFunction, generatorKind == StarGenerator);
+
+    Node pn = handler.newFunctionDefinition();
+    if (!pn)
+        return null();
+
+    if (invoked)
+        pn = handler.setLikelyIIFE(pn);
+
+    // Note the declared name and check for early errors.
+    bool tryAnnexB = false;
+    if (!checkFunctionDefinition(funName, pn, kind, generatorKind, &tryAnnexB))
+        return null();
+
+    // When fully parsing a LazyScript, we do not fully reparse its inner
+    // functions, which are also lazy. Instead, their free variables and
+    // source extents are recorded and may be skipped.
+    if (handler.canSkipLazyInnerFunctions()) {
+        if (!skipLazyInnerFunction(pn, kind, tryAnnexB))
+            return null();
+        return pn;
+    }
+
+    RootedObject proto(context);
+    if (generatorKind == StarGenerator) {
+        // If we are off the main thread, the generator meta-objects have
+        // already been created by js::StartOffThreadParseScript, so cx will not
+        // be necessary.
+        JSContext* cx = context->maybeJSContext();
+        proto = GlobalObject::getOrCreateStarGeneratorFunctionPrototype(cx, context->global());
+        if (!proto)
+            return null();
+    }
+    RootedFunction fun(context, newFunction(funName, kind, generatorKind, asyncKind, proto));
+    if (!fun)
+        return null();
+
+    // Speculatively parse using the directives of the parent parsing context.
+    // If a directive is encountered (e.g., "use strict") that changes how the
+    // function should have been parsed, we backup and reparse with the new set
+    // of directives.
+    Directives directives(pc);
+    Directives newDirectives = directives;
+
+    TokenStream::Position start(keepAtoms);
+    tokenStream.tell(&start);
+
+    // Parse the inner function. The following is a loop as we may attempt to
+    // reparse a function due to failed syntax parsing and encountering new
+    // "use foo" directives.
+    while (true) {
+        if (trySyntaxParseInnerFunction(pn, fun, inHandling, yieldHandling, kind, generatorKind,
+                                        asyncKind, tryAnnexB, directives, &newDirectives))
+        {
+            break;
+        }
+
+        // Return on error.
+        if (tokenStream.hadError() || directives == newDirectives)
+            return null();
+
+        // Assignment must be monotonic to prevent infinitely attempting to
+        // reparse.
+        MOZ_ASSERT_IF(directives.strict(), newDirectives.strict());
+        MOZ_ASSERT_IF(directives.asmJS(), newDirectives.asmJS());
+        directives = newDirectives;
+
+        tokenStream.seek(start);
+
+        // functionFormalParametersAndBody may have already set pn->pn_body before failing.
+        handler.setFunctionFormalParametersAndBody(pn, null());
+    }
+
+    return pn;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::trySyntaxParseInnerFunction(ParseNode* pn, HandleFunction fun,
+                                                      InHandling inHandling,
+                                                      YieldHandling yieldHandling,
+                                                      FunctionSyntaxKind kind,
+                                                      GeneratorKind generatorKind,
+                                                      FunctionAsyncKind asyncKind,
+                                                      bool tryAnnexB,
+                                                      Directives inheritedDirectives,
+                                                      Directives* newDirectives)
+{
+    // Try a syntax parse for this inner function.
+    do {
+        // If we're assuming this function is an IIFE, always perform a full
+        // parse to avoid the overhead of a lazy syntax-only parse. Although
+        // the prediction may be incorrect, IIFEs are common enough that it
+        // pays off for lots of code.
+        if (pn->isLikelyIIFE() && generatorKind == NotGenerator)
+            break;
+
+        Parser<SyntaxParseHandler>* parser = handler.syntaxParser;
+        if (!parser)
+            break;
+
+        UsedNameTracker::RewindToken token = usedNames.getRewindToken();
+
+        // Move the syntax parser to the current position in the stream.
+        TokenStream::Position position(keepAtoms);
+        tokenStream.tell(&position);
+        if (!parser->tokenStream.seek(position, tokenStream))
+            return false;
+
+        // Make a FunctionBox before we enter the syntax parser, because |pn|
+        // still expects a FunctionBox to be attached to it during BCE, and
+        // the syntax parser cannot attach one to it.
+        FunctionBox* funbox = newFunctionBox(pn, fun, inheritedDirectives, generatorKind,
+                                             asyncKind, tryAnnexB);
+        if (!funbox)
+            return false;
+        funbox->initWithEnclosingParseContext(pc, kind);
+
+        if (!parser->innerFunction(SyntaxParseHandler::NodeGeneric, pc, funbox, inHandling,
+                                   yieldHandling, kind, inheritedDirectives, newDirectives))
+        {
+            if (parser->hadAbortedSyntaxParse()) {
+                // Try again with a full parse. UsedNameTracker needs to be
+                // rewound to just before we tried the syntax parse for
+                // correctness.
+                parser->clearAbortedSyntaxParse();
+                usedNames.rewind(token);
+                MOZ_ASSERT_IF(parser->context->isJSContext(),
+                              !parser->context->asJSContext()->isExceptionPending());
+                break;
+            }
+            return false;
+        }
+
+        // Advance this parser over tokens processed by the syntax parser.
+        parser->tokenStream.tell(&position);
+        if (!tokenStream.seek(position, parser->tokenStream))
+            return false;
+
+        // Update the end position of the parse node.
+        pn->pn_pos.end = tokenStream.currentToken().pos.end;
+        return true;
+    } while (false);
+
+    // We failed to do a syntax parse above, so do the full parse.
+    return innerFunction(pn, pc, fun, inHandling, yieldHandling, kind, generatorKind, asyncKind,
+                         tryAnnexB, inheritedDirectives, newDirectives);
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::trySyntaxParseInnerFunction(Node pn, HandleFunction fun,
+                                                        InHandling inHandling,
+                                                        YieldHandling yieldHandling,
+                                                        FunctionSyntaxKind kind,
+                                                        GeneratorKind generatorKind,
+                                                        FunctionAsyncKind asyncKind,
+                                                        bool tryAnnexB,
+                                                        Directives inheritedDirectives,
+                                                        Directives* newDirectives)
+{
+    // This is already a syntax parser, so just parse the inner function.
+    return innerFunction(pn, pc, fun, inHandling, yieldHandling, kind, generatorKind, asyncKind,
+                         tryAnnexB, inheritedDirectives, newDirectives);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::innerFunction(Node pn, ParseContext* outerpc, FunctionBox* funbox,
+                                    InHandling inHandling, YieldHandling yieldHandling,
+                                    FunctionSyntaxKind kind, Directives inheritedDirectives,
+                                    Directives* newDirectives)
+{
+    // Note that it is possible for outerpc != this->pc, as we may be
+    // attempting to syntax parse an inner function from an outer full
+    // parser. In that case, outerpc is a ParseContext from the full parser
+    // instead of the current top of the stack of the syntax parser.
+
+    // Push a new ParseContext.
+    ParseContext funpc(this, funbox, newDirectives);
+    if (!funpc.init())
+        return false;
+
+    if (!functionFormalParametersAndBody(inHandling, yieldHandling, pn, kind))
+        return false;
+
+    return leaveInnerFunction(outerpc);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::innerFunction(Node pn, ParseContext* outerpc, HandleFunction fun,
+                                    InHandling inHandling, YieldHandling yieldHandling,
+                                    FunctionSyntaxKind kind,
+                                    GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                    bool tryAnnexB,
+                                    Directives inheritedDirectives, Directives* newDirectives)
+{
+    // Note that it is possible for outerpc != this->pc, as we may be
+    // attempting to syntax parse an inner function from an outer full
+    // parser. In that case, outerpc is a ParseContext from the full parser
+    // instead of the current top of the stack of the syntax parser.
+
+    FunctionBox* funbox = newFunctionBox(pn, fun, inheritedDirectives, generatorKind,
+                                         asyncKind, tryAnnexB);
+    if (!funbox)
+        return false;
+    funbox->initWithEnclosingParseContext(outerpc, kind);
+
+    return innerFunction(pn, outerpc, funbox, inHandling, yieldHandling, kind, inheritedDirectives,
+                         newDirectives);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::appendToCallSiteObj(Node callSiteObj)
+{
+    Node cookedNode = noSubstitutionTemplate();
+    if (!cookedNode)
+        return false;
+
+    JSAtom* atom = tokenStream.getRawTemplateStringAtom();
+    if (!atom)
+        return false;
+    Node rawNode = handler.newTemplateStringLiteral(atom, pos());
+    if (!rawNode)
+        return false;
+
+    handler.addToCallSiteObject(callSiteObj, rawNode, cookedNode);
+    return true;
+}
+
+template <>
+ParseNode*
+Parser<FullParseHandler>::standaloneLazyFunction(HandleFunction fun, bool strict,
+                                                 GeneratorKind generatorKind,
+                                                 FunctionAsyncKind asyncKind)
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    Node pn = handler.newFunctionDefinition();
+    if (!pn)
+        return null();
+
+    Directives directives(strict);
+    FunctionBox* funbox = newFunctionBox(pn, fun, directives, generatorKind, asyncKind,
+                                         /* tryAnnexB = */ false);
+    if (!funbox)
+        return null();
+    funbox->initFromLazyFunction();
+
+    Directives newDirectives = directives;
+    ParseContext funpc(this, funbox, &newDirectives);
+    if (!funpc.init())
+        return null();
+
+    // Our tokenStream has no current token, so pn's position is garbage.
+    // Substitute the position of the first token in our source. If the function
+    // is a not-async arrow, use TokenStream::Operand to keep
+    // verifyConsistentModifier from complaining (we will use
+    // TokenStream::Operand in functionArguments).
+    TokenStream::Modifier modifier = (fun->isArrow() && asyncKind == SyncFunction)
+                                     ? TokenStream::Operand : TokenStream::None;
+    if (!tokenStream.peekTokenPos(&pn->pn_pos, modifier))
+        return null();
+
+    YieldHandling yieldHandling = GetYieldHandling(generatorKind, asyncKind);
+    FunctionSyntaxKind syntaxKind = Statement;
+    if (fun->isClassConstructor())
+        syntaxKind = ClassConstructor;
+    else if (fun->isMethod())
+        syntaxKind = Method;
+    else if (fun->isGetter())
+        syntaxKind = Getter;
+    else if (fun->isSetter())
+        syntaxKind = Setter;
+    else if (fun->isArrow())
+        syntaxKind = Arrow;
+
+    if (!functionFormalParametersAndBody(InAllowed, yieldHandling, pn, syntaxKind)) {
+        MOZ_ASSERT(directives == newDirectives);
+        return null();
+    }
+
+    if (!FoldConstants(context, &pn, this))
+        return null();
+
+    return pn;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::functionFormalParametersAndBody(InHandling inHandling,
+                                                      YieldHandling yieldHandling,
+                                                      Node pn, FunctionSyntaxKind kind)
+{
+    // Given a properly initialized parse context, try to parse an actual
+    // function without concern for conversion to strict mode, use of lazy
+    // parsing and such.
+
+    FunctionBox* funbox = pc->functionBox();
+    RootedFunction fun(context, funbox->function());
+
+    AutoAwaitIsKeyword awaitIsKeyword(&tokenStream, funbox->isAsync());
+    if (!functionArguments(yieldHandling, kind, pn))
+        return false;
+
+    Maybe<ParseContext::VarScope> varScope;
+    if (funbox->hasParameterExprs) {
+        varScope.emplace(this);
+        if (!varScope->init(pc))
+            return false;
+    } else {
+        pc->functionScope().useAsVarScope(pc);
+    }
+
+    if (kind == Arrow) {
+        bool matched;
+        if (!tokenStream.matchToken(&matched, TOK_ARROW))
+            return false;
+        if (!matched) {
+            report(ParseError, false, null(), JSMSG_BAD_ARROW_ARGS);
+            return false;
+        }
+    }
+
+    // Parse the function body.
+    FunctionBodyType bodyType = StatementListBody;
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return false;
+    if (tt != TOK_LC) {
+        if ((funbox->isStarGenerator() && !funbox->isAsync()) || kind == Method ||
+            kind == GetterNoExpressionClosure || kind == SetterNoExpressionClosure ||
+            IsConstructorKind(kind)) {
+            report(ParseError, false, null(), JSMSG_CURLY_BEFORE_BODY);
+            return false;
+        }
+
+        if (kind != Arrow) {
+#if JS_HAS_EXPR_CLOSURES
+            addTelemetry(JSCompartment::DeprecatedExpressionClosure);
+            if (!warnOnceAboutExprClosure())
+                return false;
+#else
+            report(ParseError, false, null(), JSMSG_CURLY_BEFORE_BODY);
+            return false;
+#endif
+        }
+
+        tokenStream.ungetToken();
+        bodyType = ExpressionBody;
+#if JS_HAS_EXPR_CLOSURES
+        fun->setIsExprBody();
+#endif
+    }
+
+    // Arrow function parameters inherit yieldHandling from the enclosing
+    // context, but the arrow body doesn't. E.g. in |(a = yield) => yield|,
+    // |yield| in the parameters is either a name or keyword, depending on
+    // whether the arrow function is enclosed in a generator function or not.
+    // Whereas the |yield| in the function body is always parsed as a name.
+    YieldHandling bodyYieldHandling = GetYieldHandling(pc->generatorKind(), pc->asyncKind());
+    Node body = functionBody(inHandling, bodyYieldHandling, kind, bodyType);
+    if (!body)
+        return false;
+
+    if ((kind != Method && !IsConstructorKind(kind)) && fun->name()) {
+        RootedPropertyName propertyName(context, fun->name()->asPropertyName());
+        if (!checkStrictBinding(propertyName, handler.getPosition(pn)))
+            return false;
+    }
+
+    if (bodyType == StatementListBody) {
+        bool matched;
+        if (!tokenStream.matchToken(&matched, TOK_RC, TokenStream::Operand))
+            return false;
+        if (!matched) {
+            report(ParseError, false, null(), JSMSG_CURLY_AFTER_BODY);
+            return false;
+        }
+        funbox->bufEnd = pos().begin + 1;
+    } else {
+#if !JS_HAS_EXPR_CLOSURES
+        MOZ_ASSERT(kind == Arrow);
+#endif
+        if (tokenStream.hadError())
+            return false;
+        funbox->bufEnd = pos().end;
+        if (kind == Statement && !MatchOrInsertSemicolonAfterExpression(tokenStream))
+            return false;
+    }
+
+    if (IsMethodDefinitionKind(kind) && pc->superScopeNeedsHomeObject())
+        funbox->setNeedsHomeObject();
+
+    if (!finishFunction())
+        return false;
+
+    handler.setEndPosition(body, pos().begin);
+    handler.setEndPosition(pn, pos().end);
+    handler.setFunctionBody(pn, body);
+
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::functionStmt(YieldHandling yieldHandling, DefaultHandling defaultHandling,
+                                   FunctionAsyncKind asyncKind)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FUNCTION));
+
+    // Annex B.3.4 says we can parse function declarations unbraced under if
+    // or else as if it were braced. That is, |if (x) function f() {}| is
+    // parsed as |if (x) { function f() {} }|.
+    Maybe<ParseContext::Statement> synthesizedStmtForAnnexB;
+    Maybe<ParseContext::Scope> synthesizedScopeForAnnexB;
+    if (!pc->sc()->strict()) {
+        ParseContext::Statement* stmt = pc->innermostStatement();
+        if (stmt && stmt->kind() == StatementKind::If) {
+            synthesizedStmtForAnnexB.emplace(pc, StatementKind::Block);
+            synthesizedScopeForAnnexB.emplace(this);
+            if (!synthesizedScopeForAnnexB->init(pc))
+                return null();
+        }
+    }
+
+    RootedPropertyName name(context);
+    GeneratorKind generatorKind = asyncKind == AsyncFunction ? StarGenerator : NotGenerator;
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+
+    if (tt == TOK_MUL) {
+        if (asyncKind != SyncFunction) {
+            report(ParseError, false, null(), JSMSG_ASYNC_GENERATOR);
+            return null();
+        }
+        generatorKind = StarGenerator;
+        if (!tokenStream.getToken(&tt))
+            return null();
+    }
+
+    if (tt == TOK_NAME || tt == TOK_YIELD) {
+        name = bindingIdentifier(yieldHandling);
+        if (!name)
+            return null();
+    } else if (defaultHandling == AllowDefaultName) {
+        name = context->names().starDefaultStar;
+        tokenStream.ungetToken();
+    } else {
+        /* Unnamed function expressions are forbidden in statement context. */
+        report(ParseError, false, null(), JSMSG_UNNAMED_FUNCTION_STMT);
+        return null();
+    }
+
+    YieldHandling newYieldHandling = GetYieldHandling(generatorKind, asyncKind);
+    Node fun = functionDefinition(InAllowed, newYieldHandling, name, Statement, generatorKind,
+                                  asyncKind, PredictUninvoked);
+    if (!fun)
+        return null();
+
+    if (synthesizedStmtForAnnexB) {
+        Node synthesizedStmtList = handler.newStatementList(handler.getPosition(fun));
+        if (!synthesizedStmtList)
+            return null();
+        handler.addStatementToList(synthesizedStmtList, fun);
+        return finishLexicalScope(*synthesizedScopeForAnnexB, synthesizedStmtList);
+    }
+
+    return fun;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::functionExpr(InvokedPrediction invoked, FunctionAsyncKind asyncKind)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FUNCTION));
+
+    AutoAwaitIsKeyword awaitIsKeyword(&tokenStream, asyncKind == AsyncFunction);
+    GeneratorKind generatorKind = asyncKind == AsyncFunction ? StarGenerator : NotGenerator;
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+
+    if (tt == TOK_MUL) {
+        if (asyncKind != SyncFunction) {
+            report(ParseError, false, null(), JSMSG_ASYNC_GENERATOR);
+            return null();
+        }
+        generatorKind = StarGenerator;
+        if (!tokenStream.getToken(&tt))
+            return null();
+    }
+
+    YieldHandling yieldHandling = GetYieldHandling(generatorKind, asyncKind);
+
+    RootedPropertyName name(context);
+    if (tt == TOK_NAME || tt == TOK_YIELD) {
+        name = bindingIdentifier(yieldHandling);
+        if (!name)
+            return null();
+    } else {
+        tokenStream.ungetToken();
+    }
+
+    return functionDefinition(InAllowed, yieldHandling, name, Expression, generatorKind,
+                              asyncKind, invoked);
+}
+
+/*
+ * Return true if this node, known to be an unparenthesized string literal,
+ * could be the string of a directive in a Directive Prologue. Directive
+ * strings never contain escape sequences or line continuations.
+ * isEscapeFreeStringLiteral, below, checks whether the node itself could be
+ * a directive.
+ */
+static inline bool
+IsEscapeFreeStringLiteral(const TokenPos& pos, JSAtom* str)
+{
+    /*
+     * If the string's length in the source code is its length as a value,
+     * accounting for the quotes, then it must not contain any escape
+     * sequences or line continuations.
+     */
+    return pos.begin + str->length() + 2 == pos.end;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkUnescapedName()
+{
+    if (!tokenStream.currentToken().nameContainsEscape())
+        return true;
+
+    report(ParseError, false, null(), JSMSG_ESCAPED_KEYWORD);
+    return false;
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::asmJS(Node list)
+{
+    // While asm.js could technically be validated and compiled during syntax
+    // parsing, we have no guarantee that some later JS wouldn't abort the
+    // syntax parse and cause us to re-parse (and re-compile) the asm.js module.
+    // For simplicity, unconditionally abort the syntax parse when "use asm" is
+    // encountered so that asm.js is always validated/compiled exactly once
+    // during a full parse.
+    JS_ALWAYS_FALSE(abortIfSyntaxParser());
+    return false;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::asmJS(Node list)
+{
+    // Disable syntax parsing in anything nested inside the asm.js module.
+    handler.disableSyntaxParser();
+
+    // We should be encountering the "use asm" directive for the first time; if
+    // the directive is already, we must have failed asm.js validation and we're
+    // reparsing. In that case, don't try to validate again. A non-null
+    // newDirectives means we're not in a normal function.
+    if (!pc->newDirectives || pc->newDirectives->asmJS())
+        return true;
+
+    // If there is no ScriptSource, then we are doing a non-compiling parse and
+    // so we shouldn't (and can't, without a ScriptSource) compile.
+    if (ss == nullptr)
+        return true;
+
+    pc->functionBox()->useAsm = true;
+
+    // Attempt to validate and compile this asm.js module. On success, the
+    // tokenStream has been advanced to the closing }. On failure, the
+    // tokenStream is in an indeterminate state and we must reparse the
+    // function from the beginning. Reparsing is triggered by marking that a
+    // new directive has been encountered and returning 'false'.
+    bool validated;
+    if (!CompileAsmJS(context, *this, list, &validated))
+        return false;
+    if (!validated) {
+        pc->newDirectives->setAsmJS();
+        return false;
+    }
+
+    return true;
+}
+
+/*
+ * Recognize Directive Prologue members and directives. Assuming |pn| is a
+ * candidate for membership in a directive prologue, recognize directives and
+ * set |pc|'s flags accordingly. If |pn| is indeed part of a prologue, set its
+ * |pn_prologue| flag.
+ *
+ * Note that the following is a strict mode function:
+ *
+ * function foo() {
+ *   "blah" // inserted semi colon
+ *        "blurgh"
+ *   "use\x20loose"
+ *   "use strict"
+ * }
+ *
+ * That is, even though "use\x20loose" can never be a directive, now or in the
+ * future (because of the hex escape), the Directive Prologue extends through it
+ * to the "use strict" statement, which is indeed a directive.
+ */
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::maybeParseDirective(Node list, Node pn, bool* cont)
+{
+    TokenPos directivePos;
+    JSAtom* directive = handler.isStringExprStatement(pn, &directivePos);
+
+    *cont = !!directive;
+    if (!*cont)
+        return true;
+
+    if (IsEscapeFreeStringLiteral(directivePos, directive)) {
+        // Mark this statement as being a possibly legitimate part of a
+        // directive prologue, so the bytecode emitter won't warn about it being
+        // useless code. (We mustn't just omit the statement entirely yet, as it
+        // could be producing the value of an eval or JSScript execution.)
+        //
+        // Note that even if the string isn't one we recognize as a directive,
+        // the emitter still shouldn't flag it as useless, as it could become a
+        // directive in the future. We don't want to interfere with people
+        // taking advantage of directive-prologue-enabled features that appear
+        // in other browsers first.
+        handler.setPrologue(pn);
+
+        if (directive == context->names().useStrict) {
+            // Functions with non-simple parameter lists (destructuring,
+            // default or rest parameters) must not contain a "use strict"
+            // directive.
+            if (pc->isFunctionBox()) {
+                FunctionBox* funbox = pc->functionBox();
+                if (!funbox->hasSimpleParameterList()) {
+                    const char* parameterKind = funbox->hasDestructuringArgs
+                                                ? "destructuring"
+                                                : funbox->hasParameterExprs
+                                                ? "default"
+                                                : "rest";
+                    reportWithOffset(ParseError, false, directivePos.begin,
+                                     JSMSG_STRICT_NON_SIMPLE_PARAMS, parameterKind);
+                    return false;
+                }
+            }
+
+            // We're going to be in strict mode. Note that this scope explicitly
+            // had "use strict";
+            pc->sc()->setExplicitUseStrict();
+            if (!pc->sc()->strict()) {
+                // We keep track of the one possible strict violation that could
+                // occur in the directive prologue -- octal escapes -- and
+                // complain now.
+                if (tokenStream.sawOctalEscape()) {
+                    report(ParseError, false, null(), JSMSG_DEPRECATED_OCTAL);
+                    return false;
+                }
+                pc->sc()->strictScript = true;
+            }
+        } else if (directive == context->names().useAsm) {
+            if (pc->isFunctionBox())
+                return asmJS(list);
+            return report(ParseWarning, false, pn, JSMSG_USE_ASM_DIRECTIVE_FAIL);
+        }
+    }
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::statementList(YieldHandling yieldHandling)
+{
+    JS_CHECK_RECURSION(context, return null());
+
+    Node pn = handler.newStatementList(pos());
+    if (!pn)
+        return null();
+
+    bool canHaveDirectives = pc->atBodyLevel();
+    if (canHaveDirectives)
+        tokenStream.clearSawOctalEscape();
+    bool afterReturn = false;
+    bool warnedAboutStatementsAfterReturn = false;
+    uint32_t statementBegin = 0;
+    for (;;) {
+        TokenKind tt = TOK_EOF;
+        if (!tokenStream.peekToken(&tt, TokenStream::Operand)) {
+            if (tokenStream.isEOF())
+                isUnexpectedEOF_ = true;
+            return null();
+        }
+        if (tt == TOK_EOF || tt == TOK_RC)
+            break;
+        if (afterReturn) {
+            TokenPos pos(0, 0);
+            if (!tokenStream.peekTokenPos(&pos, TokenStream::Operand))
+                return null();
+            statementBegin = pos.begin;
+        }
+        Node next = statementListItem(yieldHandling, canHaveDirectives);
+        if (!next) {
+            if (tokenStream.isEOF())
+                isUnexpectedEOF_ = true;
+            return null();
+        }
+        if (!warnedAboutStatementsAfterReturn) {
+            if (afterReturn) {
+                if (!handler.isStatementPermittedAfterReturnStatement(next)) {
+                    if (!reportWithOffset(ParseWarning, false, statementBegin,
+                                          JSMSG_STMT_AFTER_RETURN))
+                    {
+                        return null();
+                    }
+                    warnedAboutStatementsAfterReturn = true;
+                }
+            } else if (handler.isReturnStatement(next)) {
+                afterReturn = true;
+            }
+        }
+
+        if (canHaveDirectives) {
+            if (!maybeParseDirective(pn, next, &canHaveDirectives))
+                return null();
+        }
+
+        handler.addStatementToList(pn, next);
+    }
+
+    return pn;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::condition(InHandling inHandling, YieldHandling yieldHandling)
+{
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_COND);
+    Node pn = exprInParens(inHandling, yieldHandling, TripledotProhibited);
+    if (!pn)
+        return null();
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_COND);
+
+    /* Check for (a = b) and warn about possible (a == b) mistype. */
+    if (handler.isUnparenthesizedAssignment(pn)) {
+        if (!report(ParseExtraWarning, false, null(), JSMSG_EQUAL_AS_ASSIGN))
+            return null();
+    }
+    return pn;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::matchLabel(YieldHandling yieldHandling, MutableHandle<PropertyName*> label)
+{
+    TokenKind tt = TOK_EOF;
+    if (!tokenStream.peekTokenSameLine(&tt, TokenStream::Operand))
+        return false;
+
+    if (tt == TOK_NAME || tt == TOK_YIELD) {
+        tokenStream.consumeKnownToken(tt, TokenStream::Operand);
+
+        label.set(labelIdentifier(yieldHandling));
+        if (!label)
+            return false;
+    } else {
+        label.set(nullptr);
+    }
+    return true;
+}
+
+template <typename ParseHandler>
+Parser<ParseHandler>::PossibleError::PossibleError(Parser<ParseHandler>& parser)
+  : parser_(parser)
+{}
+
+template <typename ParseHandler>
+typename Parser<ParseHandler>::PossibleError::Error&
+Parser<ParseHandler>::PossibleError::error(ErrorKind kind)
+{
+    if (kind == ErrorKind::Expression)
+        return exprError_;
+    MOZ_ASSERT(kind == ErrorKind::Destructuring);
+    return destructuringError_;
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::setResolved(ErrorKind kind)
+{
+    error(kind).state_ = ErrorState::None;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::PossibleError::hasError(ErrorKind kind)
+{
+    return error(kind).state_ == ErrorState::Pending;
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::setPending(ErrorKind kind, Node pn, unsigned errorNumber)
+{
+    // Don't overwrite a previously recorded error.
+    if (hasError(kind))
+        return;
+
+    // If we report an error later, we'll do it from the position where we set
+    // the state to pending.
+    Error& err = error(kind);
+    err.offset_ = (pn ? parser_.handler.getPosition(pn) : parser_.pos()).begin;
+    err.errorNumber_ = errorNumber;
+    err.state_ = ErrorState::Pending;
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::setPendingDestructuringError(Node pn, unsigned errorNumber)
+{
+    setPending(ErrorKind::Destructuring, pn, errorNumber);
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::setPendingExpressionError(Node pn, unsigned errorNumber)
+{
+    setPending(ErrorKind::Expression, pn, errorNumber);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::PossibleError::checkForError(ErrorKind kind)
+{
+    if (!hasError(kind))
+        return true;
+
+    Error& err = error(kind);
+    parser_.reportWithOffset(ParseError, false, err.offset_, err.errorNumber_);
+    return false;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::PossibleError::checkForDestructuringError()
+{
+    // Clear pending expression error, because we're definitely not in an
+    // expression context.
+    setResolved(ErrorKind::Expression);
+
+    // Report any pending destructuring error.
+    return checkForError(ErrorKind::Destructuring);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::PossibleError::checkForExpressionError()
+{
+    // Clear pending destructuring error, because we're definitely not in a
+    // destructuring context.
+    setResolved(ErrorKind::Destructuring);
+
+    // Report any pending expression error.
+    return checkForError(ErrorKind::Expression);
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::transferErrorTo(ErrorKind kind, PossibleError* other)
+{
+    if (hasError(kind) && !other->hasError(kind)) {
+        Error& err = error(kind);
+        Error& otherErr = other->error(kind);
+        otherErr.offset_ = err.offset_;
+        otherErr.errorNumber_ = err.errorNumber_;
+        otherErr.state_ = err.state_;
+    }
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::PossibleError::transferErrorsTo(PossibleError* other)
+{
+    MOZ_ASSERT(other);
+    MOZ_ASSERT(this != other);
+    MOZ_ASSERT(&parser_ == &other->parser_,
+               "Can't transfer fields to an instance which belongs to a different parser");
+
+    transferErrorTo(ErrorKind::Destructuring, other);
+    transferErrorTo(ErrorKind::Expression, other);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkAssignmentToCall(Node target, unsigned msg)
+{
+    MOZ_ASSERT(handler.isFunctionCall(target));
+
+    // Assignment to function calls is forbidden in ES6.  We're still somewhat
+    // concerned about sites using this in dead code, so forbid it only in
+    // strict mode code (or if the werror option has been set), and otherwise
+    // warn.
+    return report(ParseStrictError, pc->sc()->strict(), target, msg);
+}
+
+template <>
+bool
+Parser<FullParseHandler>::checkDestructuringName(ParseNode* expr, Maybe<DeclarationKind> maybeDecl)
+{
+    MOZ_ASSERT(!handler.isUnparenthesizedDestructuringPattern(expr));
+
+    // Parentheses are forbidden around destructuring *patterns* (but allowed
+    // around names).  Use our nicer error message for parenthesized, nested
+    // patterns.
+    if (handler.isParenthesizedDestructuringPattern(expr)) {
+        report(ParseError, false, expr, JSMSG_BAD_DESTRUCT_PARENS);
+        return false;
+    }
+
+    // This expression might be in a variable-binding pattern where only plain,
+    // unparenthesized names are permitted.
+    if (maybeDecl) {
+        // Destructuring patterns in declarations must only contain
+        // unparenthesized names.
+        if (!handler.isUnparenthesizedName(expr)) {
+            report(ParseError, false, expr, JSMSG_NO_VARIABLE_NAME);
+            return false;
+        }
+
+        RootedPropertyName name(context, expr->name());
+        return noteDeclaredName(name, *maybeDecl, handler.getPosition(expr));
+    }
+
+    // Otherwise this is an expression in destructuring outside a declaration.
+    if (!reportIfNotValidSimpleAssignmentTarget(expr, KeyedDestructuringAssignment))
+        return false;
+
+    MOZ_ASSERT(!handler.isFunctionCall(expr),
+               "function calls shouldn't be considered valid targets in "
+               "destructuring patterns");
+
+    if (handler.isNameAnyParentheses(expr)) {
+        // The arguments/eval identifiers are simple in non-strict mode code.
+        // Warn to discourage their use nonetheless.
+        return reportIfArgumentsEvalTarget(expr);
+    }
+
+    // Nothing further to do for property accesses.
+    MOZ_ASSERT(handler.isPropertyAccess(expr));
+    return true;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::checkDestructuringPattern(ParseNode* pattern,
+                                                    Maybe<DeclarationKind> maybeDecl,
+                                                    PossibleError* possibleError /* = nullptr */);
+
+template <>
+bool
+Parser<FullParseHandler>::checkDestructuringObject(ParseNode* objectPattern,
+                                                   Maybe<DeclarationKind> maybeDecl)
+{
+    MOZ_ASSERT(objectPattern->isKind(PNK_OBJECT));
+
+    for (ParseNode* member = objectPattern->pn_head; member; member = member->pn_next) {
+        ParseNode* target;
+        if (member->isKind(PNK_MUTATEPROTO)) {
+            target = member->pn_kid;
+        } else {
+            MOZ_ASSERT(member->isKind(PNK_COLON) || member->isKind(PNK_SHORTHAND));
+            MOZ_ASSERT_IF(member->isKind(PNK_SHORTHAND),
+                          member->pn_left->isKind(PNK_OBJECT_PROPERTY_NAME) &&
+                          member->pn_right->isKind(PNK_NAME) &&
+                          member->pn_left->pn_atom == member->pn_right->pn_atom);
+
+            target = member->pn_right;
+        }
+        if (handler.isUnparenthesizedAssignment(target))
+            target = target->pn_left;
+
+        if (handler.isUnparenthesizedDestructuringPattern(target)) {
+            if (!checkDestructuringPattern(target, maybeDecl))
+                return false;
+        } else {
+            if (!checkDestructuringName(target, maybeDecl))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::checkDestructuringArray(ParseNode* arrayPattern,
+                                                  Maybe<DeclarationKind> maybeDecl)
+{
+    MOZ_ASSERT(arrayPattern->isKind(PNK_ARRAY));
+
+    for (ParseNode* element = arrayPattern->pn_head; element; element = element->pn_next) {
+        if (element->isKind(PNK_ELISION))
+            continue;
+
+        ParseNode* target;
+        if (element->isKind(PNK_SPREAD)) {
+            if (element->pn_next) {
+                report(ParseError, false, element->pn_next, JSMSG_PARAMETER_AFTER_REST);
+                return false;
+            }
+            target = element->pn_kid;
+        } else if (handler.isUnparenthesizedAssignment(element)) {
+            target = element->pn_left;
+        } else {
+            target = element;
+        }
+
+        if (handler.isUnparenthesizedDestructuringPattern(target)) {
+            if (!checkDestructuringPattern(target, maybeDecl))
+                return false;
+        } else {
+            if (!checkDestructuringName(target, maybeDecl))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+/*
+ * Destructuring patterns can appear in two kinds of contexts:
+ *
+ * - assignment-like: assignment expressions and |for| loop heads.  In
+ *   these cases, the patterns' property value positions can be
+ *   arbitrary lvalue expressions; the destructuring is just a fancy
+ *   assignment.
+ *
+ * - binding-like: |var| and |let| declarations, functions' formal
+ *   parameter lists, |catch| clauses, and comprehension tails.  In
+ *   these cases, the patterns' property value positions must be
+ *   simple names; the destructuring defines them as new variables.
+ *
+ * In both cases, other code parses the pattern as an arbitrary
+ * primaryExpr, and then, here in checkDestructuringPattern, verify
+ * that the tree is a valid AssignmentPattern or BindingPattern.
+ *
+ * In assignment-like contexts, we parse the pattern with
+ * pc->inDestructuringDecl clear, so the lvalue expressions in the
+ * pattern are parsed normally.  primaryExpr links variable references
+ * into the appropriate use chains; creates placeholder definitions;
+ * and so on.  checkDestructuringPattern won't bind any new names and
+ * we specialize lvalues as appropriate.
+ *
+ * In declaration-like contexts, the normal variable reference
+ * processing would just be an obstruction, because we're going to
+ * define the names that appear in the property value positions as new
+ * variables anyway.  In this case, we parse the pattern with
+ * pc->inDestructuringDecl set, which directs primaryExpr to leave
+ * whatever name nodes it creates unconnected.  Then, here in
+ * checkDestructuringPattern, we require the pattern's property value
+ * positions to be simple names, and define them as appropriate to the
+ * context.
+ */
+template <>
+bool
+Parser<FullParseHandler>::checkDestructuringPattern(ParseNode* pattern,
+                                                    Maybe<DeclarationKind> maybeDecl,
+                                                    PossibleError* possibleError /* = nullptr */)
+{
+    if (pattern->isKind(PNK_ARRAYCOMP)) {
+        report(ParseError, false, pattern, JSMSG_ARRAY_COMP_LEFTSIDE);
+        return false;
+    }
+
+    bool isDestructuring = pattern->isKind(PNK_ARRAY)
+                           ? checkDestructuringArray(pattern, maybeDecl)
+                           : checkDestructuringObject(pattern, maybeDecl);
+
+    // Report any pending destructuring error.
+    if (isDestructuring && possibleError && !possibleError->checkForDestructuringError())
+        return false;
+
+    return isDestructuring;
+}
+
+template <>
+bool
+Parser<SyntaxParseHandler>::checkDestructuringPattern(Node pattern,
+                                                      Maybe<DeclarationKind> maybeDecl,
+                                                      PossibleError* possibleError /* = nullptr */)
+{
+    return abortIfSyntaxParser();
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::destructuringDeclaration(DeclarationKind kind, YieldHandling yieldHandling,
+                                               TokenKind tt)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(tt));
+    MOZ_ASSERT(tt == TOK_LB || tt == TOK_LC);
+
+    PossibleError possibleError(*this);
+    Node pattern;
+    {
+        pc->inDestructuringDecl = Some(kind);
+        pattern = primaryExpr(yieldHandling, TripledotProhibited, tt, &possibleError);
+        pc->inDestructuringDecl = Nothing();
+    }
+
+    if (!pattern || !checkDestructuringPattern(pattern, Some(kind), &possibleError))
+        return null();
+
+    return pattern;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::destructuringDeclarationWithoutYieldOrAwait(DeclarationKind kind,
+                                                                  YieldHandling yieldHandling,
+                                                                  TokenKind tt)
+{
+    uint32_t startYieldOffset = pc->lastYieldOffset;
+    uint32_t startAwaitOffset = pc->lastAwaitOffset;
+    Node res = destructuringDeclaration(kind, yieldHandling, tt);
+    if (res) {
+        if (pc->lastYieldOffset != startYieldOffset) {
+            reportWithOffset(ParseError, false, pc->lastYieldOffset, JSMSG_YIELD_IN_DEFAULT);
+            return null();
+        }
+        if (pc->lastAwaitOffset != startAwaitOffset) {
+            reportWithOffset(ParseError, false, pc->lastAwaitOffset, JSMSG_AWAIT_IN_DEFAULT);
+            return null();
+        }
+    }
+    return res;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::blockStatement(YieldHandling yieldHandling, unsigned errorNumber)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LC));
+
+    ParseContext::Statement stmt(pc, StatementKind::Block);
+    ParseContext::Scope scope(this);
+    if (!scope.init(pc))
+        return null();
+
+    Node list = statementList(yieldHandling);
+    if (!list)
+        return null();
+
+    MUST_MATCH_TOKEN_MOD(TOK_RC, TokenStream::Operand, errorNumber);
+
+    return finishLexicalScope(scope, list);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::expressionAfterForInOrOf(ParseNodeKind forHeadKind,
+                                               YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(forHeadKind == PNK_FORIN || forHeadKind == PNK_FOROF);
+    Node pn = forHeadKind == PNK_FOROF
+           ? assignExpr(InAllowed, yieldHandling, TripledotProhibited)
+           : expr(InAllowed, yieldHandling, TripledotProhibited);
+    return pn;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::declarationPattern(Node decl, DeclarationKind declKind, TokenKind tt,
+                                         bool initialDeclaration, YieldHandling yieldHandling,
+                                         ParseNodeKind* forHeadKind, Node* forInOrOfExpression)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LB) ||
+               tokenStream.isCurrentTokenType(TOK_LC));
+
+    Node pattern = destructuringDeclaration(declKind, yieldHandling, tt);
+    if (!pattern)
+        return null();
+
+    if (initialDeclaration && forHeadKind) {
+        bool isForIn, isForOf;
+        if (!matchInOrOf(&isForIn, &isForOf))
+            return null();
+
+        if (isForIn) {
+            *forHeadKind = PNK_FORIN;
+        } else if (isForOf) {
+            *forHeadKind = PNK_FOROF;
+
+            // Annex B.3.5 has different early errors for vars in for-of loops.
+            if (declKind == DeclarationKind::Var)
+                declKind = DeclarationKind::ForOfVar;
+        } else {
+            *forHeadKind = PNK_FORHEAD;
+        }
+
+        if (*forHeadKind != PNK_FORHEAD) {
+            *forInOrOfExpression = expressionAfterForInOrOf(*forHeadKind, yieldHandling);
+            if (!*forInOrOfExpression)
+                return null();
+
+            return pattern;
+        }
+    }
+
+    TokenKind token;
+    if (!tokenStream.getToken(&token, TokenStream::None))
+        return null();
+
+    if (token != TOK_ASSIGN) {
+        report(ParseError, false, null(), JSMSG_BAD_DESTRUCT_DECL);
+        return null();
+    }
+
+    Node init = assignExpr(forHeadKind ? InProhibited : InAllowed,
+                           yieldHandling, TripledotProhibited);
+    if (!init)
+        return null();
+
+    if (forHeadKind) {
+        // For for(;;) declarations, consistency with |for (;| parsing requires
+        // that the ';' first be examined as Operand, even though absence of a
+        // binary operator (examined with modifier None) terminated |init|.
+        // For all other declarations, through ASI's infinite majesty, a next
+        // token on a new line would begin an expression.
+        tokenStream.addModifierException(TokenStream::OperandIsNone);
+    }
+
+    return handler.newBinary(PNK_ASSIGN, pattern, init);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::initializerInNameDeclaration(Node decl, Node binding,
+                                                   Handle<PropertyName*> name,
+                                                   DeclarationKind declKind,
+                                                   bool initialDeclaration,
+                                                   YieldHandling yieldHandling,
+                                                   ParseNodeKind* forHeadKind,
+                                                   Node* forInOrOfExpression)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_ASSIGN));
+
+    Node initializer = assignExpr(forHeadKind ? InProhibited : InAllowed,
+                                  yieldHandling, TripledotProhibited);
+    if (!initializer)
+        return false;
+
+    if (forHeadKind) {
+        if (initialDeclaration) {
+            bool isForIn, isForOf;
+            if (!matchInOrOf(&isForIn, &isForOf))
+                return false;
+
+            // An initialized declaration can't appear in a for-of:
+            //
+            //   for (var/let/const x = ... of ...); // BAD
+            if (isForOf) {
+                report(ParseError, false, binding, JSMSG_BAD_FOR_LEFTSIDE);
+                return false;
+            }
+
+            if (isForIn) {
+                // Lexical declarations in for-in loops can't be initialized:
+                //
+                //   for (let/const x = ... in ...); // BAD
+                if (DeclarationKindIsLexical(declKind)) {
+                    report(ParseError, false, binding, JSMSG_BAD_FOR_LEFTSIDE);
+                    return false;
+                }
+
+                // This leaves only initialized for-in |var| declarations.  ES6
+                // forbids these; later ES un-forbids in non-strict mode code.
+                *forHeadKind = PNK_FORIN;
+                if (!report(ParseStrictError, pc->sc()->strict(), initializer,
+                            JSMSG_INVALID_FOR_IN_DECL_WITH_INIT))
+                {
+                    return false;
+                }
+
+                *forInOrOfExpression = expressionAfterForInOrOf(PNK_FORIN, yieldHandling);
+                if (!*forInOrOfExpression)
+                    return false;
+            } else {
+                *forHeadKind = PNK_FORHEAD;
+            }
+        } else {
+            MOZ_ASSERT(*forHeadKind == PNK_FORHEAD);
+
+            // In the very rare case of Parser::assignExpr consuming an
+            // ArrowFunction with block body, when full-parsing with the arrow
+            // function being a skipped lazy inner function, we don't have
+            // lookahead for the next token.  Do a one-off peek here to be
+            // consistent with what Parser::matchForInOrOf does in the other
+            // arm of this |if|.
+            //
+            // If you think this all sounds pretty code-smelly, you're almost
+            // certainly correct.
+            TokenKind ignored;
+            if (!tokenStream.peekToken(&ignored))
+                return false;
+        }
+
+        if (*forHeadKind == PNK_FORHEAD) {
+            // Per Parser::forHeadStart, the semicolon in |for (;| is
+            // ultimately gotten as Operand.  But initializer expressions
+            // terminate with the absence of an operator gotten as None,
+            // so we need an exception.
+            tokenStream.addModifierException(TokenStream::OperandIsNone);
+        }
+    }
+
+    return handler.finishInitializerAssignment(binding, initializer);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::declarationName(Node decl, DeclarationKind declKind, TokenKind tt,
+                                      bool initialDeclaration, YieldHandling yieldHandling,
+                                      ParseNodeKind* forHeadKind, Node* forInOrOfExpression)
+{
+    // Anything other than TOK_YIELD or TOK_NAME is an error.
+    if (tt != TOK_NAME && tt != TOK_YIELD) {
+        report(ParseError, false, null(), JSMSG_NO_VARIABLE_NAME);
+        return null();
+    }
+
+    RootedPropertyName name(context, bindingIdentifier(yieldHandling));
+    if (!name)
+        return null();
+
+    Node binding = newName(name);
+    if (!binding)
+        return null();
+
+    TokenPos namePos = pos();
+
+    // The '=' context after a variable name in a declaration is an opportunity
+    // for ASI, and thus for the next token to start an ExpressionStatement:
+    //
+    //  var foo   // VariableDeclaration
+    //  /bar/g;   // ExpressionStatement
+    //
+    // Therefore get the token here as Operand.
+    bool matched;
+    if (!tokenStream.matchToken(&matched, TOK_ASSIGN, TokenStream::Operand))
+        return null();
+
+    if (matched) {
+        if (!initializerInNameDeclaration(decl, binding, name, declKind, initialDeclaration,
+                                          yieldHandling, forHeadKind, forInOrOfExpression))
+        {
+            return null();
+        }
+    } else {
+        tokenStream.addModifierException(TokenStream::NoneIsOperand);
+
+        if (initialDeclaration && forHeadKind) {
+            bool isForIn, isForOf;
+            if (!matchInOrOf(&isForIn, &isForOf))
+                return null();
+
+            if (isForIn) {
+                *forHeadKind = PNK_FORIN;
+            } else if (isForOf) {
+                *forHeadKind = PNK_FOROF;
+
+                // Annex B.3.5 has different early errors for vars in for-of loops.
+                if (declKind == DeclarationKind::Var)
+                    declKind = DeclarationKind::ForOfVar;
+            } else {
+                *forHeadKind = PNK_FORHEAD;
+            }
+        }
+
+        if (forHeadKind && *forHeadKind != PNK_FORHEAD) {
+            *forInOrOfExpression = expressionAfterForInOrOf(*forHeadKind, yieldHandling);
+            if (!*forInOrOfExpression)
+                return null();
+        } else {
+            // Normal const declarations, and const declarations in for(;;)
+            // heads, must be initialized.
+            if (declKind == DeclarationKind::Const) {
+                report(ParseError, false, binding, JSMSG_BAD_CONST_DECL);
+                return null();
+            }
+        }
+    }
+
+    // Note the declared name after knowing whether or not we are in a for-of
+    // loop, due to special early error semantics in Annex B.3.5.
+    if (!noteDeclaredName(name, declKind, namePos))
+        return null();
+
+    return binding;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::declarationList(YieldHandling yieldHandling,
+                                      ParseNodeKind kind,
+                                      ParseNodeKind* forHeadKind /* = nullptr */,
+                                      Node* forInOrOfExpression /* = nullptr */)
+{
+    MOZ_ASSERT(kind == PNK_VAR || kind == PNK_LET || kind == PNK_CONST);
+
+    JSOp op;
+    DeclarationKind declKind;
+    switch (kind) {
+      case PNK_VAR:
+        op = JSOP_DEFVAR;
+        declKind = DeclarationKind::Var;
+        break;
+      case PNK_CONST:
+        op = JSOP_DEFCONST;
+        declKind = DeclarationKind::Const;
+        break;
+      case PNK_LET:
+        op = JSOP_DEFLET;
+        declKind = DeclarationKind::Let;
+        break;
+      default:
+        MOZ_CRASH("Unknown declaration kind");
+    }
+
+    Node decl = handler.newDeclarationList(kind, op);
+    if (!decl)
+        return null();
+
+    bool matched;
+    bool initialDeclaration = true;
+    do {
+        MOZ_ASSERT_IF(!initialDeclaration && forHeadKind,
+                      *forHeadKind == PNK_FORHEAD);
+
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt))
+            return null();
+
+        Node binding = (tt == TOK_LB || tt == TOK_LC)
+                       ? declarationPattern(decl, declKind, tt, initialDeclaration, yieldHandling,
+                                            forHeadKind, forInOrOfExpression)
+                       : declarationName(decl, declKind, tt, initialDeclaration, yieldHandling,
+                                         forHeadKind, forInOrOfExpression);
+        if (!binding)
+            return null();
+
+        handler.addList(decl, binding);
+
+        if (forHeadKind && *forHeadKind != PNK_FORHEAD)
+            break;
+
+        initialDeclaration = false;
+
+        if (!tokenStream.matchToken(&matched, TOK_COMMA))
+            return null();
+    } while (matched);
+
+    return decl;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::lexicalDeclaration(YieldHandling yieldHandling, bool isConst)
+{
+    /*
+     * Parse body-level lets without a new block object. ES6 specs
+     * that an execution environment's initial lexical environment
+     * is the VariableEnvironment, i.e., body-level lets are in
+     * the same environment record as vars.
+     *
+     * However, they cannot be parsed exactly as vars, as ES6
+     * requires that uninitialized lets throw ReferenceError on use.
+     *
+     * See 8.1.1.1.6 and the note in 13.2.1.
+     */
+    Node decl = declarationList(yieldHandling, isConst ? PNK_CONST : PNK_LET);
+    if (!decl || !MatchOrInsertSemicolonAfterExpression(tokenStream))
+        return null();
+
+    return decl;
+}
+
+template <>
+bool
+Parser<FullParseHandler>::namedImportsOrNamespaceImport(TokenKind tt, Node importSpecSet)
+{
+    if (tt == TOK_LC) {
+        TokenStream::Modifier modifier = TokenStream::KeywordIsName;
+        while (true) {
+            // Handle the forms |import {} from 'a'| and
+            // |import { ..., } from 'a'| (where ... is non empty), by
+            // escaping the loop early if the next token is }.
+            if (!tokenStream.peekToken(&tt, TokenStream::KeywordIsName))
+                return false;
+
+            if (tt == TOK_RC)
+                break;
+
+            // If the next token is a keyword, the previous call to
+            // peekToken matched it as a TOK_NAME, and put it in the
+            // lookahead buffer, so this call will match keywords as well.
+            MUST_MATCH_TOKEN_MOD(TOK_NAME, TokenStream::KeywordIsName, JSMSG_NO_IMPORT_NAME);
+            Rooted<PropertyName*> importName(context, tokenStream.currentName());
+            TokenPos importNamePos = pos();
+
+            TokenKind maybeAs;
+            if (!tokenStream.peekToken(&maybeAs))
+                return null();
+
+            if (maybeAs == TOK_NAME &&
+                tokenStream.nextName() == context->names().as)
+            {
+                tokenStream.consumeKnownToken(TOK_NAME);
+
+                if (!checkUnescapedName())
+                    return false;
+
+                TokenKind afterAs;
+                if (!tokenStream.getToken(&afterAs))
+                    return false;
+
+                if (afterAs != TOK_NAME && afterAs != TOK_YIELD) {
+                    report(ParseError, false, null(), JSMSG_NO_BINDING_NAME);
+                    return false;
+                }
+            } else {
+                // Keywords cannot be bound to themselves, so an import name
+                // that is a keyword is a syntax error if it is not followed
+                // by the keyword 'as'.
+                // See the ImportSpecifier production in ES6 section 15.2.2.
+                if (IsKeyword(importName)) {
+                    JSAutoByteString bytes;
+                    if (!AtomToPrintableString(context, importName, &bytes))
+                        return false;
+                    report(ParseError, false, null(), JSMSG_AS_AFTER_RESERVED_WORD, bytes.ptr());
+                    return false;
+                }
+            }
+
+            RootedPropertyName bindingAtom(context, importedBinding());
+            if (!bindingAtom)
+                return false;
+
+            Node bindingName = newName(bindingAtom);
+            if (!bindingName)
+                return false;
+            if (!noteDeclaredName(bindingAtom, DeclarationKind::Import, pos()))
+                return false;
+
+            Node importNameNode = newName(importName, importNamePos);
+            if (!importNameNode)
+                return false;
+
+            Node importSpec = handler.newBinary(PNK_IMPORT_SPEC, importNameNode, bindingName);
+            if (!importSpec)
+                return false;
+
+            handler.addList(importSpecSet, importSpec);
+
+            bool matched;
+            if (!tokenStream.matchToken(&matched, TOK_COMMA))
+                return false;
+
+            if (!matched) {
+                modifier = TokenStream::None;
+                break;
+            }
+        }
+
+        MUST_MATCH_TOKEN_MOD(TOK_RC, modifier, JSMSG_RC_AFTER_IMPORT_SPEC_LIST);
+    } else {
+        MOZ_ASSERT(tt == TOK_MUL);
+        if (!tokenStream.getToken(&tt))
+            return false;
+
+        if (tt != TOK_NAME || tokenStream.currentName() != context->names().as) {
+            report(ParseError, false, null(), JSMSG_AS_AFTER_IMPORT_STAR);
+            return false;
+        }
+
+        if (!checkUnescapedName())
+            return false;
+
+        MUST_MATCH_TOKEN(TOK_NAME, JSMSG_NO_BINDING_NAME);
+
+        Node importName = newName(context->names().star);
+        if (!importName)
+            return false;
+
+        // Namespace imports are are not indirect bindings but lexical
+        // definitions that hold a module namespace object. They are treated
+        // as const variables which are initialized during the
+        // ModuleDeclarationInstantiation step.
+        RootedPropertyName bindingName(context, importedBinding());
+        if (!bindingName)
+            return false;
+        Node bindingNameNode = newName(bindingName);
+        if (!bindingNameNode)
+            return false;
+        if (!noteDeclaredName(bindingName, DeclarationKind::Const, pos()))
+            return false;
+
+        // The namespace import name is currently required to live on the
+        // environment.
+        pc->varScope().lookupDeclaredName(bindingName)->value()->setClosedOver();
+
+        Node importSpec = handler.newBinary(PNK_IMPORT_SPEC, importName, bindingNameNode);
+        if (!importSpec)
+            return false;
+
+        handler.addList(importSpecSet, importSpec);
+    }
+
+    return true;
+}
+
+template<>
+bool
+Parser<SyntaxParseHandler>::namedImportsOrNamespaceImport(TokenKind tt, Node importSpecSet)
+{
+    MOZ_ALWAYS_FALSE(abortIfSyntaxParser());
+    return false;
+}
+
+template<>
+ParseNode*
+Parser<FullParseHandler>::importDeclaration()
+{
+    MOZ_ASSERT(tokenStream.currentToken().type == TOK_IMPORT);
+
+    if (!pc->atModuleLevel()) {
+        report(ParseError, false, null(), JSMSG_IMPORT_DECL_AT_TOP_LEVEL);
+        return null();
+    }
+
+    uint32_t begin = pos().begin;
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+
+    Node importSpecSet = handler.newList(PNK_IMPORT_SPEC_LIST);
+    if (!importSpecSet)
+        return null();
+
+    if (tt == TOK_NAME || tt == TOK_LC || tt == TOK_MUL) {
+        if (tt == TOK_NAME) {
+            // Handle the form |import a from 'b'|, by adding a single import
+            // specifier to the list, with 'default' as the import name and
+            // 'a' as the binding name. This is equivalent to
+            // |import { default as a } from 'b'|.
+            Node importName = newName(context->names().default_);
+            if (!importName)
+                return null();
+
+            RootedPropertyName bindingAtom(context, importedBinding());
+            if (!bindingAtom)
+                return null();
+
+            Node bindingName = newName(bindingAtom);
+            if (!bindingName)
+                return null();
+
+            if (!noteDeclaredName(bindingAtom, DeclarationKind::Import, pos()))
+                return null();
+
+            Node importSpec = handler.newBinary(PNK_IMPORT_SPEC, importName, bindingName);
+            if (!importSpec)
+                return null();
+
+            handler.addList(importSpecSet, importSpec);
+
+            if (!tokenStream.peekToken(&tt))
+                return null();
+
+            if (tt == TOK_COMMA) {
+                tokenStream.consumeKnownToken(tt);
+                if (!tokenStream.getToken(&tt))
+                    return null();
+
+                if (tt != TOK_LC && tt != TOK_MUL) {
+                    report(ParseError, false, null(), JSMSG_NAMED_IMPORTS_OR_NAMESPACE_IMPORT);
+                    return null();
+                }
+
+                if (!namedImportsOrNamespaceImport(tt, importSpecSet))
+                    return null();
+            }
+        } else {
+            if (!namedImportsOrNamespaceImport(tt, importSpecSet))
+                return null();
+        }
+
+        if (!tokenStream.getToken(&tt))
+            return null();
+
+        if (tt != TOK_NAME || tokenStream.currentName() != context->names().from) {
+            report(ParseError, false, null(), JSMSG_FROM_AFTER_IMPORT_CLAUSE);
+            return null();
+        }
+
+        if (!checkUnescapedName())
+            return null();
+
+        MUST_MATCH_TOKEN(TOK_STRING, JSMSG_MODULE_SPEC_AFTER_FROM);
+    } else if (tt == TOK_STRING) {
+        // Handle the form |import 'a'| by leaving the list empty. This is
+        // equivalent to |import {} from 'a'|.
+        importSpecSet->pn_pos.end = importSpecSet->pn_pos.begin;
+    } else {
+        report(ParseError, false, null(), JSMSG_DECLARATION_AFTER_IMPORT);
+        return null();
+    }
+
+    Node moduleSpec = stringLiteral();
+    if (!moduleSpec)
+        return null();
+
+    if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+        return null();
+
+    ParseNode* node =
+        handler.newImportDeclaration(importSpecSet, moduleSpec, TokenPos(begin, pos().end));
+    if (!node || !pc->sc()->asModuleContext()->builder.processImport(node))
+        return null();
+
+    return node;
+}
+
+template<>
+SyntaxParseHandler::Node
+Parser<SyntaxParseHandler>::importDeclaration()
+{
+    JS_ALWAYS_FALSE(abortIfSyntaxParser());
+    return SyntaxParseHandler::NodeFailure;
+}
+
+template<>
+bool
+Parser<FullParseHandler>::checkExportedName(JSAtom* exportName)
+{
+    if (!pc->sc()->asModuleContext()->builder.hasExportedName(exportName))
+        return true;
+
+    JSAutoByteString str;
+    if (!AtomToPrintableString(context, exportName, &str))
+        return false;
+
+    report(ParseError, false, null(), JSMSG_DUPLICATE_EXPORT_NAME, str.ptr());
+    return false;
+}
+
+template<>
+bool
+Parser<SyntaxParseHandler>::checkExportedName(JSAtom* exportName)
+{
+    MOZ_ALWAYS_FALSE(abortIfSyntaxParser());
+    return false;
+}
+
+template<>
+bool
+Parser<FullParseHandler>::checkExportedNamesForDeclaration(ParseNode* node)
+{
+    MOZ_ASSERT(node->isArity(PN_LIST));
+    for (ParseNode* binding = node->pn_head; binding; binding = binding->pn_next) {
+        if (binding->isKind(PNK_ASSIGN))
+            binding = binding->pn_left;
+        MOZ_ASSERT(binding->isKind(PNK_NAME));
+        if (!checkExportedName(binding->pn_atom))
+            return false;
+    }
+
+    return true;
+}
+
+template<>
+bool
+Parser<SyntaxParseHandler>::checkExportedNamesForDeclaration(Node node)
+{
+    MOZ_ALWAYS_FALSE(abortIfSyntaxParser());
+    return false;
+}
+
+template<>
+ParseNode*
+Parser<FullParseHandler>::exportDeclaration()
+{
+    MOZ_ASSERT(tokenStream.currentToken().type == TOK_EXPORT);
+
+    if (!pc->atModuleLevel()) {
+        report(ParseError, false, null(), JSMSG_EXPORT_DECL_AT_TOP_LEVEL);
+        return null();
+    }
+
+    uint32_t begin = pos().begin;
+
+    Node kid;
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+    switch (tt) {
+      case TOK_LC: {
+        kid = handler.newList(PNK_EXPORT_SPEC_LIST);
+        if (!kid)
+            return null();
+
+        while (true) {
+            // Handle the forms |export {}| and |export { ..., }| (where ...
+            // is non empty), by escaping the loop early if the next token
+            // is }.
+            if (!tokenStream.peekToken(&tt))
+                return null();
+            if (tt == TOK_RC)
+                break;
+
+            MUST_MATCH_TOKEN(TOK_NAME, JSMSG_NO_BINDING_NAME);
+            Node bindingName = newName(tokenStream.currentName());
+            if (!bindingName)
+                return null();
+
+            bool foundAs;
+            if (!tokenStream.matchContextualKeyword(&foundAs, context->names().as))
+                return null();
+            if (foundAs) {
+                if (!tokenStream.getToken(&tt, TokenStream::KeywordIsName))
+                    return null();
+                if (tt != TOK_NAME) {
+                    report(ParseError, false, null(), JSMSG_NO_EXPORT_NAME);
+                    return null();
+                }
+            }
+
+            Node exportName = newName(tokenStream.currentName());
+            if (!exportName)
+                return null();
+
+            if (!checkExportedName(exportName->pn_atom))
+                return null();
+
+            Node exportSpec = handler.newBinary(PNK_EXPORT_SPEC, bindingName, exportName);
+            if (!exportSpec)
+                return null();
+
+            handler.addList(kid, exportSpec);
+
+            bool matched;
+            if (!tokenStream.matchToken(&matched, TOK_COMMA))
+                return null();
+            if (!matched)
+                break;
+        }
+
+        MUST_MATCH_TOKEN(TOK_RC, JSMSG_RC_AFTER_EXPORT_SPEC_LIST);
+
+        // Careful!  If |from| follows, even on a new line, it must start a
+        // FromClause:
+        //
+        //   export { x }
+        //   from "foo"; // a single ExportDeclaration
+        //
+        // But if it doesn't, we might have an ASI opportunity in Operand
+        // context, so simply matching a contextual keyword won't work:
+        //
+        //   export { x }   // ExportDeclaration, terminated by ASI
+        //   fro\u006D      // ExpressionStatement, the name "from"
+        //
+        // In that case let MatchOrInsertSemicolonAfterNonExpression sort out
+        // ASI or any necessary error.
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt, TokenStream::Operand))
+            return null();
+
+        if (tt == TOK_NAME &&
+            tokenStream.currentToken().name() == context->names().from &&
+            !tokenStream.currentToken().nameContainsEscape())
+        {
+            MUST_MATCH_TOKEN(TOK_STRING, JSMSG_MODULE_SPEC_AFTER_FROM);
+
+            Node moduleSpec = stringLiteral();
+            if (!moduleSpec)
+                return null();
+
+            if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+                return null();
+
+            ParseNode* node = handler.newExportFromDeclaration(begin, kid, moduleSpec);
+            if (!node || !pc->sc()->asModuleContext()->builder.processExportFrom(node))
+                return null();
+
+            return node;
+        }
+
+        tokenStream.ungetToken();
+
+        if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+            return null();
+        break;
+      }
+
+      case TOK_MUL: {
+        kid = handler.newList(PNK_EXPORT_SPEC_LIST);
+        if (!kid)
+            return null();
+
+        // Handle the form |export *| by adding a special export batch
+        // specifier to the list.
+        Node exportSpec = handler.newNullary(PNK_EXPORT_BATCH_SPEC, JSOP_NOP, pos());
+        if (!exportSpec)
+            return null();
+
+        handler.addList(kid, exportSpec);
+
+        if (!tokenStream.getToken(&tt))
+            return null();
+        if (tt != TOK_NAME || tokenStream.currentName() != context->names().from) {
+            report(ParseError, false, null(), JSMSG_FROM_AFTER_EXPORT_STAR);
+            return null();
+        }
+
+        if (!checkUnescapedName())
+            return null();
+
+        MUST_MATCH_TOKEN(TOK_STRING, JSMSG_MODULE_SPEC_AFTER_FROM);
+
+        Node moduleSpec = stringLiteral();
+        if (!moduleSpec)
+            return null();
+
+        if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+            return null();
+
+        ParseNode* node = handler.newExportFromDeclaration(begin, kid, moduleSpec);
+        if (!node || !pc->sc()->asModuleContext()->builder.processExportFrom(node))
+            return null();
+
+        return node;
+
+      }
+
+      case TOK_FUNCTION:
+        kid = functionStmt(YieldIsKeyword, NameRequired);
+        if (!kid)
+            return null();
+
+        if (!checkExportedName(kid->pn_funbox->function()->name()))
+            return null();
+        break;
+
+      case TOK_CLASS: {
+        kid = classDefinition(YieldIsKeyword, ClassStatement, NameRequired);
+        if (!kid)
+            return null();
+
+        const ClassNode& cls = kid->as<ClassNode>();
+        MOZ_ASSERT(cls.names());
+        if (!checkExportedName(cls.names()->innerBinding()->pn_atom))
+            return null();
+        break;
+      }
+
+      case TOK_VAR:
+        kid = declarationList(YieldIsName, PNK_VAR);
+        if (!kid)
+            return null();
+        if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+            return null();
+        if (!checkExportedNamesForDeclaration(kid))
+            return null();
+        break;
+
+      case TOK_DEFAULT: {
+        if (!tokenStream.getToken(&tt, TokenStream::Operand))
+            return null();
+
+        if (!checkExportedName(context->names().default_))
+            return null();
+
+        ParseNode* nameNode = nullptr;
+        switch (tt) {
+          case TOK_FUNCTION:
+            kid = functionStmt(YieldIsKeyword, AllowDefaultName);
+            if (!kid)
+                return null();
+            break;
+          case TOK_CLASS:
+            kid = classDefinition(YieldIsKeyword, ClassStatement, AllowDefaultName);
+            if (!kid)
+                return null();
+            break;
+          default: {
+            if (tt == TOK_NAME && tokenStream.currentName() == context->names().async) {
+                TokenKind nextSameLine = TOK_EOF;
+                if (!tokenStream.peekTokenSameLine(&nextSameLine))
+                    return null();
+
+                if (nextSameLine == TOK_FUNCTION) {
+                    tokenStream.consumeKnownToken(nextSameLine);
+                    kid = functionStmt(YieldIsName, AllowDefaultName, AsyncFunction);
+                    if (!kid)
+                        return null();
+                    break;
+                }
+            }
+
+            tokenStream.ungetToken();
+            RootedPropertyName name(context, context->names().starDefaultStar);
+            nameNode = newName(name);
+            if (!nameNode)
+                return null();
+            if (!noteDeclaredName(name, DeclarationKind::Const, pos()))
+                return null();
+            kid = assignExpr(InAllowed, YieldIsKeyword, TripledotProhibited);
+            if (!kid)
+                return null();
+            if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+                return null();
+            break;
+          }
+        }
+
+        ParseNode* node = handler.newExportDefaultDeclaration(kid, nameNode,
+                                                              TokenPos(begin, pos().end));
+        if (!node || !pc->sc()->asModuleContext()->builder.processExport(node))
+            return null();
+
+        return node;
+      }
+
+      case TOK_CONST:
+        kid = lexicalDeclaration(YieldIsName, /* isConst = */ true);
+        if (!kid)
+            return null();
+        if (!checkExportedNamesForDeclaration(kid))
+            return null();
+        break;
+
+      case TOK_NAME:
+        if (tokenStream.currentName() == context->names().let) {
+            if (!checkUnescapedName())
+                return null();
+
+            kid = lexicalDeclaration(YieldIsName, /* isConst = */ false);
+            if (!kid)
+                return null();
+            if (!checkExportedNamesForDeclaration(kid))
+                return null();
+            break;
+        }
+        MOZ_FALLTHROUGH;
+
+      default:
+        report(ParseError, false, null(), JSMSG_DECLARATION_AFTER_EXPORT);
+        return null();
+    }
+
+    ParseNode* node = handler.newExportDeclaration(kid, TokenPos(begin, pos().end));
+    if (!node || !pc->sc()->asModuleContext()->builder.processExport(node))
+        return null();
+
+    return node;
+}
+
+template<>
+SyntaxParseHandler::Node
+Parser<SyntaxParseHandler>::exportDeclaration()
+{
+    JS_ALWAYS_FALSE(abortIfSyntaxParser());
+    return SyntaxParseHandler::NodeFailure;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::expressionStatement(YieldHandling yieldHandling, InvokedPrediction invoked)
+{
+    tokenStream.ungetToken();
+    Node pnexpr = expr(InAllowed, yieldHandling, TripledotProhibited,
+                       /* possibleError = */ nullptr, invoked);
+    if (!pnexpr)
+        return null();
+    if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+        return null();
+    return handler.newExprStatement(pnexpr, pos().end);
+}
+
+template <class ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::consequentOrAlternative(YieldHandling yieldHandling)
+{
+    TokenKind next;
+    if (!tokenStream.peekToken(&next, TokenStream::Operand))
+        return null();
+
+    if (next == TOK_FUNCTION) {
+        // Apply Annex B.3.4 in non-strict code to allow FunctionDeclaration as
+        // the consequent/alternative of an |if| or |else|.  Parser::statement
+        // will report the strict mode error.
+        if (!pc->sc()->strict()) {
+            tokenStream.consumeKnownToken(next, TokenStream::Operand);
+            return functionStmt(yieldHandling, NameRequired);
+        }
+    }
+
+    return statement(yieldHandling);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::ifStatement(YieldHandling yieldHandling)
+{
+    Vector<Node, 4> condList(context), thenList(context);
+    Vector<uint32_t, 4> posList(context);
+    Node elseBranch;
+
+    ParseContext::Statement stmt(pc, StatementKind::If);
+
+    while (true) {
+        uint32_t begin = pos().begin;
+
+        /* An IF node has three kids: condition, then, and optional else. */
+        Node cond = condition(InAllowed, yieldHandling);
+        if (!cond)
+            return null();
+
+        TokenKind tt;
+        if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+            return null();
+        if (tt == TOK_SEMI) {
+            if (!report(ParseExtraWarning, false, null(), JSMSG_EMPTY_CONSEQUENT))
+                return null();
+        }
+
+        Node thenBranch = consequentOrAlternative(yieldHandling);
+        if (!thenBranch)
+            return null();
+
+        if (!condList.append(cond) || !thenList.append(thenBranch) || !posList.append(begin))
+            return null();
+
+        bool matched;
+        if (!tokenStream.matchToken(&matched, TOK_ELSE, TokenStream::Operand))
+            return null();
+        if (matched) {
+            if (!tokenStream.matchToken(&matched, TOK_IF, TokenStream::Operand))
+                return null();
+            if (matched)
+                continue;
+            elseBranch = consequentOrAlternative(yieldHandling);
+            if (!elseBranch)
+                return null();
+        } else {
+            elseBranch = null();
+        }
+        break;
+    }
+
+    for (int i = condList.length() - 1; i >= 0; i--) {
+        elseBranch = handler.newIfStatement(posList[i], condList[i], thenList[i], elseBranch);
+        if (!elseBranch)
+            return null();
+    }
+
+    return elseBranch;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::doWhileStatement(YieldHandling yieldHandling)
+{
+    uint32_t begin = pos().begin;
+    ParseContext::Statement stmt(pc, StatementKind::DoLoop);
+    Node body = statement(yieldHandling);
+    if (!body)
+        return null();
+    MUST_MATCH_TOKEN_MOD(TOK_WHILE, TokenStream::Operand, JSMSG_WHILE_AFTER_DO);
+    Node cond = condition(InAllowed, yieldHandling);
+    if (!cond)
+        return null();
+
+    // The semicolon after do-while is even more optional than most
+    // semicolons in JS.  Web compat required this by 2004:
+    //   http://bugzilla.mozilla.org/show_bug.cgi?id=238945
+    // ES3 and ES5 disagreed, but ES6 conforms to Web reality:
+    //   https://bugs.ecmascript.org/show_bug.cgi?id=157
+    // To parse |do {} while (true) false| correctly, use Operand.
+    bool ignored;
+    if (!tokenStream.matchToken(&ignored, TOK_SEMI, TokenStream::Operand))
+        return null();
+    return handler.newDoWhileStatement(body, cond, TokenPos(begin, pos().end));
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::whileStatement(YieldHandling yieldHandling)
+{
+    uint32_t begin = pos().begin;
+    ParseContext::Statement stmt(pc, StatementKind::WhileLoop);
+    Node cond = condition(InAllowed, yieldHandling);
+    if (!cond)
+        return null();
+    Node body = statement(yieldHandling);
+    if (!body)
+        return null();
+    return handler.newWhileStatement(begin, cond, body);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::matchInOrOf(bool* isForInp, bool* isForOfp)
+{
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return false;
+
+    *isForInp = tt == TOK_IN;
+    *isForOfp = tt == TOK_NAME && tokenStream.currentToken().name() == context->names().of;
+    if (!*isForInp && !*isForOfp) {
+        tokenStream.ungetToken();
+    } else {
+        if (tt == TOK_NAME && !checkUnescapedName())
+            return false;
+    }
+
+    MOZ_ASSERT_IF(*isForInp || *isForOfp, *isForInp != *isForOfp);
+    return true;
+}
+
+template <class ParseHandler>
+bool
+Parser<ParseHandler>::validateForInOrOfLHSExpression(Node target, PossibleError* possibleError)
+{
+    if (handler.isUnparenthesizedDestructuringPattern(target))
+        return checkDestructuringPattern(target, Nothing(), possibleError);
+
+    // All other permitted targets are simple.
+    if (!reportIfNotValidSimpleAssignmentTarget(target, ForInOrOfTarget))
+        return false;
+
+    if (handler.isPropertyAccess(target))
+        return true;
+
+    if (handler.isNameAnyParentheses(target)) {
+        // The arguments/eval identifiers are simple in non-strict mode code,
+        // but warn to discourage use nonetheless.
+        if (!reportIfArgumentsEvalTarget(target))
+            return false;
+
+        handler.adjustGetToSet(target);
+        return true;
+    }
+
+    if (handler.isFunctionCall(target))
+        return checkAssignmentToCall(target, JSMSG_BAD_FOR_LEFTSIDE);
+
+    report(ParseError, false, target, JSMSG_BAD_FOR_LEFTSIDE);
+    return false;
+}
+
+template <class ParseHandler>
+bool
+Parser<ParseHandler>::forHeadStart(YieldHandling yieldHandling,
+                                   ParseNodeKind* forHeadKind,
+                                   Node* forInitialPart,
+                                   Maybe<ParseContext::Scope>& forLoopLexicalScope,
+                                   Node* forInOrOfExpression)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LP));
+
+    TokenKind tt;
+    if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+        return null();
+
+    // Super-duper easy case: |for (;| is a C-style for-loop with no init
+    // component.
+    if (tt == TOK_SEMI) {
+        *forInitialPart = null();
+        *forHeadKind = PNK_FORHEAD;
+        return true;
+    }
+
+    // Parsing after |for (var| is also relatively simple (from this method's
+    // point of view).  No block-related work complicates matters, so delegate
+    // to Parser::declaration.
+    if (tt == TOK_VAR) {
+        tokenStream.consumeKnownToken(tt, TokenStream::Operand);
+
+        // Pass null for block object because |var| declarations don't use one.
+        *forInitialPart = declarationList(yieldHandling, PNK_VAR, forHeadKind,
+                                          forInOrOfExpression);
+        return *forInitialPart != null();
+    }
+
+    // Otherwise we have a lexical declaration or an expression.
+
+    // For-in loop backwards compatibility requires that |let| starting a
+    // for-loop that's not a (new to ES6) for-of loop, in non-strict mode code,
+    // parse as an identifier.  (|let| in for-of is always a declaration.)
+    bool parsingLexicalDeclaration = false;
+    bool letIsIdentifier = false;
+    if (tt == TOK_CONST) {
+        parsingLexicalDeclaration = true;
+        tokenStream.consumeKnownToken(tt, TokenStream::Operand);
+    } else if (tt == TOK_NAME &&
+               tokenStream.nextName() == context->names().let &&
+               !tokenStream.nextNameContainsEscape())
+    {
+        // We could have a {For,Lexical}Declaration, or we could have a
+        // LeftHandSideExpression with lookahead restrictions so it's not
+        // ambiguous with the former.  Check for a continuation of the former
+        // to decide which we have.
+        tokenStream.consumeKnownToken(TOK_NAME, TokenStream::Operand);
+
+        TokenKind next;
+        if (!tokenStream.peekToken(&next))
+            return false;
+
+        parsingLexicalDeclaration = nextTokenContinuesLetDeclaration(next, yieldHandling);
+        if (!parsingLexicalDeclaration) {
+            tokenStream.ungetToken();
+            letIsIdentifier = true;
+        }
+    }
+
+    if (parsingLexicalDeclaration) {
+        forLoopLexicalScope.emplace(this);
+        if (!forLoopLexicalScope->init(pc))
+            return null();
+
+        // Push a temporary ForLoopLexicalHead Statement that allows for
+        // lexical declarations, as they are usually allowed only in braced
+        // statements.
+        ParseContext::Statement forHeadStmt(pc, StatementKind::ForLoopLexicalHead);
+
+        *forInitialPart = declarationList(yieldHandling, tt == TOK_CONST ? PNK_CONST : PNK_LET,
+                                          forHeadKind, forInOrOfExpression);
+        return *forInitialPart != null();
+    }
+
+    // Finally, handle for-loops that start with expressions.  Pass
+    // |InProhibited| so that |in| isn't parsed in a RelationalExpression as a
+    // binary operator.  |in| makes it a for-in loop, *not* an |in| expression.
+    PossibleError possibleError(*this);
+    *forInitialPart = expr(InProhibited, yieldHandling, TripledotProhibited, &possibleError);
+    if (!*forInitialPart)
+        return false;
+
+    bool isForIn, isForOf;
+    if (!matchInOrOf(&isForIn, &isForOf))
+        return false;
+
+    // If we don't encounter 'in'/'of', we have a for(;;) loop.  We've handled
+    // the init expression; the caller handles the rest.  Allow the Operand
+    // modifier when regetting: Operand must be used to examine the ';' in
+    // |for (;|, and our caller handles this case and that.
+    if (!isForIn && !isForOf) {
+        if (!possibleError.checkForExpressionError())
+            return false;
+        *forHeadKind = PNK_FORHEAD;
+        tokenStream.addModifierException(TokenStream::OperandIsNone);
+        return true;
+    }
+
+    MOZ_ASSERT(isForIn != isForOf);
+
+    // In a for-of loop, 'let' that starts the loop head is a |let| keyword,
+    // per the [lookahead ≠ let] restriction on the LeftHandSideExpression
+    // variant of such loops.  Expressions that start with |let| can't be used
+    // here.
+    //
+    //   var let = {};
+    //   for (let.prop of [1]) // BAD
+    //     break;
+    //
+    // See ES6 13.7.
+    if (isForOf && letIsIdentifier) {
+        report(ParseError, false, *forInitialPart, JSMSG_LET_STARTING_FOROF_LHS);
+        return false;
+    }
+
+    *forHeadKind = isForIn ? PNK_FORIN : PNK_FOROF;
+
+    if (!validateForInOrOfLHSExpression(*forInitialPart, &possibleError))
+        return false;
+    if (!possibleError.checkForExpressionError())
+        return false;
+
+    // Finally, parse the iterated expression, making the for-loop's closing
+    // ')' the next token.
+    *forInOrOfExpression = expressionAfterForInOrOf(*forHeadKind, yieldHandling);
+    return *forInOrOfExpression != null();
+}
+
+template <class ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::forStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FOR));
+    uint32_t begin = pos().begin;
+
+    ParseContext::Statement stmt(pc, StatementKind::ForLoop);
+
+    bool isForEach = false;
+    unsigned iflags = 0;
+
+    if (allowsForEachIn()) {
+        bool matched;
+        if (!tokenStream.matchContextualKeyword(&matched, context->names().each))
+            return null();
+        if (matched) {
+            iflags = JSITER_FOREACH;
+            isForEach = true;
+            addTelemetry(JSCompartment::DeprecatedForEach);
+            if (!warnOnceAboutForEach())
+                return null();
+        }
+    }
+
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_AFTER_FOR);
+
+    // PNK_FORHEAD, PNK_FORIN, or PNK_FOROF depending on the loop type.
+    ParseNodeKind headKind;
+
+    // |x| in either |for (x; ...; ...)| or |for (x in/of ...)|.
+    Node startNode;
+
+    // The next two variables are used to implement `for (let/const ...)`.
+    //
+    // We generate an implicit block, wrapping the whole loop, to store loop
+    // variables declared this way. Note that if the loop uses `for (var...)`
+    // instead, those variables go on some existing enclosing scope, so no
+    // implicit block scope is created.
+    //
+    // Both variables remain null/none if the loop is any other form.
+
+    // The static block scope for the implicit block scope.
+    Maybe<ParseContext::Scope> forLoopLexicalScope;
+
+    // The expression being iterated over, for for-in/of loops only.  Unused
+    // for for(;;) loops.
+    Node iteratedExpr;
+
+    // Parse the entirety of the loop-head for a for-in/of loop (so the next
+    // token is the closing ')'):
+    //
+    //   for (... in/of ...) ...
+    //                     ^next token
+    //
+    // ...OR, parse up to the first ';' in a C-style for-loop:
+    //
+    //   for (...; ...; ...) ...
+    //           ^next token
+    //
+    // In either case the subsequent token can be consistently accessed using
+    // TokenStream::None semantics.
+    if (!forHeadStart(yieldHandling, &headKind, &startNode, forLoopLexicalScope,
+                      &iteratedExpr))
+    {
+        return null();
+    }
+
+    MOZ_ASSERT(headKind == PNK_FORIN || headKind == PNK_FOROF || headKind == PNK_FORHEAD);
+
+    Node forHead;
+    if (headKind == PNK_FORHEAD) {
+        Node init = startNode;
+
+        if (isForEach) {
+            reportWithOffset(ParseError, false, begin, JSMSG_BAD_FOR_EACH_LOOP);
+            return null();
+        }
+
+        // Look for an operand: |for (;| means we might have already examined
+        // this semicolon with that modifier.
+        MUST_MATCH_TOKEN_MOD(TOK_SEMI, TokenStream::Operand, JSMSG_SEMI_AFTER_FOR_INIT);
+
+        TokenKind tt;
+        if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+            return null();
+
+        Node test;
+        TokenStream::Modifier mod;
+        if (tt == TOK_SEMI) {
+            test = null();
+            mod = TokenStream::Operand;
+        } else {
+            test = expr(InAllowed, yieldHandling, TripledotProhibited);
+            if (!test)
+                return null();
+            mod = TokenStream::None;
+        }
+
+        MUST_MATCH_TOKEN_MOD(TOK_SEMI, mod, JSMSG_SEMI_AFTER_FOR_COND);
+
+        if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+            return null();
+
+        Node update;
+        if (tt == TOK_RP) {
+            update = null();
+            mod = TokenStream::Operand;
+        } else {
+            update = expr(InAllowed, yieldHandling, TripledotProhibited);
+            if (!update)
+                return null();
+            mod = TokenStream::None;
+        }
+
+        MUST_MATCH_TOKEN_MOD(TOK_RP, mod, JSMSG_PAREN_AFTER_FOR_CTRL);
+
+        TokenPos headPos(begin, pos().end);
+        forHead = handler.newForHead(init, test, update, headPos);
+        if (!forHead)
+            return null();
+    } else {
+        MOZ_ASSERT(headKind == PNK_FORIN || headKind == PNK_FOROF);
+
+        // |target| is the LeftHandSideExpression or declaration to which the
+        // per-iteration value (an arbitrary value exposed by the iteration
+        // protocol, or a string naming a property) is assigned.
+        Node target = startNode;
+
+        // Parse the rest of the for-in/of head.
+        if (headKind == PNK_FORIN) {
+            stmt.refineForKind(StatementKind::ForInLoop);
+            iflags |= JSITER_ENUMERATE;
+        } else {
+            if (isForEach) {
+                report(ParseError, false, startNode, JSMSG_BAD_FOR_EACH_LOOP);
+                return null();
+            }
+
+            stmt.refineForKind(StatementKind::ForOfLoop);
+        }
+
+        if (!handler.isDeclarationList(target)) {
+            MOZ_ASSERT(!forLoopLexicalScope);
+            if (!checkAndMarkAsAssignmentLhs(target, PlainAssignment))
+                return null();
+        }
+
+        // Parser::declaration consumed everything up to the closing ')'.  That
+        // token follows an {Assignment,}Expression, so the next token must be
+        // consumed as if an operator continued the expression, i.e. as None.
+        MUST_MATCH_TOKEN_MOD(TOK_RP, TokenStream::None, JSMSG_PAREN_AFTER_FOR_CTRL);
+
+        TokenPos headPos(begin, pos().end);
+        forHead = handler.newForInOrOfHead(headKind, target, iteratedExpr, headPos);
+        if (!forHead)
+            return null();
+    }
+
+    Node body = statement(yieldHandling);
+    if (!body)
+        return null();
+
+    Node forLoop = handler.newForStatement(begin, forHead, body, iflags);
+    if (!forLoop)
+        return null();
+
+    if (forLoopLexicalScope)
+        return finishLexicalScope(*forLoopLexicalScope, forLoop);
+
+    return forLoop;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::switchStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_SWITCH));
+    uint32_t begin = pos().begin;
+
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_SWITCH);
+
+    Node discriminant = exprInParens(InAllowed, yieldHandling, TripledotProhibited);
+    if (!discriminant)
+        return null();
+
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_SWITCH);
+    MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_SWITCH);
+
+    ParseContext::Statement stmt(pc, StatementKind::Switch);
+    ParseContext::Scope scope(this);
+    if (!scope.init(pc))
+        return null();
+
+    Node caseList = handler.newStatementList(pos());
+    if (!caseList)
+        return null();
+
+    bool seenDefault = false;
+    TokenKind tt;
+    while (true) {
+        if (!tokenStream.getToken(&tt, TokenStream::Operand))
+            return null();
+        if (tt == TOK_RC)
+            break;
+        uint32_t caseBegin = pos().begin;
+
+        Node caseExpr;
+        switch (tt) {
+          case TOK_DEFAULT:
+            if (seenDefault) {
+                report(ParseError, false, null(), JSMSG_TOO_MANY_DEFAULTS);
+                return null();
+            }
+            seenDefault = true;
+            caseExpr = null();  // The default case has pn_left == nullptr.
+            break;
+
+          case TOK_CASE:
+            caseExpr = expr(InAllowed, yieldHandling, TripledotProhibited);
+            if (!caseExpr)
+                return null();
+            break;
+
+          default:
+            report(ParseError, false, null(), JSMSG_BAD_SWITCH);
+            return null();
+        }
+
+        MUST_MATCH_TOKEN(TOK_COLON, JSMSG_COLON_AFTER_CASE);
+
+        Node body = handler.newStatementList(pos());
+        if (!body)
+            return null();
+
+        bool afterReturn = false;
+        bool warnedAboutStatementsAfterReturn = false;
+        uint32_t statementBegin = 0;
+        while (true) {
+            if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+                return null();
+            if (tt == TOK_RC || tt == TOK_CASE || tt == TOK_DEFAULT)
+                break;
+            if (afterReturn) {
+                TokenPos pos(0, 0);
+                if (!tokenStream.peekTokenPos(&pos, TokenStream::Operand))
+                    return null();
+                statementBegin = pos.begin;
+            }
+            Node stmt = statementListItem(yieldHandling);
+            if (!stmt)
+                return null();
+            if (!warnedAboutStatementsAfterReturn) {
+                if (afterReturn) {
+                    if (!handler.isStatementPermittedAfterReturnStatement(stmt)) {
+                        if (!reportWithOffset(ParseWarning, false, statementBegin,
+                                              JSMSG_STMT_AFTER_RETURN))
+                        {
+                            return null();
+                        }
+                        warnedAboutStatementsAfterReturn = true;
+                    }
+                } else if (handler.isReturnStatement(stmt)) {
+                    afterReturn = true;
+                }
+            }
+            handler.addStatementToList(body, stmt);
+        }
+
+        Node casepn = handler.newCaseOrDefault(caseBegin, caseExpr, body);
+        if (!casepn)
+            return null();
+        handler.addCaseStatementToList(caseList, casepn);
+    }
+
+    caseList = finishLexicalScope(scope, caseList);
+    if (!caseList)
+        return null();
+
+    handler.setEndPosition(caseList, pos().end);
+
+    return handler.newSwitchStatement(begin, discriminant, caseList);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::continueStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_CONTINUE));
+    uint32_t begin = pos().begin;
+
+    RootedPropertyName label(context);
+    if (!matchLabel(yieldHandling, &label))
+        return null();
+
+    // Labeled 'continue' statements target the nearest labeled loop
+    // statements with the same label. Unlabeled 'continue' statements target
+    // the innermost loop statement.
+    auto isLoop = [](ParseContext::Statement* stmt) {
+        return StatementKindIsLoop(stmt->kind());
+    };
+
+    if (label) {
+        ParseContext::Statement* stmt = pc->innermostStatement();
+        bool foundLoop = false;
+
+        for (;;) {
+            stmt = ParseContext::Statement::findNearest(stmt, isLoop);
+            if (!stmt) {
+                report(ParseError, false, null(),
+                       foundLoop ? JSMSG_LABEL_NOT_FOUND : JSMSG_BAD_CONTINUE);
+                return null();
+            }
+
+            foundLoop = true;
+
+            // Is it labeled by our label?
+            bool foundTarget = false;
+            stmt = stmt->enclosing();
+            while (stmt && stmt->is<ParseContext::LabelStatement>()) {
+                if (stmt->as<ParseContext::LabelStatement>().label() == label) {
+                    foundTarget = true;
+                    break;
+                }
+                stmt = stmt->enclosing();
+            }
+            if (foundTarget)
+                break;
+        }
+    } else if (!pc->findInnermostStatement(isLoop)) {
+        report(ParseError, false, null(), JSMSG_BAD_CONTINUE);
+        return null();
+    }
+
+    if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+        return null();
+
+    return handler.newContinueStatement(label, TokenPos(begin, pos().end));
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::breakStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_BREAK));
+    uint32_t begin = pos().begin;
+
+    RootedPropertyName label(context);
+    if (!matchLabel(yieldHandling, &label))
+        return null();
+
+    // Labeled 'break' statements target the nearest labeled statements (could
+    // be any kind) with the same label. Unlabeled 'break' statements target
+    // the innermost loop or switch statement.
+    if (label) {
+        auto hasSameLabel = [&label](ParseContext::LabelStatement* stmt) {
+            return stmt->label() == label;
+        };
+
+        if (!pc->findInnermostStatement<ParseContext::LabelStatement>(hasSameLabel)) {
+            report(ParseError, false, null(), JSMSG_LABEL_NOT_FOUND);
+            return null();
+        }
+    } else {
+        auto isBreakTarget = [](ParseContext::Statement* stmt) {
+            return StatementKindIsUnlabeledBreakTarget(stmt->kind());
+        };
+
+        if (!pc->findInnermostStatement(isBreakTarget)) {
+            report(ParseError, false, null(), JSMSG_TOUGH_BREAK);
+            return null();
+        }
+    }
+
+    if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+        return null();
+
+    return handler.newBreakStatement(label, TokenPos(begin, pos().end));
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::returnStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_RETURN));
+    uint32_t begin = pos().begin;
+
+    MOZ_ASSERT(pc->isFunctionBox());
+    pc->functionBox()->usesReturn = true;
+
+    // Parse an optional operand.
+    //
+    // This is ugly, but we don't want to require a semicolon.
+    Node exprNode;
+    TokenKind tt = TOK_EOF;
+    if (!tokenStream.peekTokenSameLine(&tt, TokenStream::Operand))
+        return null();
+    switch (tt) {
+      case TOK_EOL:
+      case TOK_EOF:
+      case TOK_SEMI:
+      case TOK_RC:
+        exprNode = null();
+        pc->funHasReturnVoid = true;
+        break;
+      default: {
+        exprNode = expr(InAllowed, yieldHandling, TripledotProhibited);
+        if (!exprNode)
+            return null();
+        pc->funHasReturnExpr = true;
+      }
+    }
+
+    if (exprNode) {
+        if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+            return null();
+    } else {
+        if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+            return null();
+    }
+
+    Node pn = handler.newReturnStatement(exprNode, TokenPos(begin, pos().end));
+    if (!pn)
+        return null();
+
+    if (pc->isLegacyGenerator() && exprNode) {
+        /* Disallow "return v;" in legacy generators. */
+        reportBadReturn(pn, ParseError, JSMSG_BAD_GENERATOR_RETURN,
+                        JSMSG_BAD_ANON_GENERATOR_RETURN);
+        return null();
+    }
+
+    return pn;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newYieldExpression(uint32_t begin, typename ParseHandler::Node expr,
+                                         bool isYieldStar)
+{
+    Node generator = newDotGeneratorName();
+    if (!generator)
+        return null();
+    if (isYieldStar)
+        return handler.newYieldStarExpression(begin, expr, generator);
+    return handler.newYieldExpression(begin, expr, generator);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newAwaitExpression(uint32_t begin, typename ParseHandler::Node expr)
+{
+    Node generator = newDotGeneratorName();
+    if (!generator)
+        return null();
+    return handler.newAwaitExpression(begin, expr, generator);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::yieldExpression(InHandling inHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_YIELD));
+    uint32_t begin = pos().begin;
+
+    switch (pc->generatorKind()) {
+      case StarGenerator:
+      {
+        MOZ_ASSERT(pc->isFunctionBox());
+
+        pc->lastYieldOffset = begin;
+
+        Node exprNode;
+        ParseNodeKind kind = PNK_YIELD;
+        TokenKind tt = TOK_EOF;
+        if (!tokenStream.peekTokenSameLine(&tt, TokenStream::Operand))
+            return null();
+        switch (tt) {
+          // TOK_EOL is special; it implements the [no LineTerminator here]
+          // quirk in the grammar.
+          case TOK_EOL:
+          // The rest of these make up the complete set of tokens that can
+          // appear after any of the places where AssignmentExpression is used
+          // throughout the grammar.  Conveniently, none of them can also be the
+          // start an expression.
+          case TOK_EOF:
+          case TOK_SEMI:
+          case TOK_RC:
+          case TOK_RB:
+          case TOK_RP:
+          case TOK_COLON:
+          case TOK_COMMA:
+          case TOK_IN:
+            // No value.
+            exprNode = null();
+            tokenStream.addModifierException(TokenStream::NoneIsOperand);
+            break;
+          case TOK_MUL:
+            kind = PNK_YIELD_STAR;
+            tokenStream.consumeKnownToken(TOK_MUL, TokenStream::Operand);
+            MOZ_FALLTHROUGH;
+          default:
+            exprNode = assignExpr(inHandling, YieldIsKeyword, TripledotProhibited);
+            if (!exprNode)
+                return null();
+        }
+        return newYieldExpression(begin, exprNode, kind == PNK_YIELD_STAR);
+      }
+
+      case NotGenerator:
+        // We are in code that has not seen a yield, but we are in JS 1.7 or
+        // later.  Try to transition to being a legacy generator.
+        MOZ_ASSERT(tokenStream.versionNumber() >= JSVERSION_1_7);
+        MOZ_ASSERT(pc->lastYieldOffset == ParseContext::NoYieldOffset);
+
+        if (!abortIfSyntaxParser())
+            return null();
+
+        if (!pc->isFunctionBox()) {
+            report(ParseError, false, null(), JSMSG_BAD_RETURN_OR_YIELD, js_yield_str);
+            return null();
+        }
+
+        if (pc->functionBox()->isArrow()) {
+            reportWithOffset(ParseError, false, begin,
+                             JSMSG_YIELD_IN_ARROW, js_yield_str);
+            return null();
+        }
+
+        if (pc->functionBox()->function()->isMethod() ||
+            pc->functionBox()->function()->isGetter() ||
+            pc->functionBox()->function()->isSetter())
+        {
+            reportWithOffset(ParseError, false, begin,
+                             JSMSG_YIELD_IN_METHOD, js_yield_str);
+            return null();
+        }
+
+        if (pc->funHasReturnExpr
+#if JS_HAS_EXPR_CLOSURES
+            || pc->functionBox()->function()->isExprBody()
+#endif
+            )
+        {
+            /* As in Python (see PEP-255), disallow return v; in generators. */
+            reportBadReturn(null(), ParseError, JSMSG_BAD_GENERATOR_RETURN,
+                            JSMSG_BAD_ANON_GENERATOR_RETURN);
+            return null();
+        }
+
+        pc->functionBox()->setGeneratorKind(LegacyGenerator);
+        addTelemetry(JSCompartment::DeprecatedLegacyGenerator);
+
+        MOZ_FALLTHROUGH;
+
+      case LegacyGenerator:
+      {
+        // We are in a legacy generator: a function that has already seen a
+        // yield.
+        MOZ_ASSERT(pc->isFunctionBox());
+
+        pc->lastYieldOffset = begin;
+
+        // Legacy generators do not require a value.
+        Node exprNode;
+        TokenKind tt = TOK_EOF;
+        if (!tokenStream.peekTokenSameLine(&tt, TokenStream::Operand))
+            return null();
+        switch (tt) {
+          case TOK_EOF:
+          case TOK_EOL:
+          case TOK_SEMI:
+          case TOK_RC:
+          case TOK_RB:
+          case TOK_RP:
+          case TOK_COLON:
+          case TOK_COMMA:
+            // No value.
+            exprNode = null();
+            tokenStream.addModifierException(TokenStream::NoneIsOperand);
+            break;
+          default:
+            exprNode = assignExpr(inHandling, YieldIsKeyword, TripledotProhibited);
+            if (!exprNode)
+                return null();
+        }
+
+        return newYieldExpression(begin, exprNode);
+      }
+    }
+
+    MOZ_CRASH("yieldExpr");
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::withStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_WITH));
+    uint32_t begin = pos().begin;
+
+    // In most cases, we want the constructs forbidden in strict mode code to be
+    // a subset of those that JSOPTION_EXTRA_WARNINGS warns about, and we should
+    // use reportStrictModeError.  However, 'with' is the sole instance of a
+    // construct that is forbidden in strict mode code, but doesn't even merit a
+    // warning under JSOPTION_EXTRA_WARNINGS.  See
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=514576#c1.
+    if (pc->sc()->strict()) {
+        if (!report(ParseStrictError, true, null(), JSMSG_STRICT_CODE_WITH))
+            return null();
+    }
+
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_WITH);
+    Node objectExpr = exprInParens(InAllowed, yieldHandling, TripledotProhibited);
+    if (!objectExpr)
+        return null();
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_WITH);
+
+    Node innerBlock;
+    {
+        ParseContext::Statement stmt(pc, StatementKind::With);
+        innerBlock = statement(yieldHandling);
+        if (!innerBlock)
+            return null();
+    }
+
+    pc->sc()->setBindingsAccessedDynamically();
+
+    return handler.newWithStatement(begin, objectExpr, innerBlock);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::labeledItem(YieldHandling yieldHandling)
+{
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+
+    if (tt == TOK_FUNCTION) {
+        TokenKind next;
+        if (!tokenStream.peekToken(&next))
+            return null();
+
+        // GeneratorDeclaration is only matched by HoistableDeclaration in
+        // StatementListItem, so generators can't be inside labels.
+        if (next == TOK_MUL) {
+            report(ParseError, false, null(), JSMSG_GENERATOR_LABEL);
+            return null();
+        }
+
+        // Per 13.13.1 it's a syntax error if LabelledItem: FunctionDeclaration
+        // is ever matched.  Per Annex B.3.2 that modifies this text, this
+        // applies only to strict mode code.
+        if (pc->sc()->strict()) {
+            report(ParseError, false, null(), JSMSG_FUNCTION_LABEL);
+            return null();
+        }
+
+        return functionStmt(yieldHandling, NameRequired);
+    }
+
+    tokenStream.ungetToken();
+    return statement(yieldHandling);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::labeledStatement(YieldHandling yieldHandling)
+{
+    RootedPropertyName label(context, labelIdentifier(yieldHandling));
+    if (!label)
+        return null();
+
+    auto hasSameLabel = [&label](ParseContext::LabelStatement* stmt) {
+        return stmt->label() == label;
+    };
+
+    if (pc->findInnermostStatement<ParseContext::LabelStatement>(hasSameLabel)) {
+        report(ParseError, false, null(), JSMSG_DUPLICATE_LABEL);
+        return null();
+    }
+
+    uint32_t begin = pos().begin;
+
+    tokenStream.consumeKnownToken(TOK_COLON);
+
+    /* Push a label struct and parse the statement. */
+    ParseContext::LabelStatement stmt(pc, label);
+    Node pn = labeledItem(yieldHandling);
+    if (!pn)
+        return null();
+
+    return handler.newLabeledStatement(label, pn, begin);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::throwStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_THROW));
+    uint32_t begin = pos().begin;
+
+    /* ECMA-262 Edition 3 says 'throw [no LineTerminator here] Expr'. */
+    TokenKind tt = TOK_EOF;
+    if (!tokenStream.peekTokenSameLine(&tt, TokenStream::Operand))
+        return null();
+    if (tt == TOK_EOF || tt == TOK_SEMI || tt == TOK_RC) {
+        report(ParseError, false, null(), JSMSG_MISSING_EXPR_AFTER_THROW);
+        return null();
+    }
+    if (tt == TOK_EOL) {
+        report(ParseError, false, null(), JSMSG_LINE_BREAK_AFTER_THROW);
+        return null();
+    }
+
+    Node throwExpr = expr(InAllowed, yieldHandling, TripledotProhibited);
+    if (!throwExpr)
+        return null();
+
+    if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+        return null();
+
+    return handler.newThrowStatement(throwExpr, TokenPos(begin, pos().end));
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::tryStatement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_TRY));
+    uint32_t begin = pos().begin;
+
+    /*
+     * try nodes are ternary.
+     * kid1 is the try statement
+     * kid2 is the catch node list or null
+     * kid3 is the finally statement
+     *
+     * catch nodes are ternary.
+     * kid1 is the lvalue (TOK_NAME, TOK_LB, or TOK_LC)
+     * kid2 is the catch guard or null if no guard
+     * kid3 is the catch block
+     *
+     * catch lvalue nodes are either:
+     *   TOK_NAME for a single identifier
+     *   TOK_RB or TOK_RC for a destructuring left-hand side
+     *
+     * finally nodes are TOK_LC statement lists.
+     */
+
+    Node innerBlock;
+    {
+        MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_TRY);
+
+        ParseContext::Statement stmt(pc, StatementKind::Try);
+        ParseContext::Scope scope(this);
+        if (!scope.init(pc))
+            return null();
+
+        innerBlock = statementList(yieldHandling);
+        if (!innerBlock)
+            return null();
+
+        innerBlock = finishLexicalScope(scope, innerBlock);
+        if (!innerBlock)
+            return null();
+
+        MUST_MATCH_TOKEN_MOD(TOK_RC, TokenStream::Operand, JSMSG_CURLY_AFTER_TRY);
+    }
+
+    bool hasUnconditionalCatch = false;
+    Node catchList = null();
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+    if (tt == TOK_CATCH) {
+        catchList = handler.newCatchList();
+        if (!catchList)
+            return null();
+
+        do {
+            Node pnblock;
+
+            /* Check for another catch after unconditional catch. */
+            if (hasUnconditionalCatch) {
+                report(ParseError, false, null(), JSMSG_CATCH_AFTER_GENERAL);
+                return null();
+            }
+
+            /*
+             * Create a lexical scope node around the whole catch clause,
+             * including the head.
+             */
+            ParseContext::Statement stmt(pc, StatementKind::Catch);
+            ParseContext::Scope scope(this);
+            if (!scope.init(pc))
+                return null();
+
+            /*
+             * Legal catch forms are:
+             *   catch (lhs)
+             *   catch (lhs if <boolean_expression>)
+             * where lhs is a name or a destructuring left-hand side.
+             * (the latter is legal only #ifdef JS_HAS_CATCH_GUARD)
+             */
+            MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_CATCH);
+
+            if (!tokenStream.getToken(&tt))
+                return null();
+            Node catchName;
+            switch (tt) {
+              case TOK_LB:
+              case TOK_LC:
+                catchName = destructuringDeclaration(DeclarationKind::CatchParameter,
+                                                     yieldHandling, tt);
+                if (!catchName)
+                    return null();
+                break;
+
+              case TOK_NAME:
+              case TOK_YIELD: {
+                RootedPropertyName param(context, bindingIdentifier(yieldHandling));
+                if (!param)
+                    return null();
+                catchName = newName(param);
+                if (!catchName)
+                    return null();
+                if (!noteDeclaredName(param, DeclarationKind::SimpleCatchParameter, pos()))
+                    return null();
+                break;
+              }
+
+              default:
+                report(ParseError, false, null(), JSMSG_CATCH_IDENTIFIER);
+                return null();
+            }
+
+            Node catchGuard = null();
+#if JS_HAS_CATCH_GUARD
+            /*
+             * We use 'catch (x if x === 5)' (not 'catch (x : x === 5)')
+             * to avoid conflicting with the JS2/ECMAv4 type annotation
+             * catchguard syntax.
+             */
+            bool matched;
+            if (!tokenStream.matchToken(&matched, TOK_IF))
+                return null();
+            if (matched) {
+                catchGuard = expr(InAllowed, yieldHandling, TripledotProhibited);
+                if (!catchGuard)
+                    return null();
+            }
+#endif
+            MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_CATCH);
+
+            MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_CATCH);
+
+            Node catchBody = catchBlockStatement(yieldHandling, scope);
+            if (!catchBody)
+                return null();
+
+            if (!catchGuard)
+                hasUnconditionalCatch = true;
+
+            pnblock = finishLexicalScope(scope, catchBody);
+            if (!pnblock)
+                return null();
+
+            if (!handler.addCatchBlock(catchList, pnblock, catchName, catchGuard, catchBody))
+                return null();
+            handler.setEndPosition(catchList, pos().end);
+            handler.setEndPosition(pnblock, pos().end);
+
+            if (!tokenStream.getToken(&tt, TokenStream::Operand))
+                return null();
+        } while (tt == TOK_CATCH);
+    }
+
+    Node finallyBlock = null();
+
+    if (tt == TOK_FINALLY) {
+        MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_FINALLY);
+
+        ParseContext::Statement stmt(pc, StatementKind::Finally);
+        ParseContext::Scope scope(this);
+        if (!scope.init(pc))
+            return null();
+
+        finallyBlock = statementList(yieldHandling);
+        if (!finallyBlock)
+            return null();
+
+        finallyBlock = finishLexicalScope(scope, finallyBlock);
+        if (!finallyBlock)
+            return null();
+
+        MUST_MATCH_TOKEN_MOD(TOK_RC, TokenStream::Operand, JSMSG_CURLY_AFTER_FINALLY);
+    } else {
+        tokenStream.ungetToken();
+    }
+    if (!catchList && !finallyBlock) {
+        report(ParseError, false, null(), JSMSG_CATCH_OR_FINALLY);
+        return null();
+    }
+
+    return handler.newTryStatement(begin, innerBlock, catchList, finallyBlock);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::catchBlockStatement(YieldHandling yieldHandling,
+                                          ParseContext::Scope& catchParamScope)
+{
+    ParseContext::Statement stmt(pc, StatementKind::Block);
+
+    // ES 13.15.7 CatchClauseEvaluation
+    //
+    // Step 8 means that the body of a catch block always has an additional
+    // lexical scope.
+    ParseContext::Scope scope(this);
+    if (!scope.init(pc))
+        return null();
+
+    // The catch parameter names cannot be redeclared inside the catch
+    // block, so declare the name in the inner scope.
+    if (!scope.addCatchParameters(pc, catchParamScope))
+        return null();
+
+    Node list = statementList(yieldHandling);
+    if (!list)
+        return null();
+
+    MUST_MATCH_TOKEN_MOD(TOK_RC, TokenStream::Operand, JSMSG_CURLY_AFTER_CATCH);
+
+    // The catch parameter names are not bound in the body scope, so remove
+    // them before generating bindings.
+    scope.removeCatchParameters(pc, catchParamScope);
+    return finishLexicalScope(scope, list);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::debuggerStatement()
+{
+    TokenPos p;
+    p.begin = pos().begin;
+    if (!MatchOrInsertSemicolonAfterNonExpression(tokenStream))
+        return null();
+    p.end = pos().end;
+
+    pc->sc()->setBindingsAccessedDynamically();
+    pc->sc()->setHasDebuggerStatement();
+
+    return handler.newDebuggerStatement(p);
+}
+
+static JSOp
+JSOpFromPropertyType(PropertyType propType)
+{
+    switch (propType) {
+      case PropertyType::Getter:
+      case PropertyType::GetterNoExpressionClosure:
+        return JSOP_INITPROP_GETTER;
+      case PropertyType::Setter:
+      case PropertyType::SetterNoExpressionClosure:
+        return JSOP_INITPROP_SETTER;
+      case PropertyType::Normal:
+      case PropertyType::Method:
+      case PropertyType::GeneratorMethod:
+      case PropertyType::AsyncMethod:
+      case PropertyType::Constructor:
+      case PropertyType::DerivedConstructor:
+        return JSOP_INITPROP;
+      default:
+        MOZ_CRASH("unexpected property type");
+    }
+}
+
+static FunctionSyntaxKind
+FunctionSyntaxKindFromPropertyType(PropertyType propType)
+{
+    switch (propType) {
+      case PropertyType::Getter:
+        return Getter;
+      case PropertyType::GetterNoExpressionClosure:
+        return GetterNoExpressionClosure;
+      case PropertyType::Setter:
+        return Setter;
+      case PropertyType::SetterNoExpressionClosure:
+        return SetterNoExpressionClosure;
+      case PropertyType::Method:
+      case PropertyType::GeneratorMethod:
+      case PropertyType::AsyncMethod:
+        return Method;
+      case PropertyType::Constructor:
+        return ClassConstructor;
+      case PropertyType::DerivedConstructor:
+        return DerivedClassConstructor;
+      default:
+        MOZ_CRASH("unexpected property type");
+    }
+}
+
+static GeneratorKind
+GeneratorKindFromPropertyType(PropertyType propType)
+{
+    if (propType == PropertyType::GeneratorMethod)
+        return StarGenerator;
+    if (propType == PropertyType::AsyncMethod)
+        return StarGenerator;
+    return NotGenerator;
+}
+
+static FunctionAsyncKind
+AsyncKindFromPropertyType(PropertyType propType)
+{
+    if (propType == PropertyType::AsyncMethod)
+        return AsyncFunction;
+    return SyncFunction;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::classDefinition(YieldHandling yieldHandling,
+                                      ClassContext classContext,
+                                      DefaultHandling defaultHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_CLASS));
+
+    bool savedStrictness = setLocalStrictMode(true);
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+
+    RootedPropertyName name(context);
+    if (tt == TOK_NAME || tt == TOK_YIELD) {
+        name = bindingIdentifier(yieldHandling);
+        if (!name)
+            return null();
+    } else if (classContext == ClassStatement) {
+        if (defaultHandling == AllowDefaultName) {
+            name = context->names().starDefaultStar;
+            tokenStream.ungetToken();
+        } else {
+            // Class statements must have a bound name
+            report(ParseError, false, null(), JSMSG_UNNAMED_CLASS_STMT);
+            return null();
+        }
+    } else {
+        // Make sure to put it back, whatever it was
+        tokenStream.ungetToken();
+    }
+
+    RootedAtom propAtom(context);
+
+    // A named class creates a new lexical scope with a const binding of the
+    // class name.
+    Maybe<ParseContext::Statement> classStmt;
+    Maybe<ParseContext::Scope> classScope;
+    if (name) {
+        classStmt.emplace(pc, StatementKind::Block);
+        classScope.emplace(this);
+        if (!classScope->init(pc))
+            return null();
+    }
+
+    // Because the binding definitions keep track of their blockId, we need to
+    // create at least the inner binding later. Keep track of the name's position
+    // in order to provide it for the nodes created later.
+    TokenPos namePos = pos();
+
+    Node classHeritage = null();
+    bool hasHeritage;
+    if (!tokenStream.matchToken(&hasHeritage, TOK_EXTENDS))
+        return null();
+    if (hasHeritage) {
+        if (!tokenStream.getToken(&tt))
+            return null();
+        classHeritage = memberExpr(yieldHandling, TripledotProhibited, tt);
+        if (!classHeritage)
+            return null();
+    }
+
+    MUST_MATCH_TOKEN(TOK_LC, JSMSG_CURLY_BEFORE_CLASS);
+
+    Node classMethods = handler.newClassMethodList(pos().begin);
+    if (!classMethods)
+        return null();
+
+    bool seenConstructor = false;
+    for (;;) {
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt, TokenStream::KeywordIsName))
+            return null();
+        if (tt == TOK_RC)
+            break;
+
+        if (tt == TOK_SEMI)
+            continue;
+
+        bool isStatic = false;
+        if (tt == TOK_NAME && tokenStream.currentName() == context->names().static_) {
+            if (!tokenStream.peekToken(&tt, TokenStream::KeywordIsName))
+                return null();
+            if (tt == TOK_RC) {
+                tokenStream.consumeKnownToken(tt, TokenStream::KeywordIsName);
+                report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                       "property name", TokenKindToDesc(tt));
+                return null();
+            }
+
+            if (tt != TOK_LP) {
+                if (!checkUnescapedName())
+                    return null();
+
+                isStatic = true;
+            } else {
+                tokenStream.addModifierException(TokenStream::NoneIsKeywordIsName);
+                tokenStream.ungetToken();
+            }
+        } else {
+            tokenStream.ungetToken();
+        }
+
+        PropertyType propType;
+        Node propName = propertyName(yieldHandling, classMethods, &propType, &propAtom);
+        if (!propName)
+            return null();
+
+        if (propType != PropertyType::Getter && propType != PropertyType::Setter &&
+            propType != PropertyType::Method && propType != PropertyType::GeneratorMethod &&
+            propType != PropertyType::AsyncMethod &&
+            propType != PropertyType::Constructor && propType != PropertyType::DerivedConstructor)
+        {
+            report(ParseError, false, null(), JSMSG_BAD_METHOD_DEF);
+            return null();
+        }
+
+        if (propType == PropertyType::Getter)
+            propType = PropertyType::GetterNoExpressionClosure;
+        if (propType == PropertyType::Setter)
+            propType = PropertyType::SetterNoExpressionClosure;
+        if (!isStatic && propAtom == context->names().constructor) {
+            if (propType != PropertyType::Method) {
+                report(ParseError, false, propName, JSMSG_BAD_METHOD_DEF);
+                return null();
+            }
+            if (seenConstructor) {
+                report(ParseError, false, propName, JSMSG_DUPLICATE_PROPERTY, "constructor");
+                return null();
+            }
+            seenConstructor = true;
+            propType = hasHeritage ? PropertyType::DerivedConstructor : PropertyType::Constructor;
+        } else if (isStatic && propAtom == context->names().prototype) {
+            report(ParseError, false, propName, JSMSG_BAD_METHOD_DEF);
+            return null();
+        }
+
+        // FIXME: Implement ES6 function "name" property semantics
+        // (bug 883377).
+        RootedAtom funName(context);
+        switch (propType) {
+          case PropertyType::GetterNoExpressionClosure:
+          case PropertyType::SetterNoExpressionClosure:
+            if (!tokenStream.isCurrentTokenType(TOK_RB)) {
+                funName = prefixAccessorName(propType, propAtom);
+                if (!funName)
+                    return null();
+            }
+            break;
+          case PropertyType::Constructor:
+          case PropertyType::DerivedConstructor:
+            funName = name;
+            break;
+          default:
+            if (!tokenStream.isCurrentTokenType(TOK_RB))
+                funName = propAtom;
+        }
+        Node fn = methodDefinition(propType, funName);
+        if (!fn)
+            return null();
+
+        JSOp op = JSOpFromPropertyType(propType);
+        if (!handler.addClassMethodDefinition(classMethods, propName, fn, op, isStatic))
+            return null();
+    }
+
+    Node nameNode = null();
+    Node methodsOrBlock = classMethods;
+    if (name) {
+        // The inner name is immutable.
+        if (!noteDeclaredName(name, DeclarationKind::Const, namePos))
+            return null();
+
+        Node innerName = newName(name, namePos);
+        if (!innerName)
+            return null();
+
+        Node classBlock = finishLexicalScope(*classScope, classMethods);
+        if (!classBlock)
+            return null();
+
+        methodsOrBlock = classBlock;
+
+        // Pop the inner scope.
+        classScope.reset();
+        classStmt.reset();
+
+        Node outerName = null();
+        if (classContext == ClassStatement) {
+            // The outer name is mutable.
+            if (!noteDeclaredName(name, DeclarationKind::Let, namePos))
+                return null();
+
+            outerName = newName(name, namePos);
+            if (!outerName)
+                return null();
+        }
+
+        nameNode = handler.newClassNames(outerName, innerName, namePos);
+        if (!nameNode)
+            return null();
+    }
+
+    MOZ_ALWAYS_TRUE(setLocalStrictMode(savedStrictness));
+
+    return handler.newClass(nameNode, classHeritage, methodsOrBlock);
+}
+
+template <class ParseHandler>
+bool
+Parser<ParseHandler>::nextTokenContinuesLetDeclaration(TokenKind next, YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_NAME));
+    MOZ_ASSERT(tokenStream.currentName() == context->names().let);
+    MOZ_ASSERT(!tokenStream.currentToken().nameContainsEscape());
+
+#ifdef DEBUG
+    TokenKind verify;
+    MOZ_ALWAYS_TRUE(tokenStream.peekToken(&verify));
+    MOZ_ASSERT(next == verify);
+#endif
+
+    // Destructuring is (for once) the easy case.
+    if (next == TOK_LB || next == TOK_LC)
+        return true;
+
+    // Otherwise a let declaration must have a name.
+    if (next == TOK_NAME) {
+        if (tokenStream.nextName() == context->names().yield) {
+            MOZ_ASSERT(tokenStream.nextNameContainsEscape(),
+                       "token stream should interpret unescaped 'yield' as TOK_YIELD");
+
+            // Same as |next == TOK_YIELD|.
+            return yieldHandling == YieldIsName;
+        }
+
+        // One non-"yield" TOK_NAME edge case deserves special comment.
+        // Consider this:
+        //
+        //   let     // not an ASI opportunity
+        //   let;
+        //
+        // Static semantics in §13.3.1.1 turn a LexicalDeclaration that binds
+        // "let" into an early error.  Does this retroactively permit ASI so
+        // that we should parse this as two ExpressionStatements?   No.  ASI
+        // resolves during parsing.  Static semantics only apply to the full
+        // parse tree with ASI applied.  No backsies!
+        return true;
+    }
+
+    // If we have the name "yield", the grammar parameter exactly states
+    // whether this is okay.  (This wasn't true for SpiderMonkey's ancient
+    // legacy generator syntax, but that's dead now.)  If YieldIsName,
+    // declaration-parsing code will (if necessary) enforce a strict mode
+    // restriction on defining "yield".  If YieldIsKeyword, consider this the
+    // end of the declaration, in case ASI induces a semicolon that makes the
+    // "yield" valid.
+    if (next == TOK_YIELD)
+        return yieldHandling == YieldIsName;
+
+    // Otherwise not a let declaration.
+    return false;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::variableStatement(YieldHandling yieldHandling)
+{
+    Node vars = declarationList(yieldHandling, PNK_VAR);
+    if (!vars)
+        return null();
+    if (!MatchOrInsertSemicolonAfterExpression(tokenStream))
+        return null();
+    return vars;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::statement(YieldHandling yieldHandling)
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    JS_CHECK_RECURSION(context, return null());
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+
+    switch (tt) {
+      // BlockStatement[?Yield, ?Return]
+      case TOK_LC:
+        return blockStatement(yieldHandling);
+
+      // VariableStatement[?Yield]
+      case TOK_VAR:
+        return variableStatement(yieldHandling);
+
+      // EmptyStatement
+      case TOK_SEMI:
+        return handler.newEmptyStatement(pos());
+
+      // ExpressionStatement[?Yield].
+
+      case TOK_YIELD: {
+        // Don't use a ternary operator here due to obscure linker issues
+        // around using static consts in the arms of a ternary.
+        TokenStream::Modifier modifier;
+        if (yieldExpressionsSupported())
+            modifier = TokenStream::Operand;
+        else
+            modifier = TokenStream::None;
+
+        TokenKind next;
+        if (!tokenStream.peekToken(&next, modifier))
+            return null();
+
+        if (next == TOK_COLON)
+            return labeledStatement(yieldHandling);
+
+        return expressionStatement(yieldHandling);
+      }
+
+      case TOK_NAME: {
+        TokenKind next;
+        if (!tokenStream.peekToken(&next))
+            return null();
+
+        // |let| here can only be an Identifier, not a declaration.  Give nicer
+        // errors for declaration-looking typos.
+        if (!tokenStream.currentToken().nameContainsEscape() &&
+            tokenStream.currentName() == context->names().let)
+        {
+            bool forbiddenLetDeclaration = false;
+
+            if (pc->sc()->strict() || versionNumber() >= JSVERSION_1_7) {
+                // |let| can't be an Identifier in strict mode code.  Ditto for
+                // non-standard JavaScript 1.7+.
+                forbiddenLetDeclaration = true;
+            } else if (next == TOK_LB) {
+                // Enforce ExpressionStatement's 'let [' lookahead restriction.
+                forbiddenLetDeclaration = true;
+            } else if (next == TOK_LC || next == TOK_NAME) {
+                // 'let {' and 'let foo' aren't completely forbidden, if ASI
+                // causes 'let' to be the entire Statement.  But if they're
+                // same-line, we can aggressively give a better error message.
+                //
+                // Note that this ignores 'yield' as TOK_YIELD: we'll handle it
+                // correctly but with a worse error message.
+                TokenKind nextSameLine;
+                if (!tokenStream.peekTokenSameLine(&nextSameLine))
+                    return null();
+
+                MOZ_ASSERT(nextSameLine == TOK_NAME ||
+                           nextSameLine == TOK_LC ||
+                           nextSameLine == TOK_EOL);
+
+                forbiddenLetDeclaration = nextSameLine != TOK_EOL;
+            }
+
+            if (forbiddenLetDeclaration) {
+                report(ParseError, false, null(), JSMSG_FORBIDDEN_AS_STATEMENT,
+                       "lexical declarations");
+                return null();
+            }
+        }
+
+        // NOTE: It's unfortunately allowed to have a label named 'let' in
+        //       non-strict code.  💯
+        if (next == TOK_COLON)
+            return labeledStatement(yieldHandling);
+
+        return expressionStatement(yieldHandling);
+      }
+
+      case TOK_NEW:
+        return expressionStatement(yieldHandling, PredictInvoked);
+
+      default:
+        return expressionStatement(yieldHandling);
+
+      // IfStatement[?Yield, ?Return]
+      case TOK_IF:
+        return ifStatement(yieldHandling);
+
+      // BreakableStatement[?Yield, ?Return]
+      //
+      // BreakableStatement[Yield, Return]:
+      //   IterationStatement[?Yield, ?Return]
+      //   SwitchStatement[?Yield, ?Return]
+      case TOK_DO:
+        return doWhileStatement(yieldHandling);
+
+      case TOK_WHILE:
+        return whileStatement(yieldHandling);
+
+      case TOK_FOR:
+        return forStatement(yieldHandling);
+
+      case TOK_SWITCH:
+        return switchStatement(yieldHandling);
+
+      // ContinueStatement[?Yield]
+      case TOK_CONTINUE:
+        return continueStatement(yieldHandling);
+
+      // BreakStatement[?Yield]
+      case TOK_BREAK:
+        return breakStatement(yieldHandling);
+
+      // [+Return] ReturnStatement[?Yield]
+      case TOK_RETURN:
+        // The Return parameter is only used here, and the effect is easily
+        // detected this way, so don't bother passing around an extra parameter
+        // everywhere.
+        if (!pc->isFunctionBox()) {
+            report(ParseError, false, null(), JSMSG_BAD_RETURN_OR_YIELD, js_return_str);
+            return null();
+        }
+        return returnStatement(yieldHandling);
+
+      // WithStatement[?Yield, ?Return]
+      case TOK_WITH:
+        return withStatement(yieldHandling);
+
+      // LabelledStatement[?Yield, ?Return]
+      // This is really handled by TOK_NAME and TOK_YIELD cases above.
+
+      // ThrowStatement[?Yield]
+      case TOK_THROW:
+        return throwStatement(yieldHandling);
+
+      // TryStatement[?Yield, ?Return]
+      case TOK_TRY:
+        return tryStatement(yieldHandling);
+
+      // DebuggerStatement
+      case TOK_DEBUGGER:
+        return debuggerStatement();
+
+      // |function| is forbidden by lookahead restriction (unless as child
+      // statement of |if| or |else|, but Parser::consequentOrAlternative
+      // handles that).
+      case TOK_FUNCTION:
+        report(ParseError, false, null(), JSMSG_FORBIDDEN_AS_STATEMENT, "function declarations");
+        return null();
+
+      // |class| is also forbidden by lookahead restriction.
+      case TOK_CLASS:
+        report(ParseError, false, null(), JSMSG_FORBIDDEN_AS_STATEMENT, "classes");
+        return null();
+
+      // ImportDeclaration (only inside modules)
+      case TOK_IMPORT:
+        return importDeclaration();
+
+      // ExportDeclaration (only inside modules)
+      case TOK_EXPORT:
+        return exportDeclaration();
+
+      // Miscellaneous error cases arguably better caught here than elsewhere.
+
+      case TOK_CATCH:
+        report(ParseError, false, null(), JSMSG_CATCH_WITHOUT_TRY);
+        return null();
+
+      case TOK_FINALLY:
+        report(ParseError, false, null(), JSMSG_FINALLY_WITHOUT_TRY);
+        return null();
+
+      // NOTE: default case handled in the ExpressionStatement section.
+    }
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::statementListItem(YieldHandling yieldHandling,
+                                        bool canHaveDirectives /* = false */)
+{
+    MOZ_ASSERT(checkOptionsCalled);
+
+    JS_CHECK_RECURSION(context, return null());
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+
+    switch (tt) {
+      // BlockStatement[?Yield, ?Return]
+      case TOK_LC:
+        return blockStatement(yieldHandling);
+
+      // VariableStatement[?Yield]
+      case TOK_VAR:
+        return variableStatement(yieldHandling);
+
+      // EmptyStatement
+      case TOK_SEMI:
+        return handler.newEmptyStatement(pos());
+
+      // ExpressionStatement[?Yield].
+      //
+      // These should probably be handled by a single ExpressionStatement
+      // function in a default, not split up this way.
+      case TOK_STRING:
+        if (!canHaveDirectives && tokenStream.currentToken().atom() == context->names().useAsm) {
+            if (!abortIfSyntaxParser())
+                return null();
+            if (!report(ParseWarning, false, null(), JSMSG_USE_ASM_DIRECTIVE_FAIL))
+                return null();
+        }
+        return expressionStatement(yieldHandling);
+
+      case TOK_YIELD: {
+        // Don't use a ternary operator here due to obscure linker issues
+        // around using static consts in the arms of a ternary.
+        TokenStream::Modifier modifier;
+        if (yieldExpressionsSupported())
+            modifier = TokenStream::Operand;
+        else
+            modifier = TokenStream::None;
+
+        TokenKind next;
+        if (!tokenStream.peekToken(&next, modifier))
+            return null();
+
+        if (next == TOK_COLON)
+            return labeledStatement(yieldHandling);
+
+        return expressionStatement(yieldHandling);
+      }
+
+      case TOK_NAME: {
+        TokenKind next;
+        if (!tokenStream.peekToken(&next))
+            return null();
+
+        if (!tokenStream.currentToken().nameContainsEscape() &&
+            tokenStream.currentName() == context->names().let &&
+            nextTokenContinuesLetDeclaration(next, yieldHandling))
+        {
+            return lexicalDeclaration(yieldHandling, /* isConst = */ false);
+        }
+
+        if (tokenStream.currentName() == context->names().async) {
+            TokenKind nextSameLine = TOK_EOF;
+            if (!tokenStream.peekTokenSameLine(&nextSameLine))
+                return null();
+            if (nextSameLine == TOK_FUNCTION) {
+                tokenStream.consumeKnownToken(TOK_FUNCTION);
+                return functionStmt(yieldHandling, NameRequired, AsyncFunction);
+            }
+        }
+
+        if (next == TOK_COLON)
+            return labeledStatement(yieldHandling);
+
+        return expressionStatement(yieldHandling);
+      }
+
+      case TOK_NEW:
+        return expressionStatement(yieldHandling, PredictInvoked);
+
+      default:
+        return expressionStatement(yieldHandling);
+
+      // IfStatement[?Yield, ?Return]
+      case TOK_IF:
+        return ifStatement(yieldHandling);
+
+      // BreakableStatement[?Yield, ?Return]
+      //
+      // BreakableStatement[Yield, Return]:
+      //   IterationStatement[?Yield, ?Return]
+      //   SwitchStatement[?Yield, ?Return]
+      case TOK_DO:
+        return doWhileStatement(yieldHandling);
+
+      case TOK_WHILE:
+        return whileStatement(yieldHandling);
+
+      case TOK_FOR:
+        return forStatement(yieldHandling);
+
+      case TOK_SWITCH:
+        return switchStatement(yieldHandling);
+
+      // ContinueStatement[?Yield]
+      case TOK_CONTINUE:
+        return continueStatement(yieldHandling);
+
+      // BreakStatement[?Yield]
+      case TOK_BREAK:
+        return breakStatement(yieldHandling);
+
+      // [+Return] ReturnStatement[?Yield]
+      case TOK_RETURN:
+        // The Return parameter is only used here, and the effect is easily
+        // detected this way, so don't bother passing around an extra parameter
+        // everywhere.
+        if (!pc->isFunctionBox()) {
+            report(ParseError, false, null(), JSMSG_BAD_RETURN_OR_YIELD, js_return_str);
+            return null();
+        }
+        return returnStatement(yieldHandling);
+
+      // WithStatement[?Yield, ?Return]
+      case TOK_WITH:
+        return withStatement(yieldHandling);
+
+      // LabelledStatement[?Yield, ?Return]
+      // This is really handled by TOK_NAME and TOK_YIELD cases above.
+
+      // ThrowStatement[?Yield]
+      case TOK_THROW:
+        return throwStatement(yieldHandling);
+
+      // TryStatement[?Yield, ?Return]
+      case TOK_TRY:
+        return tryStatement(yieldHandling);
+
+      // DebuggerStatement
+      case TOK_DEBUGGER:
+        return debuggerStatement();
+
+      // Declaration[Yield]:
+
+      //   HoistableDeclaration[?Yield, ~Default]
+      case TOK_FUNCTION:
+        return functionStmt(yieldHandling, NameRequired);
+
+      //   ClassDeclaration[?Yield, ~Default]
+      case TOK_CLASS:
+        return classDefinition(yieldHandling, ClassStatement, NameRequired);
+
+      //   LexicalDeclaration[In, ?Yield]
+      //     LetOrConst BindingList[?In, ?Yield]
+      case TOK_CONST:
+        // [In] is the default behavior, because for-loops specially parse
+        // their heads to handle |in| in this situation.
+        return lexicalDeclaration(yieldHandling, /* isConst = */ true);
+
+      // ImportDeclaration (only inside modules)
+      case TOK_IMPORT:
+        return importDeclaration();
+
+      // ExportDeclaration (only inside modules)
+      case TOK_EXPORT:
+        return exportDeclaration();
+
+      // Miscellaneous error cases arguably better caught here than elsewhere.
+
+      case TOK_CATCH:
+        report(ParseError, false, null(), JSMSG_CATCH_WITHOUT_TRY);
+        return null();
+
+      case TOK_FINALLY:
+        report(ParseError, false, null(), JSMSG_FINALLY_WITHOUT_TRY);
+        return null();
+
+      // NOTE: default case handled in the ExpressionStatement section.
+    }
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::expr(InHandling inHandling, YieldHandling yieldHandling,
+                           TripledotHandling tripledotHandling,
+                           PossibleError* possibleError /* = nullptr */,
+                           InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    Node pn = assignExpr(inHandling, yieldHandling, tripledotHandling,
+                         possibleError, invoked);
+    if (!pn)
+        return null();
+
+    bool matched;
+    if (!tokenStream.matchToken(&matched, TOK_COMMA))
+        return null();
+    if (!matched)
+        return pn;
+
+    Node seq = handler.newCommaExpressionList(pn);
+    if (!seq)
+        return null();
+    while (true) {
+        // Trailing comma before the closing parenthesis is valid in an arrow
+        // function parameters list: `(a, b, ) => body`. Check if we are
+        // directly under CoverParenthesizedExpressionAndArrowParameterList,
+        // and the next two tokens are closing parenthesis and arrow. If all
+        // are present allow the trailing comma.
+        if (tripledotHandling == TripledotAllowed) {
+            TokenKind tt;
+            if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+                return null();
+
+            if (tt == TOK_RP) {
+                tokenStream.consumeKnownToken(TOK_RP, TokenStream::Operand);
+
+                if (!tokenStream.peekToken(&tt))
+                    return null();
+                if (tt != TOK_ARROW) {
+                    report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                        "expression", TokenKindToDesc(TOK_RP));
+                    return null();
+                }
+
+                tokenStream.ungetToken();  // put back right paren
+                tokenStream.addModifierException(TokenStream::NoneIsOperand);
+                break;
+            }
+        }
+
+        // Additional calls to assignExpr should not reuse the possibleError
+        // which had been passed into the function. Otherwise we would lose
+        // information needed to determine whether or not we're dealing with
+        // a non-recoverable situation.
+        PossibleError possibleErrorInner(*this);
+        pn = assignExpr(inHandling, yieldHandling, tripledotHandling,
+                        &possibleErrorInner);
+        if (!pn)
+            return null();
+
+        if (!possibleError) {
+            // Report any pending expression error.
+            if (!possibleErrorInner.checkForExpressionError())
+                return null();
+        } else {
+            possibleErrorInner.transferErrorsTo(possibleError);
+        }
+
+        handler.addList(seq, pn);
+
+        if (!tokenStream.matchToken(&matched, TOK_COMMA))
+            return null();
+        if (!matched)
+            break;
+    }
+    return seq;
+}
+
+static const JSOp ParseNodeKindToJSOp[] = {
+    JSOP_OR,
+    JSOP_AND,
+    JSOP_BITOR,
+    JSOP_BITXOR,
+    JSOP_BITAND,
+    JSOP_STRICTEQ,
+    JSOP_EQ,
+    JSOP_STRICTNE,
+    JSOP_NE,
+    JSOP_LT,
+    JSOP_LE,
+    JSOP_GT,
+    JSOP_GE,
+    JSOP_INSTANCEOF,
+    JSOP_IN,
+    JSOP_LSH,
+    JSOP_RSH,
+    JSOP_URSH,
+    JSOP_ADD,
+    JSOP_SUB,
+    JSOP_MUL,
+    JSOP_DIV,
+    JSOP_MOD,
+    JSOP_POW
+};
+
+static inline JSOp
+BinaryOpParseNodeKindToJSOp(ParseNodeKind pnk)
+{
+    MOZ_ASSERT(pnk >= PNK_BINOP_FIRST);
+    MOZ_ASSERT(pnk <= PNK_BINOP_LAST);
+    return ParseNodeKindToJSOp[pnk - PNK_BINOP_FIRST];
+}
+
+static ParseNodeKind
+BinaryOpTokenKindToParseNodeKind(TokenKind tok)
+{
+    MOZ_ASSERT(TokenKindIsBinaryOp(tok));
+    return ParseNodeKind(PNK_BINOP_FIRST + (tok - TOK_BINOP_FIRST));
+}
+
+static const int PrecedenceTable[] = {
+    1, /* PNK_OR */
+    2, /* PNK_AND */
+    3, /* PNK_BITOR */
+    4, /* PNK_BITXOR */
+    5, /* PNK_BITAND */
+    6, /* PNK_STRICTEQ */
+    6, /* PNK_EQ */
+    6, /* PNK_STRICTNE */
+    6, /* PNK_NE */
+    7, /* PNK_LT */
+    7, /* PNK_LE */
+    7, /* PNK_GT */
+    7, /* PNK_GE */
+    7, /* PNK_INSTANCEOF */
+    7, /* PNK_IN */
+    8, /* PNK_LSH */
+    8, /* PNK_RSH */
+    8, /* PNK_URSH */
+    9, /* PNK_ADD */
+    9, /* PNK_SUB */
+    10, /* PNK_STAR */
+    10, /* PNK_DIV */
+    10, /* PNK_MOD */
+    11  /* PNK_POW */
+};
+
+static const int PRECEDENCE_CLASSES = 11;
+
+static int
+Precedence(ParseNodeKind pnk) {
+    // Everything binds tighter than PNK_LIMIT, because we want to reduce all
+    // nodes to a single node when we reach a token that is not another binary
+    // operator.
+    if (pnk == PNK_LIMIT)
+        return 0;
+
+    MOZ_ASSERT(pnk >= PNK_BINOP_FIRST);
+    MOZ_ASSERT(pnk <= PNK_BINOP_LAST);
+    return PrecedenceTable[pnk - PNK_BINOP_FIRST];
+}
+
+template <typename ParseHandler>
+MOZ_ALWAYS_INLINE typename ParseHandler::Node
+Parser<ParseHandler>::orExpr1(InHandling inHandling, YieldHandling yieldHandling,
+                              TripledotHandling tripledotHandling,
+                              PossibleError* possibleError,
+                              InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    // Shift-reduce parser for the binary operator part of the JS expression
+    // syntax.
+
+    // Conceptually there's just one stack, a stack of pairs (lhs, op).
+    // It's implemented using two separate arrays, though.
+    Node nodeStack[PRECEDENCE_CLASSES];
+    ParseNodeKind kindStack[PRECEDENCE_CLASSES];
+    int depth = 0;
+    Node pn;
+    for (;;) {
+        pn = unaryExpr(yieldHandling, tripledotHandling, possibleError, invoked);
+        if (!pn)
+            return pn;
+
+        // If a binary operator follows, consume it and compute the
+        // corresponding operator.
+        TokenKind tok;
+        if (!tokenStream.getToken(&tok))
+            return null();
+
+        ParseNodeKind pnk;
+        if (tok == TOK_IN ? inHandling == InAllowed : TokenKindIsBinaryOp(tok)) {
+            // We're definitely not in a destructuring context, so report any
+            // pending expression error now.
+            if (possibleError && !possibleError->checkForExpressionError())
+                return null();
+            // Report an error for unary expressions on the LHS of **.
+            if (tok == TOK_POW && handler.isUnparenthesizedUnaryExpression(pn)) {
+                report(ParseError, false, null(), JSMSG_BAD_POW_LEFTSIDE);
+                return null();
+            }
+            pnk = BinaryOpTokenKindToParseNodeKind(tok);
+        } else {
+            tok = TOK_EOF;
+            pnk = PNK_LIMIT;
+        }
+
+        // From this point on, destructuring defaults are definitely an error.
+        possibleError = nullptr;
+
+        // If pnk has precedence less than or equal to another operator on the
+        // stack, reduce. This combines nodes on the stack until we form the
+        // actual lhs of pnk.
+        //
+        // The >= in this condition works because it is appendOrCreateList's
+        // job to decide if the operator in question is left- or
+        // right-associative, and build the corresponding tree.
+        while (depth > 0 && Precedence(kindStack[depth - 1]) >= Precedence(pnk)) {
+            depth--;
+            ParseNodeKind combiningPnk = kindStack[depth];
+            JSOp combiningOp = BinaryOpParseNodeKindToJSOp(combiningPnk);
+            pn = handler.appendOrCreateList(combiningPnk, nodeStack[depth], pn, pc, combiningOp);
+            if (!pn)
+                return pn;
+        }
+
+        if (pnk == PNK_LIMIT)
+            break;
+
+        nodeStack[depth] = pn;
+        kindStack[depth] = pnk;
+        depth++;
+        MOZ_ASSERT(depth <= PRECEDENCE_CLASSES);
+    }
+
+    MOZ_ASSERT(depth == 0);
+    return pn;
+}
+
+template <typename ParseHandler>
+MOZ_ALWAYS_INLINE typename ParseHandler::Node
+Parser<ParseHandler>::condExpr1(InHandling inHandling, YieldHandling yieldHandling,
+                                TripledotHandling tripledotHandling,
+                                PossibleError* possibleError,
+                                InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    Node condition = orExpr1(inHandling, yieldHandling, tripledotHandling, possibleError, invoked);
+
+    if (!condition || !tokenStream.isCurrentTokenType(TOK_HOOK))
+        return condition;
+
+    Node thenExpr = assignExpr(InAllowed, yieldHandling, TripledotProhibited);
+    if (!thenExpr)
+        return null();
+
+    MUST_MATCH_TOKEN(TOK_COLON, JSMSG_COLON_IN_COND);
+
+    Node elseExpr = assignExpr(inHandling, yieldHandling, TripledotProhibited);
+    if (!elseExpr)
+        return null();
+
+    // Advance to the next token; the caller is responsible for interpreting it.
+    TokenKind ignored;
+    if (!tokenStream.getToken(&ignored))
+        return null();
+    return handler.newConditional(condition, thenExpr, elseExpr);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkAndMarkAsAssignmentLhs(Node target, AssignmentFlavor flavor,
+                                                  PossibleError* possibleError)
+{
+    MOZ_ASSERT(flavor != KeyedDestructuringAssignment,
+               "destructuring must use special checking/marking code, not "
+               "this method");
+
+    if (handler.isUnparenthesizedDestructuringPattern(target)) {
+        if (flavor == CompoundAssignment) {
+            report(ParseError, false, null(), JSMSG_BAD_DESTRUCT_ASS);
+            return false;
+        }
+
+        return checkDestructuringPattern(target, Nothing(), possibleError);
+    }
+
+    // All other permitted targets are simple.
+    if (!reportIfNotValidSimpleAssignmentTarget(target, flavor))
+        return false;
+
+    if (handler.isPropertyAccess(target))
+        return true;
+
+    if (handler.isNameAnyParentheses(target)) {
+        // The arguments/eval identifiers are simple in non-strict mode code,
+        // but warn to discourage use nonetheless.
+        if (!reportIfArgumentsEvalTarget(target))
+            return false;
+
+        handler.adjustGetToSet(target);
+        return true;
+    }
+
+    MOZ_ASSERT(handler.isFunctionCall(target));
+    return checkAssignmentToCall(target, JSMSG_BAD_LEFTSIDE_OF_ASS);
+}
+
+class AutoClearInDestructuringDecl
+{
+    ParseContext* pc_;
+    Maybe<DeclarationKind> saved_;
+
+  public:
+    explicit AutoClearInDestructuringDecl(ParseContext* pc)
+      : pc_(pc),
+        saved_(pc->inDestructuringDecl)
+    {
+        pc->inDestructuringDecl = Nothing();
+        if (saved_ && *saved_ == DeclarationKind::FormalParameter)
+            pc->functionBox()->hasParameterExprs = true;
+    }
+
+    ~AutoClearInDestructuringDecl() {
+        pc_->inDestructuringDecl = saved_;
+    }
+};
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::assignExpr(InHandling inHandling, YieldHandling yieldHandling,
+                                 TripledotHandling tripledotHandling,
+                                 PossibleError* possibleError /* = nullptr */,
+                                 InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    JS_CHECK_RECURSION(context, return null());
+
+    // It's very common at this point to have a "detectably simple" expression,
+    // i.e. a name/number/string token followed by one of the following tokens
+    // that obviously isn't part of an expression: , ; : ) ] }
+    //
+    // (In Parsemark this happens 81.4% of the time;  in code with large
+    // numeric arrays, such as some Kraken benchmarks, it happens more often.)
+    //
+    // In such cases, we can avoid the full expression parsing route through
+    // assignExpr(), condExpr1(), orExpr1(), unaryExpr(), memberExpr(), and
+    // primaryExpr().
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+
+    bool endsExpr;
+
+    if (tt == TOK_NAME) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr) {
+            Rooted<PropertyName*> name(context, identifierReference(yieldHandling));
+            if (!name)
+                return null();
+
+            return identifierReference(name);
+        }
+    }
+
+    if (tt == TOK_NUMBER) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr)
+            return newNumber(tokenStream.currentToken());
+    }
+
+    if (tt == TOK_STRING) {
+        if (!tokenStream.nextTokenEndsExpr(&endsExpr))
+            return null();
+        if (endsExpr)
+            return stringLiteral();
+    }
+
+    if (tt == TOK_YIELD && yieldExpressionsSupported())
+        return yieldExpression(inHandling);
+
+    bool maybeAsyncArrow = false;
+    if (tt == TOK_NAME && tokenStream.currentName() == context->names().async) {
+        TokenKind nextSameLine = TOK_EOF;
+        if (!tokenStream.peekTokenSameLine(&nextSameLine))
+            return null();
+
+        if (nextSameLine == TOK_NAME || nextSameLine == TOK_YIELD)
+            maybeAsyncArrow = true;
+    }
+
+    tokenStream.ungetToken();
+
+    // Save the tokenizer state in case we find an arrow function and have to
+    // rewind.
+    TokenStream::Position start(keepAtoms);
+    tokenStream.tell(&start);
+
+    PossibleError possibleErrorInner(*this);
+    Node lhs;
+    if (maybeAsyncArrow) {
+        tokenStream.consumeKnownToken(TOK_NAME, TokenStream::Operand);
+        MOZ_ASSERT(tokenStream.currentName() == context->names().async);
+
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt))
+            return null();
+        MOZ_ASSERT(tt == TOK_NAME || tt == TOK_YIELD);
+
+        // Check yield validity here.
+        RootedPropertyName name(context, bindingIdentifier(yieldHandling));
+        if (!name)
+            return null();
+
+        if (!tokenStream.getToken(&tt))
+            return null();
+        if (tt != TOK_ARROW) {
+            report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                   "'=>' after argument list", TokenKindToDesc(tt));
+
+            return null();
+        }
+    } else {
+        lhs = condExpr1(inHandling, yieldHandling, tripledotHandling, &possibleErrorInner, invoked);
+        if (!lhs) {
+            return null();
+        }
+    }
+
+    ParseNodeKind kind;
+    JSOp op;
+    switch (tokenStream.currentToken().type) {
+      case TOK_ASSIGN:       kind = PNK_ASSIGN;       op = JSOP_NOP;    break;
+      case TOK_ADDASSIGN:    kind = PNK_ADDASSIGN;    op = JSOP_ADD;    break;
+      case TOK_SUBASSIGN:    kind = PNK_SUBASSIGN;    op = JSOP_SUB;    break;
+      case TOK_BITORASSIGN:  kind = PNK_BITORASSIGN;  op = JSOP_BITOR;  break;
+      case TOK_BITXORASSIGN: kind = PNK_BITXORASSIGN; op = JSOP_BITXOR; break;
+      case TOK_BITANDASSIGN: kind = PNK_BITANDASSIGN; op = JSOP_BITAND; break;
+      case TOK_LSHASSIGN:    kind = PNK_LSHASSIGN;    op = JSOP_LSH;    break;
+      case TOK_RSHASSIGN:    kind = PNK_RSHASSIGN;    op = JSOP_RSH;    break;
+      case TOK_URSHASSIGN:   kind = PNK_URSHASSIGN;   op = JSOP_URSH;   break;
+      case TOK_MULASSIGN:    kind = PNK_MULASSIGN;    op = JSOP_MUL;    break;
+      case TOK_DIVASSIGN:    kind = PNK_DIVASSIGN;    op = JSOP_DIV;    break;
+      case TOK_MODASSIGN:    kind = PNK_MODASSIGN;    op = JSOP_MOD;    break;
+      case TOK_POWASSIGN:    kind = PNK_POWASSIGN;    op = JSOP_POW;    break;
+
+      case TOK_ARROW: {
+
+        // A line terminator between ArrowParameters and the => should trigger a SyntaxError.
+        tokenStream.ungetToken();
+        TokenKind next;
+        if (!tokenStream.peekTokenSameLine(&next))
+            return null();
+        MOZ_ASSERT(next == TOK_ARROW || next == TOK_EOL);
+
+        if (next != TOK_ARROW) {
+            report(ParseError, false, null(), JSMSG_LINE_BREAK_BEFORE_ARROW);
+            return null();
+        }
+        tokenStream.consumeKnownToken(TOK_ARROW);
+
+        bool isBlock = false;
+        if (!tokenStream.peekToken(&next, TokenStream::Operand))
+            return null();
+        if (next == TOK_LC)
+            isBlock = true;
+
+        tokenStream.seek(start);
+
+        if (!tokenStream.peekToken(&next, TokenStream::Operand))
+            return null();
+
+        GeneratorKind generatorKind = NotGenerator;
+        FunctionAsyncKind asyncKind = SyncFunction;
+
+        if (next == TOK_NAME) {
+            tokenStream.consumeKnownToken(next, TokenStream::Operand);
+
+            if (tokenStream.currentName() == context->names().async) {
+                TokenKind nextSameLine = TOK_EOF;
+                if (!tokenStream.peekTokenSameLine(&nextSameLine))
+                    return null();
+
+                if (nextSameLine == TOK_ARROW) {
+                    tokenStream.ungetToken();
+                } else {
+                    generatorKind = StarGenerator;
+                    asyncKind = AsyncFunction;
+                }
+            } else {
+                tokenStream.ungetToken();
+            }
+        }
+
+        Node arrowFunc = functionDefinition(inHandling, yieldHandling, nullptr,
+                                            Arrow, generatorKind, asyncKind);
+        if (!arrowFunc)
+            return null();
+
+        if (isBlock) {
+            // This arrow function could be a non-trailing member of a comma
+            // expression or a semicolon terminating a full expression.  If so,
+            // the next token is that comma/semicolon, gotten with None:
+            //
+            //   a => {}, b; // as if (a => {}), b;
+            //   a => {};
+            //
+            // But if this arrow function ends a statement, ASI permits the
+            // next token to start an expression statement.  In that case the
+            // next token must be gotten as Operand:
+            //
+            //   a => {} // complete expression statement
+            //   /x/g;   // regular expression as a statement, *not* division
+            //
+            // Getting the second case right requires the first token-peek
+            // after the arrow function use Operand, and that peek must occur
+            // before Parser::expr() looks for a comma.  Do so here, then
+            // immediately add the modifier exception needed for the first
+            // case.
+            //
+            // Note that the second case occurs *only* if the arrow function
+            // has block body.  An arrow function not ending in such, ends in
+            // another AssignmentExpression that we can inductively assume was
+            // peeked consistently.
+            TokenKind ignored;
+            if (!tokenStream.peekToken(&ignored, TokenStream::Operand))
+                return null();
+            tokenStream.addModifierException(TokenStream::NoneIsOperand);
+        }
+        return arrowFunc;
+      }
+
+      default:
+        MOZ_ASSERT(!tokenStream.isCurrentTokenAssignment());
+        if (!possibleError) {
+            if (!possibleErrorInner.checkForExpressionError())
+                return null();
+        } else {
+            possibleErrorInner.transferErrorsTo(possibleError);
+        }
+        tokenStream.ungetToken();
+        return lhs;
+    }
+
+    AssignmentFlavor flavor = kind == PNK_ASSIGN ? PlainAssignment : CompoundAssignment;
+    if (!checkAndMarkAsAssignmentLhs(lhs, flavor, &possibleErrorInner))
+        return null();
+    if (!possibleErrorInner.checkForExpressionError())
+        return null();
+
+    Node rhs;
+    {
+        AutoClearInDestructuringDecl autoClear(pc);
+        rhs = assignExpr(inHandling, yieldHandling, TripledotProhibited);
+        if (!rhs)
+            return null();
+    }
+
+    return handler.newAssignment(kind, lhs, rhs, op);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::isValidSimpleAssignmentTarget(Node node,
+                                                    FunctionCallBehavior behavior /* = ForbidAssignmentToFunctionCalls */)
+{
+    // Note that this method implements *only* a boolean test.  Reporting an
+    // error for the various syntaxes that fail this, and warning for the
+    // various syntaxes that "pass" this but should not, occurs elsewhere.
+
+    if (handler.isNameAnyParentheses(node)) {
+        if (!pc->sc()->strict())
+            return true;
+
+        return !handler.nameIsArgumentsEvalAnyParentheses(node, context);
+    }
+
+    if (handler.isPropertyAccess(node))
+        return true;
+
+    if (behavior == PermitAssignmentToFunctionCalls) {
+        if (handler.isFunctionCall(node))
+            return true;
+    }
+
+    return false;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportIfArgumentsEvalTarget(Node nameNode)
+{
+    const char* chars = handler.nameIsArgumentsEvalAnyParentheses(nameNode, context);
+    if (!chars)
+        return true;
+
+    if (!report(ParseStrictError, pc->sc()->strict(), nameNode, JSMSG_BAD_STRICT_ASSIGN, chars))
+        return false;
+
+    MOZ_ASSERT(!pc->sc()->strict(),
+               "an error should have been reported if this was strict mode "
+               "code");
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::reportIfNotValidSimpleAssignmentTarget(Node target, AssignmentFlavor flavor)
+{
+    FunctionCallBehavior behavior = flavor == KeyedDestructuringAssignment
+                                    ? ForbidAssignmentToFunctionCalls
+                                    : PermitAssignmentToFunctionCalls;
+    if (isValidSimpleAssignmentTarget(target, behavior))
+        return true;
+
+    if (handler.isNameAnyParentheses(target)) {
+        // Use a special error if the target is arguments/eval.  This ensures
+        // targeting these names is consistently a SyntaxError (which error numbers
+        // below don't guarantee) while giving us a nicer error message.
+        if (!reportIfArgumentsEvalTarget(target))
+            return false;
+    }
+
+    unsigned errnum = 0;
+    const char* extra = nullptr;
+
+    switch (flavor) {
+      case IncrementAssignment:
+        errnum = JSMSG_BAD_OPERAND;
+        extra = "increment";
+        break;
+
+      case DecrementAssignment:
+        errnum = JSMSG_BAD_OPERAND;
+        extra = "decrement";
+        break;
+
+      case KeyedDestructuringAssignment:
+        errnum = JSMSG_BAD_DESTRUCT_TARGET;
+        break;
+
+      case PlainAssignment:
+      case CompoundAssignment:
+        errnum = JSMSG_BAD_LEFTSIDE_OF_ASS;
+        break;
+
+      case ForInOrOfTarget:
+        errnum = JSMSG_BAD_FOR_LEFTSIDE;
+        break;
+    }
+
+    report(ParseError, pc->sc()->strict(), target, errnum, extra);
+    return false;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkAndMarkAsIncOperand(Node target, AssignmentFlavor flavor)
+{
+    MOZ_ASSERT(flavor == IncrementAssignment || flavor == DecrementAssignment);
+
+    // Check.
+    if (!reportIfNotValidSimpleAssignmentTarget(target, flavor))
+        return false;
+
+    // Mark.
+    if (handler.isNameAnyParentheses(target)) {
+        // Assignment to arguments/eval is allowed outside strict mode code,
+        // but it's dodgy.  Report a strict warning (error, if werror was set).
+        if (!reportIfArgumentsEvalTarget(target))
+            return false;
+    } else if (handler.isFunctionCall(target)) {
+        if (!checkAssignmentToCall(target, JSMSG_BAD_INCOP_OPERAND))
+            return false;
+    }
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::unaryOpExpr(YieldHandling yieldHandling, ParseNodeKind kind, JSOp op,
+                                  uint32_t begin)
+{
+    Node kid = unaryExpr(yieldHandling, TripledotProhibited);
+    if (!kid)
+        return null();
+    return handler.newUnary(kind, op, begin, kid);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::unaryExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                                PossibleError* possibleError /* = nullptr */,
+                                InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    JS_CHECK_RECURSION(context, return null());
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+    uint32_t begin = pos().begin;
+    switch (tt) {
+      case TOK_VOID:
+        return unaryOpExpr(yieldHandling, PNK_VOID, JSOP_VOID, begin);
+      case TOK_NOT:
+        return unaryOpExpr(yieldHandling, PNK_NOT, JSOP_NOT, begin);
+      case TOK_BITNOT:
+        return unaryOpExpr(yieldHandling, PNK_BITNOT, JSOP_BITNOT, begin);
+      case TOK_ADD:
+        return unaryOpExpr(yieldHandling, PNK_POS, JSOP_POS, begin);
+      case TOK_SUB:
+        return unaryOpExpr(yieldHandling, PNK_NEG, JSOP_NEG, begin);
+
+      case TOK_TYPEOF: {
+        // The |typeof| operator is specially parsed to distinguish its
+        // application to a name, from its application to a non-name
+        // expression:
+        //
+        //   // Looks up the name, doesn't find it and so evaluates to
+        //   // "undefined".
+        //   assertEq(typeof nonExistentName, "undefined");
+        //
+        //   // Evaluates expression, triggering a runtime ReferenceError for
+        //   // the undefined name.
+        //   typeof (1, nonExistentName);
+        Node kid = unaryExpr(yieldHandling, TripledotProhibited);
+        if (!kid)
+            return null();
+
+        return handler.newTypeof(begin, kid);
+      }
+
+      case TOK_INC:
+      case TOK_DEC:
+      {
+        TokenKind tt2;
+        if (!tokenStream.getToken(&tt2, TokenStream::Operand))
+            return null();
+        Node pn2 = memberExpr(yieldHandling, TripledotProhibited, tt2);
+        if (!pn2)
+            return null();
+        AssignmentFlavor flavor = (tt == TOK_INC) ? IncrementAssignment : DecrementAssignment;
+        if (!checkAndMarkAsIncOperand(pn2, flavor))
+            return null();
+        return handler.newUpdate((tt == TOK_INC) ? PNK_PREINCREMENT : PNK_PREDECREMENT,
+                                 begin,
+                                 pn2);
+      }
+
+      case TOK_DELETE: {
+        Node expr = unaryExpr(yieldHandling, TripledotProhibited);
+        if (!expr)
+            return null();
+
+        // Per spec, deleting any unary expression is valid -- it simply
+        // returns true -- except for one case that is illegal in strict mode.
+        if (handler.isNameAnyParentheses(expr)) {
+            if (!report(ParseStrictError, pc->sc()->strict(), expr, JSMSG_DEPRECATED_DELETE_OPERAND))
+                return null();
+            pc->sc()->setBindingsAccessedDynamically();
+        }
+
+        return handler.newDelete(begin, expr);
+      }
+
+      case TOK_AWAIT: {
+        if (!pc->isAsync()) {
+            // TOK_AWAIT can be returned in module, even if it's not inside
+            // async function.
+            report(ParseError, false, null(), JSMSG_RESERVED_ID, "await");
+            return null();
+        }
+
+        Node kid = unaryExpr(yieldHandling, tripledotHandling, possibleError, invoked);
+        if (!kid)
+            return null();
+        pc->lastAwaitOffset = begin;
+        return newAwaitExpression(begin, kid);
+      }
+
+      default: {
+        Node pn = memberExpr(yieldHandling, tripledotHandling, tt, /* allowCallSyntax = */ true,
+                             possibleError, invoked);
+        if (!pn)
+            return null();
+
+        /* Don't look across a newline boundary for a postfix incop. */
+        if (!tokenStream.peekTokenSameLine(&tt))
+            return null();
+        if (tt == TOK_INC || tt == TOK_DEC) {
+            tokenStream.consumeKnownToken(tt);
+            AssignmentFlavor flavor = (tt == TOK_INC) ? IncrementAssignment : DecrementAssignment;
+            if (!checkAndMarkAsIncOperand(pn, flavor))
+                return null();
+            return handler.newUpdate((tt == TOK_INC) ? PNK_POSTINCREMENT : PNK_POSTDECREMENT,
+                                     begin,
+                                     pn);
+        }
+        return pn;
+      }
+    }
+}
+
+
+/*** Comprehensions *******************************************************************************
+ *
+ * We currently support two flavors of comprehensions, all deprecated:
+ *
+ *     [for (V of OBJ) if (COND) EXPR]  // ES6-era array comprehension
+ *     (for (V of OBJ) if (COND) EXPR)  // ES6-era generator expression
+ *
+ * (These flavors are called "ES6-era" because they were in ES6 draft
+ * specifications for a while. Shortly after this syntax was implemented in SM,
+ * TC39 decided to drop it.)
+ */
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::generatorComprehensionLambda(unsigned begin)
+{
+    Node genfn = handler.newFunctionDefinition();
+    if (!genfn)
+        return null();
+    handler.setOp(genfn, JSOP_LAMBDA);
+
+    ParseContext* outerpc = pc;
+
+    // If we are off the main thread, the generator meta-objects have
+    // already been created by js::StartOffThreadParseScript, so cx will not
+    // be necessary.
+    RootedObject proto(context);
+    JSContext* cx = context->maybeJSContext();
+    proto = GlobalObject::getOrCreateStarGeneratorFunctionPrototype(cx, context->global());
+    if (!proto)
+        return null();
+
+    RootedFunction fun(context, newFunction(/* atom = */ nullptr, Expression,
+                                            StarGenerator, SyncFunction, proto));
+    if (!fun)
+        return null();
+
+    // Create box for fun->object early to root it.
+    Directives directives(/* strict = */ outerpc->sc()->strict());
+    FunctionBox* genFunbox = newFunctionBox(genfn, fun, directives, StarGenerator, SyncFunction,
+                                            /* tryAnnexB = */ false);
+    if (!genFunbox)
+        return null();
+    genFunbox->isGenexpLambda = true;
+    genFunbox->initWithEnclosingParseContext(outerpc, Expression);
+
+    ParseContext genpc(this, genFunbox, /* newDirectives = */ nullptr);
+    if (!genpc.init())
+        return null();
+    genpc.functionScope().useAsVarScope(&genpc);
+
+    /*
+     * We assume conservatively that any deoptimization flags in pc->sc()
+     * come from the kid. So we propagate these flags into genfn. For code
+     * simplicity we also do not detect if the flags were only set in the
+     * kid and could be removed from pc->sc().
+     */
+    genFunbox->anyCxFlags = outerpc->sc()->anyCxFlags;
+
+    if (!declareDotGeneratorName())
+        return null();
+
+    Node body = handler.newStatementList(TokenPos(begin, pos().end));
+    if (!body)
+        return null();
+
+    Node comp = comprehension(StarGenerator);
+    if (!comp)
+        return null();
+
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_IN_PAREN);
+
+    handler.setBeginPosition(comp, begin);
+    handler.setEndPosition(comp, pos().end);
+    handler.addStatementToList(body, comp);
+    handler.setEndPosition(body, pos().end);
+    handler.setBeginPosition(genfn, begin);
+    handler.setEndPosition(genfn, pos().end);
+
+    Node generator = newDotGeneratorName();
+    if (!generator)
+        return null();
+    if (!handler.prependInitialYield(body, generator))
+        return null();
+
+    if (!propagateFreeNamesAndMarkClosedOverBindings(pc->varScope()))
+        return null();
+    if (!finishFunction())
+        return null();
+    if (!leaveInnerFunction(outerpc))
+        return null();
+
+    // Note that if we ever start syntax-parsing generators, we will also
+    // need to propagate the closed-over variable set to the inner
+    // lazyscript.
+    if (!handler.setComprehensionLambdaBody(genfn, body))
+        return null();
+
+    return genfn;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::comprehensionFor(GeneratorKind comprehensionKind)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FOR));
+
+    uint32_t begin = pos().begin;
+
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_AFTER_FOR);
+
+    // FIXME: Destructuring binding (bug 980828).
+
+    MUST_MATCH_TOKEN(TOK_NAME, JSMSG_NO_VARIABLE_NAME);
+    RootedPropertyName name(context, tokenStream.currentName());
+    if (name == context->names().let) {
+        report(ParseError, false, null(), JSMSG_LET_COMP_BINDING);
+        return null();
+    }
+    TokenPos namePos = pos();
+    Node lhs = newName(name);
+    if (!lhs)
+        return null();
+    bool matched;
+    if (!tokenStream.matchContextualKeyword(&matched, context->names().of))
+        return null();
+    if (!matched) {
+        report(ParseError, false, null(), JSMSG_OF_AFTER_FOR_NAME);
+        return null();
+    }
+
+    Node rhs = assignExpr(InAllowed, YieldIsKeyword, TripledotProhibited);
+    if (!rhs)
+        return null();
+
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_FOR_OF_ITERABLE);
+
+    TokenPos headPos(begin, pos().end);
+
+    ParseContext::Scope scope(this);
+    if (!scope.init(pc))
+        return null();
+
+    {
+        // Push a temporary ForLoopLexicalHead Statement that allows for
+        // lexical declarations, as they are usually allowed only in braced
+        // statements.
+        ParseContext::Statement forHeadStmt(pc, StatementKind::ForLoopLexicalHead);
+        if (!noteDeclaredName(name, DeclarationKind::Let, namePos))
+            return null();
+    }
+
+    Node decls = handler.newComprehensionBinding(lhs);
+    if (!decls)
+        return null();
+
+    Node tail = comprehensionTail(comprehensionKind);
+    if (!tail)
+        return null();
+
+    // Finish the lexical scope after parsing the tail.
+    Node lexicalScope = finishLexicalScope(scope, decls);
+    if (!lexicalScope)
+        return null();
+
+    Node head = handler.newForInOrOfHead(PNK_FOROF, lexicalScope, rhs, headPos);
+    if (!head)
+        return null();
+
+    return handler.newComprehensionFor(begin, head, tail);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::comprehensionIf(GeneratorKind comprehensionKind)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_IF));
+
+    uint32_t begin = pos().begin;
+
+    MUST_MATCH_TOKEN(TOK_LP, JSMSG_PAREN_BEFORE_COND);
+    Node cond = assignExpr(InAllowed, YieldIsKeyword, TripledotProhibited);
+    if (!cond)
+        return null();
+    MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_AFTER_COND);
+
+    /* Check for (a = b) and warn about possible (a == b) mistype. */
+    if (handler.isUnparenthesizedAssignment(cond)) {
+        if (!report(ParseExtraWarning, false, null(), JSMSG_EQUAL_AS_ASSIGN))
+            return null();
+    }
+
+    Node then = comprehensionTail(comprehensionKind);
+    if (!then)
+        return null();
+
+    return handler.newIfStatement(begin, cond, then, null());
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::comprehensionTail(GeneratorKind comprehensionKind)
+{
+    JS_CHECK_RECURSION(context, return null());
+
+    bool matched;
+    if (!tokenStream.matchToken(&matched, TOK_FOR, TokenStream::Operand))
+        return null();
+    if (matched)
+        return comprehensionFor(comprehensionKind);
+
+    if (!tokenStream.matchToken(&matched, TOK_IF, TokenStream::Operand))
+        return null();
+    if (matched)
+        return comprehensionIf(comprehensionKind);
+
+    uint32_t begin = pos().begin;
+
+    Node bodyExpr = assignExpr(InAllowed, YieldIsKeyword, TripledotProhibited);
+    if (!bodyExpr)
+        return null();
+
+    if (comprehensionKind == NotGenerator)
+        return handler.newArrayPush(begin, bodyExpr);
+
+    MOZ_ASSERT(comprehensionKind == StarGenerator);
+    Node yieldExpr = newYieldExpression(begin, bodyExpr);
+    if (!yieldExpr)
+        return null();
+    yieldExpr = handler.parenthesize(yieldExpr);
+
+    return handler.newExprStatement(yieldExpr, pos().end);
+}
+
+// Parse an ES6-era generator or array comprehension, starting at the first
+// `for`. The caller is responsible for matching the ending TOK_RP or TOK_RB.
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::comprehension(GeneratorKind comprehensionKind)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FOR));
+
+    uint32_t startYieldOffset = pc->lastYieldOffset;
+
+    Node body = comprehensionFor(comprehensionKind);
+    if (!body)
+        return null();
+
+    if (comprehensionKind != NotGenerator && pc->lastYieldOffset != startYieldOffset) {
+        reportWithOffset(ParseError, false, pc->lastYieldOffset,
+                         JSMSG_BAD_GENEXP_BODY, js_yield_str);
+        return null();
+    }
+
+    return body;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::arrayComprehension(uint32_t begin)
+{
+    Node inner = comprehension(NotGenerator);
+    if (!inner)
+        return null();
+
+    MUST_MATCH_TOKEN(TOK_RB, JSMSG_BRACKET_AFTER_ARRAY_COMPREHENSION);
+
+    Node comp = handler.newList(PNK_ARRAYCOMP, inner);
+    if (!comp)
+        return null();
+
+    handler.setBeginPosition(comp, begin);
+    handler.setEndPosition(comp, pos().end);
+
+    return comp;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::generatorComprehension(uint32_t begin)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FOR));
+
+    // We have no problem parsing generator comprehensions inside lazy
+    // functions, but the bytecode emitter currently can't handle them that way,
+    // because when it goes to emit the code for the inner generator function,
+    // it expects outer functions to have non-lazy scripts.
+    if (!abortIfSyntaxParser())
+        return null();
+
+    Node genfn = generatorComprehensionLambda(begin);
+    if (!genfn)
+        return null();
+
+    Node result = handler.newList(PNK_GENEXP, genfn, JSOP_CALL);
+    if (!result)
+        return null();
+    handler.setBeginPosition(result, begin);
+    handler.setEndPosition(result, pos().end);
+
+    return result;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::assignExprWithoutYieldOrAwait(YieldHandling yieldHandling)
+{
+    uint32_t startYieldOffset = pc->lastYieldOffset;
+    uint32_t startAwaitOffset = pc->lastAwaitOffset;
+    Node res = assignExpr(InAllowed, yieldHandling, TripledotProhibited);
+    if (res) {
+        if (pc->lastYieldOffset != startYieldOffset) {
+            reportWithOffset(ParseError, false, pc->lastYieldOffset, JSMSG_YIELD_IN_DEFAULT);
+            return null();
+        }
+        if (pc->lastAwaitOffset != startAwaitOffset) {
+            reportWithOffset(ParseError, false, pc->lastAwaitOffset, JSMSG_AWAIT_IN_DEFAULT);
+            return null();
+        }
+    }
+    return res;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::argumentList(YieldHandling yieldHandling, Node listNode, bool* isSpread,
+                                   PossibleError* possibleError /* = nullptr */)
+{
+    bool matched;
+    if (!tokenStream.matchToken(&matched, TOK_RP, TokenStream::Operand))
+        return false;
+    if (matched) {
+        handler.setEndPosition(listNode, pos().end);
+        return true;
+    }
+
+    while (true) {
+        bool spread = false;
+        uint32_t begin = 0;
+        if (!tokenStream.matchToken(&matched, TOK_TRIPLEDOT, TokenStream::Operand))
+            return false;
+        if (matched) {
+            spread = true;
+            begin = pos().begin;
+            *isSpread = true;
+        }
+
+        Node argNode = assignExpr(InAllowed, yieldHandling, TripledotProhibited, possibleError);
+        if (!argNode)
+            return false;
+        if (spread) {
+            argNode = handler.newSpread(begin, argNode);
+            if (!argNode)
+                return false;
+        }
+
+        handler.addList(listNode, argNode);
+
+        bool matched;
+        if (!tokenStream.matchToken(&matched, TOK_COMMA))
+            return false;
+        if (!matched)
+            break;
+
+        TokenKind tt;
+        if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+            return null();
+        if (tt == TOK_RP) {
+            tokenStream.addModifierException(TokenStream::NoneIsOperand);
+            break;
+        }
+    }
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return false;
+    if (tt != TOK_RP) {
+        report(ParseError, false, null(), JSMSG_PAREN_AFTER_ARGS);
+        return false;
+    }
+    handler.setEndPosition(listNode, pos().end);
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::checkAndMarkSuperScope()
+{
+    if (!pc->sc()->allowSuperProperty())
+        return false;
+    pc->setSuperScopeNeedsHomeObject();
+    return true;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::memberExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                                 TokenKind tt, bool allowCallSyntax /* = true */,
+                                 PossibleError* possibleError /* = nullptr */,
+                                 InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(tt));
+
+    Node lhs;
+
+    JS_CHECK_RECURSION(context, return null());
+
+    /* Check for new expression first. */
+    if (tt == TOK_NEW) {
+        uint32_t newBegin = pos().begin;
+        // Make sure this wasn't a |new.target| in disguise.
+        Node newTarget;
+        if (!tryNewTarget(newTarget))
+            return null();
+        if (newTarget) {
+            lhs = newTarget;
+        } else {
+            lhs = handler.newList(PNK_NEW, newBegin, JSOP_NEW);
+            if (!lhs)
+                return null();
+
+            // Gotten by tryNewTarget
+            tt = tokenStream.currentToken().type;
+            Node ctorExpr = memberExpr(yieldHandling, TripledotProhibited, tt,
+                                       /* allowCallSyntax = */ false,
+                                       /* possibleError = */ nullptr, PredictInvoked);
+            if (!ctorExpr)
+                return null();
+
+            handler.addList(lhs, ctorExpr);
+
+            bool matched;
+            if (!tokenStream.matchToken(&matched, TOK_LP))
+                return null();
+            if (matched) {
+                bool isSpread = false;
+                if (!argumentList(yieldHandling, lhs, &isSpread))
+                    return null();
+                if (isSpread)
+                    handler.setOp(lhs, JSOP_SPREADNEW);
+            }
+        }
+    } else if (tt == TOK_SUPER) {
+        Node thisName = newThisName();
+        if (!thisName)
+            return null();
+        lhs = handler.newSuperBase(thisName, pos());
+        if (!lhs)
+            return null();
+    } else {
+        lhs = primaryExpr(yieldHandling, tripledotHandling, tt, possibleError, invoked);
+        if (!lhs)
+            return null();
+    }
+
+    MOZ_ASSERT_IF(handler.isSuperBase(lhs), tokenStream.isCurrentTokenType(TOK_SUPER));
+
+    while (true) {
+        if (!tokenStream.getToken(&tt))
+            return null();
+        if (tt == TOK_EOF)
+            break;
+
+        Node nextMember;
+        if (tt == TOK_DOT) {
+            if (!tokenStream.getToken(&tt, TokenStream::KeywordIsName))
+                return null();
+            if (tt == TOK_NAME) {
+                PropertyName* field = tokenStream.currentName();
+                if (handler.isSuperBase(lhs) && !checkAndMarkSuperScope()) {
+                    report(ParseError, false, null(), JSMSG_BAD_SUPERPROP, "property");
+                    return null();
+                }
+                nextMember = handler.newPropertyAccess(lhs, field, pos().end);
+                if (!nextMember)
+                    return null();
+            } else {
+                report(ParseError, false, null(), JSMSG_NAME_AFTER_DOT);
+                return null();
+            }
+        } else if (tt == TOK_LB) {
+            Node propExpr = expr(InAllowed, yieldHandling, TripledotProhibited);
+            if (!propExpr)
+                return null();
+
+            MUST_MATCH_TOKEN(TOK_RB, JSMSG_BRACKET_IN_INDEX);
+
+            if (handler.isSuperBase(lhs) && !checkAndMarkSuperScope()) {
+                report(ParseError, false, null(), JSMSG_BAD_SUPERPROP, "member");
+                return null();
+            }
+            nextMember = handler.newPropertyByValue(lhs, propExpr, pos().end);
+            if (!nextMember)
+                return null();
+        } else if ((allowCallSyntax && tt == TOK_LP) ||
+                   tt == TOK_TEMPLATE_HEAD ||
+                   tt == TOK_NO_SUBS_TEMPLATE)
+        {
+            if (handler.isSuperBase(lhs)) {
+                if (!pc->sc()->allowSuperCall()) {
+                    report(ParseError, false, null(), JSMSG_BAD_SUPERCALL);
+                    return null();
+                }
+
+                if (tt != TOK_LP) {
+                    report(ParseError, false, null(), JSMSG_BAD_SUPER);
+                    return null();
+                }
+
+                nextMember = handler.newList(PNK_SUPERCALL, lhs, JSOP_SUPERCALL);
+                if (!nextMember)
+                    return null();
+
+                // Despite the fact that it's impossible to have |super()| in a
+                // generator, we still inherit the yieldHandling of the
+                // memberExpression, per spec. Curious.
+                bool isSpread = false;
+                if (!argumentList(yieldHandling, nextMember, &isSpread))
+                    return null();
+
+                if (isSpread)
+                    handler.setOp(nextMember, JSOP_SPREADSUPERCALL);
+
+                Node thisName = newThisName();
+                if (!thisName)
+                    return null();
+
+                nextMember = handler.newSetThis(thisName, nextMember);
+                if (!nextMember)
+                    return null();
+            } else {
+                if (options().selfHostingMode && handler.isPropertyAccess(lhs)) {
+                    report(ParseError, false, null(), JSMSG_SELFHOSTED_METHOD_CALL);
+                    return null();
+                }
+
+                nextMember = tt == TOK_LP ? handler.newCall() : handler.newTaggedTemplate();
+                if (!nextMember)
+                    return null();
+
+                JSOp op = JSOP_CALL;
+                bool maybeAsyncArrow = false;
+                if (tt == TOK_LP && handler.isNameAnyParentheses(lhs)) {
+                    if (handler.nameIsEvalAnyParentheses(lhs, context)) {
+                        // Select the right EVAL op and flag pc as having a
+                        // direct eval.
+                        op = pc->sc()->strict() ? JSOP_STRICTEVAL : JSOP_EVAL;
+                        pc->sc()->setBindingsAccessedDynamically();
+                        pc->sc()->setHasDirectEval();
+
+                        // In non-strict mode code, direct calls to eval can
+                        // add variables to the call object.
+                        if (pc->isFunctionBox() && !pc->sc()->strict())
+                            pc->functionBox()->setHasExtensibleScope();
+
+                        // If we're in a method, mark the method as requiring
+                        // support for 'super', since direct eval code can use
+                        // it. (If we're not in a method, that's fine, so
+                        // ignore the return value.)
+                        checkAndMarkSuperScope();
+                    } else if (handler.nameIsUnparenthesizedAsync(lhs, context)) {
+                        // |async (| can be the start of an async arrow
+                        // function, so we need to defer reporting possible
+                        // errors from destructuring syntax. To give better
+                        // error messages, we only allow the AsyncArrowHead
+                        // part of the CoverCallExpressionAndAsyncArrowHead
+                        // syntax when the initial name is "async".
+                        maybeAsyncArrow = true;
+                    }
+                } else if (PropertyName* prop = handler.maybeDottedProperty(lhs)) {
+                    // Use the JSOP_FUN{APPLY,CALL} optimizations given the
+                    // right syntax.
+                    if (prop == context->names().apply) {
+                        op = JSOP_FUNAPPLY;
+                        if (pc->isFunctionBox())
+                            pc->functionBox()->usesApply = true;
+                    } else if (prop == context->names().call) {
+                        op = JSOP_FUNCALL;
+                    }
+                }
+
+                handler.setBeginPosition(nextMember, lhs);
+                handler.addList(nextMember, lhs);
+
+                if (tt == TOK_LP) {
+                    bool isSpread = false;
+                    PossibleError* asyncPossibleError = maybeAsyncArrow ? possibleError : nullptr;
+                    if (!argumentList(yieldHandling, nextMember, &isSpread, asyncPossibleError))
+                        return null();
+                    if (isSpread) {
+                        if (op == JSOP_EVAL)
+                            op = JSOP_SPREADEVAL;
+                        else if (op == JSOP_STRICTEVAL)
+                            op = JSOP_STRICTSPREADEVAL;
+                        else
+                            op = JSOP_SPREADCALL;
+                    }
+                } else {
+                    if (!taggedTemplate(yieldHandling, nextMember, tt))
+                        return null();
+                }
+                handler.setOp(nextMember, op);
+            }
+        } else {
+            tokenStream.ungetToken();
+            if (handler.isSuperBase(lhs))
+                break;
+            return lhs;
+        }
+
+        lhs = nextMember;
+    }
+
+    if (handler.isSuperBase(lhs)) {
+        report(ParseError, false, null(), JSMSG_BAD_SUPER);
+        return null();
+    }
+
+    return lhs;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newName(PropertyName* name)
+{
+    return newName(name, pos());
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newName(PropertyName* name, TokenPos pos)
+{
+    return handler.newName(name, pos, context);
+}
+
+template <typename ParseHandler>
+PropertyName*
+Parser<ParseHandler>::labelOrIdentifierReference(YieldHandling yieldHandling,
+                                                 bool yieldTokenizedAsName)
+{
+    PropertyName* ident;
+    bool isYield;
+    const Token& tok = tokenStream.currentToken();
+    if (tok.type == TOK_NAME) {
+        MOZ_ASSERT(tok.name() != context->names().yield ||
+                   tok.nameContainsEscape() ||
+                   yieldTokenizedAsName,
+                   "tokenizer should have treated unescaped 'yield' as TOK_YIELD");
+        MOZ_ASSERT_IF(yieldTokenizedAsName, tok.name() == context->names().yield);
+
+        ident = tok.name();
+        isYield = ident == context->names().yield;
+    } else {
+        MOZ_ASSERT(tok.type == TOK_YIELD && !yieldTokenizedAsName);
+
+        ident = context->names().yield;
+        isYield = true;
+    }
+
+    if (!isYield) {
+        if (pc->sc()->strict()) {
+            const char* badName = ident == context->names().let
+                                  ? "let"
+                                  : ident == context->names().static_
+                                  ? "static"
+                                  : nullptr;
+            if (badName) {
+                report(ParseError, false, null(), JSMSG_RESERVED_ID, badName);
+                return nullptr;
+            }
+        }
+    } else {
+        if (yieldHandling == YieldIsKeyword ||
+            pc->sc()->strict() ||
+            versionNumber() >= JSVERSION_1_7)
+        {
+            report(ParseError, false, null(), JSMSG_RESERVED_ID, "yield");
+            return nullptr;
+        }
+    }
+
+    return ident;
+}
+
+template <typename ParseHandler>
+PropertyName*
+Parser<ParseHandler>::bindingIdentifier(YieldHandling yieldHandling)
+{
+    PropertyName* ident;
+    bool isYield;
+    const Token& tok = tokenStream.currentToken();
+    if (tok.type == TOK_NAME) {
+        MOZ_ASSERT(tok.name() != context->names().yield || tok.nameContainsEscape(),
+                   "tokenizer should have treated unescaped 'yield' as TOK_YIELD");
+
+        ident = tok.name();
+        isYield = ident == context->names().yield;
+    } else {
+        MOZ_ASSERT(tok.type == TOK_YIELD);
+
+        ident = context->names().yield;
+        isYield = true;
+    }
+
+    if (!isYield) {
+        if (pc->sc()->strict()) {
+            const char* badName = ident == context->names().arguments
+                                  ? "arguments"
+                                  : ident == context->names().eval
+                                  ? "eval"
+                                  : nullptr;
+            if (badName) {
+                report(ParseError, false, null(), JSMSG_BAD_STRICT_ASSIGN, badName);
+                return nullptr;
+            }
+
+            badName = ident == context->names().let
+                      ? "let"
+                      : ident == context->names().static_
+                      ? "static"
+                      : nullptr;
+            if (badName) {
+                report(ParseError, false, null(), JSMSG_RESERVED_ID, badName);
+                return nullptr;
+            }
+        }
+    } else {
+        if (yieldHandling == YieldIsKeyword ||
+            pc->sc()->strict() ||
+            versionNumber() >= JSVERSION_1_7)
+        {
+            report(ParseError, false, null(), JSMSG_RESERVED_ID, "yield");
+            return nullptr;
+        }
+    }
+
+    return ident;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::identifierReference(Handle<PropertyName*> name)
+{
+    Node pn = newName(name);
+    if (!pn)
+        return null();
+
+    if (!pc->inDestructuringDecl && !noteUsedName(name))
+        return null();
+
+    return pn;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::stringLiteral()
+{
+    return handler.newStringLiteral(stopStringCompression(), pos());
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::noSubstitutionTemplate()
+{
+    return handler.newTemplateStringLiteral(stopStringCompression(), pos());
+}
+
+template <typename ParseHandler>
+JSAtom * Parser<ParseHandler>::stopStringCompression() {
+    JSAtom* atom = tokenStream.currentToken().atom();
+
+    // Large strings are fast to parse but slow to compress. Stop compression on
+    // them, so we don't wait for a long time for compression to finish at the
+    // end of compilation.
+    const size_t HUGE_STRING = 50000;
+    if (sct && sct->active() && atom->length() >= HUGE_STRING)
+        sct->abort();
+    return atom;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::newRegExp()
+{
+    MOZ_ASSERT(!options().selfHostingMode);
+    // Create the regexp even when doing a syntax parse, to check the regexp's syntax.
+    const char16_t* chars = tokenStream.getTokenbuf().begin();
+    size_t length = tokenStream.getTokenbuf().length();
+    RegExpFlag flags = tokenStream.currentToken().regExpFlags();
+
+    Rooted<RegExpObject*> reobj(context);
+    reobj = RegExpObject::create(context, chars, length, flags, &tokenStream, alloc);
+    if (!reobj)
+        return null();
+
+    return handler.newRegExp(reobj, pos(), *this);
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::arrayInitializer(YieldHandling yieldHandling, PossibleError* possibleError)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LB));
+
+    uint32_t begin = pos().begin;
+    Node literal = handler.newArrayLiteral(begin);
+    if (!literal)
+        return null();
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt, TokenStream::Operand))
+        return null();
+
+    // Handle an ES6-era array comprehension first.
+    if (tt == TOK_FOR)
+        return arrayComprehension(begin);
+
+    if (tt == TOK_RB) {
+        /*
+         * Mark empty arrays as non-constant, since we cannot easily
+         * determine their type.
+         */
+        handler.setListFlag(literal, PNX_NONCONST);
+    } else {
+        tokenStream.ungetToken();
+
+        uint32_t index = 0;
+        TokenStream::Modifier modifier = TokenStream::Operand;
+        for (; ; index++) {
+            if (index >= NativeObject::MAX_DENSE_ELEMENTS_COUNT) {
+                report(ParseError, false, null(), JSMSG_ARRAY_INIT_TOO_BIG);
+                return null();
+            }
+
+            TokenKind tt;
+            if (!tokenStream.peekToken(&tt, TokenStream::Operand))
+                return null();
+            if (tt == TOK_RB)
+                break;
+
+            if (tt == TOK_COMMA) {
+                tokenStream.consumeKnownToken(TOK_COMMA, TokenStream::Operand);
+                if (!handler.addElision(literal, pos()))
+                    return null();
+            } else if (tt == TOK_TRIPLEDOT) {
+                tokenStream.consumeKnownToken(TOK_TRIPLEDOT, TokenStream::Operand);
+                uint32_t begin = pos().begin;
+                Node inner = assignExpr(InAllowed, yieldHandling, TripledotProhibited,
+                                        possibleError);
+                if (!inner)
+                    return null();
+                if (!handler.addSpreadElement(literal, begin, inner))
+                    return null();
+            } else {
+                Node element = assignExpr(InAllowed, yieldHandling, TripledotProhibited,
+                                          possibleError);
+                if (!element)
+                    return null();
+                if (foldConstants && !FoldConstants(context, &element, this))
+                    return null();
+                handler.addArrayElement(literal, element);
+            }
+
+            if (tt != TOK_COMMA) {
+                /* If we didn't already match TOK_COMMA in above case. */
+                bool matched;
+                if (!tokenStream.matchToken(&matched, TOK_COMMA))
+                    return null();
+                if (!matched) {
+                    modifier = TokenStream::None;
+                    break;
+                }
+                if (tt == TOK_TRIPLEDOT && possibleError)
+                    possibleError->setPendingDestructuringError(null(), JSMSG_REST_WITH_COMMA);
+            }
+        }
+
+        MUST_MATCH_TOKEN_MOD(TOK_RB, modifier, JSMSG_BRACKET_AFTER_LIST);
+    }
+    handler.setEndPosition(literal, pos().end);
+    return literal;
+}
+
+static JSAtom*
+DoubleToAtom(ExclusiveContext* cx, double value)
+{
+    // This is safe because doubles can not be moved.
+    Value tmp = DoubleValue(value);
+    return ToAtom<CanGC>(cx, HandleValue::fromMarkedLocation(&tmp));
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::propertyName(YieldHandling yieldHandling, Node propList,
+                                   PropertyType* propType, MutableHandleAtom propAtom)
+{
+    TokenKind ltok;
+    if (!tokenStream.getToken(&ltok, TokenStream::KeywordIsName))
+        return null();
+
+    MOZ_ASSERT(ltok != TOK_RC, "caller should have handled TOK_RC");
+
+    bool isGenerator = false;
+    bool isAsync = false;
+    if (ltok == TOK_MUL) {
+        isGenerator = true;
+        if (!tokenStream.getToken(&ltok, TokenStream::KeywordIsName))
+            return null();
+    }
+
+    if (ltok == TOK_NAME && tokenStream.currentName() == context->names().async) {
+        // AsyncMethod[Yield, Await]:
+        //   async [no LineTerminator here] PropertyName[?Yield, ?Await] ...
+        //
+        // PropertyName:
+        //   LiteralPropertyName
+        //   ComputedPropertyName[?Yield, ?Await]
+        //
+        // LiteralPropertyName:
+        //   IdentifierName
+        //   StringLiteral
+        //   NumericLiteral
+        //
+        // ComputedPropertyName[Yield, Await]:
+        //   [ ...
+        TokenKind tt = TOK_EOF;
+        if (!tokenStream.peekTokenSameLine(&tt, TokenStream::KeywordIsName))
+            return null();
+        if (tt == TOK_STRING || tt == TOK_NUMBER || tt == TOK_LB ||
+            tt == TOK_NAME || tt == TOK_YIELD)
+        {
+            isAsync = true;
+            tokenStream.consumeKnownToken(tt, TokenStream::KeywordIsName);
+            ltok = tt;
+        } else {
+            tokenStream.addModifierException(TokenStream::NoneIsKeywordIsName);
+        }
+    }
+
+    if (isAsync && isGenerator) {
+        report(ParseError, false, null(), JSMSG_ASYNC_GENERATOR);
+        return null();
+    }
+
+    propAtom.set(nullptr);
+    Node propName;
+    switch (ltok) {
+      case TOK_NUMBER:
+        propAtom.set(DoubleToAtom(context, tokenStream.currentToken().number()));
+        if (!propAtom.get())
+            return null();
+        propName = newNumber(tokenStream.currentToken());
+        if (!propName)
+            return null();
+        break;
+
+      case TOK_LB:
+        propName = computedPropertyName(yieldHandling, propList);
+        if (!propName)
+            return null();
+        break;
+
+      case TOK_NAME: {
+        propAtom.set(tokenStream.currentName());
+        // Do not look for accessor syntax on generators
+        if (isGenerator || isAsync ||
+            !(propAtom.get() == context->names().get ||
+              propAtom.get() == context->names().set))
+        {
+            propName = handler.newObjectLiteralPropertyName(propAtom, pos());
+            if (!propName)
+                return null();
+            break;
+        }
+
+        *propType = propAtom.get() == context->names().get ? PropertyType::Getter
+                                                           : PropertyType::Setter;
+
+        // We have parsed |get| or |set|. Look for an accessor property
+        // name next.
+        TokenKind tt;
+        if (!tokenStream.peekToken(&tt, TokenStream::KeywordIsName))
+            return null();
+        if (tt == TOK_NAME) {
+            if (!checkUnescapedName())
+                return null();
+
+            tokenStream.consumeKnownToken(TOK_NAME, TokenStream::KeywordIsName);
+
+            propAtom.set(tokenStream.currentName());
+            return handler.newObjectLiteralPropertyName(propAtom, pos());
+        }
+        if (tt == TOK_STRING) {
+            if (!checkUnescapedName())
+                return null();
+
+            tokenStream.consumeKnownToken(TOK_STRING, TokenStream::KeywordIsName);
+
+            propAtom.set(tokenStream.currentToken().atom());
+
+            uint32_t index;
+            if (propAtom->isIndex(&index)) {
+                propAtom.set(DoubleToAtom(context, index));
+                if (!propAtom.get())
+                    return null();
+                return handler.newNumber(index, NoDecimal, pos());
+            }
+            return stringLiteral();
+        }
+        if (tt == TOK_NUMBER) {
+            if (!checkUnescapedName())
+                return null();
+
+            tokenStream.consumeKnownToken(TOK_NUMBER, TokenStream::KeywordIsName);
+
+            propAtom.set(DoubleToAtom(context, tokenStream.currentToken().number()));
+            if (!propAtom.get())
+                return null();
+            return newNumber(tokenStream.currentToken());
+        }
+        if (tt == TOK_LB) {
+            if (!checkUnescapedName())
+                return null();
+
+            tokenStream.consumeKnownToken(TOK_LB, TokenStream::KeywordIsName);
+
+            return computedPropertyName(yieldHandling, propList);
+        }
+
+        // Not an accessor property after all.
+        propName = handler.newObjectLiteralPropertyName(propAtom.get(), pos());
+        if (!propName)
+            return null();
+        tokenStream.addModifierException(TokenStream::NoneIsKeywordIsName);
+        break;
+      }
+
+      case TOK_STRING: {
+        propAtom.set(tokenStream.currentToken().atom());
+        uint32_t index;
+        if (propAtom->isIndex(&index)) {
+            propName = handler.newNumber(index, NoDecimal, pos());
+            if (!propName)
+                return null();
+            break;
+        }
+        propName = stringLiteral();
+        if (!propName)
+            return null();
+        break;
+      }
+
+      default:
+        report(ParseError, false, null(), JSMSG_BAD_PROP_ID);
+        return null();
+    }
+
+    TokenKind tt;
+    if (!tokenStream.getToken(&tt))
+        return null();
+
+    if (tt == TOK_COLON) {
+        if (isGenerator) {
+            report(ParseError, false, null(), JSMSG_BAD_PROP_ID);
+            return null();
+        }
+        *propType = PropertyType::Normal;
+        return propName;
+    }
+
+    if (ltok == TOK_NAME && (tt == TOK_COMMA || tt == TOK_RC || tt == TOK_ASSIGN)) {
+        if (isGenerator) {
+            report(ParseError, false, null(), JSMSG_BAD_PROP_ID);
+            return null();
+        }
+        tokenStream.ungetToken();
+        *propType = tt == TOK_ASSIGN ?
+                          PropertyType::CoverInitializedName :
+                          PropertyType::Shorthand;
+        return propName;
+    }
+
+    if (tt == TOK_LP) {
+        tokenStream.ungetToken();
+        if (isGenerator)
+            *propType = PropertyType::GeneratorMethod;
+        else if (isAsync)
+            *propType = PropertyType::AsyncMethod;
+        else
+            *propType = PropertyType::Method;
+        return propName;
+    }
+
+    report(ParseError, false, null(), JSMSG_COLON_AFTER_ID);
+    return null();
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::computedPropertyName(YieldHandling yieldHandling, Node literal)
+{
+    uint32_t begin = pos().begin;
+
+    Node assignNode;
+    {
+        // Turn off the inDestructuringDecl flag when parsing computed property
+        // names. In short, when parsing 'let {[x + y]: z} = obj;', noteUsedName()
+        // should be called on x and y, but not on z. See the comment on
+        // Parser<>::checkDestructuringPattern() for details.
+        AutoClearInDestructuringDecl autoClear(pc);
+        assignNode = assignExpr(InAllowed, yieldHandling, TripledotProhibited);
+        if (!assignNode)
+            return null();
+    }
+
+    MUST_MATCH_TOKEN(TOK_RB, JSMSG_COMP_PROP_UNTERM_EXPR);
+    Node propname = handler.newComputedName(assignNode, begin, pos().end);
+    if (!propname)
+        return null();
+    handler.setListFlag(literal, PNX_NONCONST);
+    return propname;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::objectLiteral(YieldHandling yieldHandling, PossibleError* possibleError)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LC));
+
+    Node literal = handler.newObjectLiteral(pos().begin);
+    if (!literal)
+        return null();
+
+    bool seenPrototypeMutation = false;
+    bool seenCoverInitializedName = false;
+    RootedAtom propAtom(context);
+    for (;;) {
+        TokenKind tt;
+        if (!tokenStream.getToken(&tt, TokenStream::KeywordIsName))
+            return null();
+        if (tt == TOK_RC)
+            break;
+
+        tokenStream.ungetToken();
+
+        PropertyType propType;
+        Node propName = propertyName(yieldHandling, literal, &propType, &propAtom);
+        if (!propName)
+            return null();
+
+        if (propType == PropertyType::Normal) {
+            Node propExpr = assignExpr(InAllowed, yieldHandling, TripledotProhibited,
+                                       possibleError);
+            if (!propExpr)
+                return null();
+
+            if (foldConstants && !FoldConstants(context, &propExpr, this))
+                return null();
+
+            if (propAtom == context->names().proto) {
+                if (seenPrototypeMutation) {
+                    // Directly report the error when we're not in a
+                    // destructuring context.
+                    if (!possibleError) {
+                        report(ParseError, false, propName, JSMSG_DUPLICATE_PROTO_PROPERTY);
+                        return null();
+                    }
+
+                    // Otherwise delay error reporting until we've determined
+                    // whether or not we're destructuring.
+                    possibleError->setPendingExpressionError(propName,
+                                                             JSMSG_DUPLICATE_PROTO_PROPERTY);
+                }
+                seenPrototypeMutation = true;
+
+                // Note: this occurs *only* if we observe TOK_COLON!  Only
+                // __proto__: v mutates [[Prototype]].  Getters, setters,
+                // method/generator definitions, computed property name
+                // versions of all of these, and shorthands do not.
+                uint32_t begin = handler.getPosition(propName).begin;
+                if (!handler.addPrototypeMutation(literal, begin, propExpr))
+                    return null();
+            } else {
+                if (!handler.isConstant(propExpr))
+                    handler.setListFlag(literal, PNX_NONCONST);
+
+                if (!handler.addPropertyDefinition(literal, propName, propExpr))
+                    return null();
+            }
+        } else if (propType == PropertyType::Shorthand) {
+            /*
+             * Support, e.g., |var {x, y} = o| as destructuring shorthand
+             * for |var {x: x, y: y} = o|, and |var o = {x, y}| as initializer
+             * shorthand for |var o = {x: x, y: y}|.
+             */
+            TokenKind propToken = TOK_NAME;
+            if (!tokenStream.checkForKeyword(propAtom, &propToken))
+                return null();
+
+            if (propToken != TOK_NAME && propToken != TOK_YIELD) {
+                report(ParseError, false, null(), JSMSG_RESERVED_ID, TokenKindToDesc(propToken));
+                return null();
+            }
+
+            Rooted<PropertyName*> name(context,
+                                       identifierReference(yieldHandling, propToken == TOK_YIELD));
+            if (!name)
+                return null();
+
+            Node nameExpr = identifierReference(name);
+            if (!nameExpr)
+                return null();
+
+            if (!handler.addShorthand(literal, propName, nameExpr))
+                return null();
+        } else if (propType == PropertyType::CoverInitializedName) {
+            /*
+             * Support, e.g., |var {x=1, y=2} = o| as destructuring shorthand
+             * with default values, as per ES6 12.14.5
+             */
+            TokenKind propToken = TOK_NAME;
+            if (!tokenStream.checkForKeyword(propAtom, &propToken))
+                return null();
+
+            if (propToken != TOK_NAME && propToken != TOK_YIELD) {
+                report(ParseError, false, null(), JSMSG_RESERVED_ID, TokenKindToDesc(propToken));
+                return null();
+            }
+
+            Rooted<PropertyName*> name(context,
+                                       identifierReference(yieldHandling, propToken == TOK_YIELD));
+            if (!name)
+                return null();
+
+            Node lhs = identifierReference(name);
+            if (!lhs)
+                return null();
+
+            tokenStream.consumeKnownToken(TOK_ASSIGN);
+
+            if (!seenCoverInitializedName) {
+                // "shorthand default" or "CoverInitializedName" syntax is only
+                // valid in the case of destructuring.
+                seenCoverInitializedName = true;
+
+                if (!possibleError) {
+                    // Destructuring defaults are definitely not allowed in this object literal,
+                    // because of something the caller knows about the preceding code.
+                    // For example, maybe the preceding token is an operator: `x + {y=z}`.
+                    report(ParseError, false, null(), JSMSG_COLON_AFTER_ID);
+                    return null();
+                }
+
+                // Here we set a pending error so that later in the parse, once we've
+                // determined whether or not we're destructuring, the error can be
+                // reported or ignored appropriately.
+                possibleError->setPendingExpressionError(null(), JSMSG_COLON_AFTER_ID);
+            }
+
+            Node rhs;
+            {
+                // Clearing `inDestructuringDecl` allows name use to be noted
+                // in Parser::identifierReference. See bug 1255167.
+                AutoClearInDestructuringDecl autoClear(pc);
+                rhs = assignExpr(InAllowed, yieldHandling, TripledotProhibited);
+                if (!rhs)
+                    return null();
+            }
+
+            Node propExpr = handler.newAssignment(PNK_ASSIGN, lhs, rhs, JSOP_NOP);
+            if (!propExpr)
+                return null();
+
+            if (!handler.addPropertyDefinition(literal, propName, propExpr))
+                return null();
+
+            if (!abortIfSyntaxParser())
+                return null();
+        } else {
+            // FIXME: Implement ES6 function "name" property semantics
+            // (bug 883377).
+            RootedAtom funName(context);
+            if (!tokenStream.isCurrentTokenType(TOK_RB)) {
+                funName = propAtom;
+
+                if (propType == PropertyType::Getter || propType == PropertyType::Setter) {
+                    funName = prefixAccessorName(propType, propAtom);
+                    if (!funName)
+                        return null();
+                }
+            }
+
+            Node fn = methodDefinition(propType, funName);
+            if (!fn)
+                return null();
+
+            JSOp op = JSOpFromPropertyType(propType);
+            if (!handler.addObjectMethodDefinition(literal, propName, fn, op))
+                return null();
+        }
+
+        if (!tokenStream.getToken(&tt))
+            return null();
+        if (tt == TOK_RC)
+            break;
+        if (tt != TOK_COMMA) {
+            report(ParseError, false, null(), JSMSG_CURLY_AFTER_LIST);
+            return null();
+        }
+    }
+
+    handler.setEndPosition(literal, pos().end);
+    return literal;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::methodDefinition(PropertyType propType, HandleAtom funName)
+{
+    FunctionSyntaxKind kind = FunctionSyntaxKindFromPropertyType(propType);
+    GeneratorKind generatorKind = GeneratorKindFromPropertyType(propType);
+    FunctionAsyncKind asyncKind = AsyncKindFromPropertyType(propType);
+    YieldHandling yieldHandling = GetYieldHandling(generatorKind, asyncKind);
+    return functionDefinition(InAllowed, yieldHandling, funName, kind, generatorKind, asyncKind);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::tryNewTarget(Node &newTarget)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_NEW));
+
+    newTarget = null();
+
+    Node newHolder = handler.newPosHolder(pos());
+    if (!newHolder)
+        return false;
+
+    uint32_t begin = pos().begin;
+
+    // |new| expects to look for an operand, so we will honor that.
+    TokenKind next;
+    if (!tokenStream.getToken(&next, TokenStream::Operand))
+        return false;
+
+    // Don't unget the token, since lookahead cannot handle someone calling
+    // getToken() with a different modifier. Callers should inspect currentToken().
+    if (next != TOK_DOT)
+        return true;
+
+    if (!tokenStream.getToken(&next))
+        return false;
+    if (next != TOK_NAME || tokenStream.currentName() != context->names().target) {
+        report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+               "target", TokenKindToDesc(next));
+        return false;
+    }
+
+    if (!checkUnescapedName())
+        return false;
+
+    if (!pc->sc()->allowNewTarget()) {
+        reportWithOffset(ParseError, false, begin, JSMSG_BAD_NEWTARGET);
+        return false;
+    }
+
+    Node targetHolder = handler.newPosHolder(pos());
+    if (!targetHolder)
+        return false;
+
+    newTarget = handler.newNewTarget(newHolder, targetHolder);
+    return !!newTarget;
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::primaryExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                                  TokenKind tt, PossibleError* possibleError,
+                                  InvokedPrediction invoked /* = PredictUninvoked */)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(tt));
+    JS_CHECK_RECURSION(context, return null());
+
+    switch (tt) {
+      case TOK_FUNCTION:
+        return functionExpr(invoked);
+
+      case TOK_CLASS:
+        return classDefinition(yieldHandling, ClassExpression, NameRequired);
+
+      case TOK_LB:
+        return arrayInitializer(yieldHandling, possibleError);
+
+      case TOK_LC:
+        return objectLiteral(yieldHandling, possibleError);
+
+      case TOK_LP: {
+        TokenKind next;
+        if (!tokenStream.peekToken(&next, TokenStream::Operand))
+            return null();
+
+        if (next == TOK_RP) {
+            // Not valid expression syntax, but this is valid in an arrow function
+            // with no params: `() => body`.
+            tokenStream.consumeKnownToken(next, TokenStream::Operand);
+
+            if (!tokenStream.peekToken(&next))
+                return null();
+            if (next != TOK_ARROW) {
+                report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                       "expression", TokenKindToDesc(TOK_RP));
+                return null();
+            }
+
+            // Now just return something that will allow parsing to continue.
+            // It doesn't matter what; when we reach the =>, we will rewind and
+            // reparse the whole arrow function. See Parser::assignExpr.
+            return handler.newNullLiteral(pos());
+        }
+
+        if (next == TOK_FOR) {
+            uint32_t begin = pos().begin;
+            tokenStream.consumeKnownToken(next, TokenStream::Operand);
+            return generatorComprehension(begin);
+        }
+
+        // Pass |possibleError| to support destructuring in arrow parameters.
+        Node expr = exprInParens(InAllowed, yieldHandling, TripledotAllowed, possibleError);
+        if (!expr)
+            return null();
+        MUST_MATCH_TOKEN(TOK_RP, JSMSG_PAREN_IN_PAREN);
+        handler.setEndPosition(expr, pos().end);
+        return handler.parenthesize(expr);
+      }
+
+      case TOK_TEMPLATE_HEAD:
+        return templateLiteral(yieldHandling);
+
+      case TOK_NO_SUBS_TEMPLATE:
+        return noSubstitutionTemplate();
+
+      case TOK_STRING:
+        return stringLiteral();
+
+      case TOK_YIELD:
+      case TOK_NAME: {
+        if (tokenStream.currentName() == context->names().async) {
+            TokenKind nextSameLine = TOK_EOF;
+            if (!tokenStream.peekTokenSameLine(&nextSameLine))
+                return null();
+
+            if (nextSameLine == TOK_FUNCTION) {
+                tokenStream.consumeKnownToken(TOK_FUNCTION);
+                return functionExpr(PredictUninvoked, AsyncFunction);
+            }
+        }
+
+        Rooted<PropertyName*> name(context, identifierReference(yieldHandling));
+        if (!name)
+            return null();
+
+        return identifierReference(name);
+      }
+
+      case TOK_REGEXP:
+        return newRegExp();
+
+      case TOK_NUMBER:
+        return newNumber(tokenStream.currentToken());
+
+      case TOK_TRUE:
+        return handler.newBooleanLiteral(true, pos());
+      case TOK_FALSE:
+        return handler.newBooleanLiteral(false, pos());
+      case TOK_THIS: {
+        if (pc->isFunctionBox())
+            pc->functionBox()->usesThis = true;
+        Node thisName = null();
+        if (pc->sc()->thisBinding() == ThisBinding::Function) {
+            thisName = newThisName();
+            if (!thisName)
+                return null();
+        }
+        return handler.newThisLiteral(pos(), thisName);
+      }
+      case TOK_NULL:
+        return handler.newNullLiteral(pos());
+
+      case TOK_TRIPLEDOT: {
+        // This isn't valid expression syntax, but it's valid in an arrow
+        // function as a trailing rest param: `(a, b, ...rest) => body`.  Check
+        // if it's directly under
+        // CoverParenthesizedExpressionAndArrowParameterList, and check for a
+        // name, closing parenthesis, and arrow, and allow it only if all are
+        // present.
+        if (tripledotHandling != TripledotAllowed) {
+            report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                   "expression", TokenKindToDesc(tt));
+            return null();
+        }
+
+        TokenKind next;
+        if (!tokenStream.getToken(&next))
+            return null();
+
+        if (next == TOK_LB || next == TOK_LC) {
+            // Validate, but don't store the pattern right now. The whole arrow
+            // function is reparsed in functionFormalParametersAndBody().
+            if (!destructuringDeclaration(DeclarationKind::CoverArrowParameter, yieldHandling,
+                                          next))
+            {
+                return null();
+            }
+        } else {
+            // This doesn't check that the provided name is allowed, e.g. if
+            // the enclosing code is strict mode code, any of "let", "yield",
+            // or "arguments" should be prohibited.  Argument-parsing code
+            // handles that.
+            if (next != TOK_NAME && next != TOK_YIELD) {
+                report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                    "rest argument name", TokenKindToDesc(next));
+                return null();
+            }
+        }
+
+        if (!tokenStream.getToken(&next))
+            return null();
+        if (next != TOK_RP) {
+            report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                   "closing parenthesis", TokenKindToDesc(next));
+            return null();
+        }
+
+        if (!tokenStream.peekToken(&next))
+            return null();
+        if (next != TOK_ARROW) {
+            // Advance the scanner for proper error location reporting.
+            tokenStream.consumeKnownToken(next);
+            report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+                   "'=>' after argument list", TokenKindToDesc(next));
+            return null();
+        }
+
+        tokenStream.ungetToken();  // put back right paren
+
+        // Return an arbitrary expression node. See case TOK_RP above.
+        return handler.newNullLiteral(pos());
+      }
+
+      default:
+        report(ParseError, false, null(), JSMSG_UNEXPECTED_TOKEN,
+               "expression", TokenKindToDesc(tt));
+        return null();
+    }
+}
+
+template <typename ParseHandler>
+typename ParseHandler::Node
+Parser<ParseHandler>::exprInParens(InHandling inHandling, YieldHandling yieldHandling,
+                                   TripledotHandling tripledotHandling,
+                                   PossibleError* possibleError /* = nullptr */)
+{
+    MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_LP));
+    return expr(inHandling, yieldHandling, tripledotHandling, possibleError, PredictInvoked);
+}
+
+template <typename ParseHandler>
+void
+Parser<ParseHandler>::addTelemetry(JSCompartment::DeprecatedLanguageExtension e)
+{
+    JSContext* cx = context->maybeJSContext();
+    if (!cx)
+        return;
+    cx->compartment()->addTelemetry(getFilename(), e);
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::warnOnceAboutExprClosure()
+{
+#ifndef RELEASE_OR_BETA
+    JSContext* cx = context->maybeJSContext();
+    if (!cx)
+        return true;
+
+    if (!cx->compartment()->warnedAboutExprClosure) {
+        if (!report(ParseWarning, false, null(), JSMSG_DEPRECATED_EXPR_CLOSURE))
+            return false;
+        cx->compartment()->warnedAboutExprClosure = true;
+    }
+#endif
+    return true;
+}
+
+template <typename ParseHandler>
+bool
+Parser<ParseHandler>::warnOnceAboutForEach()
+{
+    JSContext* cx = context->maybeJSContext();
+    if (!cx)
+        return true;
+
+    if (!cx->compartment()->warnedAboutForEach) {
+        if (!report(ParseWarning, false, null(), JSMSG_DEPRECATED_FOR_EACH))
+            return false;
+        cx->compartment()->warnedAboutForEach = true;
+    }
+    return true;
+}
+
+template class Parser<FullParseHandler>;
+template class Parser<SyntaxParseHandler>;
+
+} /* namespace frontend */
+} /* namespace js */
diff --git a/js/src/frontend/Parser.h b/js/src/frontend/Parser.h
new file mode 100644
index 0000000000..0ad4d56a0b
--- /dev/null
+++ b/js/src/frontend/Parser.h
@@ -0,0 +1,1430 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* JS parser. */
+
+#ifndef frontend_Parser_h
+#define frontend_Parser_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Maybe.h"
+
+#include "jspubtd.h"
+
+#include "frontend/BytecodeCompiler.h"
+#include "frontend/FullParseHandler.h"
+#include "frontend/NameAnalysisTypes.h"
+#include "frontend/NameCollections.h"
+#include "frontend/SharedContext.h"
+#include "frontend/SyntaxParseHandler.h"
+
+namespace js {
+
+class ModuleObject;
+
+namespace frontend {
+
+/*
+ * The struct ParseContext stores information about the current parsing context,
+ * which is part of the parser state (see the field Parser::pc). The current
+ * parsing context is either the global context, or the function currently being
+ * parsed. When the parser encounters a function definition, it creates a new
+ * ParseContext, makes it the new current context.
+ */
+class ParseContext : public Nestable<ParseContext>
+{
+  public:
+    // The intra-function statement stack.
+    //
+    // Used for early error checking that depend on the nesting structure of
+    // statements, such as continue/break targets, labels, and unbraced
+    // lexical declarations.
+    class Statement : public Nestable<Statement>
+    {
+        StatementKind kind_;
+
+      public:
+        using Nestable<Statement>::enclosing;
+        using Nestable<Statement>::findNearest;
+
+        Statement(ParseContext* pc, StatementKind kind)
+          : Nestable<Statement>(&pc->innermostStatement_),
+            kind_(kind)
+        { }
+
+        template <typename T> inline bool is() const;
+        template <typename T> inline T& as();
+
+        StatementKind kind() const {
+            return kind_;
+        }
+
+        void refineForKind(StatementKind newForKind) {
+            MOZ_ASSERT(kind_ == StatementKind::ForLoop);
+            MOZ_ASSERT(newForKind == StatementKind::ForInLoop ||
+                       newForKind == StatementKind::ForOfLoop);
+            kind_ = newForKind;
+        }
+    };
+
+    class LabelStatement : public Statement
+    {
+        RootedAtom label_;
+
+      public:
+        LabelStatement(ParseContext* pc, JSAtom* label)
+          : Statement(pc, StatementKind::Label),
+            label_(pc->sc_->context, label)
+        { }
+
+        HandleAtom label() const {
+            return label_;
+        }
+    };
+
+    // The intra-function scope stack.
+    //
+    // Tracks declared and used names within a scope.
+    class Scope : public Nestable<Scope>
+    {
+        // Names declared in this scope. Corresponds to the union of
+        // VarDeclaredNames and LexicallyDeclaredNames in the ES spec.
+        //
+        // A 'var' declared name is a member of the declared name set of every
+        // scope in its scope contour.
+        //
+        // A lexically declared name is a member only of the declared name set of
+        // the scope in which it is declared.
+        PooledMapPtr<DeclaredNameMap> declared_;
+
+        // Monotonically increasing id.
+        uint32_t id_;
+
+        bool maybeReportOOM(ParseContext* pc, bool result) {
+            if (!result)
+                ReportOutOfMemory(pc->sc()->context);
+            return result;
+        }
+
+      public:
+        using DeclaredNamePtr = DeclaredNameMap::Ptr;
+        using AddDeclaredNamePtr = DeclaredNameMap::AddPtr;
+
+        using Nestable<Scope>::enclosing;
+
+        template <typename ParseHandler>
+        explicit Scope(Parser<ParseHandler>* parser)
+          : Nestable<Scope>(&parser->pc->innermostScope_),
+            declared_(parser->context->frontendCollectionPool()),
+            id_(parser->usedNames.nextScopeId())
+        { }
+
+        void dump(ParseContext* pc);
+
+        uint32_t id() const {
+            return id_;
+        }
+
+        MOZ_MUST_USE bool init(ParseContext* pc) {
+            if (id_ == UINT32_MAX) {
+                pc->tokenStream_.reportError(JSMSG_NEED_DIET, js_script_str);
+                return false;
+            }
+
+            return declared_.acquire(pc->sc()->context);
+        }
+
+        DeclaredNamePtr lookupDeclaredName(JSAtom* name) {
+            return declared_->lookup(name);
+        }
+
+        AddDeclaredNamePtr lookupDeclaredNameForAdd(JSAtom* name) {
+            return declared_->lookupForAdd(name);
+        }
+
+        MOZ_MUST_USE bool addDeclaredName(ParseContext* pc, AddDeclaredNamePtr& p, JSAtom* name,
+                                          DeclarationKind kind)
+        {
+            return maybeReportOOM(pc, declared_->add(p, name, DeclaredNameInfo(kind)));
+        }
+
+        // Remove all VarForAnnexBLexicalFunction declarations of a certain
+        // name from all scopes in pc's scope stack.
+        static void removeVarForAnnexBLexicalFunction(ParseContext* pc, JSAtom* name);
+
+        // Add and remove catch parameter names. Used to implement the odd
+        // semantics of catch bodies.
+        bool addCatchParameters(ParseContext* pc, Scope& catchParamScope);
+        void removeCatchParameters(ParseContext* pc, Scope& catchParamScope);
+
+        void useAsVarScope(ParseContext* pc) {
+            MOZ_ASSERT(!pc->varScope_);
+            pc->varScope_ = this;
+        }
+
+        // An iterator for the set of names a scope binds: the set of all
+        // declared names for 'var' scopes, and the set of lexically declared
+        // names for non-'var' scopes.
+        class BindingIter
+        {
+            friend class Scope;
+
+            DeclaredNameMap::Range declaredRange_;
+            mozilla::DebugOnly<uint32_t> count_;
+            bool isVarScope_;
+
+            BindingIter(Scope& scope, bool isVarScope)
+              : declaredRange_(scope.declared_->all()),
+                count_(0),
+                isVarScope_(isVarScope)
+            {
+                settle();
+            }
+
+            void settle() {
+                // Both var and lexically declared names are binding in a var
+                // scope.
+                if (isVarScope_)
+                    return;
+
+                // Otherwise, pop only lexically declared names are
+                // binding. Pop the range until we find such a name.
+                while (!declaredRange_.empty()) {
+                    if (BindingKindIsLexical(kind()))
+                        break;
+                    declaredRange_.popFront();
+                }
+            }
+
+          public:
+            bool done() const {
+                return declaredRange_.empty();
+            }
+
+            explicit operator bool() const {
+                return !done();
+            }
+
+            JSAtom* name() {
+                MOZ_ASSERT(!done());
+                return declaredRange_.front().key();
+            }
+
+            DeclarationKind declarationKind() {
+                MOZ_ASSERT(!done());
+                return declaredRange_.front().value()->kind();
+            }
+
+            BindingKind kind() {
+                return DeclarationKindToBindingKind(declarationKind());
+            }
+
+            bool closedOver() {
+                MOZ_ASSERT(!done());
+                return declaredRange_.front().value()->closedOver();
+            }
+
+            void setClosedOver() {
+                MOZ_ASSERT(!done());
+                return declaredRange_.front().value()->setClosedOver();
+            }
+
+            void operator++(int) {
+                MOZ_ASSERT(!done());
+                MOZ_ASSERT(count_ != UINT32_MAX);
+                declaredRange_.popFront();
+                settle();
+            }
+        };
+
+        inline BindingIter bindings(ParseContext* pc);
+    };
+
+    class VarScope : public Scope
+    {
+      public:
+        template <typename ParseHandler>
+        explicit VarScope(Parser<ParseHandler>* parser)
+          : Scope(parser)
+        {
+            useAsVarScope(parser->pc);
+        }
+    };
+
+  private:
+    // Context shared between parsing and bytecode generation.
+    SharedContext* sc_;
+
+    // TokenStream used for error reporting.
+    TokenStream& tokenStream_;
+
+    // The innermost statement, i.e., top of the statement stack.
+    Statement* innermostStatement_;
+
+    // The innermost scope, i.e., top of the scope stack.
+    //
+    // The outermost scope in the stack is usually varScope_. In the case of
+    // functions, the outermost scope is functionScope_, which may be
+    // varScope_. See comment above functionScope_.
+    Scope* innermostScope_;
+
+    // If isFunctionBox() and the function is a named lambda, the DeclEnv
+    // scope for named lambdas.
+    mozilla::Maybe<Scope> namedLambdaScope_;
+
+    // If isFunctionBox(), the scope for the function. If there are no
+    // parameter expressions, this is scope for the entire function. If there
+    // are parameter expressions, this holds the special function names
+    // ('.this', 'arguments') and the formal parameers.
+    mozilla::Maybe<Scope> functionScope_;
+
+    // The body-level scope. This always exists, but not necessarily at the
+    // beginning of parsing the script in the case of functions with parameter
+    // expressions.
+    Scope* varScope_;
+
+    // Inner function boxes in this context to try Annex B.3.3 semantics
+    // on. Only used when full parsing.
+    PooledVectorPtr<FunctionBoxVector> innerFunctionBoxesForAnnexB_;
+
+    // Simple formal parameter names, in order of appearance. Only used when
+    // isFunctionBox().
+    PooledVectorPtr<AtomVector> positionalFormalParameterNames_;
+
+    // Closed over binding names, in order of appearance. Null-delimited
+    // between scopes. Only used when syntax parsing.
+    PooledVectorPtr<AtomVector> closedOverBindingsForLazy_;
+
+    // Monotonically increasing id.
+    uint32_t scriptId_;
+
+    // Set when compiling a function using Parser::standaloneFunctionBody via
+    // the Function or Generator constructor.
+    bool isStandaloneFunctionBody_;
+
+    // Set when encountering a super.property inside a method. We need to mark
+    // the nearest super scope as needing a home object.
+    bool superScopeNeedsHomeObject_;
+
+  public:
+    // lastYieldOffset stores the offset of the last yield that was parsed.
+    // NoYieldOffset is its initial value.
+    static const uint32_t NoYieldOffset = UINT32_MAX;
+    uint32_t lastYieldOffset;
+
+    // lastAwaitOffset stores the offset of the last await that was parsed.
+    // NoAwaitOffset is its initial value.
+    static const uint32_t NoAwaitOffset = UINT32_MAX;
+    uint32_t         lastAwaitOffset;
+
+    // All inner functions in this context. Only used when syntax parsing.
+    Rooted<GCVector<JSFunction*, 8>> innerFunctionsForLazy;
+
+    // In a function context, points to a Directive struct that can be updated
+    // to reflect new directives encountered in the Directive Prologue that
+    // require reparsing the function. In global/module/generator-tail contexts,
+    // we don't need to reparse when encountering a DirectivePrologue so this
+    // pointer may be nullptr.
+    Directives* newDirectives;
+
+    // Set when parsing a declaration-like destructuring pattern.  This flag
+    // causes PrimaryExpr to create PN_NAME parse nodes for variable references
+    // which are not hooked into any definition's use chain, added to any tree
+    // context's AtomList, etc. etc.  checkDestructuring will do that work
+    // later.
+    //
+    // The comments atop checkDestructuring explain the distinction between
+    // assignment-like and declaration-like destructuring patterns, and why
+    // they need to be treated differently.
+    mozilla::Maybe<DeclarationKind> inDestructuringDecl;
+
+    // Set when parsing a function and it has 'return <expr>;'
+    bool funHasReturnExpr;
+
+    // Set when parsing a function and it has 'return;'
+    bool funHasReturnVoid;
+
+  public:
+    template <typename ParseHandler>
+    ParseContext(Parser<ParseHandler>* prs, SharedContext* sc, Directives* newDirectives)
+      : Nestable<ParseContext>(&prs->pc),
+        sc_(sc),
+        tokenStream_(prs->tokenStream),
+        innermostStatement_(nullptr),
+        innermostScope_(nullptr),
+        varScope_(nullptr),
+        innerFunctionBoxesForAnnexB_(prs->context->frontendCollectionPool()),
+        positionalFormalParameterNames_(prs->context->frontendCollectionPool()),
+        closedOverBindingsForLazy_(prs->context->frontendCollectionPool()),
+        scriptId_(prs->usedNames.nextScriptId()),
+        isStandaloneFunctionBody_(false),
+        superScopeNeedsHomeObject_(false),
+        lastYieldOffset(NoYieldOffset),
+        lastAwaitOffset(NoAwaitOffset),
+        innerFunctionsForLazy(prs->context, GCVector<JSFunction*, 8>(prs->context)),
+        newDirectives(newDirectives),
+        funHasReturnExpr(false),
+        funHasReturnVoid(false)
+    {
+        if (isFunctionBox()) {
+            if (functionBox()->function()->isNamedLambda())
+                namedLambdaScope_.emplace(prs);
+            functionScope_.emplace(prs);
+        }
+    }
+
+    ~ParseContext();
+
+    MOZ_MUST_USE bool init();
+
+    SharedContext* sc() {
+        return sc_;
+    }
+
+    bool isFunctionBox() const {
+        return sc_->isFunctionBox();
+    }
+
+    FunctionBox* functionBox() {
+        return sc_->asFunctionBox();
+    }
+
+    Statement* innermostStatement() {
+        return innermostStatement_;
+    }
+
+    Scope* innermostScope() {
+        // There is always at least one scope: the 'var' scope.
+        MOZ_ASSERT(innermostScope_);
+        return innermostScope_;
+    }
+
+    Scope& namedLambdaScope() {
+        MOZ_ASSERT(functionBox()->function()->isNamedLambda());
+        return *namedLambdaScope_;
+    }
+
+    Scope& functionScope() {
+        MOZ_ASSERT(isFunctionBox());
+        return *functionScope_;
+    }
+
+    Scope& varScope() {
+        MOZ_ASSERT(varScope_);
+        return *varScope_;
+    }
+
+    bool isFunctionExtraBodyVarScopeInnermost() {
+        return isFunctionBox() && functionBox()->hasParameterExprs &&
+               innermostScope() == varScope_;
+    }
+
+    template <typename Predicate /* (Statement*) -> bool */>
+    Statement* findInnermostStatement(Predicate predicate) {
+        return Statement::findNearest(innermostStatement_, predicate);
+    }
+
+    template <typename T, typename Predicate /* (Statement*) -> bool */>
+    T* findInnermostStatement(Predicate predicate) {
+        return Statement::findNearest<T>(innermostStatement_, predicate);
+    }
+
+    AtomVector& positionalFormalParameterNames() {
+        return *positionalFormalParameterNames_;
+    }
+
+    AtomVector& closedOverBindingsForLazy() {
+        return *closedOverBindingsForLazy_;
+    }
+
+    MOZ_MUST_USE bool addInnerFunctionBoxForAnnexB(FunctionBox* funbox);
+    void removeInnerFunctionBoxesForAnnexB(JSAtom* name);
+    void finishInnerFunctionBoxesForAnnexB();
+
+    // True if we are at the topmost level of a entire script or function body.
+    // For example, while parsing this code we would encounter f1 and f2 at
+    // body level, but we would not encounter f3 or f4 at body level:
+    //
+    //   function f1() { function f2() { } }
+    //   if (cond) { function f3() { if (cond) { function f4() { } } } }
+    //
+    bool atBodyLevel() {
+        return !innermostStatement_;
+    }
+
+    bool atGlobalLevel() {
+        return atBodyLevel() && sc_->isGlobalContext();
+    }
+
+    // True if we are at the topmost level of a module only.
+    bool atModuleLevel() {
+        return atBodyLevel() && sc_->isModuleContext();
+    }
+
+    void setIsStandaloneFunctionBody() {
+        isStandaloneFunctionBody_ = true;
+    }
+
+    bool isStandaloneFunctionBody() const {
+        return isStandaloneFunctionBody_;
+    }
+
+    void setSuperScopeNeedsHomeObject() {
+        MOZ_ASSERT(sc_->allowSuperProperty());
+        superScopeNeedsHomeObject_ = true;
+    }
+
+    bool superScopeNeedsHomeObject() const {
+        return superScopeNeedsHomeObject_;
+    }
+
+    bool useAsmOrInsideUseAsm() const {
+        return sc_->isFunctionBox() && sc_->asFunctionBox()->useAsmOrInsideUseAsm();
+    }
+
+    // Most functions start off being parsed as non-generators.
+    // Non-generators transition to LegacyGenerator on parsing "yield" in JS 1.7.
+    // An ES6 generator is marked as a "star generator" before its body is parsed.
+    GeneratorKind generatorKind() const {
+        return sc_->isFunctionBox() ? sc_->asFunctionBox()->generatorKind() : NotGenerator;
+    }
+
+    bool isGenerator() const {
+        return generatorKind() != NotGenerator;
+    }
+
+    bool isLegacyGenerator() const {
+        return generatorKind() == LegacyGenerator;
+    }
+
+    bool isStarGenerator() const {
+        return generatorKind() == StarGenerator;
+    }
+
+    bool isAsync() const {
+        return sc_->isFunctionBox() && sc_->asFunctionBox()->isAsync();
+    }
+
+    FunctionAsyncKind asyncKind() const {
+        return isAsync() ? AsyncFunction : SyncFunction;
+    }
+
+    bool isArrowFunction() const {
+        return sc_->isFunctionBox() && sc_->asFunctionBox()->function()->isArrow();
+    }
+
+    bool isMethod() const {
+        return sc_->isFunctionBox() && sc_->asFunctionBox()->function()->isMethod();
+    }
+
+    uint32_t scriptId() const {
+        return scriptId_;
+    }
+};
+
+template <>
+inline bool
+ParseContext::Statement::is<ParseContext::LabelStatement>() const
+{
+    return kind_ == StatementKind::Label;
+}
+
+template <typename T>
+inline T&
+ParseContext::Statement::as()
+{
+    MOZ_ASSERT(is<T>());
+    return static_cast<T&>(*this);
+}
+
+inline ParseContext::Scope::BindingIter
+ParseContext::Scope::bindings(ParseContext* pc)
+{
+    // In function scopes with parameter expressions, function special names
+    // (like '.this') are declared as vars in the function scope, despite its
+    // not being the var scope.
+    return BindingIter(*this, pc->varScope_ == this || pc->functionScope_.ptrOr(nullptr) == this);
+}
+
+inline
+Directives::Directives(ParseContext* parent)
+  : strict_(parent->sc()->strict()),
+    asmJS_(parent->useAsmOrInsideUseAsm())
+{}
+
+enum VarContext { HoistVars, DontHoistVars };
+enum PropListType { ObjectLiteral, ClassBody, DerivedClassBody };
+enum class PropertyType {
+    Normal,
+    Shorthand,
+    CoverInitializedName,
+    Getter,
+    GetterNoExpressionClosure,
+    Setter,
+    SetterNoExpressionClosure,
+    Method,
+    GeneratorMethod,
+    AsyncMethod,
+    Constructor,
+    DerivedConstructor
+};
+
+// Specify a value for an ES6 grammar parametrization.  We have no enum for
+// [Return] because its behavior is exactly equivalent to checking whether
+// we're in a function box -- easier and simpler than passing an extra
+// parameter everywhere.
+enum YieldHandling { YieldIsName, YieldIsKeyword };
+enum InHandling { InAllowed, InProhibited };
+enum DefaultHandling { NameRequired, AllowDefaultName };
+enum TripledotHandling { TripledotAllowed, TripledotProhibited };
+
+// A data structure for tracking used names per parsing session in order to
+// compute which bindings are closed over. Scripts and scopes are numbered
+// monotonically in textual order and name uses are tracked by lists of
+// (script id, scope id) pairs of their use sites.
+//
+// Intuitively, in a pair (P,S), P tracks the most nested function that has a
+// use of u, and S tracks the most nested scope that is still being parsed.
+//
+// P is used to answer the question "is u used by a nested function?"
+// S is used to answer the question "is u used in any scopes currently being
+//                                   parsed?"
+//
+// The algorithm:
+//
+// Let Used by a map of names to lists.
+//
+// 1. Number all scopes in monotonic increasing order in textual order.
+// 2. Number all scripts in monotonic increasing order in textual order.
+// 3. When an identifier u is used in scope numbered S in script numbered P,
+//    and u is found in Used,
+//   a. Append (P,S) to Used[u].
+//   b. Otherwise, assign the the list [(P,S)] to Used[u].
+// 4. When we finish parsing a scope S in script P, for each declared name d in
+//    Declared(S):
+//   a. If d is found in Used, mark d as closed over if there is a value
+//     (P_d, S_d) in Used[d] such that P_d > P and S_d > S.
+//   b. Remove all values (P_d, S_d) in Used[d] such that S_d are >= S.
+//
+// Steps 1 and 2 are implemented by UsedNameTracker::next{Script,Scope}Id.
+// Step 3 is implemented by UsedNameTracker::noteUsedInScope.
+// Step 4 is implemented by UsedNameTracker::noteBoundInScope and
+// Parser::propagateFreeNamesAndMarkClosedOverBindings.
+class UsedNameTracker
+{
+  public:
+    struct Use
+    {
+        uint32_t scriptId;
+        uint32_t scopeId;
+    };
+
+    class UsedNameInfo
+    {
+        friend class UsedNameTracker;
+
+        Vector<Use, 6> uses_;
+
+        void resetToScope(uint32_t scriptId, uint32_t scopeId);
+
+      public:
+        explicit UsedNameInfo(ExclusiveContext* cx)
+          : uses_(cx)
+        { }
+
+        UsedNameInfo(UsedNameInfo&& other)
+          : uses_(mozilla::Move(other.uses_))
+        { }
+
+        bool noteUsedInScope(uint32_t scriptId, uint32_t scopeId) {
+            if (uses_.empty() || uses_.back().scopeId < scopeId)
+                return uses_.append(Use { scriptId, scopeId });
+            return true;
+        }
+
+        void noteBoundInScope(uint32_t scriptId, uint32_t scopeId, bool* closedOver) {
+            *closedOver = false;
+            while (!uses_.empty()) {
+                Use& innermost = uses_.back();
+                if (innermost.scopeId < scopeId)
+                    break;
+                if (innermost.scriptId > scriptId)
+                    *closedOver = true;
+                uses_.popBack();
+            }
+        }
+
+        bool isUsedInScript(uint32_t scriptId) const {
+            return !uses_.empty() && uses_.back().scriptId >= scriptId;
+        }
+    };
+
+    using UsedNameMap = HashMap<JSAtom*,
+                                UsedNameInfo,
+                                DefaultHasher<JSAtom*>>;
+
+  private:
+    // The map of names to chains of uses.
+    UsedNameMap map_;
+
+    // Monotonically increasing id for all nested scripts.
+    uint32_t scriptCounter_;
+
+    // Monotonically increasing id for all nested scopes.
+    uint32_t scopeCounter_;
+
+  public:
+    explicit UsedNameTracker(ExclusiveContext* cx)
+      : map_(cx),
+        scriptCounter_(0),
+        scopeCounter_(0)
+    { }
+
+    MOZ_MUST_USE bool init() {
+        return map_.init();
+    }
+
+    uint32_t nextScriptId() {
+        MOZ_ASSERT(scriptCounter_ != UINT32_MAX,
+                   "ParseContext::Scope::init should have prevented wraparound");
+        return scriptCounter_++;
+    }
+
+    uint32_t nextScopeId() {
+        MOZ_ASSERT(scopeCounter_ != UINT32_MAX);
+        return scopeCounter_++;
+    }
+
+    UsedNameMap::Ptr lookup(JSAtom* name) const {
+        return map_.lookup(name);
+    }
+
+    MOZ_MUST_USE bool noteUse(ExclusiveContext* cx, JSAtom* name,
+                              uint32_t scriptId, uint32_t scopeId);
+
+    struct RewindToken
+    {
+      private:
+        friend class UsedNameTracker;
+        uint32_t scriptId;
+        uint32_t scopeId;
+    };
+
+    RewindToken getRewindToken() const {
+        RewindToken token;
+        token.scriptId = scriptCounter_;
+        token.scopeId = scopeCounter_;
+        return token;
+    }
+
+    // Resets state so that scriptId and scopeId are the innermost script and
+    // scope, respectively. Used for rewinding state on syntax parse failure.
+    void rewind(RewindToken token);
+
+    // Resets state to beginning of compilation.
+    void reset() {
+        map_.clear();
+        RewindToken token;
+        token.scriptId = 0;
+        token.scopeId = 0;
+        rewind(token);
+    }
+};
+
+template <typename ParseHandler>
+class Parser final : private JS::AutoGCRooter, public StrictModeGetter
+{
+  private:
+    using Node = typename ParseHandler::Node;
+
+    /*
+     * A class for temporarily stashing errors while parsing continues.
+     *
+     * The ability to stash an error is useful for handling situations where we
+     * aren't able to verify that an error has occurred until later in the parse.
+     * For instance | ({x=1}) | is always parsed as an object literal with
+     * a SyntaxError, however, in the case where it is followed by '=>' we rewind
+     * and reparse it as a valid arrow function. Here a PossibleError would be
+     * set to 'pending' when the initial SyntaxError was encountered then 'resolved'
+     * just before rewinding the parser.
+     *
+     * There are currently two kinds of PossibleErrors: Expression and
+     * Destructuring errors. Expression errors are used to mark a possible
+     * syntax error when a grammar production is used in an expression context.
+     * For example in |{x = 1}|, we mark the CoverInitializedName |x = 1| as a
+     * possible expression error, because CoverInitializedName productions
+     * are disallowed when an actual ObjectLiteral is expected.
+     * Destructuring errors are used to record possible syntax errors in
+     * destructuring contexts. For example in |[...rest, ] = []|, we initially
+     * mark the trailing comma after the spread expression as a possible
+     * destructuring error, because the ArrayAssignmentPattern grammar
+     * production doesn't allow a trailing comma after the rest element.
+     *
+     * When using PossibleError one should set a pending error at the location
+     * where an error occurs. From that point, the error may be resolved
+     * (invalidated) or left until the PossibleError is checked.
+     *
+     * Ex:
+     *   PossibleError possibleError(*this);
+     *   possibleError.setPendingExpressionError(pn, JSMSG_BAD_PROP_ID);
+     *   // A JSMSG_BAD_PROP_ID ParseError is reported, returns false.
+     *   if (!possibleError.checkForExpressionError())
+     *       return false; // we reach this point with a pending exception
+     *
+     *   PossibleError possibleError(*this);
+     *   possibleError.setPendingExpressionError(pn, JSMSG_BAD_PROP_ID);
+     *   // Returns true, no error is reported.
+     *   if (!possibleError.checkForDestructuringError())
+     *       return false; // not reached, no pending exception
+     *
+     *   PossibleError possibleError(*this);
+     *   // Returns true, no error is reported.
+     *   if (!possibleError.checkForExpressionError())
+     *       return false; // not reached, no pending exception
+     */
+    class MOZ_STACK_CLASS PossibleError
+    {
+      private:
+        enum class ErrorKind { Expression, Destructuring };
+
+        enum class ErrorState { None, Pending };
+
+        struct Error {
+            ErrorState state_ = ErrorState::None;
+
+            // Error reporting fields.
+            uint32_t offset_;
+            unsigned errorNumber_;
+        };
+
+        Parser<ParseHandler>& parser_;
+        Error exprError_;
+        Error destructuringError_;
+
+        // Returns the error report.
+        Error& error(ErrorKind kind);
+
+        // Return true if an error is pending without reporting
+        bool hasError(ErrorKind kind);
+
+        // Resolve any pending error.
+        void setResolved(ErrorKind kind);
+
+        // Set a pending error. Only a single error may be set per instance and
+        // error kind.
+        void setPending(ErrorKind kind, Node pn, unsigned errorNumber);
+
+        // If there is a pending error, report it and return false, otherwise
+        // return true.
+        bool checkForError(ErrorKind kind);
+
+        // Transfer an existing error to another instance.
+        void transferErrorTo(ErrorKind kind, PossibleError* other);
+
+      public:
+        explicit PossibleError(Parser<ParseHandler>& parser);
+
+        // Set a pending destructuring error. Only a single error may be set
+        // per instance, i.e. subsequent calls to this method are ignored and
+        // won't overwrite the existing pending error.
+        void setPendingDestructuringError(Node pn, unsigned errorNumber);
+
+        // Set a pending expression error. Only a single error may be set per
+        // instance, i.e. subsequent calls to this method are ignored and won't
+        // overwrite the existing pending error.
+        void setPendingExpressionError(Node pn, unsigned errorNumber);
+
+        // If there is a pending destructuring error, report it and return
+        // false, otherwise return true. Clears any pending expression error.
+        bool checkForDestructuringError();
+
+        // If there is a pending expression error, report it and return false,
+        // otherwise return true. Clears any pending destructuring error.
+        bool checkForExpressionError();
+
+        // Pass pending errors between possible error instances. This is useful
+        // for extending the lifetime of a pending error beyond the scope of
+        // the PossibleError where it was initially set (keeping in mind that
+        // PossibleError is a MOZ_STACK_CLASS).
+        void transferErrorsTo(PossibleError* other);
+    };
+
+  public:
+    ExclusiveContext* const context;
+
+    LifoAlloc& alloc;
+
+    TokenStream tokenStream;
+    LifoAlloc::Mark tempPoolMark;
+
+    /* list of parsed objects for GC tracing */
+    ObjectBox* traceListHead;
+
+    /* innermost parse context (stack-allocated) */
+    ParseContext* pc;
+
+    // For tracking used names in this parsing session.
+    UsedNameTracker& usedNames;
+
+    /* Compression token for aborting. */
+    SourceCompressionTask* sct;
+
+    ScriptSource*       ss;
+
+    /* Root atoms and objects allocated for the parsed tree. */
+    AutoKeepAtoms       keepAtoms;
+
+    /* Perform constant-folding; must be true when interfacing with the emitter. */
+    const bool          foldConstants:1;
+
+  private:
+#if DEBUG
+    /* Our fallible 'checkOptions' member function has been called. */
+    bool checkOptionsCalled:1;
+#endif
+
+    /*
+     * Not all language constructs can be handled during syntax parsing. If it
+     * is not known whether the parse succeeds or fails, this bit is set and
+     * the parse will return false.
+     */
+    bool abortedSyntaxParse:1;
+
+    /* Unexpected end of input, i.e. TOK_EOF not at top-level. */
+    bool isUnexpectedEOF_:1;
+
+  public:
+    /* State specific to the kind of parse being performed. */
+    ParseHandler handler;
+
+    void prepareNodeForMutation(Node node) { handler.prepareNodeForMutation(node); }
+    void freeTree(Node node) { handler.freeTree(node); }
+
+  private:
+    bool reportHelper(ParseReportKind kind, bool strict, uint32_t offset,
+                      unsigned errorNumber, va_list args);
+  public:
+    bool report(ParseReportKind kind, bool strict, Node pn, unsigned errorNumber, ...);
+    bool reportNoOffset(ParseReportKind kind, bool strict, unsigned errorNumber, ...);
+    bool reportWithOffset(ParseReportKind kind, bool strict, uint32_t offset, unsigned errorNumber,
+                          ...);
+
+    Parser(ExclusiveContext* cx, LifoAlloc& alloc, const ReadOnlyCompileOptions& options,
+           const char16_t* chars, size_t length, bool foldConstants, UsedNameTracker& usedNames,
+           Parser<SyntaxParseHandler>* syntaxParser, LazyScript* lazyOuterFunction);
+    ~Parser();
+
+    bool checkOptions();
+
+    // A Parser::Mark is the extension of the LifoAlloc::Mark to the entire
+    // Parser's state. Note: clients must still take care that any ParseContext
+    // that points into released ParseNodes is destroyed.
+    class Mark
+    {
+        friend class Parser;
+        LifoAlloc::Mark mark;
+        ObjectBox* traceListHead;
+    };
+    Mark mark() const {
+        Mark m;
+        m.mark = alloc.mark();
+        m.traceListHead = traceListHead;
+        return m;
+    }
+    void release(Mark m) {
+        alloc.release(m.mark);
+        traceListHead = m.traceListHead;
+    }
+
+    friend void js::frontend::MarkParser(JSTracer* trc, JS::AutoGCRooter* parser);
+
+    const char* getFilename() const { return tokenStream.getFilename(); }
+    JSVersion versionNumber() const { return tokenStream.versionNumber(); }
+
+    /*
+     * Parse a top-level JS script.
+     */
+    Node parse();
+
+    /*
+     * Allocate a new parsed object or function container from
+     * cx->tempLifoAlloc.
+     */
+    ObjectBox* newObjectBox(JSObject* obj);
+    FunctionBox* newFunctionBox(Node fn, JSFunction* fun, Directives directives,
+                                GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                bool tryAnnexB);
+
+    /*
+     * Create a new function object given a name (which is optional if this is
+     * a function expression).
+     */
+    JSFunction* newFunction(HandleAtom atom, FunctionSyntaxKind kind,
+                            GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                            HandleObject proto);
+
+    void trace(JSTracer* trc);
+
+    bool hadAbortedSyntaxParse() {
+        return abortedSyntaxParse;
+    }
+    void clearAbortedSyntaxParse() {
+        abortedSyntaxParse = false;
+    }
+
+    bool isUnexpectedEOF() const { return isUnexpectedEOF_; }
+
+    bool checkUnescapedName();
+
+  private:
+    Parser* thisForCtor() { return this; }
+
+    JSAtom* stopStringCompression();
+
+    Node stringLiteral();
+    Node noSubstitutionTemplate();
+    Node templateLiteral(YieldHandling yieldHandling);
+    bool taggedTemplate(YieldHandling yieldHandling, Node nodeList, TokenKind tt);
+    bool appendToCallSiteObj(Node callSiteObj);
+    bool addExprAndGetNextTemplStrToken(YieldHandling yieldHandling, Node nodeList,
+                                        TokenKind* ttp);
+    bool checkStatementsEOF();
+
+    inline Node newName(PropertyName* name);
+    inline Node newName(PropertyName* name, TokenPos pos);
+    inline Node newYieldExpression(uint32_t begin, Node expr, bool isYieldStar = false);
+    inline Node newAwaitExpression(uint32_t begin, Node expr);
+
+    inline bool abortIfSyntaxParser();
+
+  public:
+    /* Public entry points for parsing. */
+    Node statement(YieldHandling yieldHandling);
+    Node statementListItem(YieldHandling yieldHandling, bool canHaveDirectives = false);
+
+    bool maybeParseDirective(Node list, Node pn, bool* cont);
+
+    // Parse the body of an eval.
+    //
+    // Eval scripts are distinguished from global scripts in that in ES6, per
+    // 18.2.1.1 steps 9 and 10, all eval scripts are executed under a fresh
+    // lexical scope.
+    Node evalBody(EvalSharedContext* evalsc);
+
+    // Parse the body of a global script.
+    Node globalBody(GlobalSharedContext* globalsc);
+
+    // Parse a module.
+    Node moduleBody(ModuleSharedContext* modulesc);
+
+    // Parse a function, given only its body. Used for the Function and
+    // Generator constructors.
+    Node standaloneFunctionBody(HandleFunction fun, HandleScope enclosingScope,
+                                Handle<PropertyNameVector> formals,
+                                GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                Directives inheritedDirectives, Directives* newDirectives);
+
+    // Parse a function, given only its arguments and body. Used for lazily
+    // parsed functions.
+    Node standaloneLazyFunction(HandleFunction fun, bool strict,
+                                GeneratorKind generatorKind, FunctionAsyncKind asyncKind);
+
+    // Parse an inner function given an enclosing ParseContext and a
+    // FunctionBox for the inner function.
+    bool innerFunction(Node pn, ParseContext* outerpc, FunctionBox* funbox, InHandling inHandling,
+                       YieldHandling yieldHandling, FunctionSyntaxKind kind,
+                       Directives inheritedDirectives, Directives* newDirectives);
+
+    // Parse a function's formal parameters and its body assuming its function
+    // ParseContext is already on the stack.
+    bool functionFormalParametersAndBody(InHandling inHandling, YieldHandling yieldHandling,
+                                         Node pn, FunctionSyntaxKind kind);
+
+    // Determine whether |yield| is a valid name in the current context, or
+    // whether it's prohibited due to strictness, JS version, or occurrence
+    // inside a star generator.
+    bool yieldExpressionsSupported() {
+        return (versionNumber() >= JSVERSION_1_7 || pc->isGenerator()) && !pc->isAsync();
+    }
+
+    // Match the current token against the BindingIdentifier production with
+    // the given Yield parameter.  If there is no match, report a syntax
+    // error.
+    PropertyName* bindingIdentifier(YieldHandling yieldHandling);
+
+    virtual bool strictMode() { return pc->sc()->strict(); }
+    bool setLocalStrictMode(bool strict) {
+        MOZ_ASSERT(tokenStream.debugHasNoLookahead());
+        return pc->sc()->setLocalStrictMode(strict);
+    }
+
+    const ReadOnlyCompileOptions& options() const {
+        return tokenStream.options();
+    }
+
+  private:
+    enum InvokedPrediction { PredictUninvoked = false, PredictInvoked = true };
+    enum ForInitLocation { InForInit, NotInForInit };
+
+  private:
+    /*
+     * JS parsers, from lowest to highest precedence.
+     *
+     * Each parser must be called during the dynamic scope of a ParseContext
+     * object, pointed to by this->pc.
+     *
+     * Each returns a parse node tree or null on error.
+     *
+     * Parsers whose name has a '1' suffix leave the TokenStream state
+     * pointing to the token one past the end of the parsed fragment.  For a
+     * number of the parsers this is convenient and avoids a lot of
+     * unnecessary ungetting and regetting of tokens.
+     *
+     * Some parsers have two versions:  an always-inlined version (with an 'i'
+     * suffix) and a never-inlined version (with an 'n' suffix).
+     */
+    Node functionStmt(YieldHandling yieldHandling, DefaultHandling defaultHandling,
+                      FunctionAsyncKind asyncKind = SyncFunction);
+    Node functionExpr(InvokedPrediction invoked = PredictUninvoked,
+                      FunctionAsyncKind asyncKind = SyncFunction);
+
+    Node statementList(YieldHandling yieldHandling);
+
+    Node blockStatement(YieldHandling yieldHandling,
+                        unsigned errorNumber = JSMSG_CURLY_IN_COMPOUND);
+    Node doWhileStatement(YieldHandling yieldHandling);
+    Node whileStatement(YieldHandling yieldHandling);
+
+    Node forStatement(YieldHandling yieldHandling);
+    bool forHeadStart(YieldHandling yieldHandling,
+                      ParseNodeKind* forHeadKind,
+                      Node* forInitialPart,
+                      mozilla::Maybe<ParseContext::Scope>& forLetImpliedScope,
+                      Node* forInOrOfExpression);
+    bool validateForInOrOfLHSExpression(Node target, PossibleError* possibleError);
+    Node expressionAfterForInOrOf(ParseNodeKind forHeadKind, YieldHandling yieldHandling);
+
+    Node switchStatement(YieldHandling yieldHandling);
+    Node continueStatement(YieldHandling yieldHandling);
+    Node breakStatement(YieldHandling yieldHandling);
+    Node returnStatement(YieldHandling yieldHandling);
+    Node withStatement(YieldHandling yieldHandling);
+    Node throwStatement(YieldHandling yieldHandling);
+    Node tryStatement(YieldHandling yieldHandling);
+    Node catchBlockStatement(YieldHandling yieldHandling, ParseContext::Scope& catchParamScope);
+    Node debuggerStatement();
+
+    Node variableStatement(YieldHandling yieldHandling);
+
+    Node labeledStatement(YieldHandling yieldHandling);
+    Node labeledItem(YieldHandling yieldHandling);
+
+    Node ifStatement(YieldHandling yieldHandling);
+    Node consequentOrAlternative(YieldHandling yieldHandling);
+
+    // While on a |let| TOK_NAME token, examine |next|.  Indicate whether
+    // |next|, the next token already gotten with modifier TokenStream::None,
+    // continues a LexicalDeclaration.
+    bool nextTokenContinuesLetDeclaration(TokenKind next, YieldHandling yieldHandling);
+
+    Node lexicalDeclaration(YieldHandling yieldHandling, bool isConst);
+
+    Node importDeclaration();
+    Node exportDeclaration();
+    Node expressionStatement(YieldHandling yieldHandling,
+                             InvokedPrediction invoked = PredictUninvoked);
+
+    // Declaration parsing.  The main entrypoint is Parser::declarationList,
+    // with sub-functionality split out into the remaining methods.
+
+    // |blockScope| may be non-null only when |kind| corresponds to a lexical
+    // declaration (that is, PNK_LET or PNK_CONST).
+    //
+    // The for* parameters, for normal declarations, should be null/ignored.
+    // They should be non-null only when Parser::forHeadStart parses a
+    // declaration at the start of a for-loop head.
+    //
+    // In this case, on success |*forHeadKind| is PNK_FORHEAD, PNK_FORIN, or
+    // PNK_FOROF, corresponding to the three for-loop kinds.  The precise value
+    // indicates what was parsed.
+    //
+    // If parsing recognized a for(;;) loop, the next token is the ';' within
+    // the loop-head that separates the init/test parts.
+    //
+    // Otherwise, for for-in/of loops, the next token is the ')' ending the
+    // loop-head.  Additionally, the expression that the loop iterates over was
+    // parsed into |*forInOrOfExpression|.
+    Node declarationList(YieldHandling yieldHandling,
+                         ParseNodeKind kind,
+                         ParseNodeKind* forHeadKind = nullptr,
+                         Node* forInOrOfExpression = nullptr);
+
+    // The items in a declaration list are either patterns or names, with or
+    // without initializers.  These two methods parse a single pattern/name and
+    // any associated initializer -- and if parsing an |initialDeclaration|
+    // will, if parsing in a for-loop head (as specified by |forHeadKind| being
+    // non-null), consume additional tokens up to the closing ')' in a
+    // for-in/of loop head, returning the iterated expression in
+    // |*forInOrOfExpression|.  (An "initial declaration" is the first
+    // declaration in a declaration list: |a| but not |b| in |var a, b|, |{c}|
+    // but not |d| in |let {c} = 3, d|.)
+    Node declarationPattern(Node decl, DeclarationKind declKind, TokenKind tt,
+                            bool initialDeclaration, YieldHandling yieldHandling,
+                            ParseNodeKind* forHeadKind, Node* forInOrOfExpression);
+    Node declarationName(Node decl, DeclarationKind declKind, TokenKind tt,
+                         bool initialDeclaration, YieldHandling yieldHandling,
+                         ParseNodeKind* forHeadKind, Node* forInOrOfExpression);
+
+    // Having parsed a name (not found in a destructuring pattern) declared by
+    // a declaration, with the current token being the '=' separating the name
+    // from its initializer, parse and bind that initializer -- and possibly
+    // consume trailing in/of and subsequent expression, if so directed by
+    // |forHeadKind|.
+    bool initializerInNameDeclaration(Node decl, Node binding, Handle<PropertyName*> name,
+                                      DeclarationKind declKind, bool initialDeclaration,
+                                      YieldHandling yieldHandling, ParseNodeKind* forHeadKind,
+                                      Node* forInOrOfExpression);
+
+    Node expr(InHandling inHandling, YieldHandling yieldHandling,
+              TripledotHandling tripledotHandling, PossibleError* possibleError = nullptr,
+              InvokedPrediction invoked = PredictUninvoked);
+    Node assignExpr(InHandling inHandling, YieldHandling yieldHandling,
+                    TripledotHandling tripledotHandling, PossibleError* possibleError = nullptr,
+                    InvokedPrediction invoked = PredictUninvoked);
+    Node assignExprWithoutYieldOrAwait(YieldHandling yieldHandling);
+    Node yieldExpression(InHandling inHandling);
+    Node condExpr1(InHandling inHandling, YieldHandling yieldHandling,
+                   TripledotHandling tripledotHandling,
+                   PossibleError* possibleError,
+                   InvokedPrediction invoked = PredictUninvoked);
+    Node orExpr1(InHandling inHandling, YieldHandling yieldHandling,
+                 TripledotHandling tripledotHandling,
+                 PossibleError* possibleError,
+                 InvokedPrediction invoked = PredictUninvoked);
+    Node unaryExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                   PossibleError* possibleError = nullptr,
+                   InvokedPrediction invoked = PredictUninvoked);
+    Node memberExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                    TokenKind tt, bool allowCallSyntax = true,
+                    PossibleError* possibleError = nullptr,
+                    InvokedPrediction invoked = PredictUninvoked);
+    Node primaryExpr(YieldHandling yieldHandling, TripledotHandling tripledotHandling,
+                     TokenKind tt, PossibleError* possibleError,
+                     InvokedPrediction invoked = PredictUninvoked);
+    Node exprInParens(InHandling inHandling, YieldHandling yieldHandling,
+                      TripledotHandling tripledotHandling, PossibleError* possibleError = nullptr);
+
+    bool tryNewTarget(Node& newTarget);
+    bool checkAndMarkSuperScope();
+
+    Node methodDefinition(PropertyType propType, HandleAtom funName);
+
+    /*
+     * Additional JS parsers.
+     */
+    bool functionArguments(YieldHandling yieldHandling, FunctionSyntaxKind kind,
+                           Node funcpn);
+
+    Node functionDefinition(InHandling inHandling, YieldHandling yieldHandling, HandleAtom name,
+                            FunctionSyntaxKind kind,
+                            GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                            InvokedPrediction invoked = PredictUninvoked);
+
+    // Parse a function body.  Pass StatementListBody if the body is a list of
+    // statements; pass ExpressionBody if the body is a single expression.
+    enum FunctionBodyType { StatementListBody, ExpressionBody };
+    Node functionBody(InHandling inHandling, YieldHandling yieldHandling, FunctionSyntaxKind kind,
+                      FunctionBodyType type);
+
+    Node unaryOpExpr(YieldHandling yieldHandling, ParseNodeKind kind, JSOp op, uint32_t begin);
+
+    Node condition(InHandling inHandling, YieldHandling yieldHandling);
+
+    /* comprehensions */
+    Node generatorComprehensionLambda(unsigned begin);
+    Node comprehensionFor(GeneratorKind comprehensionKind);
+    Node comprehensionIf(GeneratorKind comprehensionKind);
+    Node comprehensionTail(GeneratorKind comprehensionKind);
+    Node comprehension(GeneratorKind comprehensionKind);
+    Node arrayComprehension(uint32_t begin);
+    Node generatorComprehension(uint32_t begin);
+
+    bool argumentList(YieldHandling yieldHandling, Node listNode, bool* isSpread,
+                      PossibleError* possibleError = nullptr);
+    Node destructuringDeclaration(DeclarationKind kind, YieldHandling yieldHandling,
+                                  TokenKind tt);
+    Node destructuringDeclarationWithoutYieldOrAwait(DeclarationKind kind, YieldHandling yieldHandling,
+                                                     TokenKind tt);
+
+    bool namedImportsOrNamespaceImport(TokenKind tt, Node importSpecSet);
+    bool checkExportedName(JSAtom* exportName);
+    bool checkExportedNamesForDeclaration(Node node);
+
+    enum ClassContext { ClassStatement, ClassExpression };
+    Node classDefinition(YieldHandling yieldHandling, ClassContext classContext,
+                         DefaultHandling defaultHandling);
+
+    PropertyName* labelOrIdentifierReference(YieldHandling yieldHandling,
+                                             bool yieldTokenizedAsName);
+
+    PropertyName* labelIdentifier(YieldHandling yieldHandling) {
+        return labelOrIdentifierReference(yieldHandling, false);
+    }
+
+    PropertyName* identifierReference(YieldHandling yieldHandling,
+                                      bool yieldTokenizedAsName = false)
+    {
+        return labelOrIdentifierReference(yieldHandling, yieldTokenizedAsName);
+    }
+
+    PropertyName* importedBinding() {
+        return bindingIdentifier(YieldIsName);
+    }
+
+    Node identifierReference(Handle<PropertyName*> name);
+
+    bool matchLabel(YieldHandling yieldHandling, MutableHandle<PropertyName*> label);
+
+    bool allowsForEachIn() {
+#if !JS_HAS_FOR_EACH_IN
+        return false;
+#else
+        return versionNumber() >= JSVERSION_1_6;
+#endif
+    }
+
+    enum AssignmentFlavor {
+        PlainAssignment,
+        CompoundAssignment,
+        KeyedDestructuringAssignment,
+        IncrementAssignment,
+        DecrementAssignment,
+        ForInOrOfTarget
+    };
+
+    bool checkAndMarkAsAssignmentLhs(Node pn, AssignmentFlavor flavor,
+                                     PossibleError* possibleError=nullptr);
+    bool matchInOrOf(bool* isForInp, bool* isForOfp);
+
+    bool hasUsedFunctionSpecialName(HandlePropertyName name);
+    bool declareFunctionArgumentsObject();
+    bool declareFunctionThis();
+    Node newInternalDotName(HandlePropertyName name);
+    Node newThisName();
+    Node newDotGeneratorName();
+    bool declareDotGeneratorName();
+
+    bool checkFunctionDefinition(HandleAtom funAtom, Node pn, FunctionSyntaxKind kind,
+                                 GeneratorKind generatorKind, bool* tryAnnexB);
+    bool skipLazyInnerFunction(Node pn, FunctionSyntaxKind kind, bool tryAnnexB);
+    bool innerFunction(Node pn, ParseContext* outerpc, HandleFunction fun,
+                       InHandling inHandling, YieldHandling yieldHandling,
+                       FunctionSyntaxKind kind,
+                       GeneratorKind generatorKind, FunctionAsyncKind asyncKind, bool tryAnnexB,
+                       Directives inheritedDirectives, Directives* newDirectives);
+    bool trySyntaxParseInnerFunction(Node pn, HandleFunction fun, InHandling inHandling,
+                                     YieldHandling yieldHandling, FunctionSyntaxKind kind,
+                                     GeneratorKind generatorKind, FunctionAsyncKind asyncKind,
+                                     bool tryAnnexB,
+                                     Directives inheritedDirectives, Directives* newDirectives);
+    bool finishFunctionScopes();
+    bool finishFunction();
+    bool leaveInnerFunction(ParseContext* outerpc);
+
+  public:
+    enum FunctionCallBehavior {
+        PermitAssignmentToFunctionCalls,
+        ForbidAssignmentToFunctionCalls
+    };
+
+    bool isValidSimpleAssignmentTarget(Node node,
+                                       FunctionCallBehavior behavior = ForbidAssignmentToFunctionCalls);
+
+  private:
+    bool reportIfArgumentsEvalTarget(Node nameNode);
+    bool reportIfNotValidSimpleAssignmentTarget(Node target, AssignmentFlavor flavor);
+
+    bool checkAndMarkAsIncOperand(Node kid, AssignmentFlavor flavor);
+    bool checkStrictAssignment(Node lhs);
+    bool checkStrictBinding(PropertyName* name, TokenPos pos);
+
+    bool hasValidSimpleStrictParameterNames();
+
+    bool isValidStrictBinding(PropertyName* name);
+
+    void reportRedeclaration(HandlePropertyName name, DeclarationKind kind, TokenPos pos);
+    bool notePositionalFormalParameter(Node fn, HandlePropertyName name,
+                                       bool disallowDuplicateParams, bool* duplicatedParam);
+    bool noteDestructuredPositionalFormalParameter(Node fn, Node destruct);
+    mozilla::Maybe<DeclarationKind> isVarRedeclaredInEval(HandlePropertyName name,
+                                                          DeclarationKind kind);
+    bool tryDeclareVar(HandlePropertyName name, DeclarationKind kind,
+                       mozilla::Maybe<DeclarationKind>* redeclaredKind);
+    bool tryDeclareVarForAnnexBLexicalFunction(HandlePropertyName name, bool* tryAnnexB);
+    bool checkLexicalDeclarationDirectlyWithinBlock(ParseContext::Statement& stmt,
+                                                    DeclarationKind kind, TokenPos pos);
+    bool noteDeclaredName(HandlePropertyName name, DeclarationKind kind, TokenPos pos);
+    bool noteUsedName(HandlePropertyName name);
+    bool hasUsedName(HandlePropertyName name);
+
+    // Required on Scope exit.
+    bool propagateFreeNamesAndMarkClosedOverBindings(ParseContext::Scope& scope);
+
+    mozilla::Maybe<GlobalScope::Data*> newGlobalScopeData(ParseContext::Scope& scope);
+    mozilla::Maybe<ModuleScope::Data*> newModuleScopeData(ParseContext::Scope& scope);
+    mozilla::Maybe<EvalScope::Data*> newEvalScopeData(ParseContext::Scope& scope);
+    mozilla::Maybe<FunctionScope::Data*> newFunctionScopeData(ParseContext::Scope& scope,
+                                                              bool hasParameterExprs);
+    mozilla::Maybe<VarScope::Data*> newVarScopeData(ParseContext::Scope& scope);
+    mozilla::Maybe<LexicalScope::Data*> newLexicalScopeData(ParseContext::Scope& scope);
+    Node finishLexicalScope(ParseContext::Scope& scope, Node body);
+
+    Node propertyName(YieldHandling yieldHandling, Node propList,
+                      PropertyType* propType, MutableHandleAtom propAtom);
+    Node computedPropertyName(YieldHandling yieldHandling, Node literal);
+    Node arrayInitializer(YieldHandling yieldHandling, PossibleError* possibleError);
+    Node newRegExp();
+
+    Node objectLiteral(YieldHandling yieldHandling, PossibleError* possibleError);
+
+    // Top-level entrypoint into destructuring pattern checking/name-analyzing.
+    bool checkDestructuringPattern(Node pattern, mozilla::Maybe<DeclarationKind> maybeDecl,
+                                   PossibleError* possibleError = nullptr);
+
+    // Recursive methods for checking/name-analyzing subcomponents of a
+    // destructuring pattern.  The array/object methods *must* be passed arrays
+    // or objects.  The name method may be passed anything but will report an
+    // error if not passed a name.
+    bool checkDestructuringArray(Node arrayPattern, mozilla::Maybe<DeclarationKind> maybeDecl);
+    bool checkDestructuringObject(Node objectPattern, mozilla::Maybe<DeclarationKind> maybeDecl);
+    bool checkDestructuringName(Node expr, mozilla::Maybe<DeclarationKind> maybeDecl);
+
+    bool checkAssignmentToCall(Node node, unsigned errnum);
+
+    Node newNumber(const Token& tok) {
+        return handler.newNumber(tok.number(), tok.decimalPoint(), tok.pos);
+    }
+
+    static Node null() { return ParseHandler::null(); }
+
+    bool reportBadReturn(Node pn, ParseReportKind kind, unsigned errnum, unsigned anonerrnum);
+
+    JSAtom* prefixAccessorName(PropertyType propType, HandleAtom propAtom);
+
+    TokenPos pos() const { return tokenStream.currentToken().pos; }
+
+    bool asmJS(Node list);
+
+    void addTelemetry(JSCompartment::DeprecatedLanguageExtension e);
+
+    bool warnOnceAboutExprClosure();
+    bool warnOnceAboutForEach();
+};
+
+} /* namespace frontend */
+} /* namespace js */
+
+#endif /* frontend_Parser_h */
diff --git a/js/src/frontend/SharedContext.h b/js/src/frontend/SharedContext.h
new file mode 100644
index 0000000000..39df47c20a
--- /dev/null
+++ b/js/src/frontend/SharedContext.h
@@ -0,0 +1,639 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_SharedContext_h
+#define frontend_SharedContext_h
+
+#include "jsatom.h"
+#include "jsopcode.h"
+#include "jspubtd.h"
+#include "jsscript.h"
+#include "jstypes.h"
+
+#include "builtin/ModuleObject.h"
+#include "ds/InlineTable.h"
+#include "frontend/ParseNode.h"
+#include "frontend/TokenStream.h"
+#include "vm/EnvironmentObject.h"
+
+namespace js {
+namespace frontend {
+
+enum class StatementKind : uint8_t
+{
+    Label,
+    Block,
+    If,
+    Switch,
+    With,
+    Catch,
+    Try,
+    Finally,
+    ForLoopLexicalHead,
+    ForLoop,
+    ForInLoop,
+    ForOfLoop,
+    DoLoop,
+    WhileLoop,
+
+    // Used only by BytecodeEmitter.
+    Spread
+};
+
+static inline bool
+StatementKindIsLoop(StatementKind kind)
+{
+    return kind == StatementKind::ForLoop ||
+           kind == StatementKind::ForInLoop ||
+           kind == StatementKind::ForOfLoop ||
+           kind == StatementKind::DoLoop ||
+           kind == StatementKind::WhileLoop ||
+           kind == StatementKind::Spread;
+}
+
+static inline bool
+StatementKindIsUnlabeledBreakTarget(StatementKind kind)
+{
+    return StatementKindIsLoop(kind) || kind == StatementKind::Switch;
+}
+
+// A base class for nestable structures in the frontend, such as statements
+// and scopes.
+template <typename Concrete>
+class MOZ_STACK_CLASS Nestable
+{
+    Concrete** stack_;
+    Concrete*  enclosing_;
+
+  protected:
+    explicit Nestable(Concrete** stack)
+      : stack_(stack),
+        enclosing_(*stack)
+    {
+        *stack_ = static_cast<Concrete*>(this);
+    }
+
+    // These method are protected. Some derived classes, such as ParseContext,
+    // do not expose the ability to walk the stack.
+    Concrete* enclosing() const {
+        return enclosing_;
+    }
+
+    template <typename Predicate /* (Concrete*) -> bool */>
+    static Concrete* findNearest(Concrete* it, Predicate predicate) {
+        while (it && !predicate(it))
+            it = it->enclosing();
+        return it;
+    }
+
+    template <typename T>
+    static T* findNearest(Concrete* it) {
+        while (it && !it->template is<T>())
+            it = it->enclosing();
+        return it ? &it->template as<T>() : nullptr;
+    }
+
+    template <typename T, typename Predicate /* (T*) -> bool */>
+    static T* findNearest(Concrete* it, Predicate predicate) {
+        while (it && (!it->template is<T>() || !predicate(&it->template as<T>())))
+            it = it->enclosing();
+        return it ? &it->template as<T>() : nullptr;
+    }
+
+  public:
+    ~Nestable() {
+        MOZ_ASSERT(*stack_ == static_cast<Concrete*>(this));
+        *stack_ = enclosing_;
+    }
+};
+
+// These flags apply to both global and function contexts.
+class AnyContextFlags
+{
+    // This class's data is all private and so only visible to these friends.
+    friend class SharedContext;
+
+    // True if "use strict"; appears in the body instead of being inherited.
+    bool hasExplicitUseStrict:1;
+
+    // The (static) bindings of this script need to support dynamic name
+    // read/write access. Here, 'dynamic' means dynamic dictionary lookup on
+    // the scope chain for a dynamic set of keys. The primary examples are:
+    //  - direct eval
+    //  - function::
+    //  - with
+    // since both effectively allow any name to be accessed. Non-examples are:
+    //  - upvars of nested functions
+    //  - function statement
+    // since the set of assigned name is known dynamically.
+    //
+    // Note: access through the arguments object is not considered dynamic
+    // binding access since it does not go through the normal name lookup
+    // mechanism. This is debatable and could be changed (although care must be
+    // taken not to turn off the whole 'arguments' optimization). To answer the
+    // more general "is this argument aliased" question, script->needsArgsObj
+    // should be tested (see JSScript::argIsAliased).
+    bool bindingsAccessedDynamically:1;
+
+    // Whether this script, or any of its inner scripts contains a debugger
+    // statement which could potentially read or write anywhere along the
+    // scope chain.
+    bool hasDebuggerStatement:1;
+
+    // A direct eval occurs in the body of the script.
+    bool hasDirectEval:1;
+
+  public:
+    AnyContextFlags()
+     :  hasExplicitUseStrict(false),
+        bindingsAccessedDynamically(false),
+        hasDebuggerStatement(false),
+        hasDirectEval(false)
+    { }
+};
+
+class FunctionContextFlags
+{
+    // This class's data is all private and so only visible to these friends.
+    friend class FunctionBox;
+
+    // This function does something that can extend the set of bindings in its
+    // call objects --- it does a direct eval in non-strict code, or includes a
+    // function statement (as opposed to a function definition).
+    //
+    // This flag is *not* inherited by enclosed or enclosing functions; it
+    // applies only to the function in whose flags it appears.
+    //
+    bool hasExtensibleScope:1;
+
+    // Technically, every function has a binding named 'arguments'. Internally,
+    // this binding is only added when 'arguments' is mentioned by the function
+    // body. This flag indicates whether 'arguments' has been bound either
+    // through implicit use:
+    //   function f() { return arguments }
+    // or explicit redeclaration:
+    //   function f() { var arguments; return arguments }
+    //
+    // Note 1: overwritten arguments (function() { arguments = 3 }) will cause
+    // this flag to be set but otherwise require no special handling:
+    // 'arguments' is just a local variable and uses of 'arguments' will just
+    // read the local's current slot which may have been assigned. The only
+    // special semantics is that the initial value of 'arguments' is the
+    // arguments object (not undefined, like normal locals).
+    //
+    // Note 2: if 'arguments' is bound as a formal parameter, there will be an
+    // 'arguments' in Bindings, but, as the "LOCAL" in the name indicates, this
+    // flag will not be set. This is because, as a formal, 'arguments' will
+    // have no special semantics: the initial value is unconditionally the
+    // actual argument (or undefined if nactual < nformal).
+    //
+    bool argumentsHasLocalBinding:1;
+
+    // In many cases where 'arguments' has a local binding (as described above)
+    // we do not need to actually create an arguments object in the function
+    // prologue: instead we can analyze how 'arguments' is used (using the
+    // simple dataflow analysis in analyzeSSA) to determine that uses of
+    // 'arguments' can just read from the stack frame directly. However, the
+    // dataflow analysis only looks at how JSOP_ARGUMENTS is used, so it will
+    // be unsound in several cases. The frontend filters out such cases by
+    // setting this flag which eagerly sets script->needsArgsObj to true.
+    //
+    bool definitelyNeedsArgsObj:1;
+
+    bool needsHomeObject:1;
+    bool isDerivedClassConstructor:1;
+
+    // Whether this function has a .this binding. If true, we need to emit
+    // JSOP_FUNCTIONTHIS in the prologue to initialize it.
+    bool hasThisBinding:1;
+
+    // Whether this function has nested functions.
+    bool hasInnerFunctions:1;
+
+  public:
+    FunctionContextFlags()
+     :  hasExtensibleScope(false),
+        argumentsHasLocalBinding(false),
+        definitelyNeedsArgsObj(false),
+        needsHomeObject(false),
+        isDerivedClassConstructor(false),
+        hasThisBinding(false),
+        hasInnerFunctions(false)
+    { }
+};
+
+// List of directives that may be encountered in a Directive Prologue (ES5 15.1).
+class Directives
+{
+    bool strict_;
+    bool asmJS_;
+
+  public:
+    explicit Directives(bool strict) : strict_(strict), asmJS_(false) {}
+    explicit Directives(ParseContext* parent);
+
+    void setStrict() { strict_ = true; }
+    bool strict() const { return strict_; }
+
+    void setAsmJS() { asmJS_ = true; }
+    bool asmJS() const { return asmJS_; }
+
+    Directives& operator=(Directives rhs) {
+        strict_ = rhs.strict_;
+        asmJS_ = rhs.asmJS_;
+        return *this;
+    }
+    bool operator==(const Directives& rhs) const {
+        return strict_ == rhs.strict_ && asmJS_ == rhs.asmJS_;
+    }
+    bool operator!=(const Directives& rhs) const {
+        return !(*this == rhs);
+    }
+};
+
+// The kind of this-binding for the current scope. Note that arrow functions
+// (and generator expression lambdas) have a lexical this-binding so their
+// ThisBinding is the same as the ThisBinding of their enclosing scope and can
+// be any value.
+enum class ThisBinding { Global, Function, Module };
+
+class GlobalSharedContext;
+class EvalSharedContext;
+class ModuleSharedContext;
+
+/*
+ * The struct SharedContext is part of the current parser context (see
+ * ParseContext). It stores information that is reused between the parser and
+ * the bytecode emitter.
+ */
+class SharedContext
+{
+  public:
+    ExclusiveContext* const context;
+    AnyContextFlags anyCxFlags;
+    bool strictScript;
+    bool localStrict;
+    bool extraWarnings;
+
+  protected:
+    enum class Kind {
+        ObjectBox,
+        Global,
+        Eval,
+        Module
+    };
+
+    Kind kind_;
+
+    ThisBinding thisBinding_;
+
+    bool allowNewTarget_;
+    bool allowSuperProperty_;
+    bool allowSuperCall_;
+    bool inWith_;
+    bool needsThisTDZChecks_;
+
+    void computeAllowSyntax(Scope* scope);
+    void computeInWith(Scope* scope);
+    void computeThisBinding(Scope* scope);
+
+  public:
+    SharedContext(ExclusiveContext* cx, Kind kind, Directives directives, bool extraWarnings)
+      : context(cx),
+        anyCxFlags(),
+        strictScript(directives.strict()),
+        localStrict(false),
+        extraWarnings(extraWarnings),
+        kind_(kind),
+        thisBinding_(ThisBinding::Global),
+        allowNewTarget_(false),
+        allowSuperProperty_(false),
+        allowSuperCall_(false),
+        inWith_(false),
+        needsThisTDZChecks_(false)
+    { }
+
+    // If this is the outermost SharedContext, the Scope that encloses
+    // it. Otherwise nullptr.
+    virtual Scope* compilationEnclosingScope() const = 0;
+
+    virtual ObjectBox* toObjectBox() { return nullptr; }
+    bool isObjectBox() { return toObjectBox(); }
+    bool isFunctionBox() { return isObjectBox() && toObjectBox()->isFunctionBox(); }
+    inline FunctionBox* asFunctionBox();
+    bool isModuleContext() { return kind_ == Kind::Module; }
+    inline ModuleSharedContext* asModuleContext();
+    bool isGlobalContext() { return kind_ == Kind::Global; }
+    inline GlobalSharedContext* asGlobalContext();
+    bool isEvalContext() { return kind_ == Kind::Eval; }
+    inline EvalSharedContext* asEvalContext();
+
+    ThisBinding thisBinding()          const { return thisBinding_; }
+
+    bool allowNewTarget()              const { return allowNewTarget_; }
+    bool allowSuperProperty()          const { return allowSuperProperty_; }
+    bool allowSuperCall()              const { return allowSuperCall_; }
+    bool inWith()                      const { return inWith_; }
+    bool needsThisTDZChecks()          const { return needsThisTDZChecks_; }
+
+    bool hasExplicitUseStrict()        const { return anyCxFlags.hasExplicitUseStrict; }
+    bool bindingsAccessedDynamically() const { return anyCxFlags.bindingsAccessedDynamically; }
+    bool hasDebuggerStatement()        const { return anyCxFlags.hasDebuggerStatement; }
+    bool hasDirectEval()               const { return anyCxFlags.hasDirectEval; }
+
+    void setExplicitUseStrict()           { anyCxFlags.hasExplicitUseStrict        = true; }
+    void setBindingsAccessedDynamically() { anyCxFlags.bindingsAccessedDynamically = true; }
+    void setHasDebuggerStatement()        { anyCxFlags.hasDebuggerStatement        = true; }
+    void setHasDirectEval()               { anyCxFlags.hasDirectEval               = true; }
+
+    inline bool allBindingsClosedOver();
+
+    bool strict() const {
+        return strictScript || localStrict;
+    }
+    bool setLocalStrictMode(bool strict) {
+        bool retVal = localStrict;
+        localStrict = strict;
+        return retVal;
+    }
+
+    // JSOPTION_EXTRA_WARNINGS warnings or strict mode errors.
+    bool needStrictChecks() const {
+        return strict() || extraWarnings;
+    }
+
+    bool isDotVariable(JSAtom* atom) const {
+        return atom == context->names().dotGenerator || atom == context->names().dotThis;
+    }
+};
+
+class MOZ_STACK_CLASS GlobalSharedContext : public SharedContext
+{
+    ScopeKind scopeKind_;
+
+  public:
+    Rooted<GlobalScope::Data*> bindings;
+
+    GlobalSharedContext(ExclusiveContext* cx, ScopeKind scopeKind, Directives directives,
+                        bool extraWarnings)
+      : SharedContext(cx, Kind::Global, directives, extraWarnings),
+        scopeKind_(scopeKind),
+        bindings(cx)
+    {
+        MOZ_ASSERT(scopeKind == ScopeKind::Global || scopeKind == ScopeKind::NonSyntactic);
+        thisBinding_ = ThisBinding::Global;
+    }
+
+    Scope* compilationEnclosingScope() const override {
+        return nullptr;
+    }
+
+    ScopeKind scopeKind() const {
+        return scopeKind_;
+    }
+};
+
+inline GlobalSharedContext*
+SharedContext::asGlobalContext()
+{
+    MOZ_ASSERT(isGlobalContext());
+    return static_cast<GlobalSharedContext*>(this);
+}
+
+class MOZ_STACK_CLASS EvalSharedContext : public SharedContext
+{
+    RootedScope enclosingScope_;
+
+  public:
+    Rooted<EvalScope::Data*> bindings;
+
+    EvalSharedContext(ExclusiveContext* cx, JSObject* enclosingEnv, Scope* enclosingScope,
+                      Directives directives, bool extraWarnings);
+
+    Scope* compilationEnclosingScope() const override {
+        return enclosingScope_;
+    }
+};
+
+inline EvalSharedContext*
+SharedContext::asEvalContext()
+{
+    MOZ_ASSERT(isEvalContext());
+    return static_cast<EvalSharedContext*>(this);
+}
+
+class FunctionBox : public ObjectBox, public SharedContext
+{
+    // The parser handles tracing the fields below via the ObjectBox linked
+    // list.
+
+    Scope* enclosingScope_;
+
+    // Names from the named lambda scope, if a named lambda.
+    LexicalScope::Data* namedLambdaBindings_;
+
+    // Names from the function scope.
+    FunctionScope::Data* functionScopeBindings_;
+
+    // Names from the extra 'var' scope of the function, if the parameter list
+    // has expressions.
+    VarScope::Data* extraVarScopeBindings_;
+
+    void initWithEnclosingScope(Scope* enclosingScope);
+
+  public:
+    ParseNode*      functionNode;           /* back pointer used by asm.js for error messages */
+    uint32_t        bufStart;
+    uint32_t        bufEnd;
+    uint32_t        startLine;
+    uint32_t        startColumn;
+    uint16_t        length;
+
+    uint8_t         generatorKindBits_;     /* The GeneratorKind of this function. */
+    uint8_t         asyncKindBits_;         /* The FunctionAsyncKing of this function. */
+
+    bool            isGenexpLambda:1;       /* lambda from generator expression */
+    bool            hasDestructuringArgs:1; /* parameter list contains destructuring expression */
+    bool            hasParameterExprs:1;    /* parameter list contains expressions */
+    bool            hasDirectEvalInParameterExpr:1; /* parameter list contains direct eval */
+    bool            hasDuplicateParameters:1; /* parameter list contains duplicate names */
+    bool            useAsm:1;               /* see useAsmOrInsideUseAsm */
+    bool            insideUseAsm:1;         /* see useAsmOrInsideUseAsm */
+    bool            isAnnexB:1;             /* need to emit a synthesized Annex B assignment */
+    bool            wasEmitted:1;           /* Bytecode has been emitted for this function. */
+
+    // Fields for use in heuristics.
+    bool            declaredArguments:1;    /* the Parser declared 'arguments' */
+    bool            usesArguments:1;        /* contains a free use of 'arguments' */
+    bool            usesApply:1;            /* contains an f.apply() call */
+    bool            usesThis:1;             /* contains 'this' */
+    bool            usesReturn:1;           /* contains a 'return' statement */
+
+    FunctionContextFlags funCxFlags;
+
+    FunctionBox(ExclusiveContext* cx, LifoAlloc& alloc, ObjectBox* traceListHead, JSFunction* fun,
+                Directives directives, bool extraWarnings, GeneratorKind generatorKind,
+                FunctionAsyncKind asyncKind);
+
+    MutableHandle<LexicalScope::Data*> namedLambdaBindings() {
+        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
+        return MutableHandle<LexicalScope::Data*>::fromMarkedLocation(&namedLambdaBindings_);
+    }
+
+    MutableHandle<FunctionScope::Data*> functionScopeBindings() {
+        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
+        return MutableHandle<FunctionScope::Data*>::fromMarkedLocation(&functionScopeBindings_);
+    }
+
+    MutableHandle<VarScope::Data*> extraVarScopeBindings() {
+        MOZ_ASSERT(context->compartment()->runtimeFromAnyThread()->keepAtoms());
+        return MutableHandle<VarScope::Data*>::fromMarkedLocation(&extraVarScopeBindings_);
+    }
+
+    void initFromLazyFunction();
+    void initStandaloneFunction(Scope* enclosingScope);
+    void initWithEnclosingParseContext(ParseContext* enclosing, FunctionSyntaxKind kind);
+
+    ObjectBox* toObjectBox() override { return this; }
+    JSFunction* function() const { return &object->as<JSFunction>(); }
+
+    Scope* compilationEnclosingScope() const override {
+        // This method is used to distinguish the outermost SharedContext. If
+        // a FunctionBox is the outermost SharedContext, it must be a lazy
+        // function.
+        MOZ_ASSERT_IF(function()->isInterpretedLazy(),
+                      enclosingScope_ == function()->lazyScript()->enclosingScope());
+        return enclosingScope_;
+    }
+
+    bool needsCallObjectRegardlessOfBindings() const {
+        return hasExtensibleScope() ||
+               needsHomeObject() ||
+               isDerivedClassConstructor() ||
+               isGenerator();
+    }
+
+    bool hasExtraBodyVarScope() const {
+        return hasParameterExprs &&
+               (extraVarScopeBindings_ ||
+                needsExtraBodyVarEnvironmentRegardlessOfBindings());
+    }
+
+    bool needsExtraBodyVarEnvironmentRegardlessOfBindings() const {
+        MOZ_ASSERT(hasParameterExprs);
+        return hasExtensibleScope() || isGenerator();
+    }
+
+    bool isLikelyConstructorWrapper() const {
+        return usesArguments && usesApply && usesThis && !usesReturn;
+    }
+
+    GeneratorKind generatorKind() const { return GeneratorKindFromBits(generatorKindBits_); }
+    bool isGenerator() const { return generatorKind() != NotGenerator; }
+    bool isLegacyGenerator() const { return generatorKind() == LegacyGenerator; }
+    bool isStarGenerator() const { return generatorKind() == StarGenerator; }
+    FunctionAsyncKind asyncKind() const { return AsyncKindFromBits(asyncKindBits_); }
+    bool isAsync() const { return asyncKind() == AsyncFunction; }
+    bool isArrow() const { return function()->isArrow(); }
+
+    void setGeneratorKind(GeneratorKind kind) {
+        // A generator kind can be set at initialization, or when "yield" is
+        // first seen.  In both cases the transition can only happen from
+        // NotGenerator.
+        MOZ_ASSERT(!isGenerator());
+        generatorKindBits_ = GeneratorKindAsBits(kind);
+    }
+
+    bool hasExtensibleScope()        const { return funCxFlags.hasExtensibleScope; }
+    bool hasThisBinding()            const { return funCxFlags.hasThisBinding; }
+    bool argumentsHasLocalBinding()  const { return funCxFlags.argumentsHasLocalBinding; }
+    bool definitelyNeedsArgsObj()    const { return funCxFlags.definitelyNeedsArgsObj; }
+    bool needsHomeObject()           const { return funCxFlags.needsHomeObject; }
+    bool isDerivedClassConstructor() const { return funCxFlags.isDerivedClassConstructor; }
+    bool hasInnerFunctions()         const { return funCxFlags.hasInnerFunctions; }
+
+    void setHasExtensibleScope()           { funCxFlags.hasExtensibleScope       = true; }
+    void setHasThisBinding()               { funCxFlags.hasThisBinding           = true; }
+    void setArgumentsHasLocalBinding()     { funCxFlags.argumentsHasLocalBinding = true; }
+    void setDefinitelyNeedsArgsObj()       { MOZ_ASSERT(funCxFlags.argumentsHasLocalBinding);
+                                             funCxFlags.definitelyNeedsArgsObj   = true; }
+    void setNeedsHomeObject()              { MOZ_ASSERT(function()->allowSuperProperty());
+                                             funCxFlags.needsHomeObject          = true; }
+    void setDerivedClassConstructor()      { MOZ_ASSERT(function()->isClassConstructor());
+                                             funCxFlags.isDerivedClassConstructor = true; }
+    void setHasInnerFunctions()            { funCxFlags.hasInnerFunctions         = true; }
+
+    bool hasSimpleParameterList() const {
+        return !function()->hasRest() && !hasParameterExprs && !hasDestructuringArgs;
+    }
+
+    bool hasMappedArgsObj() const {
+        return !strict() && hasSimpleParameterList();
+    }
+
+    // Return whether this or an enclosing function is being parsed and
+    // validated as asm.js. Note: if asm.js validation fails, this will be false
+    // while the function is being reparsed. This flag can be used to disable
+    // certain parsing features that are necessary in general, but unnecessary
+    // for validated asm.js.
+    bool useAsmOrInsideUseAsm() const {
+        return useAsm || insideUseAsm;
+    }
+
+    void setStart(const TokenStream& tokenStream) {
+        bufStart = tokenStream.currentToken().pos.begin;
+        tokenStream.srcCoords.lineNumAndColumnIndex(bufStart, &startLine, &startColumn);
+    }
+
+    void trace(JSTracer* trc) override;
+};
+
+inline FunctionBox*
+SharedContext::asFunctionBox()
+{
+    MOZ_ASSERT(isFunctionBox());
+    return static_cast<FunctionBox*>(this);
+}
+
+class MOZ_STACK_CLASS ModuleSharedContext : public SharedContext
+{
+    RootedModuleObject module_;
+    RootedScope enclosingScope_;
+
+  public:
+    Rooted<ModuleScope::Data*> bindings;
+    ModuleBuilder& builder;
+
+    ModuleSharedContext(ExclusiveContext* cx, ModuleObject* module, Scope* enclosingScope,
+                        ModuleBuilder& builder);
+
+    HandleModuleObject module() const { return module_; }
+    Scope* compilationEnclosingScope() const override { return enclosingScope_; }
+};
+
+inline ModuleSharedContext*
+SharedContext::asModuleContext()
+{
+    MOZ_ASSERT(isModuleContext());
+    return static_cast<ModuleSharedContext*>(this);
+}
+
+// In generators, we treat all bindings as closed so that they get stored on
+// the heap.  This way there is less information to copy off the stack when
+// suspending, and back on when resuming.  It also avoids the need to create
+// and invalidate DebugScope proxies for unaliased locals in a generator
+// frame, as the generator frame will be copied out to the heap and released
+// only by GC.
+inline bool
+SharedContext::allBindingsClosedOver()
+{
+    return bindingsAccessedDynamically() || (isFunctionBox() && asFunctionBox()->isGenerator());
+}
+
+} // namespace frontend
+} // namespace js
+
+#endif /* frontend_SharedContext_h */
diff --git a/js/src/frontend/SourceNotes.h b/js/src/frontend/SourceNotes.h
new file mode 100644
index 0000000000..dd2a95ad1e
--- /dev/null
+++ b/js/src/frontend/SourceNotes.h
@@ -0,0 +1,207 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_SourceNotes_h
+#define frontend_SourceNotes_h
+
+#include <stdint.h>
+
+#include "jstypes.h"
+
+typedef uint8_t jssrcnote;
+
+namespace js {
+
+/*
+ * Source notes generated along with bytecode for decompiling and debugging.
+ * A source note is a uint8_t with 5 bits of type and 3 of offset from the pc
+ * of the previous note. If 3 bits of offset aren't enough, extended delta
+ * notes (SRC_XDELTA) consisting of 2 set high order bits followed by 6 offset
+ * bits are emitted before the next note. Some notes have operand offsets
+ * encoded immediately after them, in note bytes or byte-triples.
+ *
+ *                 Source Note               Extended Delta
+ *              +7-6-5-4-3+2-1-0+           +7-6-5+4-3-2-1-0+
+ *              |note-type|delta|           |1 1| ext-delta |
+ *              +---------+-----+           +---+-----------+
+ *
+ * At most one "gettable" note (i.e., a note of type other than SRC_NEWLINE,
+ * SRC_COLSPAN, SRC_SETLINE, and SRC_XDELTA) applies to a given bytecode.
+ *
+ * NB: the js_SrcNoteSpec array in BytecodeEmitter.cpp is indexed by this
+ * enum, so its initializers need to match the order here.
+ */
+#define FOR_EACH_SRC_NOTE_TYPE(M)                                                                  \
+    M(SRC_NULL,         "null",        0)  /* Terminates a note vector. */                         \
+    M(SRC_IF,           "if",          0)  /* JSOP_IFEQ bytecode is from an if-then. */            \
+    M(SRC_IF_ELSE,      "if-else",     1)  /* JSOP_IFEQ bytecode is from an if-then-else. */       \
+    M(SRC_COND,         "cond",        1)  /* JSOP_IFEQ is from conditional ?: operator. */        \
+    M(SRC_FOR,          "for",         3)  /* JSOP_NOP or JSOP_POP in for(;;) loop head. */        \
+    M(SRC_WHILE,        "while",       1)  /* JSOP_GOTO to for or while loop condition from before \
+                                              loop, else JSOP_NOP at top of do-while loop. */      \
+    M(SRC_FOR_IN,       "for-in",      1)  /* JSOP_GOTO to for-in loop condition from before       \
+                                              loop. */                                             \
+    M(SRC_FOR_OF,       "for-of",      1)  /* JSOP_GOTO to for-of loop condition from before       \
+                                              loop. */                                             \
+    M(SRC_CONTINUE,     "continue",    0)  /* JSOP_GOTO is a continue. */                          \
+    M(SRC_BREAK,        "break",       0)  /* JSOP_GOTO is a break. */                             \
+    M(SRC_BREAK2LABEL,  "break2label", 0)  /* JSOP_GOTO for 'break label'. */                      \
+    M(SRC_SWITCHBREAK,  "switchbreak", 0)  /* JSOP_GOTO is a break in a switch. */                 \
+    M(SRC_TABLESWITCH,  "tableswitch", 1)  /* JSOP_TABLESWITCH; offset points to end of switch. */ \
+    M(SRC_CONDSWITCH,   "condswitch",  2)  /* JSOP_CONDSWITCH; 1st offset points to end of switch, \
+                                              2nd points to first JSOP_CASE. */                    \
+    M(SRC_NEXTCASE,     "nextcase",    1)  /* Distance forward from one CASE in a CONDSWITCH to    \
+                                              the next. */                                         \
+    M(SRC_ASSIGNOP,     "assignop",    0)  /* += or another assign-op follows. */                  \
+    M(SRC_TRY,          "try",         1)  /* JSOP_TRY, offset points to goto at the end of the    \
+                                              try block. */                                        \
+    /* All notes above here are "gettable".  See SN_IS_GETTABLE below. */                          \
+    M(SRC_COLSPAN,      "colspan",     1)  /* Number of columns this opcode spans. */              \
+    M(SRC_NEWLINE,      "newline",     0)  /* Bytecode follows a source newline. */                \
+    M(SRC_SETLINE,      "setline",     1)  /* A file-absolute source line number note. */          \
+    M(SRC_UNUSED20,     "unused20",    0)  /* Unused. */                                           \
+    M(SRC_UNUSED21,     "unused21",    0)  /* Unused. */                                           \
+    M(SRC_UNUSED22,     "unused22",    0)  /* Unused. */                                           \
+    M(SRC_UNUSED23,     "unused23",    0)  /* Unused. */                                           \
+    M(SRC_XDELTA,       "xdelta",      0)  /* 24-31 are for extended delta notes. */
+
+enum SrcNoteType {
+#define DEFINE_SRC_NOTE_TYPE(sym, name, arity) sym,
+    FOR_EACH_SRC_NOTE_TYPE(DEFINE_SRC_NOTE_TYPE)
+#undef DEFINE_SRC_NOTE_TYPE
+
+    SRC_LAST,
+    SRC_LAST_GETTABLE = SRC_TRY
+};
+
+static_assert(SRC_XDELTA == 24, "SRC_XDELTA should be 24");
+
+/* A source note array is terminated by an all-zero element. */
+inline void
+SN_MAKE_TERMINATOR(jssrcnote* sn)
+{
+    *sn = SRC_NULL;
+}
+
+inline bool
+SN_IS_TERMINATOR(jssrcnote* sn)
+{
+    return *sn == SRC_NULL;
+}
+
+} // namespace js
+
+#define SN_TYPE_BITS            5
+#define SN_DELTA_BITS           3
+#define SN_XDELTA_BITS          6
+#define SN_TYPE_MASK            (JS_BITMASK(SN_TYPE_BITS) << SN_DELTA_BITS)
+#define SN_DELTA_MASK           ((ptrdiff_t)JS_BITMASK(SN_DELTA_BITS))
+#define SN_XDELTA_MASK          ((ptrdiff_t)JS_BITMASK(SN_XDELTA_BITS))
+
+#define SN_MAKE_NOTE(sn,t,d)    (*(sn) = (jssrcnote)                          \
+                                          (((t) << SN_DELTA_BITS)             \
+                                           | ((d) & SN_DELTA_MASK)))
+#define SN_MAKE_XDELTA(sn,d)    (*(sn) = (jssrcnote)                          \
+                                          ((SRC_XDELTA << SN_DELTA_BITS)      \
+                                           | ((d) & SN_XDELTA_MASK)))
+
+#define SN_IS_XDELTA(sn)        ((*(sn) >> SN_DELTA_BITS) >= SRC_XDELTA)
+#define SN_TYPE(sn)             ((js::SrcNoteType)(SN_IS_XDELTA(sn)           \
+                                                   ? SRC_XDELTA               \
+                                                   : *(sn) >> SN_DELTA_BITS))
+#define SN_SET_TYPE(sn,type)    SN_MAKE_NOTE(sn, type, SN_DELTA(sn))
+#define SN_IS_GETTABLE(sn)      (SN_TYPE(sn) <= SRC_LAST_GETTABLE)
+
+#define SN_DELTA(sn)            ((ptrdiff_t)(SN_IS_XDELTA(sn)                 \
+                                             ? *(sn) & SN_XDELTA_MASK         \
+                                             : *(sn) & SN_DELTA_MASK))
+#define SN_SET_DELTA(sn,delta)  (SN_IS_XDELTA(sn)                             \
+                                 ? SN_MAKE_XDELTA(sn, delta)                  \
+                                 : SN_MAKE_NOTE(sn, SN_TYPE(sn), delta))
+
+#define SN_DELTA_LIMIT          ((ptrdiff_t)JS_BIT(SN_DELTA_BITS))
+#define SN_XDELTA_LIMIT         ((ptrdiff_t)JS_BIT(SN_XDELTA_BITS))
+
+/*
+ * Offset fields follow certain notes and are frequency-encoded: an offset in
+ * [0,0x7f] consumes one byte, an offset in [0x80,0x7fffffff] takes four, and
+ * the high bit of the first byte is set.
+ */
+#define SN_4BYTE_OFFSET_FLAG    0x80
+#define SN_4BYTE_OFFSET_MASK    0x7f
+
+#define SN_OFFSET_BITS          31
+#define SN_MAX_OFFSET (((size_t) 1 << SN_OFFSET_BITS) - 1)
+
+inline bool
+SN_REPRESENTABLE_OFFSET(ptrdiff_t offset)
+{
+    return 0 <= offset && size_t(offset) <= SN_MAX_OFFSET;
+}
+
+/*
+ * SRC_COLSPAN values represent changes to the column number. Colspans are
+ * signed: negative changes arise in describing constructs like for(;;) loops,
+ * that generate code in non-source order. (Negative colspans also have a
+ * history of indicating bugs in updating ParseNodes' source locations.)
+ *
+ * We store colspans using the same variable-length encoding as offsets,
+ * described above. However, unlike offsets, colspans are signed, so we truncate
+ * colspans (SN_COLSPAN_TO_OFFSET) for storage as offsets, and sign-extend
+ * offsets into colspans when we read them (SN_OFFSET_TO_COLSPAN).
+ */
+#define SN_COLSPAN_SIGN_BIT (1 << (SN_OFFSET_BITS - 1))
+#define SN_MIN_COLSPAN (-SN_COLSPAN_SIGN_BIT)
+#define SN_MAX_COLSPAN (SN_COLSPAN_SIGN_BIT - 1)
+
+inline bool
+SN_REPRESENTABLE_COLSPAN(ptrdiff_t colspan)
+{
+    return SN_MIN_COLSPAN <= colspan && colspan <= SN_MAX_COLSPAN;
+}
+
+inline ptrdiff_t
+SN_OFFSET_TO_COLSPAN(ptrdiff_t offset) {
+    // There should be no bits set outside the field we're going to sign-extend.
+    MOZ_ASSERT(!(offset & ~((1U << SN_OFFSET_BITS) - 1)));
+    // Sign-extend the least significant SN_OFFSET_BITS bits.
+    return (offset ^ SN_COLSPAN_SIGN_BIT) - SN_COLSPAN_SIGN_BIT;
+}
+
+inline ptrdiff_t
+SN_COLSPAN_TO_OFFSET(ptrdiff_t colspan) {
+    // Truncate the two's complement colspan, for storage as an offset.
+    ptrdiff_t offset = colspan & ((1U << SN_OFFSET_BITS) - 1);
+    // When we read this back, we'd better get the value we stored.
+    MOZ_ASSERT(SN_OFFSET_TO_COLSPAN(offset) == colspan);
+    return offset;
+}
+
+#define SN_LENGTH(sn)           ((js_SrcNoteSpec[SN_TYPE(sn)].arity == 0) ? 1 \
+                                 : js::SrcNoteLength(sn))
+#define SN_NEXT(sn)             ((sn) + SN_LENGTH(sn))
+
+struct JSSrcNoteSpec {
+    const char*     name;      /* name for disassembly/debugging output */
+    int8_t          arity;      /* number of offset operands */
+};
+
+extern JS_FRIEND_DATA(const JSSrcNoteSpec) js_SrcNoteSpec[];
+
+namespace js {
+
+extern JS_FRIEND_API(unsigned)
+SrcNoteLength(jssrcnote* sn);
+
+/*
+ * Get and set the offset operand identified by which (0 for the first, etc.).
+ */
+extern JS_FRIEND_API(ptrdiff_t)
+GetSrcNoteOffset(jssrcnote* sn, unsigned which);
+
+} // namespace js
+
+#endif /* frontend_SourceNotes_h */
diff --git a/js/src/frontend/SyntaxParseHandler.h b/js/src/frontend/SyntaxParseHandler.h
new file mode 100644
index 0000000000..75c7e33337
--- /dev/null
+++ b/js/src/frontend/SyntaxParseHandler.h
@@ -0,0 +1,599 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_SyntaxParseHandler_h
+#define frontend_SyntaxParseHandler_h
+
+#include "mozilla/Attributes.h"
+
+#include "frontend/ParseNode.h"
+#include "frontend/TokenStream.h"
+
+namespace js {
+namespace frontend {
+
+template <typename ParseHandler>
+class Parser;
+
+// Parse handler used when processing the syntax in a block of code, to generate
+// the minimal information which is required to detect syntax errors and allow
+// bytecode to be emitted for outer functions.
+//
+// When parsing, we start at the top level with a full parse, and when possible
+// only check the syntax for inner functions, so that they can be lazily parsed
+// into bytecode when/if they first run. Checking the syntax of a function is
+// several times faster than doing a full parse/emit, and lazy parsing improves
+// both performance and memory usage significantly when pages contain large
+// amounts of code that never executes (which happens often).
+class SyntaxParseHandler
+{
+    // Remember the last encountered name or string literal during syntax parses.
+    JSAtom* lastAtom;
+    TokenPos lastStringPos;
+    TokenStream& tokenStream;
+
+  public:
+    enum Node {
+        NodeFailure = 0,
+        NodeGeneric,
+        NodeGetProp,
+        NodeStringExprStatement,
+        NodeReturn,
+        NodeBreak,
+        NodeThrow,
+        NodeEmptyStatement,
+
+        NodeVarDeclaration,
+        NodeLexicalDeclaration,
+
+        NodeFunctionDefinition,
+
+        // This is needed for proper assignment-target handling.  ES6 formally
+        // requires function calls *not* pass IsValidSimpleAssignmentTarget,
+        // but at last check there were still sites with |f() = 5| and similar
+        // in code not actually executed (or at least not executed enough to be
+        // noticed).
+        NodeFunctionCall,
+
+        // Nodes representing *parenthesized* IsValidSimpleAssignmentTarget
+        // nodes.  We can't simply treat all such parenthesized nodes
+        // identically, because in assignment and increment/decrement contexts
+        // ES6 says that parentheses constitute a syntax error.
+        //
+        //   var obj = {};
+        //   var val;
+        //   (val) = 3; (obj.prop) = 4;       // okay per ES5's little mind
+        //   [(a)] = [3]; [(obj.prop)] = [4]; // invalid ES6 syntax
+        //   // ...and so on for the other IsValidSimpleAssignmentTarget nodes
+        //
+        // We don't know in advance in the current parser when we're parsing
+        // in a place where name parenthesization changes meaning, so we must
+        // have multiple node values for these cases.
+        NodeParenthesizedArgumentsName,
+        NodeParenthesizedEvalName,
+        NodeParenthesizedName,
+
+        NodeDottedProperty,
+        NodeElement,
+
+        // Destructuring target patterns can't be parenthesized: |([a]) = [3];|
+        // must be a syntax error.  (We can't use NodeGeneric instead of these
+        // because that would trigger invalid-left-hand-side ReferenceError
+        // semantics when SyntaxError semantics are desired.)
+        NodeParenthesizedArray,
+        NodeParenthesizedObject,
+
+        // In rare cases a parenthesized |node| doesn't have the same semantics
+        // as |node|.  Each such node has a special Node value, and we use a
+        // different Node value to represent the parenthesized form.  See also
+        // is{Unp,P}arenthesized*(Node), parenthesize(Node), and the various
+        // functions that deal in NodeUnparenthesized* below.
+
+        // Nodes representing unparenthesized names.
+        NodeUnparenthesizedArgumentsName,
+        NodeUnparenthesizedAsyncName,
+        NodeUnparenthesizedEvalName,
+        NodeUnparenthesizedName,
+
+        // Valuable for recognizing potential destructuring patterns.
+        NodeUnparenthesizedArray,
+        NodeUnparenthesizedObject,
+
+        // The directive prologue at the start of a FunctionBody or ScriptBody
+        // is the longest sequence (possibly empty) of string literal
+        // expression statements at the start of a function.  Thus we need this
+        // to treat |"use strict";| as a possible Use Strict Directive and
+        // |("use strict");| as a useless statement.
+        NodeUnparenthesizedString,
+
+        // Legacy generator expressions of the form |(expr for (...))| and
+        // array comprehensions of the form |[expr for (...)]|) don't permit
+        // |expr| to be a comma expression.  Thus we need this to treat
+        // |(a(), b for (x in []))| as a syntax error and
+        // |((a(), b) for (x in []))| as a generator that calls |a| and then
+        // yields |b| each time it's resumed.
+        NodeUnparenthesizedCommaExpr,
+
+        // Assignment expressions in condition contexts could be typos for
+        // equality checks.  (Think |if (x = y)| versus |if (x == y)|.)  Thus
+        // we need this to treat |if (x = y)| as a possible typo and
+        // |if ((x = y))| as a deliberate assignment within a condition.
+        //
+        // (Technically this isn't needed, as these are *only* extraWarnings
+        // warnings, and parsing with that option disables syntax parsing.  But
+        // it seems best to be consistent, and perhaps the syntax parser will
+        // eventually enforce extraWarnings and will require this then.)
+        NodeUnparenthesizedAssignment,
+
+        // This node is necessary to determine if the base operand in an
+        // exponentiation operation is an unparenthesized unary expression.
+        // We want to reject |-2 ** 3|, but still need to allow |(-2) ** 3|.
+        NodeUnparenthesizedUnary,
+
+        // This node is necessary to determine if the LHS of a property access is
+        // super related.
+        NodeSuperBase
+    };
+
+    bool isPropertyAccess(Node node) {
+        return node == NodeDottedProperty || node == NodeElement;
+    }
+
+    bool isFunctionCall(Node node) {
+        // Note: super() is a special form, *not* a function call.
+        return node == NodeFunctionCall;
+    }
+
+    static bool isUnparenthesizedDestructuringPattern(Node node) {
+        return node == NodeUnparenthesizedArray || node == NodeUnparenthesizedObject;
+    }
+
+    static bool isParenthesizedDestructuringPattern(Node node) {
+        // Technically this isn't a destructuring target at all -- the grammar
+        // doesn't treat it as such.  But we need to know when this happens to
+        // consider it a SyntaxError rather than an invalid-left-hand-side
+        // ReferenceError.
+        return node == NodeParenthesizedArray || node == NodeParenthesizedObject;
+    }
+
+    static bool isDestructuringPatternAnyParentheses(Node node) {
+        return isUnparenthesizedDestructuringPattern(node) ||
+                isParenthesizedDestructuringPattern(node);
+    }
+
+  public:
+    SyntaxParseHandler(ExclusiveContext* cx, LifoAlloc& alloc,
+                       TokenStream& tokenStream, Parser<SyntaxParseHandler>* syntaxParser,
+                       LazyScript* lazyOuterFunction)
+      : lastAtom(nullptr),
+        tokenStream(tokenStream)
+    {}
+
+    static Node null() { return NodeFailure; }
+
+    void prepareNodeForMutation(Node node) {}
+    void freeTree(Node node) {}
+
+    void trace(JSTracer* trc) {}
+
+    Node newName(PropertyName* name, const TokenPos& pos, ExclusiveContext* cx) {
+        lastAtom = name;
+        if (name == cx->names().arguments)
+            return NodeUnparenthesizedArgumentsName;
+        if (name == cx->names().async)
+            return NodeUnparenthesizedAsyncName;
+        if (name == cx->names().eval)
+            return NodeUnparenthesizedEvalName;
+        return NodeUnparenthesizedName;
+    }
+
+    Node newComputedName(Node expr, uint32_t start, uint32_t end) {
+        return NodeGeneric;
+    }
+
+    Node newObjectLiteralPropertyName(JSAtom* atom, const TokenPos& pos) {
+        return NodeUnparenthesizedName;
+    }
+
+    Node newNumber(double value, DecimalPoint decimalPoint, const TokenPos& pos) { return NodeGeneric; }
+    Node newBooleanLiteral(bool cond, const TokenPos& pos) { return NodeGeneric; }
+
+    Node newStringLiteral(JSAtom* atom, const TokenPos& pos) {
+        lastAtom = atom;
+        lastStringPos = pos;
+        return NodeUnparenthesizedString;
+    }
+
+    Node newTemplateStringLiteral(JSAtom* atom, const TokenPos& pos) {
+        return NodeGeneric;
+    }
+
+    Node newCallSiteObject(uint32_t begin) {
+        return NodeGeneric;
+    }
+
+    void addToCallSiteObject(Node callSiteObj, Node rawNode, Node cookedNode) {}
+
+    Node newThisLiteral(const TokenPos& pos, Node thisName) { return NodeGeneric; }
+    Node newNullLiteral(const TokenPos& pos) { return NodeGeneric; }
+
+    template <class Boxer>
+    Node newRegExp(RegExpObject* reobj, const TokenPos& pos, Boxer& boxer) { return NodeGeneric; }
+
+    Node newConditional(Node cond, Node thenExpr, Node elseExpr) { return NodeGeneric; }
+
+    Node newElision() { return NodeGeneric; }
+
+    Node newDelete(uint32_t begin, Node expr) {
+        return NodeUnparenthesizedUnary;
+    }
+
+    Node newTypeof(uint32_t begin, Node kid) {
+        return NodeUnparenthesizedUnary;
+    }
+
+    Node newUnary(ParseNodeKind kind, JSOp op, uint32_t begin, Node kid) {
+        return NodeUnparenthesizedUnary;
+    }
+
+    Node newUpdate(ParseNodeKind kind, uint32_t begin, Node kid) {
+        return NodeGeneric;
+    }
+
+    Node newSpread(uint32_t begin, Node kid) {
+        return NodeGeneric;
+    }
+
+    Node newArrayPush(uint32_t begin, Node kid) {
+        return NodeGeneric;
+    }
+
+    Node newBinary(ParseNodeKind kind, JSOp op = JSOP_NOP) { return NodeGeneric; }
+    Node newBinary(ParseNodeKind kind, Node left, JSOp op = JSOP_NOP) { return NodeGeneric; }
+    Node newBinary(ParseNodeKind kind, Node left, Node right, JSOp op = JSOP_NOP) {
+        return NodeGeneric;
+    }
+    Node appendOrCreateList(ParseNodeKind kind, Node left, Node right,
+                            ParseContext* pc, JSOp op = JSOP_NOP) {
+        return NodeGeneric;
+    }
+
+    Node newTernary(ParseNodeKind kind, Node first, Node second, Node third, JSOp op = JSOP_NOP) {
+        return NodeGeneric;
+    }
+
+    // Expressions
+
+    Node newArrayComprehension(Node body, const TokenPos& pos) { return NodeGeneric; }
+    Node newArrayLiteral(uint32_t begin) { return NodeUnparenthesizedArray; }
+    MOZ_MUST_USE bool addElision(Node literal, const TokenPos& pos) { return true; }
+    MOZ_MUST_USE bool addSpreadElement(Node literal, uint32_t begin, Node inner) { return true; }
+    void addArrayElement(Node literal, Node element) { }
+
+    Node newCall() { return NodeFunctionCall; }
+    Node newTaggedTemplate() { return NodeGeneric; }
+
+    Node newObjectLiteral(uint32_t begin) { return NodeUnparenthesizedObject; }
+    Node newClassMethodList(uint32_t begin) { return NodeGeneric; }
+    Node newClassNames(Node outer, Node inner, const TokenPos& pos) { return NodeGeneric; }
+    Node newClass(Node name, Node heritage, Node methodBlock) { return NodeGeneric; }
+
+    Node newNewTarget(Node newHolder, Node targetHolder) { return NodeGeneric; }
+    Node newPosHolder(const TokenPos& pos) { return NodeGeneric; }
+    Node newSuperBase(Node thisName, const TokenPos& pos) { return NodeSuperBase; }
+
+    MOZ_MUST_USE bool addPrototypeMutation(Node literal, uint32_t begin, Node expr) { return true; }
+    MOZ_MUST_USE bool addPropertyDefinition(Node literal, Node name, Node expr) { return true; }
+    MOZ_MUST_USE bool addShorthand(Node literal, Node name, Node expr) { return true; }
+    MOZ_MUST_USE bool addObjectMethodDefinition(Node literal, Node name, Node fn, JSOp op) { return true; }
+    MOZ_MUST_USE bool addClassMethodDefinition(Node literal, Node name, Node fn, JSOp op, bool isStatic) { return true; }
+    Node newYieldExpression(uint32_t begin, Node value, Node gen) { return NodeGeneric; }
+    Node newYieldStarExpression(uint32_t begin, Node value, Node gen) { return NodeGeneric; }
+    Node newAwaitExpression(uint32_t begin, Node value, Node gen) { return NodeGeneric; }
+
+    // Statements
+
+    Node newStatementList(const TokenPos& pos) { return NodeGeneric; }
+    void addStatementToList(Node list, Node stmt) {}
+    void addCaseStatementToList(Node list, Node stmt) {}
+    MOZ_MUST_USE bool prependInitialYield(Node stmtList, Node gen) { return true; }
+    Node newEmptyStatement(const TokenPos& pos) { return NodeEmptyStatement; }
+
+    Node newSetThis(Node thisName, Node value) { return value; }
+
+    Node newExprStatement(Node expr, uint32_t end) {
+        return expr == NodeUnparenthesizedString ? NodeStringExprStatement : NodeGeneric;
+    }
+
+    Node newIfStatement(uint32_t begin, Node cond, Node then, Node else_) { return NodeGeneric; }
+    Node newDoWhileStatement(Node body, Node cond, const TokenPos& pos) { return NodeGeneric; }
+    Node newWhileStatement(uint32_t begin, Node cond, Node body) { return NodeGeneric; }
+    Node newSwitchStatement(uint32_t begin, Node discriminant, Node caseList) { return NodeGeneric; }
+    Node newCaseOrDefault(uint32_t begin, Node expr, Node body) { return NodeGeneric; }
+    Node newContinueStatement(PropertyName* label, const TokenPos& pos) { return NodeGeneric; }
+    Node newBreakStatement(PropertyName* label, const TokenPos& pos) { return NodeBreak; }
+    Node newReturnStatement(Node expr, const TokenPos& pos) { return NodeReturn; }
+    Node newWithStatement(uint32_t begin, Node expr, Node body) { return NodeGeneric; }
+
+    Node newLabeledStatement(PropertyName* label, Node stmt, uint32_t begin) {
+        return NodeGeneric;
+    }
+
+    Node newThrowStatement(Node expr, const TokenPos& pos) { return NodeThrow; }
+    Node newTryStatement(uint32_t begin, Node body, Node catchList, Node finallyBlock) {
+        return NodeGeneric;
+    }
+    Node newDebuggerStatement(const TokenPos& pos) { return NodeGeneric; }
+
+    Node newPropertyAccess(Node pn, PropertyName* name, uint32_t end) {
+        lastAtom = name;
+        return NodeDottedProperty;
+    }
+
+    Node newPropertyByValue(Node pn, Node kid, uint32_t end) { return NodeElement; }
+
+    MOZ_MUST_USE bool addCatchBlock(Node catchList, Node letBlock, Node catchName,
+                                    Node catchGuard, Node catchBody) { return true; }
+
+    MOZ_MUST_USE bool setLastFunctionFormalParameterDefault(Node funcpn, Node pn) { return true; }
+    Node newFunctionDefinition() { return NodeFunctionDefinition; }
+    bool setComprehensionLambdaBody(Node pn, Node body) { return true; }
+    void setFunctionFormalParametersAndBody(Node pn, Node kid) {}
+    void setFunctionBody(Node pn, Node kid) {}
+    void setFunctionBox(Node pn, FunctionBox* funbox) {}
+    void addFunctionFormalParameter(Node pn, Node argpn) {}
+
+    Node newForStatement(uint32_t begin, Node forHead, Node body, unsigned iflags) {
+        return NodeGeneric;
+    }
+
+    Node newComprehensionFor(uint32_t begin, Node forHead, Node body) {
+        return NodeGeneric;
+    }
+
+    Node newComprehensionBinding(Node kid) {
+        // Careful: we're asking this well after the name was parsed, so the
+        // value returned may not correspond to |kid|'s actual name.  But it
+        // *will* be truthy iff |kid| was a name, so we're safe.
+        MOZ_ASSERT(isUnparenthesizedName(kid));
+        return NodeGeneric;
+    }
+
+    Node newForHead(Node init, Node test, Node update, const TokenPos& pos) {
+        return NodeGeneric;
+    }
+
+    Node newForInOrOfHead(ParseNodeKind kind, Node target, Node iteratedExpr, const TokenPos& pos) {
+        return NodeGeneric;
+    }
+
+    MOZ_MUST_USE bool finishInitializerAssignment(Node pn, Node init) { return true; }
+
+    void setBeginPosition(Node pn, Node oth) {}
+    void setBeginPosition(Node pn, uint32_t begin) {}
+
+    void setEndPosition(Node pn, Node oth) {}
+    void setEndPosition(Node pn, uint32_t end) {}
+
+    void setPosition(Node pn, const TokenPos& pos) {}
+    TokenPos getPosition(Node pn) {
+        return tokenStream.currentToken().pos;
+    }
+
+    Node newList(ParseNodeKind kind, JSOp op = JSOP_NOP) {
+        MOZ_ASSERT(kind != PNK_VAR);
+        MOZ_ASSERT(kind != PNK_LET);
+        MOZ_ASSERT(kind != PNK_CONST);
+        return NodeGeneric;
+    }
+    Node newList(ParseNodeKind kind, uint32_t begin, JSOp op = JSOP_NOP) {
+        return newList(kind, op);
+    }
+    Node newList(ParseNodeKind kind, Node kid, JSOp op = JSOP_NOP) {
+        return newList(kind, op);
+    }
+
+    Node newDeclarationList(ParseNodeKind kind, JSOp op = JSOP_NOP) {
+        if (kind == PNK_VAR)
+            return NodeVarDeclaration;
+        MOZ_ASSERT(kind == PNK_LET || kind == PNK_CONST);
+        return NodeLexicalDeclaration;
+    }
+    Node newDeclarationList(ParseNodeKind kind, Node kid, JSOp op = JSOP_NOP) {
+        return newDeclarationList(kind, op);
+    }
+
+    bool isDeclarationList(Node node) {
+        return node == NodeVarDeclaration || node == NodeLexicalDeclaration;
+    }
+
+    Node singleBindingFromDeclaration(Node decl) {
+        MOZ_ASSERT(isDeclarationList(decl));
+
+        // This is, unfortunately, very dodgy.  Obviously NodeVarDeclaration
+        // and NodeLexicalDeclaration can store no info on the arbitrary
+        // number of bindings it could contain.
+        //
+        // But this method is called only for cloning for-in/of declarations
+        // as initialization targets.  That context simplifies matters.  If the
+        // binding is a single name, it'll always syntax-parse (or it would
+        // already have been rejected as assigning/binding a forbidden name).
+        // Otherwise the binding is a destructuring pattern.  But syntax
+        // parsing would *already* have aborted when it saw a destructuring
+        // pattern.  So we can just say any old thing here, because the only
+        // time we'll be wrong is a case that syntax parsing has already
+        // rejected.  Use NodeUnparenthesizedName so the SyntaxParseHandler
+        // Parser::cloneLeftHandSide can assert it sees only this.
+        return NodeUnparenthesizedName;
+    }
+
+    Node newCatchList() {
+        return newList(PNK_CATCHLIST, JSOP_NOP);
+    }
+
+    Node newCommaExpressionList(Node kid) {
+        return NodeUnparenthesizedCommaExpr;
+    }
+
+    void addList(Node list, Node kid) {
+        MOZ_ASSERT(list == NodeGeneric ||
+                   list == NodeUnparenthesizedArray ||
+                   list == NodeUnparenthesizedObject ||
+                   list == NodeUnparenthesizedCommaExpr ||
+                   list == NodeVarDeclaration ||
+                   list == NodeLexicalDeclaration ||
+                   list == NodeFunctionCall);
+    }
+
+    Node newAssignment(ParseNodeKind kind, Node lhs, Node rhs, JSOp op) {
+        if (kind == PNK_ASSIGN)
+            return NodeUnparenthesizedAssignment;
+        return newBinary(kind, lhs, rhs, op);
+    }
+
+    bool isUnparenthesizedCommaExpression(Node node) {
+        return node == NodeUnparenthesizedCommaExpr;
+    }
+
+    bool isUnparenthesizedAssignment(Node node) {
+        return node == NodeUnparenthesizedAssignment;
+    }
+
+    bool isUnparenthesizedUnaryExpression(Node node) {
+        return node == NodeUnparenthesizedUnary;
+    }
+
+    bool isReturnStatement(Node node) {
+        return node == NodeReturn;
+    }
+
+    bool isStatementPermittedAfterReturnStatement(Node pn) {
+        return pn == NodeFunctionDefinition || pn == NodeVarDeclaration ||
+               pn == NodeBreak ||
+               pn == NodeThrow ||
+               pn == NodeEmptyStatement;
+    }
+
+    bool isSuperBase(Node pn) {
+        return pn == NodeSuperBase;
+    }
+
+    void setOp(Node pn, JSOp op) {}
+    void setListFlag(Node pn, unsigned flag) {}
+    MOZ_MUST_USE Node parenthesize(Node node) {
+        // A number of nodes have different behavior upon parenthesization, but
+        // only in some circumstances.  Convert these nodes to special
+        // parenthesized forms.
+        if (node == NodeUnparenthesizedArgumentsName)
+            return NodeParenthesizedArgumentsName;
+        if (node == NodeUnparenthesizedEvalName)
+            return NodeParenthesizedEvalName;
+        if (node == NodeUnparenthesizedName || node == NodeUnparenthesizedAsyncName)
+            return NodeParenthesizedName;
+
+        if (node == NodeUnparenthesizedArray)
+            return NodeParenthesizedArray;
+        if (node == NodeUnparenthesizedObject)
+            return NodeParenthesizedObject;
+
+        // Other nodes need not be recognizable after parenthesization; convert
+        // them to a generic node.
+        if (node == NodeUnparenthesizedString ||
+            node == NodeUnparenthesizedCommaExpr ||
+            node == NodeUnparenthesizedAssignment ||
+            node == NodeUnparenthesizedUnary)
+        {
+            return NodeGeneric;
+        }
+
+        // In all other cases, the parenthesized form of |node| is equivalent
+        // to the unparenthesized form: return |node| unchanged.
+        return node;
+    }
+    MOZ_MUST_USE Node setLikelyIIFE(Node pn) {
+        return pn; // Remain in syntax-parse mode.
+    }
+    void setPrologue(Node pn) {}
+
+    bool isConstant(Node pn) { return false; }
+
+    bool isUnparenthesizedName(Node node) {
+        return node == NodeUnparenthesizedArgumentsName ||
+               node == NodeUnparenthesizedAsyncName ||
+               node == NodeUnparenthesizedEvalName ||
+               node == NodeUnparenthesizedName;
+    }
+
+    bool isNameAnyParentheses(Node node) {
+        if (isUnparenthesizedName(node))
+            return true;
+        return node == NodeParenthesizedArgumentsName ||
+               node == NodeParenthesizedEvalName ||
+               node == NodeParenthesizedName;
+    }
+
+    bool nameIsEvalAnyParentheses(Node node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this function on known names");
+        return node == NodeUnparenthesizedEvalName || node == NodeParenthesizedEvalName;
+    }
+
+    const char* nameIsArgumentsEvalAnyParentheses(Node node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this method on known names");
+
+        if (nameIsEvalAnyParentheses(node, cx))
+            return js_eval_str;
+        if (node == NodeUnparenthesizedArgumentsName || node == NodeParenthesizedArgumentsName)
+            return js_arguments_str;
+        return nullptr;
+    }
+
+    bool nameIsUnparenthesizedAsync(Node node, ExclusiveContext* cx) {
+        MOZ_ASSERT(isNameAnyParentheses(node),
+                   "must only call this function on known names");
+        return node == NodeUnparenthesizedAsyncName;
+    }
+
+    PropertyName* maybeDottedProperty(Node node) {
+        // Note: |super.apply(...)| is a special form that calls an "apply"
+        // method retrieved from one value, but using a *different* value as
+        // |this|.  It's not really eligible for the funapply/funcall
+        // optimizations as they're currently implemented (assuming a single
+        // value is used for both retrieval and |this|).
+        if (node != NodeDottedProperty)
+            return nullptr;
+        return lastAtom->asPropertyName();
+    }
+
+    JSAtom* isStringExprStatement(Node pn, TokenPos* pos) {
+        if (pn == NodeStringExprStatement) {
+            *pos = lastStringPos;
+            return lastAtom;
+        }
+        return nullptr;
+    }
+
+    bool canSkipLazyInnerFunctions() {
+        return false;
+    }
+    bool canSkipLazyClosedOverBindings() {
+        return false;
+    }
+    JSAtom* nextLazyClosedOverBinding() {
+        MOZ_CRASH("SyntaxParseHandler::canSkipLazyClosedOverBindings must return false");
+    }
+
+    void adjustGetToSet(Node node) {}
+
+    void disableSyntaxParser() {
+    }
+};
+
+} // namespace frontend
+} // namespace js
+
+#endif /* frontend_SyntaxParseHandler_h */
diff --git a/js/src/frontend/TokenKind.h b/js/src/frontend/TokenKind.h
new file mode 100644
index 0000000000..6f22d78e5f
--- /dev/null
+++ b/js/src/frontend/TokenKind.h
@@ -0,0 +1,245 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_TokenKind_h
+#define frontend_TokenKind_h
+
+/*
+ * List of token kinds and their ranges.
+ *
+ * The format for each line is:
+ *
+ *   macro(<TOKEN_KIND_NAME>, <DESCRIPTION>)
+ *
+ * or
+ *
+ *   range(<TOKEN_RANGE_NAME>, <TOKEN_KIND_NAME>)
+ *
+ * where ;
+ * <TOKEN_KIND_NAME> is a legal C identifier of the token, that will be used in
+ * the JS engine source, with `TOK_` prefix.
+ *
+ * <DESCRIPTION> is a string that describe about the token, and will be used in
+ * error message.
+ *
+ * <TOKEN_RANGE_NAME> is a legal C identifier of the range that will be used to
+ * JS engine source, with `TOK_` prefix. It should end with `_FIRST` or `_LAST`.
+ * This is used to check TokenKind by range-testing:
+ *   TOK_BINOP_FIRST <= tt && tt <= TOK_BINOP_LAST
+ *
+ * Second argument of `range` is the actual value of the <TOKEN_RANGE_NAME>,
+ * should be same as one of <TOKEN_KIND_NAME> in other `macro`s.
+ *
+ * To use this macro, define two macros for `macro` and `range`, and pass them
+ * as arguments.
+ *
+ *   #define EMIT_TOKEN(name, desc) ...
+ *   #define EMIT_RANGE(name, value) ...
+ *   FOR_EACH_TOKEN_KIND_WITH_RANGE(EMIT_TOKEN, EMIT_RANGE)
+ *   #undef EMIT_TOKEN
+ *   #undef EMIT_RANGE
+ *
+ * If you don't need range data, use FOR_EACH_TOKEN_KIND instead.
+ *
+ *   #define EMIT_TOKEN(name, desc) ...
+ *   FOR_EACH_TOKEN_KIND(EMIT_TOKEN)
+ *   #undef EMIT_TOKEN
+ *
+ * Note that this list does not contain ERROR and LIMIT.
+ */
+#define FOR_EACH_TOKEN_KIND_WITH_RANGE(macro, range) \
+    macro(EOF,         "end of script") \
+    \
+    /* only returned by peekTokenSameLine() */ \
+    macro(EOL,          "line terminator") \
+    \
+    macro(SEMI,         "';'") \
+    macro(COMMA,        "','") \
+    macro(HOOK,         "'?'")    /* conditional */ \
+    macro(COLON,        "':'")    /* conditional */ \
+    macro(INC,          "'++'")   /* increment */ \
+    macro(DEC,          "'--'")   /* decrement */ \
+    macro(DOT,          "'.'")    /* member operator */ \
+    macro(TRIPLEDOT,    "'...'")  /* rest arguments and spread operator */ \
+    macro(LB,           "'['") \
+    macro(RB,           "']'") \
+    macro(LC,           "'{'") \
+    macro(RC,           "'}'") \
+    macro(LP,           "'('") \
+    macro(RP,           "')'") \
+    macro(NAME,         "identifier") \
+    macro(NUMBER,       "numeric literal") \
+    macro(STRING,       "string literal") \
+    \
+    /* start of template literal with substitutions */ \
+    macro(TEMPLATE_HEAD,    "'${'") \
+    /* template literal without substitutions */ \
+    macro(NO_SUBS_TEMPLATE, "template literal") \
+    \
+    macro(REGEXP,       "regular expression literal") \
+    macro(TRUE,         "boolean literal 'true'") \
+    macro(FALSE,        "boolean literal 'false'") \
+    macro(NULL,         "null literal") \
+    macro(THIS,         "keyword 'this'") \
+    macro(FUNCTION,     "keyword 'function'") \
+    macro(IF,           "keyword 'if'") \
+    macro(ELSE,         "keyword 'else'") \
+    macro(SWITCH,       "keyword 'switch'") \
+    macro(CASE,         "keyword 'case'") \
+    macro(DEFAULT,      "keyword 'default'") \
+    macro(WHILE,        "keyword 'while'") \
+    macro(DO,           "keyword 'do'") \
+    macro(FOR,          "keyword 'for'") \
+    macro(BREAK,        "keyword 'break'") \
+    macro(CONTINUE,     "keyword 'continue'") \
+    macro(VAR,          "keyword 'var'") \
+    macro(CONST,        "keyword 'const'") \
+    macro(WITH,         "keyword 'with'") \
+    macro(RETURN,       "keyword 'return'") \
+    macro(NEW,          "keyword 'new'") \
+    macro(DELETE,       "keyword 'delete'") \
+    macro(TRY,          "keyword 'try'") \
+    macro(CATCH,        "keyword 'catch'") \
+    macro(FINALLY,      "keyword 'finally'") \
+    macro(THROW,        "keyword 'throw'") \
+    macro(DEBUGGER,     "keyword 'debugger'") \
+    macro(YIELD,        "keyword 'yield'") \
+    macro(AWAIT,        "keyword 'await'") \
+    macro(EXPORT,       "keyword 'export'") \
+    macro(IMPORT,       "keyword 'import'") \
+    macro(CLASS,        "keyword 'class'") \
+    macro(EXTENDS,      "keyword 'extends'") \
+    macro(SUPER,        "keyword 'super'") \
+    macro(RESERVED,     "reserved keyword") \
+    /* reserved keywords in strict mode */ \
+    macro(STRICT_RESERVED, "reserved keyword") \
+    \
+    /* \
+     * The following token types occupy contiguous ranges to enable easy \
+     * range-testing. \
+     */ \
+    /* \
+     * Binary operators tokens, TOK_OR thru TOK_POW. These must be in the same \
+     * order as F(OR) and friends in FOR_EACH_PARSE_NODE_KIND in ParseNode.h. \
+     */ \
+    macro(OR,           "'||'")   /* logical or */ \
+    range(BINOP_FIRST, OR) \
+    macro(AND,          "'&&'")   /* logical and */ \
+    macro(BITOR,        "'|'")    /* bitwise-or */ \
+    macro(BITXOR,       "'^'")    /* bitwise-xor */ \
+    macro(BITAND,       "'&'")    /* bitwise-and */ \
+    \
+    /* Equality operation tokens, per TokenKindIsEquality. */ \
+    macro(STRICTEQ,     "'==='") \
+    range(EQUALITY_START, STRICTEQ) \
+    macro(EQ,           "'=='") \
+    macro(STRICTNE,     "'!=='") \
+    macro(NE,           "'!='") \
+    range(EQUALITY_LAST, NE) \
+    \
+    /* Relational ops, per TokenKindIsRelational. */ \
+    macro(LT,           "'<'") \
+    range(RELOP_START, LT) \
+    macro(LE,           "'<='") \
+    macro(GT,           "'>'") \
+    macro(GE,           "'>='") \
+    range(RELOP_LAST, GE) \
+    \
+    macro(INSTANCEOF,   "keyword 'instanceof'") \
+    macro(IN,           "keyword 'in'") \
+    \
+    /* Shift ops, per TokenKindIsShift. */ \
+    macro(LSH,          "'<<'") \
+    range(SHIFTOP_START, LSH) \
+    macro(RSH,          "'>>'") \
+    macro(URSH,         "'>>>'") \
+    range(SHIFTOP_LAST, URSH) \
+    \
+    macro(ADD,          "'+'") \
+    macro(SUB,          "'-'") \
+    macro(MUL,          "'*'") \
+    macro(DIV,          "'/'") \
+    macro(MOD,          "'%'") \
+    macro(POW,          "'**'") \
+    range(BINOP_LAST, POW) \
+    \
+    /* Unary operation tokens. */ \
+    macro(TYPEOF,       "keyword 'typeof'") \
+    macro(VOID,         "keyword 'void'") \
+    macro(NOT,          "'!'") \
+    macro(BITNOT,       "'~'") \
+    \
+    macro(ARROW,        "'=>'")   /* function arrow */ \
+    \
+    /* Assignment ops, per TokenKindIsAssignment */ \
+    macro(ASSIGN,       "'='") \
+    range(ASSIGNMENT_START, ASSIGN) \
+    macro(ADDASSIGN,    "'+='") \
+    macro(SUBASSIGN,    "'-='") \
+    macro(BITORASSIGN,  "'|='") \
+    macro(BITXORASSIGN, "'^='") \
+    macro(BITANDASSIGN, "'&='") \
+    macro(LSHASSIGN,    "'<<='") \
+    macro(RSHASSIGN,    "'>>='") \
+    macro(URSHASSIGN,   "'>>>='") \
+    macro(MULASSIGN,    "'*='") \
+    macro(DIVASSIGN,    "'/='") \
+    macro(MODASSIGN,    "'%='") \
+    macro(POWASSIGN,    "'**='") \
+    range(ASSIGNMENT_LAST, POWASSIGN)
+
+#define TOKEN_KIND_RANGE_EMIT_NONE(name, value)
+#define FOR_EACH_TOKEN_KIND(macro) \
+    FOR_EACH_TOKEN_KIND_WITH_RANGE(macro, TOKEN_KIND_RANGE_EMIT_NONE)
+
+namespace js {
+namespace frontend {
+
+// Values of this type are used to index into arrays such as isExprEnding[],
+// so the first value must be zero.
+enum TokenKind {
+#define EMIT_ENUM(name, desc) TOK_##name,
+#define EMIT_ENUM_RANGE(name, value) TOK_##name = TOK_##value,
+    FOR_EACH_TOKEN_KIND_WITH_RANGE(EMIT_ENUM, EMIT_ENUM_RANGE)
+#undef EMIT_ENUM
+#undef EMIT_ENUM_RANGE
+    TOK_LIMIT                      // domain size
+};
+
+inline bool
+TokenKindIsBinaryOp(TokenKind tt)
+{
+    return TOK_BINOP_FIRST <= tt && tt <= TOK_BINOP_LAST;
+}
+
+inline bool
+TokenKindIsEquality(TokenKind tt)
+{
+    return TOK_EQUALITY_START <= tt && tt <= TOK_EQUALITY_LAST;
+}
+
+inline bool
+TokenKindIsRelational(TokenKind tt)
+{
+    return TOK_RELOP_START <= tt && tt <= TOK_RELOP_LAST;
+}
+
+inline bool
+TokenKindIsShift(TokenKind tt)
+{
+    return TOK_SHIFTOP_START <= tt && tt <= TOK_SHIFTOP_LAST;
+}
+
+inline bool
+TokenKindIsAssignment(TokenKind tt)
+{
+    return TOK_ASSIGNMENT_START <= tt && tt <= TOK_ASSIGNMENT_LAST;
+}
+
+} // namespace frontend
+} // namespace js
+
+#endif /* frontend_TokenKind_h */
diff --git a/js/src/frontend/TokenStream.cpp b/js/src/frontend/TokenStream.cpp
new file mode 100644
index 0000000000..c166ed4145
--- /dev/null
+++ b/js/src/frontend/TokenStream.cpp
@@ -0,0 +1,1962 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// JS lexical scanner.
+
+#include "frontend/TokenStream.h"
+
+#include "mozilla/IntegerTypeTraits.h"
+#include "mozilla/PodOperations.h"
+
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jscompartment.h"
+#include "jsexn.h"
+#include "jsnum.h"
+
+#include "frontend/BytecodeCompiler.h"
+#include "js/CharacterEncoding.h"
+#include "js/UniquePtr.h"
+#include "vm/HelperThreads.h"
+#include "vm/Keywords.h"
+#include "vm/StringBuffer.h"
+#include "vm/Unicode.h"
+
+using namespace js;
+using namespace js::frontend;
+
+using mozilla::Maybe;
+using mozilla::PodAssign;
+using mozilla::PodCopy;
+using mozilla::PodZero;
+
+struct KeywordInfo {
+    const char* chars;         // C string with keyword text
+    TokenKind   tokentype;
+};
+
+static const KeywordInfo keywords[] = {
+#define KEYWORD_INFO(keyword, name, type) \
+    {js_##keyword##_str, type},
+    FOR_EACH_JAVASCRIPT_KEYWORD(KEYWORD_INFO)
+#undef KEYWORD_INFO
+};
+
+// Returns a KeywordInfo for the specified characters, or nullptr if the string
+// is not a keyword.
+template <typename CharT>
+static const KeywordInfo*
+FindKeyword(const CharT* s, size_t length)
+{
+    MOZ_ASSERT(length != 0);
+
+    size_t i;
+    const KeywordInfo* kw;
+    const char* chars;
+
+#define JSKW_LENGTH()           length
+#define JSKW_AT(column)         s[column]
+#define JSKW_GOT_MATCH(index)   i = (index); goto got_match;
+#define JSKW_TEST_GUESS(index)  i = (index); goto test_guess;
+#define JSKW_NO_MATCH()         goto no_match;
+#include "jsautokw.h"
+#undef JSKW_NO_MATCH
+#undef JSKW_TEST_GUESS
+#undef JSKW_GOT_MATCH
+#undef JSKW_AT
+#undef JSKW_LENGTH
+
+  got_match:
+    return &keywords[i];
+
+  test_guess:
+    kw = &keywords[i];
+    chars = kw->chars;
+    do {
+        if (*s++ != (unsigned char)(*chars++))
+            goto no_match;
+    } while (--length != 0);
+    return kw;
+
+  no_match:
+    return nullptr;
+}
+
+static const KeywordInfo*
+FindKeyword(JSLinearString* str)
+{
+    JS::AutoCheckCannotGC nogc;
+    return str->hasLatin1Chars()
+           ? FindKeyword(str->latin1Chars(nogc), str->length())
+           : FindKeyword(str->twoByteChars(nogc), str->length());
+}
+
+template <typename CharT>
+static bool
+IsIdentifier(const CharT* chars, size_t length)
+{
+    if (length == 0)
+        return false;
+
+    if (!unicode::IsIdentifierStart(char16_t(*chars)))
+        return false;
+
+    const CharT* end = chars + length;
+    while (++chars != end) {
+        if (!unicode::IsIdentifierPart(char16_t(*chars)))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+frontend::IsIdentifier(JSLinearString* str)
+{
+    JS::AutoCheckCannotGC nogc;
+    return str->hasLatin1Chars()
+           ? ::IsIdentifier(str->latin1Chars(nogc), str->length())
+           : ::IsIdentifier(str->twoByteChars(nogc), str->length());
+}
+
+bool
+frontend::IsIdentifier(const char16_t* chars, size_t length)
+{
+    return ::IsIdentifier(chars, length);
+}
+
+bool
+frontend::IsKeyword(JSLinearString* str)
+{
+    return FindKeyword(str) != nullptr;
+}
+
+TokenStream::SourceCoords::SourceCoords(ExclusiveContext* cx, uint32_t ln)
+  : lineStartOffsets_(cx), initialLineNum_(ln), lastLineIndex_(0)
+{
+    // This is actually necessary!  Removing it causes compile errors on
+    // GCC and clang.  You could try declaring this:
+    //
+    //   const uint32_t TokenStream::SourceCoords::MAX_PTR;
+    //
+    // which fixes the GCC/clang error, but causes bustage on Windows.  Sigh.
+    //
+    uint32_t maxPtr = MAX_PTR;
+
+    // The first line begins at buffer offset 0.  MAX_PTR is the sentinel.  The
+    // appends cannot fail because |lineStartOffsets_| has statically-allocated
+    // elements.
+    MOZ_ASSERT(lineStartOffsets_.capacity() >= 2);
+    MOZ_ALWAYS_TRUE(lineStartOffsets_.reserve(2));
+    lineStartOffsets_.infallibleAppend(0);
+    lineStartOffsets_.infallibleAppend(maxPtr);
+}
+
+MOZ_ALWAYS_INLINE bool
+TokenStream::SourceCoords::add(uint32_t lineNum, uint32_t lineStartOffset)
+{
+    uint32_t lineIndex = lineNumToIndex(lineNum);
+    uint32_t sentinelIndex = lineStartOffsets_.length() - 1;
+
+    MOZ_ASSERT(lineStartOffsets_[0] == 0 && lineStartOffsets_[sentinelIndex] == MAX_PTR);
+
+    if (lineIndex == sentinelIndex) {
+        // We haven't seen this newline before.  Update lineStartOffsets_
+        // only if lineStartOffsets_.append succeeds, to keep sentinel.
+        // Otherwise return false to tell TokenStream about OOM.
+        uint32_t maxPtr = MAX_PTR;
+        if (!lineStartOffsets_.append(maxPtr))
+            return false;
+
+        lineStartOffsets_[lineIndex] = lineStartOffset;
+    } else {
+        // We have seen this newline before (and ungot it).  Do nothing (other
+        // than checking it hasn't mysteriously changed).
+        // This path can be executed after hitting OOM, so check lineIndex.
+        MOZ_ASSERT_IF(lineIndex < sentinelIndex, lineStartOffsets_[lineIndex] == lineStartOffset);
+    }
+    return true;
+}
+
+MOZ_ALWAYS_INLINE bool
+TokenStream::SourceCoords::fill(const TokenStream::SourceCoords& other)
+{
+    MOZ_ASSERT(lineStartOffsets_.back() == MAX_PTR);
+    MOZ_ASSERT(other.lineStartOffsets_.back() == MAX_PTR);
+
+    if (lineStartOffsets_.length() >= other.lineStartOffsets_.length())
+        return true;
+
+    uint32_t sentinelIndex = lineStartOffsets_.length() - 1;
+    lineStartOffsets_[sentinelIndex] = other.lineStartOffsets_[sentinelIndex];
+
+    for (size_t i = sentinelIndex + 1; i < other.lineStartOffsets_.length(); i++) {
+        if (!lineStartOffsets_.append(other.lineStartOffsets_[i]))
+            return false;
+    }
+    return true;
+}
+
+MOZ_ALWAYS_INLINE uint32_t
+TokenStream::SourceCoords::lineIndexOf(uint32_t offset) const
+{
+    uint32_t iMin, iMax, iMid;
+
+    if (lineStartOffsets_[lastLineIndex_] <= offset) {
+        // If we reach here, offset is on a line the same as or higher than
+        // last time.  Check first for the +0, +1, +2 cases, because they
+        // typically cover 85--98% of cases.
+        if (offset < lineStartOffsets_[lastLineIndex_ + 1])
+            return lastLineIndex_;      // lineIndex is same as last time
+
+        // If we reach here, there must be at least one more entry (plus the
+        // sentinel).  Try it.
+        lastLineIndex_++;
+        if (offset < lineStartOffsets_[lastLineIndex_ + 1])
+            return lastLineIndex_;      // lineIndex is one higher than last time
+
+        // The same logic applies here.
+        lastLineIndex_++;
+        if (offset < lineStartOffsets_[lastLineIndex_ + 1]) {
+            return lastLineIndex_;      // lineIndex is two higher than last time
+        }
+
+        // No luck.  Oh well, we have a better-than-default starting point for
+        // the binary search.
+        iMin = lastLineIndex_ + 1;
+        MOZ_ASSERT(iMin < lineStartOffsets_.length() - 1);   // -1 due to the sentinel
+
+    } else {
+        iMin = 0;
+    }
+
+    // This is a binary search with deferred detection of equality, which was
+    // marginally faster in this case than a standard binary search.
+    // The -2 is because |lineStartOffsets_.length() - 1| is the sentinel, and we
+    // want one before that.
+    iMax = lineStartOffsets_.length() - 2;
+    while (iMax > iMin) {
+        iMid = iMin + (iMax - iMin) / 2;
+        if (offset >= lineStartOffsets_[iMid + 1])
+            iMin = iMid + 1;    // offset is above lineStartOffsets_[iMid]
+        else
+            iMax = iMid;        // offset is below or within lineStartOffsets_[iMid]
+    }
+    MOZ_ASSERT(iMax == iMin);
+    MOZ_ASSERT(lineStartOffsets_[iMin] <= offset && offset < lineStartOffsets_[iMin + 1]);
+    lastLineIndex_ = iMin;
+    return iMin;
+}
+
+uint32_t
+TokenStream::SourceCoords::lineNum(uint32_t offset) const
+{
+    uint32_t lineIndex = lineIndexOf(offset);
+    return lineIndexToNum(lineIndex);
+}
+
+uint32_t
+TokenStream::SourceCoords::columnIndex(uint32_t offset) const
+{
+    uint32_t lineIndex = lineIndexOf(offset);
+    uint32_t lineStartOffset = lineStartOffsets_[lineIndex];
+    MOZ_ASSERT(offset >= lineStartOffset);
+    return offset - lineStartOffset;
+}
+
+void
+TokenStream::SourceCoords::lineNumAndColumnIndex(uint32_t offset, uint32_t* lineNum,
+                                                 uint32_t* columnIndex) const
+{
+    uint32_t lineIndex = lineIndexOf(offset);
+    *lineNum = lineIndexToNum(lineIndex);
+    uint32_t lineStartOffset = lineStartOffsets_[lineIndex];
+    MOZ_ASSERT(offset >= lineStartOffset);
+    *columnIndex = offset - lineStartOffset;
+}
+
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable:4351)
+#endif
+
+TokenStream::TokenStream(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
+                         const char16_t* base, size_t length, StrictModeGetter* smg)
+  : srcCoords(cx, options.lineno),
+    options_(options),
+    tokens(),
+    cursor(),
+    lookahead(),
+    lineno(options.lineno),
+    flags(),
+    linebase(0),
+    prevLinebase(size_t(-1)),
+    userbuf(cx, base, length, options.column),
+    filename(options.filename()),
+    displayURL_(nullptr),
+    sourceMapURL_(nullptr),
+    tokenbuf(cx),
+    cx(cx),
+    mutedErrors(options.mutedErrors()),
+    strictModeGetter(smg)
+{
+    // Nb: the following tables could be static, but initializing them here is
+    // much easier.  Don't worry, the time to initialize them for each
+    // TokenStream is trivial.  See bug 639420.
+
+    // See Parser::assignExpr() for an explanation of isExprEnding[].
+    memset(isExprEnding, 0, sizeof(isExprEnding));
+    isExprEnding[TOK_COMMA] = 1;
+    isExprEnding[TOK_SEMI]  = 1;
+    isExprEnding[TOK_COLON] = 1;
+    isExprEnding[TOK_RP]    = 1;
+    isExprEnding[TOK_RB]    = 1;
+    isExprEnding[TOK_RC]    = 1;
+}
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
+bool
+TokenStream::checkOptions()
+{
+    // Constrain starting columns to half of the range of a signed 32-bit value,
+    // to avoid overflow.
+    if (options().column >= mozilla::MaxValue<int32_t>::value / 2 + 1) {
+        reportErrorNoOffset(JSMSG_BAD_COLUMN_NUMBER);
+        return false;
+    }
+
+    return true;
+}
+
+TokenStream::~TokenStream()
+{
+}
+
+// Use the fastest available getc.
+#if defined(HAVE_GETC_UNLOCKED)
+# define fast_getc getc_unlocked
+#elif defined(HAVE__GETC_NOLOCK)
+# define fast_getc _getc_nolock
+#else
+# define fast_getc getc
+#endif
+
+MOZ_ALWAYS_INLINE void
+TokenStream::updateLineInfoForEOL()
+{
+    prevLinebase = linebase;
+    linebase = userbuf.offset();
+    lineno++;
+    if (!srcCoords.add(lineno, linebase))
+        flags.hitOOM = true;
+}
+
+MOZ_ALWAYS_INLINE void
+TokenStream::updateFlagsForEOL()
+{
+    flags.isDirtyLine = false;
+}
+
+// This gets the next char, normalizing all EOL sequences to '\n' as it goes.
+int32_t
+TokenStream::getChar()
+{
+    int32_t c;
+    if (MOZ_LIKELY(userbuf.hasRawChars())) {
+        c = userbuf.getRawChar();
+
+        // Normalize the char16_t if it was a newline.
+        if (MOZ_UNLIKELY(c == '\n'))
+            goto eol;
+        if (MOZ_UNLIKELY(c == '\r')) {
+            // If it's a \r\n sequence: treat as a single EOL, skip over the \n.
+            if (MOZ_LIKELY(userbuf.hasRawChars()))
+                userbuf.matchRawChar('\n');
+            goto eol;
+        }
+        if (MOZ_UNLIKELY(c == LINE_SEPARATOR || c == PARA_SEPARATOR))
+            goto eol;
+
+        return c;
+    }
+
+    flags.isEOF = true;
+    return EOF;
+
+  eol:
+    updateLineInfoForEOL();
+    return '\n';
+}
+
+// This gets the next char. It does nothing special with EOL sequences, not
+// even updating the line counters.  It can be used safely if (a) the
+// resulting char is guaranteed to be ungotten (by ungetCharIgnoreEOL()) if
+// it's an EOL, and (b) the line-related state (lineno, linebase) is not used
+// before it's ungotten.
+int32_t
+TokenStream::getCharIgnoreEOL()
+{
+    if (MOZ_LIKELY(userbuf.hasRawChars()))
+        return userbuf.getRawChar();
+
+    flags.isEOF = true;
+    return EOF;
+}
+
+void
+TokenStream::ungetChar(int32_t c)
+{
+    if (c == EOF)
+        return;
+    MOZ_ASSERT(!userbuf.atStart());
+    userbuf.ungetRawChar();
+    if (c == '\n') {
+#ifdef DEBUG
+        int32_t c2 = userbuf.peekRawChar();
+        MOZ_ASSERT(TokenBuf::isRawEOLChar(c2));
+#endif
+
+        // If it's a \r\n sequence, also unget the \r.
+        if (!userbuf.atStart())
+            userbuf.matchRawCharBackwards('\r');
+
+        MOZ_ASSERT(prevLinebase != size_t(-1));    // we should never get more than one EOL char
+        linebase = prevLinebase;
+        prevLinebase = size_t(-1);
+        lineno--;
+    } else {
+        MOZ_ASSERT(userbuf.peekRawChar() == c);
+    }
+}
+
+void
+TokenStream::ungetCharIgnoreEOL(int32_t c)
+{
+    if (c == EOF)
+        return;
+    MOZ_ASSERT(!userbuf.atStart());
+    userbuf.ungetRawChar();
+}
+
+// Return true iff |n| raw characters can be read from this without reading past
+// EOF or a newline, and copy those characters into |cp| if so.  The characters
+// are not consumed: use skipChars(n) to do so after checking that the consumed
+// characters had appropriate values.
+bool
+TokenStream::peekChars(int n, char16_t* cp)
+{
+    int i, j;
+    int32_t c;
+
+    for (i = 0; i < n; i++) {
+        c = getCharIgnoreEOL();
+        if (c == EOF)
+            break;
+        if (c == '\n') {
+            ungetCharIgnoreEOL(c);
+            break;
+        }
+        cp[i] = char16_t(c);
+    }
+    for (j = i - 1; j >= 0; j--)
+        ungetCharIgnoreEOL(cp[j]);
+    return i == n;
+}
+
+size_t
+TokenStream::TokenBuf::findEOLMax(size_t start, size_t max)
+{
+    const char16_t* p = rawCharPtrAt(start);
+
+    size_t n = 0;
+    while (true) {
+        if (p >= limit_)
+            break;
+        if (n >= max)
+            break;
+        n++;
+        if (TokenBuf::isRawEOLChar(*p++))
+            break;
+    }
+    return start + n;
+}
+
+bool
+TokenStream::advance(size_t position)
+{
+    const char16_t* end = userbuf.rawCharPtrAt(position);
+    while (userbuf.addressOfNextRawChar() < end)
+        getChar();
+
+    Token* cur = &tokens[cursor];
+    cur->pos.begin = userbuf.offset();
+    MOZ_MAKE_MEM_UNDEFINED(&cur->type, sizeof(cur->type));
+    lookahead = 0;
+
+    if (flags.hitOOM)
+        return reportError(JSMSG_OUT_OF_MEMORY);
+
+    return true;
+}
+
+void
+TokenStream::tell(Position* pos)
+{
+    pos->buf = userbuf.addressOfNextRawChar(/* allowPoisoned = */ true);
+    pos->flags = flags;
+    pos->lineno = lineno;
+    pos->linebase = linebase;
+    pos->prevLinebase = prevLinebase;
+    pos->lookahead = lookahead;
+    pos->currentToken = currentToken();
+    for (unsigned i = 0; i < lookahead; i++)
+        pos->lookaheadTokens[i] = tokens[(cursor + 1 + i) & ntokensMask];
+}
+
+void
+TokenStream::seek(const Position& pos)
+{
+    userbuf.setAddressOfNextRawChar(pos.buf, /* allowPoisoned = */ true);
+    flags = pos.flags;
+    lineno = pos.lineno;
+    linebase = pos.linebase;
+    prevLinebase = pos.prevLinebase;
+    lookahead = pos.lookahead;
+
+    tokens[cursor] = pos.currentToken;
+    for (unsigned i = 0; i < lookahead; i++)
+        tokens[(cursor + 1 + i) & ntokensMask] = pos.lookaheadTokens[i];
+}
+
+bool
+TokenStream::seek(const Position& pos, const TokenStream& other)
+{
+    if (!srcCoords.fill(other.srcCoords))
+        return false;
+    seek(pos);
+    return true;
+}
+
+bool
+TokenStream::reportStrictModeErrorNumberVA(uint32_t offset, bool strictMode, unsigned errorNumber,
+                                           va_list args)
+{
+    // In strict mode code, this is an error, not merely a warning.
+    unsigned flags;
+    if (strictMode)
+        flags = JSREPORT_ERROR;
+    else if (options().extraWarningsOption)
+        flags = JSREPORT_WARNING | JSREPORT_STRICT;
+    else
+        return true;
+
+    return reportCompileErrorNumberVA(offset, flags, errorNumber, args);
+}
+
+void
+CompileError::throwError(JSContext* cx)
+{
+    if (JSREPORT_IS_WARNING(flags)) {
+        CallWarningReporter(cx, this);
+        return;
+    }
+
+    // If there's a runtime exception type associated with this error
+    // number, set that as the pending exception.  For errors occuring at
+    // compile time, this is very likely to be a JSEXN_SYNTAXERR.
+    //
+    // If an exception is thrown but not caught, the JSREPORT_EXCEPTION
+    // flag will be set in report.flags.  Proper behavior for an error
+    // reporter is to ignore a report with this flag for all but top-level
+    // compilation errors.  The exception will remain pending, and so long
+    // as the non-top-level "load", "eval", or "compile" native function
+    // returns false, the top-level reporter will eventually receive the
+    // uncaught exception report.
+    ErrorToException(cx, this, nullptr, nullptr);
+}
+
+bool
+TokenStream::reportCompileErrorNumberVA(uint32_t offset, unsigned flags, unsigned errorNumber,
+                                        va_list args)
+{
+    bool warning = JSREPORT_IS_WARNING(flags);
+
+    if (warning && options().werrorOption) {
+        flags &= ~JSREPORT_WARNING;
+        warning = false;
+    }
+
+    // On the main thread, report the error immediately. When compiling off
+    // thread, save the error so that the main thread can report it later.
+    CompileError tempErr;
+    CompileError* tempErrPtr = &tempErr;
+    if (!cx->isJSContext() && !cx->addPendingCompileError(&tempErrPtr))
+        return false;
+    CompileError& err = *tempErrPtr;
+
+    err.flags = flags;
+    err.errorNumber = errorNumber;
+    err.filename = filename;
+    err.isMuted = mutedErrors;
+    if (offset == NoOffset) {
+        err.lineno = 0;
+        err.column = 0;
+    } else {
+        err.lineno = srcCoords.lineNum(offset);
+        err.column = srcCoords.columnIndex(offset);
+    }
+
+    // If we have no location information, try to get one from the caller.
+    bool callerFilename = false;
+    if (offset != NoOffset && !err.filename && cx->isJSContext()) {
+        NonBuiltinFrameIter iter(cx->asJSContext(),
+                                 FrameIter::FOLLOW_DEBUGGER_EVAL_PREV_LINK,
+                                 cx->compartment()->principals());
+        if (!iter.done() && iter.filename()) {
+            callerFilename = true;
+            err.filename = iter.filename();
+            err.lineno = iter.computeLine(&err.column);
+        }
+    }
+
+    if (!ExpandErrorArgumentsVA(cx, GetErrorMessage, nullptr, errorNumber,
+                                nullptr, ArgumentsAreLatin1, &err, args))
+    {
+        return false;
+    }
+
+    // Given a token, T, that we want to complain about: if T's (starting)
+    // lineno doesn't match TokenStream's lineno, that means we've scanned past
+    // the line that T starts on, which makes it hard to print some or all of
+    // T's (starting) line for context.
+    //
+    // So we don't even try, leaving report.linebuf and friends zeroed.  This
+    // means that any error involving a multi-line token (e.g. an unterminated
+    // multi-line string literal) won't have a context printed.
+    if (offset != NoOffset && err.lineno == lineno && !callerFilename) {
+        // We show only a portion (a "window") of the line around the erroneous
+        // token -- the first char in the token, plus |windowRadius| chars
+        // before it and |windowRadius - 1| chars after it.  This is because
+        // lines can be very long and printing the whole line is (a) not that
+        // helpful, and (b) can waste a lot of memory.  See bug 634444.
+        static const size_t windowRadius = 60;
+
+        // The window must start within the current line, no earlier than
+        // windowRadius characters before offset.
+        size_t windowStart = (offset - linebase > windowRadius) ?
+                             offset - windowRadius :
+                             linebase;
+
+        // The window must start within the portion of the current line
+        // that we actually have in our buffer.
+        if (windowStart < userbuf.startOffset())
+            windowStart = userbuf.startOffset();
+
+        // The window must end within the current line, no later than
+        // windowRadius after offset.
+        size_t windowEnd = userbuf.findEOLMax(offset, windowRadius);
+        size_t windowLength = windowEnd - windowStart;
+        MOZ_ASSERT(windowLength <= windowRadius * 2);
+
+        // Create the windowed strings.
+        StringBuffer windowBuf(cx);
+        if (!windowBuf.append(userbuf.rawCharPtrAt(windowStart), windowLength) ||
+            !windowBuf.append('\0'))
+        {
+            return false;
+        }
+
+        // The window into the offending source line, without final \n.
+        UniqueTwoByteChars linebuf(windowBuf.stealChars());
+        if (!linebuf)
+            return false;
+
+        err.initOwnedLinebuf(linebuf.release(), windowLength, offset - windowStart);
+    }
+
+    if (cx->isJSContext())
+        err.throwError(cx->asJSContext());
+
+    return warning;
+}
+
+bool
+TokenStream::reportStrictModeError(unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportStrictModeErrorNumberVA(currentToken().pos.begin, strictMode(),
+                                                errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+bool
+TokenStream::reportError(unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportCompileErrorNumberVA(currentToken().pos.begin, JSREPORT_ERROR, errorNumber,
+                                             args);
+    va_end(args);
+    return result;
+}
+
+bool
+TokenStream::reportErrorNoOffset(unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportCompileErrorNumberVA(NoOffset, JSREPORT_ERROR, errorNumber,
+                                             args);
+    va_end(args);
+    return result;
+}
+
+bool
+TokenStream::reportWarning(unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    bool result = reportCompileErrorNumberVA(currentToken().pos.begin, JSREPORT_WARNING,
+                                             errorNumber, args);
+    va_end(args);
+    return result;
+}
+
+bool
+TokenStream::reportStrictWarningErrorNumberVA(uint32_t offset, unsigned errorNumber, va_list args)
+{
+    if (!options().extraWarningsOption)
+        return true;
+
+    return reportCompileErrorNumberVA(offset, JSREPORT_STRICT|JSREPORT_WARNING, errorNumber, args);
+}
+
+void
+TokenStream::reportAsmJSError(uint32_t offset, unsigned errorNumber, ...)
+{
+    va_list args;
+    va_start(args, errorNumber);
+    unsigned flags = options().throwOnAsmJSValidationFailureOption
+                     ? JSREPORT_ERROR
+                     : JSREPORT_WARNING;
+    reportCompileErrorNumberVA(offset, flags, errorNumber, args);
+    va_end(args);
+}
+
+// We have encountered a '\': check for a Unicode escape sequence after it.
+// Return the length of the escape sequence and the character code point (by
+// value) if we found a Unicode escape sequence.  Otherwise, return 0.  In both
+// cases, do not advance along the buffer.
+uint32_t
+TokenStream::peekUnicodeEscape(uint32_t* codePoint)
+{
+    int32_t c = getCharIgnoreEOL();
+    if (c != 'u') {
+        ungetCharIgnoreEOL(c);
+        return 0;
+    }
+
+    char16_t cp[3];
+    uint32_t length;
+    c = getCharIgnoreEOL();
+    if (JS7_ISHEX(c) && peekChars(3, cp) &&
+        JS7_ISHEX(cp[0]) && JS7_ISHEX(cp[1]) && JS7_ISHEX(cp[2]))
+    {
+        *codePoint = (JS7_UNHEX(c) << 12) |
+                     (JS7_UNHEX(cp[0]) << 8) |
+                     (JS7_UNHEX(cp[1]) << 4) |
+                     JS7_UNHEX(cp[2]);
+        length = 5;
+    } else if (c == '{') {
+        length = peekExtendedUnicodeEscape(codePoint);
+    } else {
+        length = 0;
+    }
+
+    ungetCharIgnoreEOL(c);
+    ungetCharIgnoreEOL('u');
+    return length;
+}
+
+uint32_t
+TokenStream::peekExtendedUnicodeEscape(uint32_t* codePoint)
+{
+    // The opening brace character was already read.
+    int32_t c = getCharIgnoreEOL();
+
+    // Skip leading zeros.
+    uint32_t leadingZeros = 0;
+    while (c == '0') {
+        leadingZeros++;
+        c = getCharIgnoreEOL();
+    }
+
+    char16_t cp[6];
+    size_t i = 0;
+    uint32_t code = 0;
+    while (JS7_ISHEX(c) && i < 6) {
+        cp[i++] = c;
+        code = code << 4 | JS7_UNHEX(c);
+        c = getCharIgnoreEOL();
+    }
+
+    uint32_t length;
+    if (c == '}' && (leadingZeros > 0 || i > 0) && code <= unicode::NonBMPMax) {
+        *codePoint = code;
+        length = leadingZeros + i + 3;
+    } else {
+        length = 0;
+    }
+
+    ungetCharIgnoreEOL(c);
+    while (i--)
+        ungetCharIgnoreEOL(cp[i]);
+    while (leadingZeros--)
+        ungetCharIgnoreEOL('0');
+
+    return length;
+}
+
+uint32_t
+TokenStream::matchUnicodeEscapeIdStart(uint32_t* codePoint)
+{
+    uint32_t length = peekUnicodeEscape(codePoint);
+    if (length > 0 && unicode::IsIdentifierStart(*codePoint)) {
+        skipChars(length);
+        return length;
+    }
+    return 0;
+}
+
+bool
+TokenStream::matchUnicodeEscapeIdent(uint32_t* codePoint)
+{
+    uint32_t length = peekUnicodeEscape(codePoint);
+    if (length > 0 && unicode::IsIdentifierPart(*codePoint)) {
+        skipChars(length);
+        return true;
+    }
+    return false;
+}
+
+// Helper function which returns true if the first length(q) characters in p are
+// the same as the characters in q.
+static bool
+CharsMatch(const char16_t* p, const char* q) {
+    while (*q) {
+        if (*p++ != *q++)
+            return false;
+    }
+    return true;
+}
+
+bool
+TokenStream::getDirectives(bool isMultiline, bool shouldWarnDeprecated)
+{
+    // Match directive comments used in debugging, such as "//# sourceURL" and
+    // "//# sourceMappingURL". Use of "//@" instead of "//#" is deprecated.
+    //
+    // To avoid a crashing bug in IE, several JavaScript transpilers wrap single
+    // line comments containing a source mapping URL inside a multiline
+    // comment. To avoid potentially expensive lookahead and backtracking, we
+    // only check for this case if we encounter a '#' character.
+
+    if (!getDisplayURL(isMultiline, shouldWarnDeprecated))
+        return false;
+    if (!getSourceMappingURL(isMultiline, shouldWarnDeprecated))
+        return false;
+
+    return true;
+}
+
+bool
+TokenStream::getDirective(bool isMultiline, bool shouldWarnDeprecated,
+                          const char* directive, int directiveLength,
+                          const char* errorMsgPragma,
+                          UniqueTwoByteChars* destination)
+{
+    MOZ_ASSERT(directiveLength <= 18);
+    char16_t peeked[18];
+    int32_t c;
+
+    if (peekChars(directiveLength, peeked) && CharsMatch(peeked, directive)) {
+        if (shouldWarnDeprecated &&
+            !reportWarning(JSMSG_DEPRECATED_PRAGMA, errorMsgPragma))
+            return false;
+
+        skipChars(directiveLength);
+        tokenbuf.clear();
+
+        while ((c = peekChar()) && c != EOF && !unicode::IsSpaceOrBOM2(c)) {
+            getChar();
+            // Debugging directives can occur in both single- and multi-line
+            // comments. If we're currently inside a multi-line comment, we also
+            // need to recognize multi-line comment terminators.
+            if (isMultiline && c == '*' && peekChar() == '/') {
+                ungetChar('*');
+                break;
+            }
+            if (!tokenbuf.append(c))
+                return false;
+        }
+
+        if (tokenbuf.empty()) {
+            // The directive's URL was missing, but this is not quite an
+            // exception that we should stop and drop everything for.
+            return true;
+        }
+
+        size_t length = tokenbuf.length();
+
+        *destination = cx->make_pod_array<char16_t>(length + 1);
+        if (!*destination)
+            return false;
+
+        PodCopy(destination->get(), tokenbuf.begin(), length);
+        (*destination)[length] = '\0';
+    }
+
+    return true;
+}
+
+bool
+TokenStream::getDisplayURL(bool isMultiline, bool shouldWarnDeprecated)
+{
+    // Match comments of the form "//# sourceURL=<url>" or
+    // "/\* //# sourceURL=<url> *\/"
+    //
+    // Note that while these are labeled "sourceURL" in the source text,
+    // internally we refer to it as a "displayURL" to distinguish what the
+    // developer would like to refer to the source as from the source's actual
+    // URL.
+
+    return getDirective(isMultiline, shouldWarnDeprecated, " sourceURL=", 11,
+                        "sourceURL", &displayURL_);
+}
+
+bool
+TokenStream::getSourceMappingURL(bool isMultiline, bool shouldWarnDeprecated)
+{
+    // Match comments of the form "//# sourceMappingURL=<url>" or
+    // "/\* //# sourceMappingURL=<url> *\/"
+
+    return getDirective(isMultiline, shouldWarnDeprecated, " sourceMappingURL=", 18,
+                        "sourceMappingURL", &sourceMapURL_);
+}
+
+MOZ_ALWAYS_INLINE Token*
+TokenStream::newToken(ptrdiff_t adjust)
+{
+    cursor = (cursor + 1) & ntokensMask;
+    Token* tp = &tokens[cursor];
+    tp->pos.begin = userbuf.offset() + adjust;
+
+    // NOTE: tp->pos.end is not set until the very end of getTokenInternal().
+    MOZ_MAKE_MEM_UNDEFINED(&tp->pos.end, sizeof(tp->pos.end));
+
+    return tp;
+}
+
+MOZ_ALWAYS_INLINE JSAtom*
+TokenStream::atomize(ExclusiveContext* cx, CharBuffer& cb)
+{
+    return AtomizeChars(cx, cb.begin(), cb.length());
+}
+
+#ifdef DEBUG
+static bool
+IsTokenSane(Token* tp)
+{
+    // Nb: TOK_EOL should never be used in an actual Token;  it should only be
+    // returned as a TokenKind from peekTokenSameLine().
+    if (tp->type < 0 || tp->type >= TOK_LIMIT || tp->type == TOK_EOL)
+        return false;
+
+    if (tp->pos.end < tp->pos.begin)
+        return false;
+
+    return true;
+}
+#endif
+
+bool
+TokenStream::putIdentInTokenbuf(const char16_t* identStart)
+{
+    int32_t c;
+    uint32_t qc;
+    const char16_t* tmp = userbuf.addressOfNextRawChar();
+    userbuf.setAddressOfNextRawChar(identStart);
+
+    tokenbuf.clear();
+    for (;;) {
+        c = getCharIgnoreEOL();
+        if (!unicode::IsIdentifierPart(char16_t(c))) {
+            if (c != '\\' || !matchUnicodeEscapeIdent(&qc))
+                break;
+            c = qc;
+        }
+        if (!tokenbuf.append(c)) {
+            userbuf.setAddressOfNextRawChar(tmp);
+            return false;
+        }
+    }
+    userbuf.setAddressOfNextRawChar(tmp);
+    return true;
+}
+
+bool
+TokenStream::checkForKeyword(const KeywordInfo* kw, TokenKind* ttp)
+{
+    if (!awaitIsKeyword && kw->tokentype == TOK_AWAIT) {
+        if (ttp)
+            *ttp = TOK_NAME;
+        return true;
+    }
+
+    if (kw->tokentype == TOK_RESERVED)
+        return reportError(JSMSG_RESERVED_ID, kw->chars);
+
+    if (kw->tokentype == TOK_STRICT_RESERVED)
+        return reportStrictModeError(JSMSG_RESERVED_ID, kw->chars);
+
+    // Working keyword.
+    *ttp = kw->tokentype;
+    return true;
+}
+
+bool
+TokenStream::checkForKeyword(JSAtom* atom, TokenKind* ttp)
+{
+    const KeywordInfo* kw = FindKeyword(atom);
+    if (!kw)
+        return true;
+
+    return checkForKeyword(kw, ttp);
+}
+
+enum FirstCharKind {
+    // A char16_t has the 'OneChar' kind if it, by itself, constitutes a valid
+    // token that cannot also be a prefix of a longer token.  E.g. ';' has the
+    // OneChar kind, but '+' does not, because '++' and '+=' are valid longer tokens
+    // that begin with '+'.
+    //
+    // The few token kinds satisfying these properties cover roughly 35--45%
+    // of the tokens seen in practice.
+    //
+    // We represent the 'OneChar' kind with any positive value less than
+    // TOK_LIMIT.  This representation lets us associate each one-char token
+    // char16_t with a TokenKind and thus avoid a subsequent char16_t-to-TokenKind
+    // conversion.
+    OneChar_Min = 0,
+    OneChar_Max = TOK_LIMIT - 1,
+
+    Space = TOK_LIMIT,
+    Ident,
+    Dec,
+    String,
+    EOL,
+    BasePrefix,
+    Other,
+
+    LastCharKind = Other
+};
+
+// OneChar: 40,  41,  44,  58,  59,  63,  91,  93,  123, 125, 126:
+//          '(', ')', ',', ':', ';', '?', '[', ']', '{', '}', '~'
+// Ident:   36, 65..90, 95, 97..122: '$', 'A'..'Z', '_', 'a'..'z'
+// Dot:     46: '.'
+// Equals:  61: '='
+// String:  34, 39: '"', '\''
+// Dec:     49..57: '1'..'9'
+// Plus:    43: '+'
+// BasePrefix:  48: '0'
+// Space:   9, 11, 12, 32: '\t', '\v', '\f', ' '
+// EOL:     10, 13: '\n', '\r'
+//
+#define T_COMMA     TOK_COMMA
+#define T_COLON     TOK_COLON
+#define T_BITNOT    TOK_BITNOT
+#define Templat     String
+#define _______     Other
+static const uint8_t firstCharKinds[] = {
+/*         0        1        2        3        4        5        6        7        8        9    */
+/*   0+ */ _______, _______, _______, _______, _______, _______, _______, _______, _______,   Space,
+/*  10+ */     EOL,   Space,   Space,     EOL, _______, _______, _______, _______, _______, _______,
+/*  20+ */ _______, _______, _______, _______, _______, _______, _______, _______, _______, _______,
+/*  30+ */ _______, _______,   Space, _______,  String, _______,   Ident, _______, _______,  String,
+/*  40+ */  TOK_LP,  TOK_RP, _______, _______, T_COMMA,_______,  _______, _______,BasePrefix,  Dec,
+/*  50+ */     Dec,     Dec,     Dec,     Dec,     Dec,     Dec,     Dec,    Dec,  T_COLON,TOK_SEMI,
+/*  60+ */ _______, _______, _______,TOK_HOOK, _______,   Ident,   Ident,   Ident,   Ident,   Ident,
+/*  70+ */   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,
+/*  80+ */   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,
+/*  90+ */   Ident,  TOK_LB, _______,  TOK_RB, _______,   Ident, Templat,   Ident,   Ident,   Ident,
+/* 100+ */   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,
+/* 110+ */   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,   Ident,
+/* 120+ */   Ident,   Ident,   Ident,  TOK_LC, _______,  TOK_RC,T_BITNOT, _______
+};
+#undef T_COMMA
+#undef T_COLON
+#undef T_BITNOT
+#undef Templat
+#undef _______
+
+static_assert(LastCharKind < (1 << (sizeof(firstCharKinds[0]) * 8)),
+              "Elements of firstCharKinds[] are too small");
+
+bool
+TokenStream::getTokenInternal(TokenKind* ttp, Modifier modifier)
+{
+    int c;
+    uint32_t qc;
+    Token* tp;
+    FirstCharKind c1kind;
+    const char16_t* numStart;
+    bool hasExp;
+    DecimalPoint decimalPoint;
+    const char16_t* identStart;
+    bool hadUnicodeEscape;
+
+    // Check if in the middle of a template string. Have to get this out of
+    // the way first.
+    if (MOZ_UNLIKELY(modifier == TemplateTail)) {
+        if (!getStringOrTemplateToken('`', &tp))
+            goto error;
+        goto out;
+    }
+
+  retry:
+    if (MOZ_UNLIKELY(!userbuf.hasRawChars())) {
+        tp = newToken(0);
+        tp->type = TOK_EOF;
+        flags.isEOF = true;
+        goto out;
+    }
+
+    c = userbuf.getRawChar();
+    MOZ_ASSERT(c != EOF);
+
+    // Chars not in the range 0..127 are rare.  Getting them out of the way
+    // early allows subsequent checking to be faster.
+    if (MOZ_UNLIKELY(c >= 128)) {
+        if (unicode::IsSpaceOrBOM2(c)) {
+            if (c == LINE_SEPARATOR || c == PARA_SEPARATOR) {
+                updateLineInfoForEOL();
+                updateFlagsForEOL();
+            }
+
+            goto retry;
+        }
+
+        tp = newToken(-1);
+
+        static_assert('$' < 128,
+                      "IdentifierStart contains '$', but as !IsUnicodeIDStart('$'), "
+                      "ensure that '$' is never handled here");
+        static_assert('_' < 128,
+                      "IdentifierStart contains '_', but as !IsUnicodeIDStart('_'), "
+                      "ensure that '_' is never handled here");
+        if (unicode::IsUnicodeIDStart(c)) {
+            identStart = userbuf.addressOfNextRawChar() - 1;
+            hadUnicodeEscape = false;
+            goto identifier;
+        }
+
+        goto badchar;
+    }
+
+    // Get the token kind, based on the first char.  The ordering of c1kind
+    // comparison is based on the frequency of tokens in real code -- Parsemark
+    // (which represents typical JS code on the web) and the Unreal demo (which
+    // represents asm.js code).
+    //
+    //                  Parsemark   Unreal
+    //  OneChar         32.9%       39.7%
+    //  Space           25.0%        0.6%
+    //  Ident           19.2%       36.4%
+    //  Dec              7.2%        5.1%
+    //  String           7.9%        0.0%
+    //  EOL              1.7%        0.0%
+    //  BasePrefix       0.4%        4.9%
+    //  Other            5.7%       13.3%
+    //
+    // The ordering is based mostly only Parsemark frequencies, with Unreal
+    // frequencies used to break close categories (e.g. |Dec| and |String|).
+    // |Other| is biggish, but no other token kind is common enough for it to
+    // be worth adding extra values to FirstCharKind.
+    //
+    c1kind = FirstCharKind(firstCharKinds[c]);
+
+    // Look for an unambiguous single-char token.
+    //
+    if (c1kind <= OneChar_Max) {
+        tp = newToken(-1);
+        tp->type = TokenKind(c1kind);
+        goto out;
+    }
+
+    // Skip over non-EOL whitespace chars.
+    //
+    if (c1kind == Space)
+        goto retry;
+
+    // Look for an identifier.
+    //
+    if (c1kind == Ident) {
+        tp = newToken(-1);
+        identStart = userbuf.addressOfNextRawChar() - 1;
+        hadUnicodeEscape = false;
+
+      identifier:
+        for (;;) {
+            c = getCharIgnoreEOL();
+            if (c == EOF)
+                break;
+            if (!unicode::IsIdentifierPart(char16_t(c))) {
+                if (c != '\\' || !matchUnicodeEscapeIdent(&qc))
+                    break;
+                hadUnicodeEscape = true;
+            }
+        }
+        ungetCharIgnoreEOL(c);
+
+        // Identifiers containing no Unicode escapes can be processed directly
+        // from userbuf.  The rest must use the escapes converted via tokenbuf
+        // before atomizing.
+        const char16_t* chars;
+        size_t length;
+        if (hadUnicodeEscape) {
+            if (!putIdentInTokenbuf(identStart))
+                goto error;
+
+            chars = tokenbuf.begin();
+            length = tokenbuf.length();
+        } else {
+            chars = identStart;
+            length = userbuf.addressOfNextRawChar() - identStart;
+        }
+
+        // Represent keywords as keyword tokens unless told otherwise.
+        if (modifier != KeywordIsName) {
+            if (const KeywordInfo* kw = FindKeyword(chars, length)) {
+                // That said, keywords can't contain escapes.  (Contexts where
+                // keywords are treated as names, that also sometimes treat
+                // keywords as keywords, must manually check this requirement.)
+                // There are two exceptions
+                // 1) StrictReservedWords: These keywords need to be treated as
+                //    names in non-strict mode.
+                // 2) yield is also treated as a name if it contains an escape
+                //    sequence. The parser must handle this case separately.
+                if (hadUnicodeEscape && !(
+                        (kw->tokentype == TOK_STRICT_RESERVED && !strictMode()) ||
+                         kw->tokentype == TOK_YIELD))
+                {
+                    reportError(JSMSG_ESCAPED_KEYWORD);
+                    goto error;
+                }
+
+                tp->type = TOK_NAME;
+                if (!checkForKeyword(kw, &tp->type))
+                    goto error;
+                if (tp->type != TOK_NAME && !hadUnicodeEscape)
+                    goto out;
+            }
+        }
+
+        JSAtom* atom = AtomizeChars(cx, chars, length);
+        if (!atom)
+            goto error;
+        tp->type = TOK_NAME;
+        tp->setName(atom->asPropertyName());
+        goto out;
+    }
+
+    // Look for a decimal number.
+    //
+    if (c1kind == Dec) {
+        tp = newToken(-1);
+        numStart = userbuf.addressOfNextRawChar() - 1;
+
+      decimal:
+        decimalPoint = NoDecimal;
+        hasExp = false;
+        while (JS7_ISDEC(c))
+            c = getCharIgnoreEOL();
+
+        if (c == '.') {
+            decimalPoint = HasDecimal;
+          decimal_dot:
+            do {
+                c = getCharIgnoreEOL();
+            } while (JS7_ISDEC(c));
+        }
+        if (c == 'e' || c == 'E') {
+            hasExp = true;
+            c = getCharIgnoreEOL();
+            if (c == '+' || c == '-')
+                c = getCharIgnoreEOL();
+            if (!JS7_ISDEC(c)) {
+                ungetCharIgnoreEOL(c);
+                reportError(JSMSG_MISSING_EXPONENT);
+                goto error;
+            }
+            do {
+                c = getCharIgnoreEOL();
+            } while (JS7_ISDEC(c));
+        }
+        ungetCharIgnoreEOL(c);
+
+        if (c != EOF && unicode::IsIdentifierStart(char16_t(c))) {
+            reportError(JSMSG_IDSTART_AFTER_NUMBER);
+            goto error;
+        }
+
+        // Unlike identifiers and strings, numbers cannot contain escaped
+        // chars, so we don't need to use tokenbuf.  Instead we can just
+        // convert the char16_t characters in userbuf to the numeric value.
+        double dval;
+        if (!((decimalPoint == HasDecimal) || hasExp)) {
+            if (!GetDecimalInteger(cx, numStart, userbuf.addressOfNextRawChar(), &dval))
+                goto error;
+        } else {
+            const char16_t* dummy;
+            if (!js_strtod(cx, numStart, userbuf.addressOfNextRawChar(), &dummy, &dval))
+                goto error;
+        }
+        tp->type = TOK_NUMBER;
+        tp->setNumber(dval, decimalPoint);
+        goto out;
+    }
+
+    // Look for a string or a template string.
+    //
+    if (c1kind == String) {
+        if (!getStringOrTemplateToken(c, &tp))
+            goto error;
+        goto out;
+    }
+
+    // Skip over EOL chars, updating line state along the way.
+    //
+    if (c1kind == EOL) {
+        // If it's a \r\n sequence: treat as a single EOL, skip over the \n.
+        if (c == '\r' && userbuf.hasRawChars())
+            userbuf.matchRawChar('\n');
+        updateLineInfoForEOL();
+        updateFlagsForEOL();
+        goto retry;
+    }
+
+    // Look for a hexadecimal, octal, or binary number.
+    //
+    if (c1kind == BasePrefix) {
+        tp = newToken(-1);
+        int radix;
+        c = getCharIgnoreEOL();
+        if (c == 'x' || c == 'X') {
+            radix = 16;
+            c = getCharIgnoreEOL();
+            if (!JS7_ISHEX(c)) {
+                ungetCharIgnoreEOL(c);
+                reportError(JSMSG_MISSING_HEXDIGITS);
+                goto error;
+            }
+            numStart = userbuf.addressOfNextRawChar() - 1;  // one past the '0x'
+            while (JS7_ISHEX(c))
+                c = getCharIgnoreEOL();
+        } else if (c == 'b' || c == 'B') {
+            radix = 2;
+            c = getCharIgnoreEOL();
+            if (c != '0' && c != '1') {
+                ungetCharIgnoreEOL(c);
+                reportError(JSMSG_MISSING_BINARY_DIGITS);
+                goto error;
+            }
+            numStart = userbuf.addressOfNextRawChar() - 1;  // one past the '0b'
+            while (c == '0' || c == '1')
+                c = getCharIgnoreEOL();
+        } else if (c == 'o' || c == 'O') {
+            radix = 8;
+            c = getCharIgnoreEOL();
+            if (c < '0' || c > '7') {
+                ungetCharIgnoreEOL(c);
+                reportError(JSMSG_MISSING_OCTAL_DIGITS);
+                goto error;
+            }
+            numStart = userbuf.addressOfNextRawChar() - 1;  // one past the '0o'
+            while ('0' <= c && c <= '7')
+                c = getCharIgnoreEOL();
+        } else if (JS7_ISDEC(c)) {
+            radix = 8;
+            numStart = userbuf.addressOfNextRawChar() - 1;  // one past the '0'
+            while (JS7_ISDEC(c)) {
+                // Octal integer literals are not permitted in strict mode code.
+                if (!reportStrictModeError(JSMSG_DEPRECATED_OCTAL))
+                    goto error;
+
+                // Outside strict mode, we permit 08 and 09 as decimal numbers,
+                // which makes our behaviour a superset of the ECMA numeric
+                // grammar. We might not always be so permissive, so we warn
+                // about it.
+                if (c >= '8') {
+                    if (!reportWarning(JSMSG_BAD_OCTAL, c == '8' ? "08" : "09")) {
+                        goto error;
+                    }
+                    goto decimal;   // use the decimal scanner for the rest of the number
+                }
+                c = getCharIgnoreEOL();
+            }
+        } else {
+            // '0' not followed by 'x', 'X' or a digit;  scan as a decimal number.
+            numStart = userbuf.addressOfNextRawChar() - 1;
+            goto decimal;
+        }
+        ungetCharIgnoreEOL(c);
+
+        if (c != EOF && unicode::IsIdentifierStart(char16_t(c))) {
+            reportError(JSMSG_IDSTART_AFTER_NUMBER);
+            goto error;
+        }
+
+        double dval;
+        const char16_t* dummy;
+        if (!GetPrefixInteger(cx, numStart, userbuf.addressOfNextRawChar(), radix, &dummy, &dval))
+            goto error;
+        tp->type = TOK_NUMBER;
+        tp->setNumber(dval, NoDecimal);
+        goto out;
+    }
+
+    // This handles everything else.
+    //
+    MOZ_ASSERT(c1kind == Other);
+    tp = newToken(-1);
+    switch (c) {
+      case '.':
+        c = getCharIgnoreEOL();
+        if (JS7_ISDEC(c)) {
+            numStart = userbuf.addressOfNextRawChar() - 2;
+            decimalPoint = HasDecimal;
+            hasExp = false;
+            goto decimal_dot;
+        }
+        if (c == '.') {
+            if (matchChar('.')) {
+                tp->type = TOK_TRIPLEDOT;
+                goto out;
+            }
+        }
+        ungetCharIgnoreEOL(c);
+        tp->type = TOK_DOT;
+        goto out;
+
+      case '=':
+        if (matchChar('='))
+            tp->type = matchChar('=') ? TOK_STRICTEQ : TOK_EQ;
+        else if (matchChar('>'))
+            tp->type = TOK_ARROW;
+        else
+            tp->type = TOK_ASSIGN;
+        goto out;
+
+      case '+':
+        if (matchChar('+'))
+            tp->type = TOK_INC;
+        else
+            tp->type = matchChar('=') ? TOK_ADDASSIGN : TOK_ADD;
+        goto out;
+
+      case '\\': {
+        uint32_t escapeLength = matchUnicodeEscapeIdStart(&qc);
+        if (escapeLength > 0) {
+            identStart = userbuf.addressOfNextRawChar() - escapeLength - 1;
+            hadUnicodeEscape = true;
+            goto identifier;
+        }
+        goto badchar;
+      }
+
+      case '|':
+        if (matchChar('|'))
+            tp->type = TOK_OR;
+        else
+            tp->type = matchChar('=') ? TOK_BITORASSIGN : TOK_BITOR;
+        goto out;
+
+      case '^':
+        tp->type = matchChar('=') ? TOK_BITXORASSIGN : TOK_BITXOR;
+        goto out;
+
+      case '&':
+        if (matchChar('&'))
+            tp->type = TOK_AND;
+        else
+            tp->type = matchChar('=') ? TOK_BITANDASSIGN : TOK_BITAND;
+        goto out;
+
+      case '!':
+        if (matchChar('='))
+            tp->type = matchChar('=') ? TOK_STRICTNE : TOK_NE;
+        else
+            tp->type = TOK_NOT;
+        goto out;
+
+      case '<':
+        // NB: treat HTML begin-comment as comment-till-end-of-line.
+        if (matchChar('!')) {
+            if (matchChar('-')) {
+                if (matchChar('-'))
+                    goto skipline;
+                ungetChar('-');
+            }
+            ungetChar('!');
+        }
+        if (matchChar('<')) {
+            tp->type = matchChar('=') ? TOK_LSHASSIGN : TOK_LSH;
+        } else {
+            tp->type = matchChar('=') ? TOK_LE : TOK_LT;
+        }
+        goto out;
+
+      case '>':
+        if (matchChar('>')) {
+            if (matchChar('>'))
+                tp->type = matchChar('=') ? TOK_URSHASSIGN : TOK_URSH;
+            else
+                tp->type = matchChar('=') ? TOK_RSHASSIGN : TOK_RSH;
+        } else {
+            tp->type = matchChar('=') ? TOK_GE : TOK_GT;
+        }
+        goto out;
+
+      case '*':
+        if (matchChar('*'))
+            tp->type = matchChar('=') ? TOK_POWASSIGN : TOK_POW;
+        else
+            tp->type = matchChar('=') ? TOK_MULASSIGN : TOK_MUL;
+        goto out;
+
+      case '/':
+        // Look for a single-line comment.
+        if (matchChar('/')) {
+            c = peekChar();
+            if (c == '@' || c == '#') {
+                bool shouldWarn = getChar() == '@';
+                if (!getDirectives(false, shouldWarn))
+                    goto error;
+            }
+
+        skipline:
+            while ((c = getChar()) != EOF && c != '\n')
+                continue;
+            ungetChar(c);
+            cursor = (cursor - 1) & ntokensMask;
+            goto retry;
+        }
+
+        // Look for a multi-line comment.
+        if (matchChar('*')) {
+            unsigned linenoBefore = lineno;
+            while ((c = getChar()) != EOF &&
+                   !(c == '*' && matchChar('/'))) {
+                if (c == '@' || c == '#') {
+                    bool shouldWarn = c == '@';
+                    if (!getDirectives(true, shouldWarn))
+                        goto error;
+                }
+            }
+            if (c == EOF) {
+                reportError(JSMSG_UNTERMINATED_COMMENT);
+                goto error;
+            }
+            if (linenoBefore != lineno)
+                updateFlagsForEOL();
+            cursor = (cursor - 1) & ntokensMask;
+            goto retry;
+        }
+
+        // Look for a regexp.
+        if (modifier == Operand) {
+            tokenbuf.clear();
+
+            bool inCharClass = false;
+            for (;;) {
+                c = getChar();
+                if (c == '\\') {
+                    if (!tokenbuf.append(c))
+                        goto error;
+                    c = getChar();
+                } else if (c == '[') {
+                    inCharClass = true;
+                } else if (c == ']') {
+                    inCharClass = false;
+                } else if (c == '/' && !inCharClass) {
+                    // For compat with IE, allow unescaped / in char classes.
+                    break;
+                }
+                if (c == '\n' || c == EOF) {
+                    ungetChar(c);
+                    reportError(JSMSG_UNTERMINATED_REGEXP);
+                    goto error;
+                }
+                if (!tokenbuf.append(c))
+                    goto error;
+            }
+
+            RegExpFlag reflags = NoFlags;
+            unsigned length = tokenbuf.length() + 1;
+            while (true) {
+                c = peekChar();
+                if (c == 'g' && !(reflags & GlobalFlag))
+                    reflags = RegExpFlag(reflags | GlobalFlag);
+                else if (c == 'i' && !(reflags & IgnoreCaseFlag))
+                    reflags = RegExpFlag(reflags | IgnoreCaseFlag);
+                else if (c == 'm' && !(reflags & MultilineFlag))
+                    reflags = RegExpFlag(reflags | MultilineFlag);
+                else if (c == 'y' && !(reflags & StickyFlag))
+                    reflags = RegExpFlag(reflags | StickyFlag);
+                else if (c == 'u' && !(reflags & UnicodeFlag))
+                    reflags = RegExpFlag(reflags | UnicodeFlag);
+                else
+                    break;
+                getChar();
+                length++;
+            }
+
+            c = peekChar();
+            if (JS7_ISLET(c)) {
+                char buf[2] = { '\0', '\0' };
+                tp->pos.begin += length + 1;
+                buf[0] = char(c);
+                reportError(JSMSG_BAD_REGEXP_FLAG, buf);
+                (void) getChar();
+                goto error;
+            }
+            tp->type = TOK_REGEXP;
+            tp->setRegExpFlags(reflags);
+            goto out;
+        }
+
+        tp->type = matchChar('=') ? TOK_DIVASSIGN : TOK_DIV;
+        goto out;
+
+      case '%':
+        tp->type = matchChar('=') ? TOK_MODASSIGN : TOK_MOD;
+        goto out;
+
+      case '-':
+        if (matchChar('-')) {
+            if (peekChar() == '>' && !flags.isDirtyLine)
+                goto skipline;
+            tp->type = TOK_DEC;
+        } else {
+            tp->type = matchChar('=') ? TOK_SUBASSIGN : TOK_SUB;
+        }
+        goto out;
+
+      badchar:
+      default:
+        reportError(JSMSG_ILLEGAL_CHARACTER);
+        goto error;
+    }
+
+    MOZ_CRASH("should have jumped to |out| or |error|");
+
+  out:
+    if (flags.hitOOM)
+        return reportError(JSMSG_OUT_OF_MEMORY);
+
+    flags.isDirtyLine = true;
+    tp->pos.end = userbuf.offset();
+#ifdef DEBUG
+    // Save the modifier used to get this token, so that if an ungetToken()
+    // occurs and then the token is re-gotten (or peeked, etc.), we can assert
+    // that both gets have used the same modifiers.
+    tp->modifier = modifier;
+    tp->modifierException = NoException;
+#endif
+    MOZ_ASSERT(IsTokenSane(tp));
+    *ttp = tp->type;
+    return true;
+
+  error:
+    if (flags.hitOOM)
+        return reportError(JSMSG_OUT_OF_MEMORY);
+
+    flags.isDirtyLine = true;
+    tp->pos.end = userbuf.offset();
+    MOZ_MAKE_MEM_UNDEFINED(&tp->type, sizeof(tp->type));
+    flags.hadError = true;
+#ifdef DEBUG
+    // Poisoning userbuf on error establishes an invariant: once an erroneous
+    // token has been seen, userbuf will not be consulted again.  This is true
+    // because the parser will deal with the illegal token by aborting parsing
+    // immediately.
+    userbuf.poison();
+#endif
+    MOZ_MAKE_MEM_UNDEFINED(ttp, sizeof(*ttp));
+    return false;
+}
+
+bool
+TokenStream::getBracedUnicode(uint32_t* cp)
+{
+    consumeKnownChar('{');
+
+    bool first = true;
+    int32_t c;
+    uint32_t code = 0;
+    while (true) {
+        c = getCharIgnoreEOL();
+        if (c == EOF)
+            return false;
+        if (c == '}') {
+            if (first)
+                return false;
+            break;
+        }
+
+        if (!JS7_ISHEX(c))
+            return false;
+
+        code = (code << 4) | JS7_UNHEX(c);
+        if (code > unicode::NonBMPMax)
+            return false;
+        first = false;
+    }
+
+    *cp = code;
+    return true;
+}
+
+bool
+TokenStream::getStringOrTemplateToken(int untilChar, Token** tp)
+{
+    int c;
+    int nc = -1;
+
+    bool parsingTemplate = (untilChar == '`');
+
+    *tp = newToken(-1);
+    tokenbuf.clear();
+
+    // We need to detect any of these chars:  " or ', \n (or its
+    // equivalents), \\, EOF.  Because we detect EOL sequences here and
+    // put them back immediately, we can use getCharIgnoreEOL().
+    while ((c = getCharIgnoreEOL()) != untilChar) {
+        if (c == EOF) {
+            ungetCharIgnoreEOL(c);
+            reportError(JSMSG_UNTERMINATED_STRING);
+            return false;
+        }
+
+        if (c == '\\') {
+            switch (c = getChar()) {
+              case 'b': c = '\b'; break;
+              case 'f': c = '\f'; break;
+              case 'n': c = '\n'; break;
+              case 'r': c = '\r'; break;
+              case 't': c = '\t'; break;
+              case 'v': c = '\v'; break;
+
+              case '\n':
+                // ES5 7.8.4: an escaped line terminator represents
+                // no character.
+                continue;
+
+              // Unicode character specification.
+              case 'u': {
+                if (peekChar() == '{') {
+                    uint32_t code;
+                    if (!getBracedUnicode(&code)) {
+                        reportError(JSMSG_MALFORMED_ESCAPE, "Unicode");
+                        return false;
+                    }
+
+                    MOZ_ASSERT(code <= unicode::NonBMPMax);
+                    if (code < unicode::NonBMPMin) {
+                        c = code;
+                    } else {
+                        if (!tokenbuf.append(unicode::LeadSurrogate(code)))
+                            return false;
+                        c = unicode::TrailSurrogate(code);
+                    }
+                    break;
+                }
+
+                char16_t cp[4];
+                if (peekChars(4, cp) &&
+                    JS7_ISHEX(cp[0]) && JS7_ISHEX(cp[1]) && JS7_ISHEX(cp[2]) && JS7_ISHEX(cp[3]))
+                {
+                    c = JS7_UNHEX(cp[0]);
+                    c = (c << 4) + JS7_UNHEX(cp[1]);
+                    c = (c << 4) + JS7_UNHEX(cp[2]);
+                    c = (c << 4) + JS7_UNHEX(cp[3]);
+                    skipChars(4);
+                } else {
+                    reportError(JSMSG_MALFORMED_ESCAPE, "Unicode");
+                    return false;
+                }
+                break;
+              }
+
+              // Hexadecimal character specification.
+              case 'x': {
+                char16_t cp[2];
+                if (peekChars(2, cp) && JS7_ISHEX(cp[0]) && JS7_ISHEX(cp[1])) {
+                    c = (JS7_UNHEX(cp[0]) << 4) + JS7_UNHEX(cp[1]);
+                    skipChars(2);
+                } else {
+                    reportError(JSMSG_MALFORMED_ESCAPE, "hexadecimal");
+                    return false;
+                }
+                break;
+              }
+
+              default:
+                // Octal character specification.
+                if (JS7_ISOCT(c)) {
+                    int32_t val = JS7_UNOCT(c);
+
+                    c = peekChar();
+
+                    // Strict mode code allows only \0, then a non-digit.
+                    if (val != 0 || JS7_ISDEC(c)) {
+                        if (parsingTemplate) {
+                            reportError(JSMSG_DEPRECATED_OCTAL);
+                            return false;
+                        }
+                        if (!reportStrictModeError(JSMSG_DEPRECATED_OCTAL))
+                            return false;
+                        flags.sawOctalEscape = true;
+                    }
+
+                    if (JS7_ISOCT(c)) {
+                        val = 8 * val + JS7_UNOCT(c);
+                        getChar();
+                        c = peekChar();
+                        if (JS7_ISOCT(c)) {
+                            int32_t save = val;
+                            val = 8 * val + JS7_UNOCT(c);
+                            if (val <= 0xFF)
+                                getChar();
+                            else
+                                val = save;
+                        }
+                    }
+
+                    c = char16_t(val);
+                }
+                break;
+            }
+        } else if (TokenBuf::isRawEOLChar(c)) {
+            if (!parsingTemplate) {
+                ungetCharIgnoreEOL(c);
+                reportError(JSMSG_UNTERMINATED_STRING);
+                return false;
+            }
+            if (c == '\r') {
+                c = '\n';
+                if (userbuf.peekRawChar() == '\n')
+                    skipCharsIgnoreEOL(1);
+            }
+            updateLineInfoForEOL();
+            updateFlagsForEOL();
+        } else if (parsingTemplate && c == '$') {
+            if ((nc = getCharIgnoreEOL()) == '{')
+                break;
+            ungetCharIgnoreEOL(nc);
+        }
+
+        if (!tokenbuf.append(c)) {
+            ReportOutOfMemory(cx);
+            return false;
+        }
+    }
+
+    JSAtom* atom = atomize(cx, tokenbuf);
+    if (!atom)
+        return false;
+
+    if (!parsingTemplate) {
+        (*tp)->type = TOK_STRING;
+    } else {
+        if (c == '$' && nc == '{')
+            (*tp)->type = TOK_TEMPLATE_HEAD;
+        else
+            (*tp)->type = TOK_NO_SUBS_TEMPLATE;
+    }
+
+    (*tp)->setAtom(atom);
+    return true;
+}
+
+JS_FRIEND_API(int)
+js_fgets(char* buf, int size, FILE* file)
+{
+    int n, i, c;
+    bool crflag;
+
+    n = size - 1;
+    if (n < 0)
+        return -1;
+
+    crflag = false;
+    for (i = 0; i < n && (c = fast_getc(file)) != EOF; i++) {
+        buf[i] = c;
+        if (c == '\n') {        // any \n ends a line
+            i++;                // keep the \n; we know there is room for \0
+            break;
+        }
+        if (crflag) {           // \r not followed by \n ends line at the \r
+            ungetc(c, file);
+            break;              // and overwrite c in buf with \0
+        }
+        crflag = (c == '\r');
+    }
+
+    buf[i] = '\0';
+    return i;
+}
+
+const char*
+frontend::TokenKindToDesc(TokenKind tt)
+{
+    switch (tt) {
+#define EMIT_CASE(name, desc) case TOK_##name: return desc;
+      FOR_EACH_TOKEN_KIND(EMIT_CASE)
+#undef EMIT_CASE
+      case TOK_LIMIT:
+        MOZ_ASSERT_UNREACHABLE("TOK_LIMIT should not be passed.");
+        break;
+    }
+
+    return "<bad TokenKind>";
+}
+
+#ifdef DEBUG
+const char*
+TokenKindToString(TokenKind tt)
+{
+    switch (tt) {
+#define EMIT_CASE(name, desc) case TOK_##name: return "TOK_" #name;
+      FOR_EACH_TOKEN_KIND(EMIT_CASE)
+#undef EMIT_CASE
+      case TOK_LIMIT: break;
+    }
+
+    return "<bad TokenKind>";
+}
+#endif
diff --git a/js/src/frontend/TokenStream.h b/js/src/frontend/TokenStream.h
new file mode 100644
index 0000000000..29dcead62e
--- /dev/null
+++ b/js/src/frontend/TokenStream.h
@@ -0,0 +1,1057 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef frontend_TokenStream_h
+#define frontend_TokenStream_h
+
+// JS lexical scanner interface.
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/PodOperations.h"
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+
+#include "jscntxt.h"
+#include "jspubtd.h"
+
+#include "frontend/TokenKind.h"
+#include "js/UniquePtr.h"
+#include "js/Vector.h"
+#include "vm/RegExpObject.h"
+
+struct KeywordInfo;
+
+namespace js {
+namespace frontend {
+
+class AutoAwaitIsKeyword;
+
+struct TokenPos {
+    uint32_t    begin;  // Offset of the token's first char.
+    uint32_t    end;    // Offset of 1 past the token's last char.
+
+    TokenPos() {}
+    TokenPos(uint32_t begin, uint32_t end) : begin(begin), end(end) {}
+
+    // Return a TokenPos that covers left, right, and anything in between.
+    static TokenPos box(const TokenPos& left, const TokenPos& right) {
+        MOZ_ASSERT(left.begin <= left.end);
+        MOZ_ASSERT(left.end <= right.begin);
+        MOZ_ASSERT(right.begin <= right.end);
+        return TokenPos(left.begin, right.end);
+    }
+
+    bool operator==(const TokenPos& bpos) const {
+        return begin == bpos.begin && end == bpos.end;
+    }
+
+    bool operator!=(const TokenPos& bpos) const {
+        return begin != bpos.begin || end != bpos.end;
+    }
+
+    bool operator <(const TokenPos& bpos) const {
+        return begin < bpos.begin;
+    }
+
+    bool operator <=(const TokenPos& bpos) const {
+        return begin <= bpos.begin;
+    }
+
+    bool operator >(const TokenPos& bpos) const {
+        return !(*this <= bpos);
+    }
+
+    bool operator >=(const TokenPos& bpos) const {
+        return !(*this < bpos);
+    }
+
+    bool encloses(const TokenPos& pos) const {
+        return begin <= pos.begin && pos.end <= end;
+    }
+};
+
+enum DecimalPoint { NoDecimal = false, HasDecimal = true };
+
+class TokenStream;
+
+struct Token
+{
+  private:
+    // Sometimes the parser needs to inform the tokenizer to interpret
+    // subsequent text in a particular manner: for example, to tokenize a
+    // keyword as an identifier, not as the actual keyword, on the right-hand
+    // side of a dotted property access.  Such information is communicated to
+    // the tokenizer as a Modifier when getting the next token.
+    //
+    // Ideally this definition would reside in TokenStream as that's the real
+    // user, but the debugging-use of it here causes a cyclic dependency (and
+    // C++ provides no way to forward-declare an enum inside a class).  So
+    // define it here, then typedef it into TokenStream with static consts to
+    // bring the initializers into scope.
+    enum Modifier
+    {
+        // Normal operation.
+        None,
+
+        // Looking for an operand, not an operator.  In practice, this means
+        // that when '/' is seen, we look for a regexp instead of just returning
+        // TOK_DIV.
+        Operand,
+
+        // Treat keywords as names by returning TOK_NAME.
+        KeywordIsName,
+
+        // Treat subsequent characters as the tail of a template literal, after
+        // a template substitution, beginning with a "}", continuing with zero
+        // or more template literal characters, and ending with either "${" or
+        // the end of the template literal.  For example:
+        //
+        //   var entity = "world";
+        //   var s = `Hello ${entity}!`;
+        //                          ^ TemplateTail context
+        TemplateTail,
+    };
+    enum ModifierException
+    {
+        NoException,
+
+        // Used in following 2 cases:
+        // a) After |yield| we look for a token on the same line that starts an
+        // expression (Operand): |yield <expr>|.  If no token is found, the
+        // |yield| stands alone, and the next token on a subsequent line must
+        // be: a comma continuing a comma expression, a semicolon terminating
+        // the statement that ended with |yield|, or the start of another
+        // statement (possibly an expression statement).  The comma/semicolon
+        // cases are gotten as operators (None), contrasting with Operand
+        // earlier.
+        // b) After an arrow function with a block body in an expression
+        // statement, the next token must be: a colon in a conditional
+        // expression, a comma continuing a comma expression, a semicolon
+        // terminating the statement, or the token on a subsequent line that is
+        // the start of another statement (possibly an expression statement).
+        // Colon is gotten as operator (None), and it should only be gotten in
+        // conditional expression and missing it results in SyntaxError.
+        // Comma/semicolon cases are also gotten as operators (None), and 4th
+        // case is gotten after them.  If no comma/semicolon found but EOL,
+        // the next token should be gotten as operand in 4th case (especially if
+        // '/' is the first character).  So we should peek the token as
+        // operand before try getting colon/comma/semicolon.
+        // See also the comment in Parser::assignExpr().
+        NoneIsOperand,
+
+        // If a semicolon is inserted automatically, the next token is already
+        // gotten with None, but we expect Operand.
+        OperandIsNone,
+
+        // If name of method definition is `get` or `set`, the next token is
+        // already gotten with KeywordIsName, but we expect None.
+        NoneIsKeywordIsName,
+    };
+    friend class TokenStream;
+
+  public:
+    TokenKind           type;           // char value or above enumerator
+    TokenPos            pos;            // token position in file
+    union {
+      private:
+        friend struct Token;
+        PropertyName*   name;          // non-numeric atom
+        JSAtom*         atom;          // potentially-numeric atom
+        struct {
+            double      value;          // floating point number
+            DecimalPoint decimalPoint;  // literal contains '.'
+        } number;
+        RegExpFlag      reflags;        // regexp flags; use tokenbuf to access
+                                        //   regexp chars
+    } u;
+#ifdef DEBUG
+    Modifier modifier;                  // Modifier used to get this token
+    ModifierException modifierException; // Exception for this modifier
+#endif
+
+    // Mutators
+
+    void setName(PropertyName* name) {
+        MOZ_ASSERT(type == TOK_NAME);
+        u.name = name;
+    }
+
+    void setAtom(JSAtom* atom) {
+        MOZ_ASSERT(type == TOK_STRING ||
+                   type == TOK_TEMPLATE_HEAD ||
+                   type == TOK_NO_SUBS_TEMPLATE);
+        u.atom = atom;
+    }
+
+    void setRegExpFlags(js::RegExpFlag flags) {
+        MOZ_ASSERT(type == TOK_REGEXP);
+        MOZ_ASSERT((flags & AllFlags) == flags);
+        u.reflags = flags;
+    }
+
+    void setNumber(double n, DecimalPoint decimalPoint) {
+        MOZ_ASSERT(type == TOK_NUMBER);
+        u.number.value = n;
+        u.number.decimalPoint = decimalPoint;
+    }
+
+    // Type-safe accessors
+
+    PropertyName* name() const {
+        MOZ_ASSERT(type == TOK_NAME);
+        return u.name->JSAtom::asPropertyName(); // poor-man's type verification
+    }
+
+    bool nameContainsEscape() const {
+        PropertyName* n = name();
+        return pos.begin + n->length() != pos.end;
+    }
+
+    JSAtom* atom() const {
+        MOZ_ASSERT(type == TOK_STRING ||
+                   type == TOK_TEMPLATE_HEAD ||
+                   type == TOK_NO_SUBS_TEMPLATE);
+        return u.atom;
+    }
+
+    js::RegExpFlag regExpFlags() const {
+        MOZ_ASSERT(type == TOK_REGEXP);
+        MOZ_ASSERT((u.reflags & AllFlags) == u.reflags);
+        return u.reflags;
+    }
+
+    double number() const {
+        MOZ_ASSERT(type == TOK_NUMBER);
+        return u.number.value;
+    }
+
+    DecimalPoint decimalPoint() const {
+        MOZ_ASSERT(type == TOK_NUMBER);
+        return u.number.decimalPoint;
+    }
+};
+
+class CompileError : public JSErrorReport {
+public:
+    void throwError(JSContext* cx);
+};
+
+// Ideally, tokenizing would be entirely independent of context.  But the
+// strict mode flag, which is in SharedContext, affects tokenizing, and
+// TokenStream needs to see it.
+//
+// This class is a tiny back-channel from TokenStream to the strict mode flag
+// that avoids exposing the rest of SharedContext to TokenStream.
+//
+class StrictModeGetter {
+  public:
+    virtual bool strictMode() = 0;
+};
+
+// TokenStream is the lexical scanner for Javascript source text.
+//
+// It takes a buffer of char16_t characters and linearly scans it into |Token|s.
+// Internally the class uses a four element circular buffer |tokens| of
+// |Token|s. As an index for |tokens|, the member |cursor| points to the
+// current token.
+// Calls to getToken() increase |cursor| by one and return the new current
+// token. If a TokenStream was just created, the current token is initialized
+// with random data (i.e. not initialized). It is therefore important that
+// one of the first four member functions listed below is called first.
+// The circular buffer lets us go back up to two tokens from the last
+// scanned token. Internally, the relative number of backward steps that were
+// taken (via ungetToken()) after the last token was scanned is stored in
+// |lookahead|.
+//
+// The following table lists in which situations it is safe to call each listed
+// function. No checks are made by the functions in non-debug builds.
+//
+// Function Name     | Precondition; changes to |lookahead|
+// ------------------+---------------------------------------------------------
+// getToken          | none; if |lookahead > 0| then |lookahead--|
+// peekToken         | none; if |lookahead == 0| then |lookahead == 1|
+// peekTokenSameLine | none; if |lookahead == 0| then |lookahead == 1|
+// matchToken        | none; if |lookahead > 0| and the match succeeds then
+//                   |       |lookahead--|
+// consumeKnownToken | none; if |lookahead > 0| then |lookahead--|
+// ungetToken        | 0 <= |lookahead| <= |maxLookahead - 1|; |lookahead++|
+//
+// The behavior of the token scanning process (see getTokenInternal()) can be
+// modified by calling one of the first four above listed member functions with
+// an optional argument of type Modifier.  However, the modifier will be
+// ignored unless |lookahead == 0| holds.  Due to constraints of the grammar,
+// this turns out not to be a problem in practice. See the
+// mozilla.dev.tech.js-engine.internals thread entitled 'Bug in the scanner?'
+// for more details:
+// https://groups.google.com/forum/?fromgroups=#!topic/mozilla.dev.tech.js-engine.internals/2JLH5jRcr7E).
+//
+// The methods seek() and tell() allow to rescan from a previous visited
+// location of the buffer.
+//
+class MOZ_STACK_CLASS TokenStream
+{
+    // Unicode separators that are treated as line terminators, in addition to \n, \r.
+    enum {
+        LINE_SEPARATOR = 0x2028,
+        PARA_SEPARATOR = 0x2029
+    };
+
+    static const size_t ntokens = 4;                // 1 current + 2 lookahead, rounded
+                                                    // to power of 2 to avoid divmod by 3
+    static const unsigned maxLookahead = 2;
+    static const unsigned ntokensMask = ntokens - 1;
+
+  public:
+    typedef Vector<char16_t, 32> CharBuffer;
+
+    TokenStream(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
+                const char16_t* base, size_t length, StrictModeGetter* smg);
+
+    ~TokenStream();
+
+    MOZ_MUST_USE bool checkOptions();
+
+    // Accessors.
+    const Token& currentToken() const { return tokens[cursor]; }
+    bool isCurrentTokenType(TokenKind type) const {
+        return currentToken().type == type;
+    }
+    const CharBuffer& getTokenbuf() const { return tokenbuf; }
+    const char* getFilename() const { return filename; }
+    bool getMutedErrors() const { return mutedErrors; }
+    JSVersion versionNumber() const { return VersionNumber(options().version); }
+    JSVersion versionWithFlags() const { return options().version; }
+
+    PropertyName* currentName() const {
+        if (isCurrentTokenType(TOK_YIELD))
+            return cx->names().yield;
+        MOZ_ASSERT(isCurrentTokenType(TOK_NAME));
+        return currentToken().name();
+    }
+
+    PropertyName* nextName() const {
+        if (nextToken().type == TOK_YIELD)
+            return cx->names().yield;
+        MOZ_ASSERT(nextToken().type == TOK_NAME);
+        return nextToken().name();
+    }
+
+    bool nextNameContainsEscape() const {
+        if (nextToken().type == TOK_YIELD)
+            return false;
+        MOZ_ASSERT(nextToken().type == TOK_NAME);
+        return nextToken().nameContainsEscape();
+    }
+
+    bool isCurrentTokenAssignment() const {
+        return TokenKindIsAssignment(currentToken().type);
+    }
+
+    // Flag methods.
+    bool isEOF() const { return flags.isEOF; }
+    bool sawOctalEscape() const { return flags.sawOctalEscape; }
+    bool hadError() const { return flags.hadError; }
+    void clearSawOctalEscape() { flags.sawOctalEscape = false; }
+
+    // TokenStream-specific error reporters.
+    bool reportError(unsigned errorNumber, ...);
+    bool reportErrorNoOffset(unsigned errorNumber, ...);
+    bool reportWarning(unsigned errorNumber, ...);
+
+    static const uint32_t NoOffset = UINT32_MAX;
+
+    // General-purpose error reporters.  You should avoid calling these
+    // directly, and instead use the more succinct alternatives (e.g.
+    // reportError()) in TokenStream, Parser, and BytecodeEmitter.
+    bool reportCompileErrorNumberVA(uint32_t offset, unsigned flags, unsigned errorNumber,
+                                    va_list args);
+    bool reportStrictModeErrorNumberVA(uint32_t offset, bool strictMode, unsigned errorNumber,
+                                       va_list args);
+    bool reportStrictWarningErrorNumberVA(uint32_t offset, unsigned errorNumber,
+                                          va_list args);
+
+    // asm.js reporter
+    void reportAsmJSError(uint32_t offset, unsigned errorNumber, ...);
+
+    JSAtom* getRawTemplateStringAtom() {
+        MOZ_ASSERT(currentToken().type == TOK_TEMPLATE_HEAD ||
+                   currentToken().type == TOK_NO_SUBS_TEMPLATE);
+        const char16_t* cur = userbuf.rawCharPtrAt(currentToken().pos.begin + 1);
+        const char16_t* end;
+        if (currentToken().type == TOK_TEMPLATE_HEAD) {
+            // Of the form    |`...${|   or   |}...${|
+            end = userbuf.rawCharPtrAt(currentToken().pos.end - 2);
+        } else {
+            // NO_SUBS_TEMPLATE is of the form   |`...`|   or   |}...`|
+            end = userbuf.rawCharPtrAt(currentToken().pos.end - 1);
+        }
+
+        CharBuffer charbuf(cx);
+        while (cur < end) {
+            int32_t ch = *cur;
+            if (ch == '\r') {
+                ch = '\n';
+                if ((cur + 1 < end) && (*(cur + 1) == '\n'))
+                    cur++;
+            }
+            if (!charbuf.append(ch))
+                return nullptr;
+            cur++;
+        }
+        return AtomizeChars(cx, charbuf.begin(), charbuf.length());
+    }
+
+  private:
+    // These are private because they should only be called by the tokenizer
+    // while tokenizing not by, for example, BytecodeEmitter.
+    bool reportStrictModeError(unsigned errorNumber, ...);
+    bool strictMode() const { return strictModeGetter && strictModeGetter->strictMode(); }
+
+    static JSAtom* atomize(ExclusiveContext* cx, CharBuffer& cb);
+    MOZ_MUST_USE bool putIdentInTokenbuf(const char16_t* identStart);
+
+    struct Flags
+    {
+        bool isEOF:1;           // Hit end of file.
+        bool isDirtyLine:1;     // Non-whitespace since start of line.
+        bool sawOctalEscape:1;  // Saw an octal character escape.
+        bool hadError:1;        // Hit a syntax error, at start or during a
+                                // token.
+        bool hitOOM:1;          // Hit OOM.
+
+        Flags()
+          : isEOF(), isDirtyLine(), sawOctalEscape(), hadError(), hitOOM()
+        {}
+    };
+
+    bool awaitIsKeyword = false;
+    friend class AutoAwaitIsKeyword;
+
+  public:
+    typedef Token::Modifier Modifier;
+    static constexpr Modifier None = Token::None;
+    static constexpr Modifier Operand = Token::Operand;
+    static constexpr Modifier KeywordIsName = Token::KeywordIsName;
+    static constexpr Modifier TemplateTail = Token::TemplateTail;
+
+    typedef Token::ModifierException ModifierException;
+    static constexpr ModifierException NoException = Token::NoException;
+    static constexpr ModifierException NoneIsOperand = Token::NoneIsOperand;
+    static constexpr ModifierException OperandIsNone = Token::OperandIsNone;
+    static constexpr ModifierException NoneIsKeywordIsName = Token::NoneIsKeywordIsName;
+
+    void addModifierException(ModifierException modifierException) {
+#ifdef DEBUG
+        const Token& next = nextToken();
+        if (next.modifierException == NoneIsOperand)
+        {
+            // Token after yield expression without operand already has
+            // NoneIsOperand exception.
+            MOZ_ASSERT(modifierException == OperandIsNone);
+            MOZ_ASSERT(next.type != TOK_DIV,
+                       "next token requires contextual specifier to be parsed unambiguously");
+
+            // Do not update modifierException.
+            return;
+        }
+
+        MOZ_ASSERT(next.modifierException == NoException);
+        switch (modifierException) {
+          case NoneIsOperand:
+            MOZ_ASSERT(next.modifier == Operand);
+            MOZ_ASSERT(next.type != TOK_DIV,
+                       "next token requires contextual specifier to be parsed unambiguously");
+            break;
+          case OperandIsNone:
+            MOZ_ASSERT(next.modifier == None);
+            MOZ_ASSERT(next.type != TOK_DIV && next.type != TOK_REGEXP,
+                       "next token requires contextual specifier to be parsed unambiguously");
+            break;
+          case NoneIsKeywordIsName:
+            MOZ_ASSERT(next.modifier == KeywordIsName);
+            MOZ_ASSERT(next.type != TOK_NAME);
+            break;
+          default:
+            MOZ_CRASH("unexpected modifier exception");
+        }
+        tokens[(cursor + 1) & ntokensMask].modifierException = modifierException;
+#endif
+    }
+
+    void
+    verifyConsistentModifier(Modifier modifier, Token lookaheadToken) {
+#ifdef DEBUG
+        // Easy case: modifiers match.
+        if (modifier == lookaheadToken.modifier)
+            return;
+
+        if (lookaheadToken.modifierException == OperandIsNone) {
+            // getToken(Operand) permissibly following getToken().
+            if (modifier == Operand && lookaheadToken.modifier == None)
+                return;
+        }
+
+        if (lookaheadToken.modifierException == NoneIsOperand) {
+            // getToken() permissibly following getToken(Operand).
+            if (modifier == None && lookaheadToken.modifier == Operand)
+                return;
+        }
+
+        if (lookaheadToken.modifierException == NoneIsKeywordIsName) {
+            // getToken() permissibly following getToken(KeywordIsName).
+            if (modifier == None && lookaheadToken.modifier == KeywordIsName)
+                return;
+        }
+
+        MOZ_ASSERT_UNREACHABLE("this token was previously looked up with a "
+                               "different modifier, potentially making "
+                               "tokenization non-deterministic");
+#endif
+    }
+
+    // Advance to the next token.  If the token stream encountered an error,
+    // return false.  Otherwise return true and store the token kind in |*ttp|.
+    MOZ_MUST_USE bool getToken(TokenKind* ttp, Modifier modifier = None) {
+        // Check for a pushed-back token resulting from mismatching lookahead.
+        if (lookahead != 0) {
+            MOZ_ASSERT(!flags.hadError);
+            lookahead--;
+            cursor = (cursor + 1) & ntokensMask;
+            TokenKind tt = currentToken().type;
+            MOZ_ASSERT(tt != TOK_EOL);
+            verifyConsistentModifier(modifier, currentToken());
+            *ttp = tt;
+            return true;
+        }
+
+        return getTokenInternal(ttp, modifier);
+    }
+
+    // Push the last scanned token back into the stream.
+    void ungetToken() {
+        MOZ_ASSERT(lookahead < maxLookahead);
+        lookahead++;
+        cursor = (cursor - 1) & ntokensMask;
+    }
+
+    MOZ_MUST_USE bool peekToken(TokenKind* ttp, Modifier modifier = None) {
+        if (lookahead > 0) {
+            MOZ_ASSERT(!flags.hadError);
+            verifyConsistentModifier(modifier, nextToken());
+            *ttp = nextToken().type;
+            return true;
+        }
+        if (!getTokenInternal(ttp, modifier))
+            return false;
+        ungetToken();
+        return true;
+    }
+
+    MOZ_MUST_USE bool peekTokenPos(TokenPos* posp, Modifier modifier = None) {
+        if (lookahead == 0) {
+            TokenKind tt;
+            if (!getTokenInternal(&tt, modifier))
+                return false;
+            ungetToken();
+            MOZ_ASSERT(hasLookahead());
+        } else {
+            MOZ_ASSERT(!flags.hadError);
+            verifyConsistentModifier(modifier, nextToken());
+        }
+        *posp = nextToken().pos;
+        return true;
+    }
+
+    // This is like peekToken(), with one exception:  if there is an EOL
+    // between the end of the current token and the start of the next token, it
+    // return true and store TOK_EOL in |*ttp|.  In that case, no token with
+    // TOK_EOL is actually created, just a TOK_EOL TokenKind is returned, and
+    // currentToken() shouldn't be consulted.  (This is the only place TOK_EOL
+    // is produced.)
+    MOZ_ALWAYS_INLINE MOZ_MUST_USE bool
+    peekTokenSameLine(TokenKind* ttp, Modifier modifier = None) {
+        const Token& curr = currentToken();
+
+        // If lookahead != 0, we have scanned ahead at least one token, and
+        // |lineno| is the line that the furthest-scanned token ends on.  If
+        // it's the same as the line that the current token ends on, that's a
+        // stronger condition than what we are looking for, and we don't need
+        // to return TOK_EOL.
+        if (lookahead != 0) {
+            bool onThisLine;
+            if (!srcCoords.isOnThisLine(curr.pos.end, lineno, &onThisLine))
+                return reportError(JSMSG_OUT_OF_MEMORY);
+            if (onThisLine) {
+                MOZ_ASSERT(!flags.hadError);
+                verifyConsistentModifier(modifier, nextToken());
+                *ttp = nextToken().type;
+                return true;
+            }
+        }
+
+        // The above check misses two cases where we don't have to return
+        // TOK_EOL.
+        // - The next token starts on the same line, but is a multi-line token.
+        // - The next token starts on the same line, but lookahead==2 and there
+        //   is a newline between the next token and the one after that.
+        // The following test is somewhat expensive but gets these cases (and
+        // all others) right.
+        TokenKind tmp;
+        if (!getToken(&tmp, modifier))
+            return false;
+        const Token& next = currentToken();
+        ungetToken();
+
+        *ttp = srcCoords.lineNum(curr.pos.end) == srcCoords.lineNum(next.pos.begin)
+             ? next.type
+             : TOK_EOL;
+        return true;
+    }
+
+    // Get the next token from the stream if its kind is |tt|.
+    MOZ_MUST_USE bool matchToken(bool* matchedp, TokenKind tt, Modifier modifier = None) {
+        TokenKind token;
+        if (!getToken(&token, modifier))
+            return false;
+        if (token == tt) {
+            *matchedp = true;
+        } else {
+            ungetToken();
+            *matchedp = false;
+        }
+        return true;
+    }
+
+    void consumeKnownToken(TokenKind tt, Modifier modifier = None) {
+        bool matched;
+        MOZ_ASSERT(hasLookahead());
+        MOZ_ALWAYS_TRUE(matchToken(&matched, tt, modifier));
+        MOZ_ALWAYS_TRUE(matched);
+    }
+
+    // Like matchToken(..., TOK_NAME) but further matching the name token only
+    // if it has the given characters, without containing escape sequences.
+    // If the name token has the given characters yet *does* contain an escape,
+    // a syntax error will be reported.
+    //
+    // This latter behavior makes this method unsuitable for use in any context
+    // where ASI might occur.  In such places, an escaped "contextual keyword"
+    // on a new line is the start of an ExpressionStatement, not a continuation
+    // of a StatementListItem (or ImportDeclaration or ExportDeclaration, in
+    // modules).
+    MOZ_MUST_USE bool matchContextualKeyword(bool* matchedp, Handle<PropertyName*> keyword,
+                                             Modifier modifier = None)
+    {
+        TokenKind token;
+        if (!getToken(&token, modifier))
+            return false;
+        if (token == TOK_NAME && currentToken().name() == keyword) {
+            if (currentToken().nameContainsEscape()) {
+                reportError(JSMSG_ESCAPED_KEYWORD);
+                return false;
+            }
+
+            *matchedp = true;
+        } else {
+            *matchedp = false;
+            ungetToken();
+        }
+        return true;
+    }
+
+    MOZ_MUST_USE bool nextTokenEndsExpr(bool* endsExpr) {
+        TokenKind tt;
+        if (!peekToken(&tt))
+            return false;
+        *endsExpr = isExprEnding[tt];
+        return true;
+    }
+
+    class MOZ_STACK_CLASS Position {
+      public:
+        // The Token fields may contain pointers to atoms, so for correct
+        // rooting we must ensure collection of atoms is disabled while objects
+        // of this class are live.  Do this by requiring a dummy AutoKeepAtoms
+        // reference in the constructor.
+        //
+        // This class is explicity ignored by the analysis, so don't add any
+        // more pointers to GC things here!
+        explicit Position(AutoKeepAtoms&) { }
+      private:
+        Position(const Position&) = delete;
+        friend class TokenStream;
+        const char16_t* buf;
+        Flags flags;
+        unsigned lineno;
+        size_t linebase;
+        size_t prevLinebase;
+        Token currentToken;
+        unsigned lookahead;
+        Token lookaheadTokens[maxLookahead];
+    };
+
+    MOZ_MUST_USE bool advance(size_t position);
+    void tell(Position*);
+    void seek(const Position& pos);
+    MOZ_MUST_USE bool seek(const Position& pos, const TokenStream& other);
+#ifdef DEBUG
+    inline bool debugHasNoLookahead() const {
+        return lookahead == 0;
+    }
+#endif
+
+    const char16_t* rawCharPtrAt(size_t offset) const {
+        return userbuf.rawCharPtrAt(offset);
+    }
+
+    const char16_t* rawLimit() const {
+        return userbuf.limit();
+    }
+
+    bool hasDisplayURL() const {
+        return displayURL_ != nullptr;
+    }
+
+    char16_t* displayURL() {
+        return displayURL_.get();
+    }
+
+    bool hasSourceMapURL() const {
+        return sourceMapURL_ != nullptr;
+    }
+
+    char16_t* sourceMapURL() {
+        return sourceMapURL_.get();
+    }
+
+    // If |atom| is not a keyword in this version, return true with *ttp
+    // unchanged.
+    //
+    // If it is a reserved word in this version and strictness mode, and thus
+    // can't be present in correct code, report a SyntaxError and return false.
+    //
+    // If it is a keyword, like "if", return true with the keyword's TokenKind
+    // in *ttp.
+    MOZ_MUST_USE bool checkForKeyword(JSAtom* atom, TokenKind* ttp);
+
+    // Same semantics as above, but for the provided keyword.
+    MOZ_MUST_USE bool checkForKeyword(const KeywordInfo* kw, TokenKind* ttp);
+
+    // This class maps a userbuf offset (which is 0-indexed) to a line number
+    // (which is 1-indexed) and a column index (which is 0-indexed).
+    class SourceCoords
+    {
+        // For a given buffer holding source code, |lineStartOffsets_| has one
+        // element per line of source code, plus one sentinel element.  Each
+        // non-sentinel element holds the buffer offset for the start of the
+        // corresponding line of source code.  For this example script:
+        //
+        // 1  // xyz            [line starts at offset 0]
+        // 2  var x;            [line starts at offset 7]
+        // 3                    [line starts at offset 14]
+        // 4  var y;            [line starts at offset 15]
+        //
+        // |lineStartOffsets_| is:
+        //
+        //   [0, 7, 14, 15, MAX_PTR]
+        //
+        // To convert a "line number" to a "line index" (i.e. an index into
+        // |lineStartOffsets_|), subtract |initialLineNum_|.  E.g. line 3's
+        // line index is (3 - initialLineNum_), which is 2.  Therefore
+        // lineStartOffsets_[2] holds the buffer offset for the start of line 3,
+        // which is 14.  (Note that |initialLineNum_| is often 1, but not
+        // always.)
+        //
+        // The first element is always 0, and the last element is always the
+        // MAX_PTR sentinel.
+        //
+        // offset-to-line/column lookups are O(log n) in the worst case (binary
+        // search), but in practice they're heavily clustered and we do better
+        // than that by using the previous lookup's result (lastLineIndex_) as
+        // a starting point.
+        //
+        // Checking if an offset lies within a particular line number
+        // (isOnThisLine()) is O(1).
+        //
+        Vector<uint32_t, 128> lineStartOffsets_;
+        uint32_t            initialLineNum_;
+
+        // This is mutable because it's modified on every search, but that fact
+        // isn't visible outside this class.
+        mutable uint32_t    lastLineIndex_;
+
+        uint32_t lineIndexOf(uint32_t offset) const;
+
+        static const uint32_t MAX_PTR = UINT32_MAX;
+
+        uint32_t lineIndexToNum(uint32_t lineIndex) const { return lineIndex + initialLineNum_; }
+        uint32_t lineNumToIndex(uint32_t lineNum)   const { return lineNum   - initialLineNum_; }
+
+      public:
+        SourceCoords(ExclusiveContext* cx, uint32_t ln);
+
+        MOZ_MUST_USE bool add(uint32_t lineNum, uint32_t lineStartOffset);
+        MOZ_MUST_USE bool fill(const SourceCoords& other);
+
+        bool isOnThisLine(uint32_t offset, uint32_t lineNum, bool* onThisLine) const {
+            uint32_t lineIndex = lineNumToIndex(lineNum);
+            if (lineIndex + 1 >= lineStartOffsets_.length()) // +1 due to sentinel
+                return false;
+            *onThisLine = lineStartOffsets_[lineIndex] <= offset &&
+                          offset < lineStartOffsets_[lineIndex + 1];
+            return true;
+        }
+
+        uint32_t lineNum(uint32_t offset) const;
+        uint32_t columnIndex(uint32_t offset) const;
+        void lineNumAndColumnIndex(uint32_t offset, uint32_t* lineNum, uint32_t* columnIndex) const;
+    };
+
+    SourceCoords srcCoords;
+
+    JSAtomState& names() const {
+        return cx->names();
+    }
+
+    ExclusiveContext* context() const {
+        return cx;
+    }
+
+    const ReadOnlyCompileOptions& options() const {
+        return options_;
+    }
+
+  private:
+    // This is the low-level interface to the JS source code buffer.  It just
+    // gets raw chars, basically.  TokenStreams functions are layered on top
+    // and do some extra stuff like converting all EOL sequences to '\n',
+    // tracking the line number, and setting |flags.isEOF|.  (The "raw" in "raw
+    // chars" refers to the lack of EOL sequence normalization.)
+    //
+    // buf[0..length-1] often represents a substring of some larger source,
+    // where we have only the substring in memory. The |startOffset| argument
+    // indicates the offset within this larger string at which our string
+    // begins, the offset of |buf[0]|.
+    class TokenBuf {
+      public:
+        TokenBuf(ExclusiveContext* cx, const char16_t* buf, size_t length, size_t startOffset)
+          : base_(buf),
+            startOffset_(startOffset),
+            limit_(buf + length),
+            ptr(buf)
+        { }
+
+        bool hasRawChars() const {
+            return ptr < limit_;
+        }
+
+        bool atStart() const {
+            return offset() == 0;
+        }
+
+        size_t startOffset() const {
+            return startOffset_;
+        }
+
+        size_t offset() const {
+            return startOffset_ + mozilla::PointerRangeSize(base_, ptr);
+        }
+
+        const char16_t* rawCharPtrAt(size_t offset) const {
+            MOZ_ASSERT(startOffset_ <= offset);
+            MOZ_ASSERT(offset - startOffset_ <= mozilla::PointerRangeSize(base_, limit_));
+            return base_ + (offset - startOffset_);
+        }
+
+        const char16_t* limit() const {
+            return limit_;
+        }
+
+        char16_t getRawChar() {
+            return *ptr++;      // this will nullptr-crash if poisoned
+        }
+
+        char16_t peekRawChar() const {
+            return *ptr;        // this will nullptr-crash if poisoned
+        }
+
+        bool matchRawChar(char16_t c) {
+            if (*ptr == c) {    // this will nullptr-crash if poisoned
+                ptr++;
+                return true;
+            }
+            return false;
+        }
+
+        bool matchRawCharBackwards(char16_t c) {
+            MOZ_ASSERT(ptr);     // make sure it hasn't been poisoned
+            if (*(ptr - 1) == c) {
+                ptr--;
+                return true;
+            }
+            return false;
+        }
+
+        void ungetRawChar() {
+            MOZ_ASSERT(ptr);     // make sure it hasn't been poisoned
+            ptr--;
+        }
+
+        const char16_t* addressOfNextRawChar(bool allowPoisoned = false) const {
+            MOZ_ASSERT_IF(!allowPoisoned, ptr);     // make sure it hasn't been poisoned
+            return ptr;
+        }
+
+        // Use this with caution!
+        void setAddressOfNextRawChar(const char16_t* a, bool allowPoisoned = false) {
+            MOZ_ASSERT_IF(!allowPoisoned, a);
+            ptr = a;
+        }
+
+#ifdef DEBUG
+        // Poison the TokenBuf so it cannot be accessed again.
+        void poison() {
+            ptr = nullptr;
+        }
+#endif
+
+        static bool isRawEOLChar(int32_t c) {
+            return c == '\n' || c == '\r' || c == LINE_SEPARATOR || c == PARA_SEPARATOR;
+        }
+
+        // Returns the offset of the next EOL, but stops once 'max' characters
+        // have been scanned (*including* the char at startOffset_).
+        size_t findEOLMax(size_t start, size_t max);
+
+      private:
+        const char16_t* base_;          // base of buffer
+        uint32_t startOffset_;          // offset of base_[0]
+        const char16_t* limit_;         // limit for quick bounds check
+        const char16_t* ptr;            // next char to get
+    };
+
+    MOZ_MUST_USE bool getTokenInternal(TokenKind* ttp, Modifier modifier);
+
+    MOZ_MUST_USE bool getBracedUnicode(uint32_t* code);
+    MOZ_MUST_USE bool getStringOrTemplateToken(int untilChar, Token** tp);
+
+    int32_t getChar();
+    int32_t getCharIgnoreEOL();
+    void ungetChar(int32_t c);
+    void ungetCharIgnoreEOL(int32_t c);
+    Token* newToken(ptrdiff_t adjust);
+    uint32_t peekUnicodeEscape(uint32_t* codePoint);
+    uint32_t peekExtendedUnicodeEscape(uint32_t* codePoint);
+    uint32_t matchUnicodeEscapeIdStart(uint32_t* codePoint);
+    bool matchUnicodeEscapeIdent(uint32_t* codePoint);
+    bool peekChars(int n, char16_t* cp);
+
+    MOZ_MUST_USE bool getDirectives(bool isMultiline, bool shouldWarnDeprecated);
+    MOZ_MUST_USE bool getDirective(bool isMultiline, bool shouldWarnDeprecated,
+                                   const char* directive, int directiveLength,
+                                   const char* errorMsgPragma,
+                                   UniquePtr<char16_t[], JS::FreePolicy>* destination);
+    MOZ_MUST_USE bool getDisplayURL(bool isMultiline, bool shouldWarnDeprecated);
+    MOZ_MUST_USE bool getSourceMappingURL(bool isMultiline, bool shouldWarnDeprecated);
+
+    // |expect| cannot be an EOL char.
+    bool matchChar(int32_t expect) {
+        MOZ_ASSERT(!TokenBuf::isRawEOLChar(expect));
+        return MOZ_LIKELY(userbuf.hasRawChars()) &&
+               userbuf.matchRawChar(expect);
+    }
+
+    void consumeKnownChar(int32_t expect) {
+        mozilla::DebugOnly<int32_t> c = getChar();
+        MOZ_ASSERT(c == expect);
+    }
+
+    int32_t peekChar() {
+        int32_t c = getChar();
+        ungetChar(c);
+        return c;
+    }
+
+    void skipChars(int n) {
+        while (--n >= 0)
+            getChar();
+    }
+
+    void skipCharsIgnoreEOL(int n) {
+        while (--n >= 0)
+            getCharIgnoreEOL();
+    }
+
+    void updateLineInfoForEOL();
+    void updateFlagsForEOL();
+
+    const Token& nextToken() const {
+        MOZ_ASSERT(hasLookahead());
+        return tokens[(cursor + 1) & ntokensMask];
+    }
+
+    bool hasLookahead() const { return lookahead > 0; }
+
+    // Options used for parsing/tokenizing.
+    const ReadOnlyCompileOptions& options_;
+
+    Token               tokens[ntokens];    // circular token buffer
+    unsigned            cursor;             // index of last parsed token
+    unsigned            lookahead;          // count of lookahead tokens
+    unsigned            lineno;             // current line number
+    Flags               flags;              // flags -- see above
+    size_t              linebase;           // start of current line
+    size_t              prevLinebase;       // start of previous line;  size_t(-1) if on the first line
+    TokenBuf            userbuf;            // user input buffer
+    const char*         filename;           // input filename or null
+    UniqueTwoByteChars  displayURL_;        // the user's requested source URL or null
+    UniqueTwoByteChars  sourceMapURL_;      // source map's filename or null
+    CharBuffer          tokenbuf;           // current token string buffer
+    uint8_t             isExprEnding[TOK_LIMIT];// which tokens definitely terminate exprs?
+    ExclusiveContext*   const cx;
+    bool                mutedErrors;
+    StrictModeGetter*   strictModeGetter;  // used to test for strict mode
+};
+
+class MOZ_STACK_CLASS AutoAwaitIsKeyword
+{
+private:
+    TokenStream* ts_;
+    bool oldAwaitIsKeyword_;
+
+public:
+    AutoAwaitIsKeyword(TokenStream* ts, bool awaitIsKeyword) {
+        ts_ = ts;
+        oldAwaitIsKeyword_ = ts_->awaitIsKeyword;
+        ts_->awaitIsKeyword = awaitIsKeyword;
+    }
+
+    ~AutoAwaitIsKeyword() {
+        ts_->awaitIsKeyword = oldAwaitIsKeyword_;
+        ts_ = nullptr;
+    }
+};
+
+extern const char*
+TokenKindToDesc(TokenKind tt);
+
+} // namespace frontend
+} // namespace js
+
+extern JS_FRIEND_API(int)
+js_fgets(char* buf, int size, FILE* file);
+
+#ifdef DEBUG
+extern const char*
+TokenKindToString(js::frontend::TokenKind tt);
+#endif
+
+#endif /* frontend_TokenStream_h */