Add m-esr52 at 52.6.0

1 files changed, 1451 insertions, 0 deletions

diff --git a/js/src/vm/Scope.h b/js/src/vm/Scope.h
new file mode 100644
index 0000000000..5304d6713e
--- /dev/null
+++ b/js/src/vm/Scope.h
@@ -0,0 +1,1451 @@
+/* -*- 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 vm_Scope_h
+#define vm_Scope_h
+
+#include "mozilla/Maybe.h"
+#include "mozilla/Variant.h"
+
+#include "jsobj.h"
+#include "jsopcode.h"
+
+#include "gc/Heap.h"
+#include "gc/Policy.h"
+#include "js/UbiNode.h"
+#include "js/UniquePtr.h"
+#include "vm/Xdr.h"
+
+namespace js {
+
+class ModuleObject;
+
+enum class BindingKind : uint8_t
+{
+    Import,
+    FormalParameter,
+    Var,
+    Let,
+    Const,
+
+    // So you think named lambda callee names are consts? Nope! They don't
+    // throw when being assigned to in sloppy mode.
+    NamedLambdaCallee
+};
+
+static inline bool
+BindingKindIsLexical(BindingKind kind)
+{
+    return kind == BindingKind::Let || kind == BindingKind::Const;
+}
+
+enum class ScopeKind : uint8_t
+{
+    // FunctionScope
+    Function,
+
+    // VarScope
+    FunctionBodyVar,
+    ParameterExpressionVar,
+
+    // LexicalScope
+    Lexical,
+    SimpleCatch,
+    Catch,
+    NamedLambda,
+    StrictNamedLambda,
+
+    // WithScope
+    With,
+
+    // EvalScope
+    Eval,
+    StrictEval,
+
+    // GlobalScope
+    Global,
+    NonSyntactic,
+
+    // ModuleScope
+    Module
+};
+
+static inline bool
+ScopeKindIsCatch(ScopeKind kind)
+{
+    return kind == ScopeKind::SimpleCatch || kind == ScopeKind::Catch;
+}
+
+const char* BindingKindString(BindingKind kind);
+const char* ScopeKindString(ScopeKind kind);
+
+class BindingName
+{
+    // A JSAtom* with its low bit used as a tag for whether it is closed over
+    // (i.e., exists in the environment shape).
+    uintptr_t bits_;
+
+    static const uintptr_t ClosedOverFlag = 0x1;
+    static const uintptr_t FlagMask = 0x1;
+
+  public:
+    BindingName()
+      : bits_(0)
+    { }
+
+    BindingName(JSAtom* name, bool closedOver)
+      : bits_(uintptr_t(name) | (closedOver ? ClosedOverFlag : 0x0))
+    { }
+
+    JSAtom* name() const {
+        return reinterpret_cast<JSAtom*>(bits_ & ~FlagMask);
+    }
+
+    bool closedOver() const {
+        return bits_ & ClosedOverFlag;
+    }
+
+    void trace(JSTracer* trc);
+};
+
+class BindingLocation
+{
+  public:
+    enum class Kind {
+        Global,
+        Argument,
+        Frame,
+        Environment,
+        Import,
+        NamedLambdaCallee
+    };
+
+  private:
+    Kind kind_;
+    uint32_t slot_;
+
+    BindingLocation(Kind kind, uint32_t slot)
+      : kind_(kind),
+        slot_(slot)
+    { }
+
+  public:
+    static BindingLocation Global() {
+        return BindingLocation(Kind::Global, UINT32_MAX);
+    }
+
+    static BindingLocation Argument(uint16_t slot) {
+        return BindingLocation(Kind::Argument, slot);
+    }
+
+    static BindingLocation Frame(uint32_t slot) {
+        MOZ_ASSERT(slot < LOCALNO_LIMIT);
+        return BindingLocation(Kind::Frame, slot);
+    }
+
+    static BindingLocation Environment(uint32_t slot) {
+        MOZ_ASSERT(slot < ENVCOORD_SLOT_LIMIT);
+        return BindingLocation(Kind::Environment, slot);
+    }
+
+    static BindingLocation Import() {
+        return BindingLocation(Kind::Import, UINT32_MAX);
+    }
+
+    static BindingLocation NamedLambdaCallee() {
+        return BindingLocation(Kind::NamedLambdaCallee, UINT32_MAX);
+    }
+
+    bool operator==(const BindingLocation& other) const {
+        return kind_ == other.kind_ && slot_ == other.slot_;
+    }
+
+    bool operator!=(const BindingLocation& other) const {
+        return !operator==(other);
+    }
+
+    Kind kind() const {
+        return kind_;
+    }
+
+    uint32_t slot() const {
+        MOZ_ASSERT(kind_ == Kind::Frame || kind_ == Kind::Environment);
+        return slot_;
+    }
+
+    uint16_t argumentSlot() const {
+        MOZ_ASSERT(kind_ == Kind::Argument);
+        return mozilla::AssertedCast<uint16_t>(slot_);
+    }
+};
+
+//
+// The base class of all Scopes.
+//
+class Scope : public js::gc::TenuredCell
+{
+    friend class GCMarker;
+
+    // The kind determines data_.
+    ScopeKind kind_;
+
+    // The enclosing scope or nullptr.
+    GCPtrScope enclosing_;
+
+    // If there are any aliased bindings, the shape for the
+    // EnvironmentObject. Otherwise nullptr.
+    GCPtrShape environmentShape_;
+
+  protected:
+    uintptr_t data_;
+
+    Scope(ScopeKind kind, Scope* enclosing, Shape* environmentShape)
+      : kind_(kind),
+        enclosing_(enclosing),
+        environmentShape_(environmentShape),
+        data_(0)
+    { }
+
+    static Scope* create(ExclusiveContext* cx, ScopeKind kind, HandleScope enclosing,
+                         HandleShape envShape);
+
+    template <typename T, typename D>
+    static Scope* create(ExclusiveContext* cx, ScopeKind kind, HandleScope enclosing,
+                         HandleShape envShape, mozilla::UniquePtr<T, D> data);
+
+    template <typename ConcreteScope, XDRMode mode>
+    static bool XDRSizedBindingNames(XDRState<mode>* xdr, Handle<ConcreteScope*> scope,
+                                     MutableHandle<typename ConcreteScope::Data*> data);
+
+    Shape* maybeCloneEnvironmentShape(JSContext* cx);
+
+    template <typename T, typename D>
+    void initData(mozilla::UniquePtr<T, D> data) {
+        MOZ_ASSERT(!data_);
+        data_ = reinterpret_cast<uintptr_t>(data.release());
+    }
+
+  public:
+    static const JS::TraceKind TraceKind = JS::TraceKind::Scope;
+
+    template <typename T>
+    bool is() const {
+        return kind_ == T::classScopeKind_;
+    }
+
+    template <typename T>
+    T& as() {
+        MOZ_ASSERT(this->is<T>());
+        return *static_cast<T*>(this);
+    }
+
+    template <typename T>
+    const T& as() const {
+        MOZ_ASSERT(this->is<T>());
+        return *static_cast<const T*>(this);
+    }
+
+    ScopeKind kind() const {
+        return kind_;
+    }
+
+    Scope* enclosing() const {
+        return enclosing_;
+    }
+
+    Shape* environmentShape() const {
+        return environmentShape_;
+    }
+
+    bool hasEnvironment() const {
+        switch (kind()) {
+          case ScopeKind::With:
+          case ScopeKind::Global:
+          case ScopeKind::NonSyntactic:
+            return true;
+          default:
+            // If there's a shape, an environment must be created for this scope.
+            return environmentShape_ != nullptr;
+        }
+    }
+
+    uint32_t chainLength() const;
+    uint32_t environmentChainLength() const;
+
+    template <typename T>
+    bool hasOnChain() const {
+        for (const Scope* it = this; it; it = it->enclosing()) {
+            if (it->is<T>())
+                return true;
+        }
+        return false;
+    }
+
+    bool hasOnChain(ScopeKind kind) const {
+        for (const Scope* it = this; it; it = it->enclosing()) {
+            if (it->kind() == kind)
+                return true;
+        }
+        return false;
+    }
+
+    static Scope* clone(JSContext* cx, HandleScope scope, HandleScope enclosing);
+
+    void traceChildren(JSTracer* trc);
+    void finalize(FreeOp* fop);
+
+    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
+
+    void dump();
+};
+
+//
+// A lexical scope that holds let and const bindings. There are 4 kinds of
+// LexicalScopes.
+//
+// Lexical
+//   A plain lexical scope.
+//
+// SimpleCatch
+//   Holds the single catch parameter of a catch block.
+//
+// Catch
+//   Holds the catch parameters (and only the catch parameters) of a catch
+//   block.
+//
+// NamedLambda
+// StrictNamedLambda
+//   Holds the single name of the callee for a named lambda expression.
+//
+// All kinds of LexicalScopes correspond to LexicalEnvironmentObjects on the
+// environment chain.
+//
+class LexicalScope : public Scope
+{
+    friend class Scope;
+    friend class BindingIter;
+
+  public:
+    // Data is public because it is created by the frontend. See
+    // Parser<FullParseHandler>::newLexicalScopeData.
+    struct Data
+    {
+        // Bindings are sorted by kind in both frames and environments.
+        //
+        //   lets - [0, constStart)
+        // consts - [constStart, length)
+        uint32_t constStart;
+        uint32_t length;
+
+        // Frame slots [0, nextFrameSlot) are live when this is the innermost
+        // scope.
+        uint32_t nextFrameSlot;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static LexicalScope* create(ExclusiveContext* cx, ScopeKind kind, Handle<Data*> data,
+                                uint32_t firstFrameSlot, HandleScope enclosing);
+
+    template <XDRMode mode>
+    static bool XDR(XDRState<mode>* xdr, ScopeKind kind, HandleScope enclosing,
+                    MutableHandleScope scope);
+
+  private:
+    static LexicalScope* createWithData(ExclusiveContext* cx, ScopeKind kind,
+                                        MutableHandle<UniquePtr<Data>> data,
+                                        uint32_t firstFrameSlot, HandleScope enclosing);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    static uint32_t nextFrameSlot(Scope* start);
+
+  public:
+    uint32_t firstFrameSlot() const;
+
+    uint32_t nextFrameSlot() const {
+        return data().nextFrameSlot;
+    }
+
+    // Returns an empty shape for extensible global and non-syntactic lexical
+    // scopes.
+    static Shape* getEmptyExtensibleEnvironmentShape(ExclusiveContext* cx);
+};
+
+template <>
+inline bool
+Scope::is<LexicalScope>() const
+{
+    return kind_ == ScopeKind::Lexical ||
+           kind_ == ScopeKind::SimpleCatch ||
+           kind_ == ScopeKind::Catch ||
+           kind_ == ScopeKind::NamedLambda ||
+           kind_ == ScopeKind::StrictNamedLambda;
+}
+
+//
+// Scope corresponding to a function. Holds formal parameter names and, if the
+// function parameters contain no expressions that might possibly be
+// evaluated, the function's var bindings.  For example, in these functions,
+// the FunctionScope will store a/b/c bindings but not d/e/f bindings:
+//
+//   function f1(a, b) {
+//     var c;
+//     let e;
+//     const f = 3;
+//   }
+//   function f2([a], b = 4, ...c) {
+//     var d, e, f; // stored in VarScope
+//   }
+//
+// Corresponds to CallObject on environment chain.
+//
+class FunctionScope : public Scope
+{
+    friend class GCMarker;
+    friend class BindingIter;
+    friend class PositionalFormalParameterIter;
+    friend class Scope;
+    static const ScopeKind classScopeKind_ = ScopeKind::Function;
+
+  public:
+    // Data is public because it is created by the
+    // frontend. See Parser<FullParseHandler>::newFunctionScopeData.
+    struct Data
+    {
+        // The canonical function of the scope, as during a scope walk we
+        // often query properties of the JSFunction (e.g., is the function an
+        // arrow).
+        GCPtrFunction canonicalFunction;
+
+        // If parameter expressions are present, parameters act like lexical
+        // bindings.
+        bool hasParameterExprs;
+
+        // Bindings are sorted by kind in both frames and environments.
+        //
+        // Positional formal parameter names are those that are not
+        // destructured. They may be referred to by argument slots if
+        // !script()->hasParameterExprs().
+        //
+        // An argument slot that needs to be skipped due to being destructured
+        // or having defaults will have a nullptr name in the name array to
+        // advance the argument slot.
+        //
+        // positional formals - [0, nonPositionalFormalStart)
+        //      other formals - [nonPositionalParamStart, varStart)
+        //               vars - [varStart, length)
+        uint16_t nonPositionalFormalStart;
+        uint16_t varStart;
+        uint32_t length;
+
+        // Frame slots [0, nextFrameSlot) are live when this is the innermost
+        // scope.
+        uint32_t nextFrameSlot;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static FunctionScope* create(ExclusiveContext* cx, Handle<Data*> data,
+                                 bool hasParameterExprs, bool needsEnvironment,
+                                 HandleFunction fun, HandleScope enclosing);
+
+    static FunctionScope* clone(JSContext* cx, Handle<FunctionScope*> scope, HandleFunction fun,
+                                HandleScope enclosing);
+
+    template <XDRMode mode>
+    static bool XDR(XDRState<mode>* xdr, HandleFunction fun, HandleScope enclosing,
+                    MutableHandleScope scope);
+
+  private:
+    static FunctionScope* createWithData(ExclusiveContext* cx, MutableHandle<UniquePtr<Data>> data,
+                                         bool hasParameterExprs, bool needsEnvironment,
+                                         HandleFunction fun, HandleScope enclosing);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+  public:
+    uint32_t nextFrameSlot() const {
+        return data().nextFrameSlot;
+    }
+
+    JSFunction* canonicalFunction() const {
+        return data().canonicalFunction;
+    }
+
+    JSScript* script() const;
+
+    bool hasParameterExprs() const {
+        return data().hasParameterExprs;
+    }
+
+    uint32_t numPositionalFormalParameters() const {
+        return data().nonPositionalFormalStart;
+    }
+
+    static Shape* getEmptyEnvironmentShape(ExclusiveContext* cx, bool hasParameterExprs);
+};
+
+//
+// Scope holding only vars. There are 2 kinds of VarScopes.
+//
+// FunctionBodyVar
+//   Corresponds to the extra var scope present in functions with parameter
+//   expressions. See examples in comment above FunctionScope.
+//
+// ParameterExpressionVar
+//   Each parameter expression is evaluated in its own var environment. For
+//   example, f() below will print 'fml', then 'global'. That's right.
+//
+//     var a = 'global';
+//     function f(x = (eval(`var a = 'fml'`), a), y = a) {
+//       print(x);
+//       print(y);
+//     };
+//
+// Corresponds to VarEnvironmentObject on environment chain.
+//
+class VarScope : public Scope
+{
+    friend class GCMarker;
+    friend class BindingIter;
+    friend class Scope;
+
+  public:
+    // Data is public because it is created by the
+    // frontend. See Parser<FullParseHandler>::newVarScopeData.
+    struct Data
+    {
+        // All bindings are vars.
+        uint32_t length;
+
+        // Frame slots [firstFrameSlot(), nextFrameSlot) are live when this is
+        // the innermost scope.
+        uint32_t nextFrameSlot;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static VarScope* create(ExclusiveContext* cx, ScopeKind kind, Handle<Data*> data,
+                            uint32_t firstFrameSlot, bool needsEnvironment,
+                            HandleScope enclosing);
+
+    template <XDRMode mode>
+    static bool XDR(XDRState<mode>* xdr, ScopeKind kind, HandleScope enclosing,
+                    MutableHandleScope scope);
+
+  private:
+    static VarScope* createWithData(ExclusiveContext* cx, ScopeKind kind, MutableHandle<UniquePtr<Data>> data,
+                                    uint32_t firstFrameSlot, bool needsEnvironment,
+                                    HandleScope enclosing);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+  public:
+    uint32_t firstFrameSlot() const;
+
+    uint32_t nextFrameSlot() const {
+        return data().nextFrameSlot;
+    }
+
+    static Shape* getEmptyEnvironmentShape(ExclusiveContext* cx);
+};
+
+template <>
+inline bool
+Scope::is<VarScope>() const
+{
+    return kind_ == ScopeKind::FunctionBodyVar || kind_ == ScopeKind::ParameterExpressionVar;
+}
+
+//
+// Scope corresponding to both the global object scope and the global lexical
+// scope.
+//
+// Both are extensible and are singletons across <script> tags, so these
+// scopes are a fragment of the names in global scope. In other words, two
+// global scripts may have two different GlobalScopes despite having the same
+// GlobalObject.
+//
+// There are 2 kinds of GlobalScopes.
+//
+// Global
+//   Corresponds to a GlobalObject and its global LexicalEnvironmentObject on
+//   the environment chain.
+//
+// NonSyntactic
+//   Corresponds to a non-GlobalObject created by the embedding on the
+//   environment chain. This distinction is important for optimizations.
+//
+class GlobalScope : public Scope
+{
+    friend class Scope;
+    friend class BindingIter;
+
+  public:
+    // Data is public because it is created by the frontend. See
+    // Parser<FullParseHandler>::newGlobalScopeData.
+    struct Data
+    {
+        // Bindings are sorted by kind.
+        //
+        // top-level funcs - [0, varStart)
+        //            vars - [varStart, letStart)
+        //            lets - [letStart, constStart)
+        //          consts - [constStart, length)
+        uint32_t varStart;
+        uint32_t letStart;
+        uint32_t constStart;
+        uint32_t length;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static GlobalScope* create(ExclusiveContext* cx, ScopeKind kind, Handle<Data*> data);
+
+    static GlobalScope* createEmpty(ExclusiveContext* cx, ScopeKind kind) {
+        return create(cx, kind, nullptr);
+    }
+
+    static GlobalScope* clone(JSContext* cx, Handle<GlobalScope*> scope, ScopeKind kind);
+
+    template <XDRMode mode>
+    static bool XDR(XDRState<mode>* xdr, ScopeKind kind, MutableHandleScope scope);
+
+  private:
+    static GlobalScope* createWithData(ExclusiveContext* cx, ScopeKind kind,
+                                       MutableHandle<UniquePtr<Data>> data);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+  public:
+    bool isSyntactic() const {
+        return kind() != ScopeKind::NonSyntactic;
+    }
+
+    bool hasBindings() const {
+        return data().length > 0;
+    }
+};
+
+template <>
+inline bool
+Scope::is<GlobalScope>() const
+{
+    return kind_ == ScopeKind::Global || kind_ == ScopeKind::NonSyntactic;
+}
+
+//
+// Scope of a 'with' statement. Has no bindings.
+//
+// Corresponds to a WithEnvironmentObject on the environment chain.
+class WithScope : public Scope
+{
+    friend class Scope;
+    static const ScopeKind classScopeKind_ = ScopeKind::With;
+
+  public:
+    static WithScope* create(ExclusiveContext* cx, HandleScope enclosing);
+};
+
+//
+// Scope of an eval. Holds var bindings. There are 2 kinds of EvalScopes.
+//
+// StrictEval
+//   A strict eval. Corresponds to a VarEnvironmentObject, where its var
+//   bindings lives.
+//
+// Eval
+//   A sloppy eval. This is an empty scope, used only in the frontend, to
+//   detect redeclaration errors. It has no Environment. Any `var`s declared
+//   in the eval code are bound on the nearest enclosing var environment.
+//
+class EvalScope : public Scope
+{
+    friend class Scope;
+    friend class BindingIter;
+
+  public:
+    // Data is public because it is created by the frontend. See
+    // Parser<FullParseHandler>::newEvalScopeData.
+    struct Data
+    {
+        // All bindings in an eval script are 'var' bindings. The implicit
+        // lexical scope around the eval is present regardless of strictness
+        // and is its own LexicalScope. However, we need to track top-level
+        // functions specially for redeclaration checks.
+        //
+        // top-level funcs - [0, varStart)
+        //            vars - [varStart, length)
+        uint32_t varStart;
+        uint32_t length;
+
+        // Frame slots [0, nextFrameSlot) are live when this is the innermost
+        // scope.
+        uint32_t nextFrameSlot;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static EvalScope* create(ExclusiveContext* cx, ScopeKind kind, Handle<Data*> data,
+                             HandleScope enclosing);
+
+    template <XDRMode mode>
+    static bool XDR(XDRState<mode>* xdr, ScopeKind kind, HandleScope enclosing,
+                    MutableHandleScope scope);
+
+  private:
+    static EvalScope* createWithData(ExclusiveContext* cx, ScopeKind kind, MutableHandle<UniquePtr<Data>> data,
+                                     HandleScope enclosing);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+  public:
+    // Starting a scope, the nearest var scope that a direct eval can
+    // introduce vars on.
+    static Scope* nearestVarScopeForDirectEval(Scope* scope);
+
+    uint32_t nextFrameSlot() const {
+        return data().nextFrameSlot;
+    }
+
+    bool strict() const {
+        return kind() == ScopeKind::StrictEval;
+    }
+
+    bool hasBindings() const {
+        return data().length > 0;
+    }
+
+    bool isNonGlobal() const {
+        if (strict())
+            return true;
+        return !nearestVarScopeForDirectEval(enclosing())->is<GlobalScope>();
+    }
+
+    static Shape* getEmptyEnvironmentShape(ExclusiveContext* cx);
+};
+
+template <>
+inline bool
+Scope::is<EvalScope>() const
+{
+    return kind_ == ScopeKind::Eval || kind_ == ScopeKind::StrictEval;
+}
+
+//
+// Scope corresponding to the toplevel script in an ES module.
+//
+// Like GlobalScopes, these scopes contain both vars and lexical bindings, as
+// the treating of imports and exports requires putting them in one scope.
+//
+// Corresponds to a ModuleEnvironmentObject on the environment chain.
+//
+class ModuleScope : public Scope
+{
+    friend class GCMarker;
+    friend class BindingIter;
+    friend class Scope;
+    static const ScopeKind classScopeKind_ = ScopeKind::Module;
+
+  public:
+    // Data is public because it is created by the frontend. See
+    // Parser<FullParseHandler>::newModuleScopeData.
+    struct Data
+    {
+        // The module of the scope.
+        GCPtr<ModuleObject*> module;
+
+        // Bindings are sorted by kind.
+        //
+        // imports - [0, varStart)
+        //    vars - [varStart, letStart)
+        //    lets - [letStart, constStart)
+        //  consts - [constStart, length)
+        uint32_t varStart;
+        uint32_t letStart;
+        uint32_t constStart;
+        uint32_t length;
+
+        // Frame slots [0, nextFrameSlot) are live when this is the innermost
+        // scope.
+        uint32_t nextFrameSlot;
+
+        // The array of tagged JSAtom* names, allocated beyond the end of the
+        // struct.
+        BindingName names[1];
+
+        void trace(JSTracer* trc);
+    };
+
+    static size_t sizeOfData(uint32_t length) {
+        return sizeof(Data) + (length ? length - 1 : 0) * sizeof(BindingName);
+    }
+
+    static ModuleScope* create(ExclusiveContext* cx, Handle<Data*> data,
+                               Handle<ModuleObject*> module, HandleScope enclosing);
+
+  private:
+    static ModuleScope* createWithData(ExclusiveContext* cx, MutableHandle<UniquePtr<Data>> data,
+                                       Handle<ModuleObject*> module, HandleScope enclosing);
+
+    Data& data() {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+    const Data& data() const {
+        return *reinterpret_cast<Data*>(data_);
+    }
+
+  public:
+    uint32_t nextFrameSlot() const {
+        return data().nextFrameSlot;
+    }
+
+    ModuleObject* module() const {
+        return data().module;
+    }
+
+    JSScript* script() const;
+
+    static Shape* getEmptyEnvironmentShape(ExclusiveContext* cx);
+};
+
+//
+// An iterator for a Scope's bindings. This is the source of truth for frame
+// and environment object layout.
+//
+// It may be placed in GC containers; for example:
+//
+//   for (Rooted<BindingIter> bi(cx, BindingIter(scope)); bi; bi++) {
+//     use(bi);
+//     SomeMayGCOperation();
+//     use(bi);
+//   }
+//
+class BindingIter
+{
+  protected:
+    // Bindings are sorted by kind. Because different Scopes have differently
+    // laid out Data for packing, BindingIter must handle all binding kinds.
+    //
+    // Kind ranges:
+    //
+    //            imports - [0, positionalFormalStart)
+    // positional formals - [positionalFormalStart, nonPositionalFormalStart)
+    //      other formals - [nonPositionalParamStart, topLevelFunctionStart)
+    //    top-level funcs - [topLevelFunctionStart, varStart)
+    //               vars - [varStart, letStart)
+    //               lets - [letStart, constStart)
+    //             consts - [constStart, length)
+    //
+    // Access method when not closed over:
+    //
+    //            imports - name
+    // positional formals - argument slot
+    //      other formals - frame slot
+    //    top-level funcs - frame slot
+    //               vars - frame slot
+    //               lets - frame slot
+    //             consts - frame slot
+    //
+    // Access method when closed over:
+    //
+    //            imports - name
+    // positional formals - environment slot or name
+    //      other formals - environment slot or name
+    //    top-level funcs - environment slot or name
+    //               vars - environment slot or name
+    //               lets - environment slot or name
+    //             consts - environment slot or name
+    uint32_t positionalFormalStart_;
+    uint32_t nonPositionalFormalStart_;
+    uint32_t topLevelFunctionStart_;
+    uint32_t varStart_;
+    uint32_t letStart_;
+    uint32_t constStart_;
+    uint32_t length_;
+
+    uint32_t index_;
+
+    enum Flags : uint8_t {
+        CannotHaveSlots = 0,
+        CanHaveArgumentSlots = 1 << 0,
+        CanHaveFrameSlots = 1 << 1,
+        CanHaveEnvironmentSlots = 1 << 2,
+
+        // See comment in settle below.
+        HasFormalParameterExprs = 1 << 3,
+        IgnoreDestructuredFormalParameters = 1 << 4,
+
+        // Truly I hate named lambdas.
+        IsNamedLambda = 1 << 5
+    };
+
+    static const uint8_t CanHaveSlotsMask = 0x7;
+
+    uint8_t flags_;
+    uint16_t argumentSlot_;
+    uint32_t frameSlot_;
+    uint32_t environmentSlot_;
+
+    BindingName* names_;
+
+    void init(uint32_t positionalFormalStart, uint32_t nonPositionalFormalStart,
+              uint32_t topLevelFunctionStart, uint32_t varStart,
+              uint32_t letStart, uint32_t constStart,
+              uint8_t flags, uint32_t firstFrameSlot, uint32_t firstEnvironmentSlot,
+              BindingName* names, uint32_t length)
+    {
+        positionalFormalStart_ = positionalFormalStart;
+        nonPositionalFormalStart_ = nonPositionalFormalStart;
+        topLevelFunctionStart_ = topLevelFunctionStart;
+        varStart_ = varStart;
+        letStart_ = letStart;
+        constStart_ = constStart;
+        length_ = length;
+        index_ = 0;
+        flags_ = flags;
+        argumentSlot_ = 0;
+        frameSlot_ = firstFrameSlot;
+        environmentSlot_ = firstEnvironmentSlot;
+        names_ = names;
+
+        settle();
+    }
+
+    void init(LexicalScope::Data& data, uint32_t firstFrameSlot, uint8_t flags);
+    void init(FunctionScope::Data& data, uint8_t flags);
+    void init(VarScope::Data& data, uint32_t firstFrameSlot);
+    void init(GlobalScope::Data& data);
+    void init(EvalScope::Data& data, bool strict);
+    void init(ModuleScope::Data& data);
+
+    bool hasFormalParameterExprs() const {
+        return flags_ & HasFormalParameterExprs;
+    }
+
+    bool ignoreDestructuredFormalParameters() const {
+        return flags_ & IgnoreDestructuredFormalParameters;
+    }
+
+    bool isNamedLambda() const {
+        return flags_ & IsNamedLambda;
+    }
+
+    void increment() {
+        MOZ_ASSERT(!done());
+        if (flags_ & CanHaveSlotsMask) {
+            if (canHaveArgumentSlots()) {
+                if (index_ < nonPositionalFormalStart_) {
+                    MOZ_ASSERT(index_ >= positionalFormalStart_);
+                    argumentSlot_++;
+                }
+            }
+            if (closedOver()) {
+                // Imports must not be given known slots. They are
+                // indirect bindings.
+                MOZ_ASSERT(kind() != BindingKind::Import);
+                MOZ_ASSERT(canHaveEnvironmentSlots());
+                environmentSlot_++;
+            } else if (canHaveFrameSlots()) {
+                // Usually positional formal parameters don't have frame
+                // slots, except when there are parameter expressions, in
+                // which case they act like lets.
+                if (index_ >= nonPositionalFormalStart_ || (hasFormalParameterExprs() && name()))
+                    frameSlot_++;
+            }
+        }
+        index_++;
+    }
+
+    void settle() {
+        if (ignoreDestructuredFormalParameters()) {
+            while (!done() && !name())
+                increment();
+        }
+    }
+
+  public:
+    explicit BindingIter(Scope* scope);
+    explicit BindingIter(JSScript* script);
+
+    BindingIter(LexicalScope::Data& data, uint32_t firstFrameSlot, bool isNamedLambda) {
+        init(data, firstFrameSlot, isNamedLambda ? IsNamedLambda : 0);
+    }
+
+    BindingIter(FunctionScope::Data& data, bool hasParameterExprs) {
+        init(data,
+             IgnoreDestructuredFormalParameters |
+             (hasParameterExprs ? HasFormalParameterExprs : 0));
+    }
+
+    BindingIter(VarScope::Data& data, uint32_t firstFrameSlot) {
+        init(data, firstFrameSlot);
+    }
+
+    explicit BindingIter(GlobalScope::Data& data) {
+        init(data);
+    }
+
+    explicit BindingIter(ModuleScope::Data& data) {
+        init(data);
+    }
+
+    BindingIter(EvalScope::Data& data, bool strict) {
+        init(data, strict);
+    }
+
+    explicit BindingIter(const BindingIter& bi) = default;
+
+    bool done() const {
+        return index_ == length_;
+    }
+
+    explicit operator bool() const {
+        return !done();
+    }
+
+    void operator++(int) {
+        increment();
+        settle();
+    }
+
+    bool isLast() const {
+        MOZ_ASSERT(!done());
+        return index_ + 1 == length_;
+    }
+
+    bool canHaveArgumentSlots() const {
+        return flags_ & CanHaveArgumentSlots;
+    }
+
+    bool canHaveFrameSlots() const {
+        return flags_ & CanHaveFrameSlots;
+    }
+
+    bool canHaveEnvironmentSlots() const {
+        return flags_ & CanHaveEnvironmentSlots;
+    }
+
+    JSAtom* name() const {
+        MOZ_ASSERT(!done());
+        return names_[index_].name();
+    }
+
+    bool closedOver() const {
+        MOZ_ASSERT(!done());
+        return names_[index_].closedOver();
+    }
+
+    BindingLocation location() const {
+        MOZ_ASSERT(!done());
+        if (!(flags_ & CanHaveSlotsMask))
+            return BindingLocation::Global();
+        if (index_ < positionalFormalStart_)
+            return BindingLocation::Import();
+        if (closedOver()) {
+            MOZ_ASSERT(canHaveEnvironmentSlots());
+            return BindingLocation::Environment(environmentSlot_);
+        }
+        if (index_ < nonPositionalFormalStart_ && canHaveArgumentSlots())
+            return BindingLocation::Argument(argumentSlot_);
+        if (canHaveFrameSlots())
+            return BindingLocation::Frame(frameSlot_);
+        MOZ_ASSERT(isNamedLambda());
+        return BindingLocation::NamedLambdaCallee();
+    }
+
+    BindingKind kind() const {
+        MOZ_ASSERT(!done());
+        if (index_ < positionalFormalStart_)
+            return BindingKind::Import;
+        if (index_ < topLevelFunctionStart_) {
+            // When the parameter list has expressions, the parameters act
+            // like lexical bindings and have TDZ.
+            if (hasFormalParameterExprs())
+                return BindingKind::Let;
+            return BindingKind::FormalParameter;
+        }
+        if (index_ < letStart_)
+            return BindingKind::Var;
+        if (index_ < constStart_)
+            return BindingKind::Let;
+        if (isNamedLambda())
+            return BindingKind::NamedLambdaCallee;
+        return BindingKind::Const;
+    }
+
+    bool isTopLevelFunction() const {
+        MOZ_ASSERT(!done());
+        return index_ >= topLevelFunctionStart_ && index_ < varStart_;
+    }
+
+    bool hasArgumentSlot() const {
+        MOZ_ASSERT(!done());
+        if (hasFormalParameterExprs())
+            return false;
+        return index_ >= positionalFormalStart_ && index_ < nonPositionalFormalStart_;
+    }
+
+    uint16_t argumentSlot() const {
+        MOZ_ASSERT(canHaveArgumentSlots());
+        return mozilla::AssertedCast<uint16_t>(index_);
+    }
+
+    uint32_t nextFrameSlot() const {
+        MOZ_ASSERT(canHaveFrameSlots());
+        return frameSlot_;
+    }
+
+    uint32_t nextEnvironmentSlot() const {
+        MOZ_ASSERT(canHaveEnvironmentSlots());
+        return environmentSlot_;
+    }
+
+    void trace(JSTracer* trc);
+};
+
+void DumpBindings(JSContext* cx, Scope* scope);
+JSAtom* FrameSlotName(JSScript* script, jsbytecode* pc);
+
+//
+// A refinement BindingIter that only iterates over positional formal
+// parameters of a function.
+//
+class PositionalFormalParameterIter : public BindingIter
+{
+    void settle() {
+        if (index_ >= nonPositionalFormalStart_)
+            index_ = length_;
+    }
+
+  public:
+    explicit PositionalFormalParameterIter(JSScript* script);
+
+    void operator++(int) {
+        BindingIter::operator++(1);
+        settle();
+    }
+
+    bool isDestructured() const {
+        return !name();
+    }
+};
+
+//
+// Iterator for walking the scope chain.
+//
+// It may be placed in GC containers; for example:
+//
+//   for (Rooted<ScopeIter> si(cx, ScopeIter(scope)); si; si++) {
+//     use(si);
+//     SomeMayGCOperation();
+//     use(si);
+//   }
+//
+class MOZ_STACK_CLASS ScopeIter
+{
+    Scope* scope_;
+
+  public:
+    explicit ScopeIter(Scope* scope)
+      : scope_(scope)
+    { }
+
+    explicit ScopeIter(JSScript* script);
+
+    explicit ScopeIter(const ScopeIter& si)
+      : scope_(si.scope_)
+    { }
+
+    bool done() const {
+        return !scope_;
+    }
+
+    explicit operator bool() const {
+        return !done();
+    }
+
+    void operator++(int) {
+        MOZ_ASSERT(!done());
+        scope_ = scope_->enclosing();
+    }
+
+    Scope* scope() const {
+        MOZ_ASSERT(!done());
+        return scope_;
+    }
+
+    ScopeKind kind() const {
+        MOZ_ASSERT(!done());
+        return scope_->kind();
+    }
+
+    // Returns the shape of the environment if it is known. It is possible to
+    // hasSyntacticEnvironment and to have no known shape, e.g., eval.
+    Shape* environmentShape() const {
+        return scope()->environmentShape();
+    }
+
+    // Returns whether this scope has a syntactic environment (i.e., an
+    // Environment that isn't a non-syntactic With or NonSyntacticVariables)
+    // on the environment chain.
+    bool hasSyntacticEnvironment() const;
+
+    void trace(JSTracer* trc) {
+        if (scope_)
+            TraceRoot(trc, &scope_, "scope iter scope");
+    }
+};
+
+//
+// Specializations of Rooted containers for the iterators.
+//
+
+template <typename Outer>
+class BindingIterOperations
+{
+    const BindingIter& iter() const { return static_cast<const Outer*>(this)->get(); }
+
+  public:
+    bool done() const { return iter().done(); }
+    explicit operator bool() const { return !done(); }
+    bool isLast() const { return iter().isLast(); }
+    bool canHaveArgumentSlots() const { return iter().canHaveArgumentSlots(); }
+    bool canHaveFrameSlots() const { return iter().canHaveFrameSlots(); }
+    bool canHaveEnvironmentSlots() const { return iter().canHaveEnvironmentSlots(); }
+    JSAtom* name() const { return iter().name(); }
+    bool closedOver() const { return iter().closedOver(); }
+    BindingLocation location() const { return iter().location(); }
+    BindingKind kind() const { return iter().kind(); }
+    bool isTopLevelFunction() const { return iter().isTopLevelFunction(); }
+    bool hasArgumentSlot() const { return iter().hasArgumentSlot(); }
+    uint16_t argumentSlot() const { return iter().argumentSlot(); }
+    uint32_t nextFrameSlot() const { return iter().nextFrameSlot(); }
+    uint32_t nextEnvironmentSlot() const { return iter().nextEnvironmentSlot(); }
+};
+
+template <typename Outer>
+class MutableBindingIterOperations : public BindingIterOperations<Outer>
+{
+    BindingIter& iter() { return static_cast<Outer*>(this)->get(); }
+
+  public:
+    void operator++(int) { iter().operator++(1); }
+};
+
+template <typename Outer>
+class ScopeIterOperations
+{
+    const ScopeIter& iter() const { return static_cast<const Outer*>(this)->get(); }
+
+  public:
+    bool done() const { return iter().done(); }
+    explicit operator bool() const { return !done(); }
+    Scope* scope() const { return iter().scope(); }
+    ScopeKind kind() const { return iter().kind(); }
+    Shape* environmentShape() const { return iter().environmentShape(); }
+    bool hasSyntacticEnvironment() const { return iter().hasSyntacticEnvironment(); }
+};
+
+template <typename Outer>
+class MutableScopeIterOperations : public ScopeIterOperations<Outer>
+{
+    ScopeIter& iter() { return static_cast<Outer*>(this)->get(); }
+
+  public:
+    void operator++(int) { iter().operator++(1); }
+};
+
+#define SPECIALIZE_ROOTING_CONTAINERS(Iter, BaseIter)                    \
+    template <>                                                          \
+    class RootedBase<Iter>                                               \
+      : public Mutable##BaseIter##Operations<JS::Rooted<Iter>>           \
+    { };                                                                 \
+                                                                         \
+    template <>                                                          \
+    class MutableHandleBase<Iter>                                        \
+      : public Mutable##BaseIter##Operations<JS::MutableHandle<Iter>>    \
+    { };                                                                 \
+                                                                         \
+    template <>                                                          \
+    class HandleBase<Iter>                                               \
+      : public BaseIter##Operations<JS::Handle<Iter>>                    \
+    { };                                                                 \
+                                                                         \
+    template <>                                                          \
+    class PersistentRootedBase<Iter>                                     \
+      : public Mutable##BaseIter##Operations<JS::PersistentRooted<Iter>> \
+    { }
+
+SPECIALIZE_ROOTING_CONTAINERS(BindingIter, BindingIter);
+SPECIALIZE_ROOTING_CONTAINERS(PositionalFormalParameterIter, BindingIter);
+SPECIALIZE_ROOTING_CONTAINERS(ScopeIter, ScopeIter);
+
+#undef SPECIALIZE_ROOTING_CONTAINERS
+
+//
+// Allow using is<T> and as<T> on Rooted<Scope*> and Handle<Scope*>.
+//
+
+template <typename Outer>
+struct ScopeCastOperation
+{
+    template <class U>
+    JS::Handle<U*> as() const {
+        const Outer& self = *static_cast<const Outer*>(this);
+        MOZ_ASSERT_IF(self, self->template is<U>());
+        return Handle<U*>::fromMarkedLocation(reinterpret_cast<U* const*>(self.address()));
+    }
+};
+
+template <>
+class RootedBase<Scope*> : public ScopeCastOperation<JS::Rooted<Scope*>>
+{ };
+
+template <>
+class HandleBase<Scope*> : public ScopeCastOperation<JS::Handle<Scope*>>
+{ };
+
+template <>
+class MutableHandleBase<Scope*> : public ScopeCastOperation<JS::MutableHandle<Scope*>>
+{ };
+
+} // namespace js
+
+namespace JS {
+
+template <>
+struct GCPolicy<js::ScopeKind> : public IgnoreGCPolicy<js::ScopeKind>
+{ };
+
+template <typename T>
+struct ScopeDataGCPolicy
+{
+    static T initial() {
+        return nullptr;
+    }
+
+    static void trace(JSTracer* trc, T* vp, const char* name) {
+        if (*vp)
+            (*vp)->trace(trc);
+    }
+};
+
+#define DEFINE_SCOPE_DATA_GCPOLICY(Data)                        \
+    template <>                                                 \
+    struct MapTypeToRootKind<Data*> {                           \
+        static const RootKind kind = RootKind::Traceable;       \
+    };                                                          \
+    template <>                                                 \
+    struct GCPolicy<Data*> : public ScopeDataGCPolicy<Data*>    \
+    { }
+
+DEFINE_SCOPE_DATA_GCPOLICY(js::LexicalScope::Data);
+DEFINE_SCOPE_DATA_GCPOLICY(js::FunctionScope::Data);
+DEFINE_SCOPE_DATA_GCPOLICY(js::VarScope::Data);
+DEFINE_SCOPE_DATA_GCPOLICY(js::GlobalScope::Data);
+DEFINE_SCOPE_DATA_GCPOLICY(js::EvalScope::Data);
+DEFINE_SCOPE_DATA_GCPOLICY(js::ModuleScope::Data);
+
+#undef DEFINE_SCOPE_DATA_GCPOLICY
+
+namespace ubi {
+
+template <>
+class Concrete<js::Scope> : TracerConcrete<js::Scope>
+{
+  protected:
+    explicit Concrete(js::Scope* ptr) : TracerConcrete<js::Scope>(ptr) { }
+
+  public:
+    static void construct(void* storage, js::Scope* ptr) {
+        new (storage) Concrete(ptr);
+    }
+
+    CoarseType coarseType() const final { return CoarseType::Script; }
+
+    Size size(mozilla::MallocSizeOf mallocSizeOf) const override;
+
+    const char16_t* typeName() const override { return concreteTypeName; }
+    static const char16_t concreteTypeName[];
+};
+
+} // namespace ubi
+} // namespace JS
+
+#endif // vm_Scope_h