Implement Symbol​.prototype​.description

Resolves #1096

2 files changed, 33 insertions, 0 deletions

diff --git a/js/src/builtin/SymbolObject.cpp b/js/src/builtin/SymbolObject.cpp
index cf48402d69..ae38d5371b 100644
--- a/js/src/builtin/SymbolObject.cpp
+++ b/js/src/builtin/SymbolObject.cpp
@@ -33,6 +33,7 @@ SymbolObject::create(JSContext* cx, JS::HandleSymbol symbol)
 }
 
 const JSPropertySpec SymbolObject::properties[] = {
+    JS_PSG("description", descriptionGetter, 0),
     JS_PS_END
 };
 
@@ -227,6 +228,34 @@ SymbolObject::toPrimitive(JSContext* cx, unsigned argc, Value* vp)
     return CallNonGenericMethod<IsSymbol, valueOf_impl>(cx, args);
 }
 
+// ES2019 Stage 4 Draft / November 28, 2018
+// Symbol description accessor
+// See: https://tc39.github.io/proposal-Symbol-description/
+bool
+SymbolObject::descriptionGetter_impl(JSContext* cx, const CallArgs& args)
+{
+    // Get symbol object pointer.
+    HandleValue thisv = args.thisv();
+    MOZ_ASSERT(IsSymbol(thisv));
+    Rooted<Symbol*> sym(cx, thisv.isSymbol()
+                            ? thisv.toSymbol()
+                            : thisv.toObject().as<SymbolObject>().unbox());
+
+    // Return the symbol's description if present, otherwise return undefined.
+    if (JSString* str = sym->description())
+        args.rval().setString(str);
+    else
+        args.rval().setUndefined();
+    return true;
+}
+
+bool
+SymbolObject::descriptionGetter(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return CallNonGenericMethod<IsSymbol, descriptionGetter_impl>(cx, args);
+}
+
 JSObject*
 js::InitSymbolClass(JSContext* cx, HandleObject obj)
 {
diff --git a/js/src/builtin/SymbolObject.h b/js/src/builtin/SymbolObject.h
index 0f204b494a..e10b42d532 100644
--- a/js/src/builtin/SymbolObject.h
+++ b/js/src/builtin/SymbolObject.h
@@ -52,6 +52,10 @@ class SymbolObject : public NativeObject
     static MOZ_MUST_USE bool valueOf(JSContext* cx, unsigned argc, Value* vp);
     static MOZ_MUST_USE bool toPrimitive(JSContext* cx, unsigned argc, Value* vp);
 
+    // Properties defined on Symbol.prototype.
+    static MOZ_MUST_USE bool descriptionGetter_impl(JSContext* cx, const CallArgs& args);
+    static MOZ_MUST_USE bool descriptionGetter(JSContext* cx, unsigned argc, Value *vp);
+
     static const JSPropertySpec properties[];
     static const JSFunctionSpec methods[];
     static const JSFunctionSpec staticMethods[];