Upgrade Symbol implementation to match current ES6 behavior.

src/symbol.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 18 matching lines @@
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Array = global.Array;
 
 var $Symbol = global.Symbol;
 
 // -------------------------------------------------------------------
 
 function SymbolConstructor(x) {
-  var value =
-    IS_SYMBOL(x) ? x : %CreateSymbol(IS_UNDEFINED(x) ? x : ToString(x));
   if (%_IsConstructCall()) {
-    %_SetValueOf(this, value);
-  } else {
-    return value;
+    throw MakeTypeError('not_constructor', ["Symbol"]);
   }
-}
-
-function SymbolGetName() {
-  var symbol = IS_SYMBOL_WRAPPER(this) ? %_ValueOf(this) : this;
-  if (!IS_SYMBOL(symbol)) {
-    throw MakeTypeError(
-        'incompatible_method_receiver', ["Symbol.prototype.name", this]);
-  }
-  return %SymbolName(symbol);
+  // NOTE: Passing in a Symbol value will throw on ToString().
+  return %CreateSymbol(IS_UNDEFINED(x) ? x : ToString(x));
 }
 
 function SymbolToString() {
-  throw MakeTypeError('symbol_to_string');
+  if (IS_SYMBOL(this)) {
+    throw MakeTypeError('symbol_to_string', []);
+  } else if (!IS_SYMBOL_WRAPPER(this)) {
+    throw MakeTypeError(
+      'incompatible_method_receiver', ["Symbol.prototype.toString", this]);
+  }
+  var description = %SymbolDescription(%_ValueOf(this));
+  return "Symbol(" + (IS_UNDEFINED(description) ? "" : description) + ")";
 }
 
 function SymbolValueOf() {
-  // NOTE: Both Symbol objects and values can enter here as
-  // 'this'. This is not as dictated by ECMA-262.
-  if (!IS_SYMBOL(this) && !IS_SYMBOL_WRAPPER(this)) {
+  if (IS_SYMBOL(this)) {
+    throw MakeTypeError('symbol_to_value', []);

[rossberg, 2014/02/04 15:16:25]

We should leave this out for now (and also not do it in toString). I consider
this a spec bug, since it seems inconsistent with the rest of the language. It
also breaks our optimisation of not wrapping primitives, as you seem to have
observed (unless we move this file to sloppy mode).

[sof, 2014/02/04 15:40:58]

Not just non-strict, but the methods would also have to be marked as non-native.
What has changed here since e.g.,
  
 https://mail.mozilla.org/pipermail/es-discuss/2013-October/033876.html

Defining away what was the main part of this CL, is a suboptimal situation (for
me.) But OK.

+  } else if (!IS_SYMBOL_WRAPPER(this)) {
     throw MakeTypeError(
-        'incompatible_method_receiver', ["Symbol.prototype.valueOf", this]);
+      'incompatible_method_receiver', ["Symbol.prototype.valueOf", this]);
   }
   return %_ValueOf(this);
 }
 
 
 // ES6 19.1.2.8
 function ObjectGetOwnPropertySymbols(obj) {
   if (!IS_SPEC_OBJECT(obj)) {
     throw MakeTypeError("called_on_non_object",
                         ["Object.getOwnPropertySymbols"]);
   }
 
   // TODO(arv): Proxies use a shared trap for String and Symbol keys.
 
   return ObjectGetOwnPropertyKeys(obj, true);
 }
 
 
 //-------------------------------------------------------------------
 
 function SetUpSymbol() {
   %CheckIsBootstrapping();
 
   %SetCode($Symbol, SymbolConstructor);
-  %FunctionSetPrototype($Symbol, new $Symbol());
+  %FunctionSetPrototype($Symbol, new $Object());
+
   %SetProperty($Symbol.prototype, "constructor", $Symbol, DONT_ENUM);
-
-  InstallGetter($Symbol.prototype, "name", SymbolGetName);
   InstallFunctions($Symbol.prototype, DONT_ENUM, $Array(
     "toString", SymbolToString,
     "valueOf", SymbolValueOf
   ));
 }
 
 SetUpSymbol();
 
 
 function ExtendObject() {
   %CheckIsBootstrapping();
 
   InstallFunctions($Object, DONT_ENUM, $Array(
     "getOwnPropertySymbols", ObjectGetOwnPropertySymbols
   ));
 }
 
 ExtendObject();