Upgrade Symbol implementation to match current ES6 behavior.

src/symbol.js

Index: src/symbol.js
diff --git a/src/symbol.js b/src/symbol.js
index be308d947cb0353dd9eb10aa4077a473536884f7..ff05d28421ed65a2ebe2df989afa54dbcf45981c 100644
--- a/src/symbol.js
+++ b/src/symbol.js
@@ -36,34 +36,30 @@ 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"]);
   }
+  // NOTE: Passing in a Symbol value will throw on ToString().
+  return %CreateSymbol(IS_UNDEFINED(x) ? x : ToString(x));
 }
 
-function SymbolGetName() {
-  var symbol = IS_SYMBOL_WRAPPER(this) ? %_ValueOf(this) : this;
-  if (!IS_SYMBOL(symbol)) {
+function SymbolToString() {
+  if (IS_SYMBOL(this)) {
+    throw MakeTypeError('symbol_to_string', []);
+  } else if (!IS_SYMBOL_WRAPPER(this)) {
     throw MakeTypeError(
-        'incompatible_method_receiver', ["Symbol.prototype.name", this]);
+      'incompatible_method_receiver', ["Symbol.prototype.toString", this]);
   }
-  return %SymbolName(symbol);
-}
-
-function SymbolToString() {
-  throw MakeTypeError('symbol_to_string');
+  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);
 }
@@ -88,10 +84,9 @@ function SetUpSymbol() {
   %CheckIsBootstrapping();
 
   %SetCode($Symbol, SymbolConstructor);
-  %FunctionSetPrototype($Symbol, new $Symbol());
-  %SetProperty($Symbol.prototype, "constructor", $Symbol, DONT_ENUM);
+  %FunctionSetPrototype($Symbol, new $Object());
 
-  InstallGetter($Symbol.prototype, "name", SymbolGetName);
+  %SetProperty($Symbol.prototype, "constructor", $Symbol, DONT_ENUM);
   InstallFunctions($Symbol.prototype, DONT_ENUM, $Array(
     "toString", SymbolToString,
     "valueOf", SymbolValueOf