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 050e7d918a02e83934883f280ec75be9424ba9db..9be1c1fd8c4c879f962e3e2b3c60372d4c8bd7f1 100644
--- a/src/symbol.js
+++ b/src/symbol.js
@@ -36,36 +36,55 @@ 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);
+    throw MakeTypeError('not_constructor', ["Symbol"]);
   } else {
+    // NOTE: Passing in a Symbol value will throw on ToString().
+    var value = %CreateSymbol(IS_UNDEFINED(x) ? x : ToString(x));
     return value;
   }
 }
 
-function SymbolGetName() {
-  var symbol = IS_SYMBOL_WRAPPER(this) ? %_ValueOf(this) : this;
-  if (!IS_SYMBOL(symbol)) {
-    throw MakeTypeError(
-        'incompatible_method_receiver', ["Symbol.prototype.name", this]);
+// The wrapper object for Symbols.
+function $SymbolWrapper(x) {
+  if (!%_IsConstructCall()) {
+    throw MakeTypeError('constructor_not_function', ["Symbol"]);
+  } else if (!IS_SYMBOL(x)) {
+    // A bug elsewhere; shouldn't be possible.
+    throw MakeTypeError('symbol_value_expected', []);
+  } else {
+    %SymbolSetSymbolData(this, x);
   }
-  return %SymbolName(symbol);
 }
 
 function SymbolToString() {
-  throw MakeTypeError('symbol_to_string');
+  if (this === $SymbolWrapper.prototype) {
+    return "Symbol";
+  } else if (!IS_SYMBOL_WRAPPER(this)) {
+    throw MakeTypeError(
+      'incompatible_method_receiver', ["Symbol.prototype.toString", this]);
+  } else {
+    var symbol = %SymbolGetSymbolData(this);
+    if (IS_UNDEFINED(symbol)) {
+      throw MakeTypeError('symbol_data_undefined', []);
+    } else {
+      var description = %SymbolDescription(symbol);
+      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_WRAPPER(this)) {
     throw MakeTypeError(
-        'incompatible_method_receiver', ["Symbol.prototype.valueOf", this]);
+      'incompatible_method_receiver', ["Symbol.prototype.valueOf", this]);
+  } else {
+    var symbol = %SymbolGetSymbolData(this);
+    if (IS_UNDEFINED(symbol)) {
+      throw MakeTypeError('symbol_data_undefined', [])
+    }
+    return symbol;
   }
-  return %_ValueOf(this);
 }
 
 //-------------------------------------------------------------------
@@ -73,12 +92,15 @@ function SymbolValueOf() {
 function SetUpSymbol() {
   %CheckIsBootstrapping();
 
+  // The global function for creating new Symbol values.
   %SetCode($Symbol, SymbolConstructor);
-  %FunctionSetPrototype($Symbol, new $Symbol());
-  %SetProperty($Symbol.prototype, "constructor", $Symbol, DONT_ENUM);
+  %FunctionSetPrototype($Symbol, $Function.prototype);
+
+  // A [[Class]] of "Symbol" is assumed for wrapper objects.
+  %FunctionSetInstanceClassName($SymbolWrapper, "Symbol");
+  %SetProperty($SymbolWrapper.prototype, "constructor", $Symbol, DONT_ENUM);
 
-  InstallGetter($Symbol.prototype, "name", SymbolGetName);
-  InstallFunctions($Symbol.prototype, DONT_ENUM, $Array(
+  InstallFunctions($SymbolWrapper.prototype, DONT_ENUM, $Array(
     "toString", SymbolToString,
     "valueOf", SymbolValueOf
   ));