Upgrade Symbol implementation to match current ES6 behavior.

src/runtime.js

 // Copyright 2006-2008 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 62 matching lines @@
         if (IS_BOOLEAN(y)) return %NumberEquals(%ToNumber(x), %ToNumber(y));
         if (IS_NULL_OR_UNDEFINED(y)) return 1;  // not equal
         y = %ToPrimitive(y, NO_HINT);
       }
     } else if (IS_SYMBOL(x)) {
       while (true) {
         if (IS_SYMBOL(y)) return %_ObjectEquals(x, y) ? 0 : 1;
         if (!IS_SPEC_OBJECT(y)) return 1;  // not equal
         y = %ToPrimitive(y, NO_HINT);
       }
+    } else if (IS_SYMBOL_WRAPPER(x) && IS_SYMBOL_WRAPPER(y)) {

[rossberg, 2014/02/14 10:55:30]

This should be subsumed by the default case below.

[sof, 2014/02/14 14:20:02]

Yes. I noticed we were unnecessarily calling ToPrimitive() in two cases
involving symbol values, so added explicit checks. (This matters now that Symbol
wrappers throw on ToPrimitive().)

The spec hasn't changed here, so simply not correct as-was.

+      return %_ObjectEquals(x, y) ? 0 : 1;
     } else if (IS_BOOLEAN(x)) {
       if (IS_BOOLEAN(y)) return %_ObjectEquals(x, y) ? 0 : 1;
       if (IS_NULL_OR_UNDEFINED(y)) return 1;
       if (IS_NUMBER(y)) return %NumberEquals(%ToNumber(x), y);
       if (IS_STRING(y)) return %NumberEquals(%ToNumber(x), %ToNumber(y));
       if (IS_SYMBOL(y)) return 1;  // not equal
       // y is object.
       x = %ToNumber(x);
       y = %ToPrimitive(y, NO_HINT);
     } else if (IS_NULL_OR_UNDEFINED(x)) {
@@ skipping 401 matching lines @@
    -------------------------------------
 */
 
 // ECMA-262, section 9.1, page 30. Use null/undefined for no hint,
 // (1) for number hint, and (2) for string hint.
 function ToPrimitive(x, hint) {
   // Fast case check.
   if (IS_STRING(x)) return x;
   // Normal behavior.
   if (!IS_SPEC_OBJECT(x)) return x;
-  if (IS_SYMBOL_WRAPPER(x)) return %_ValueOf(x);
+  if (IS_SYMBOL_WRAPPER(x)) throw MakeTypeError('symbol_to_primitive', []);
   if (hint == NO_HINT) hint = (IS_DATE(x)) ? STRING_HINT : NUMBER_HINT;
   return (hint == NUMBER_HINT) ? %DefaultNumber(x) : %DefaultString(x);
 }
 
 
 // ECMA-262, section 9.2, page 30
 function ToBoolean(x) {
   if (IS_BOOLEAN(x)) return x;
   if (IS_STRING(x)) return x.length != 0;
   if (x == null) return false;
@@ skipping 26 matching lines @@
   return (IS_NULL(x)) ? 0 : ToNumber(%DefaultNumber(x));
 }
 
 
 // ECMA-262, section 9.8, page 35.
 function ToString(x) {
   if (IS_STRING(x)) return x;
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   if (IS_UNDEFINED(x)) return 'undefined';
+  if (IS_SYMBOL(x)) throw %MakeTypeError('symbol_to_string', []);
   return (IS_NULL(x)) ? 'null' : %ToString(%DefaultString(x));
 }
 
 function NonStringToString(x) {
   if (IS_NUMBER(x)) return %_NumberToString(x);
   if (IS_BOOLEAN(x)) return x ? 'true' : 'false';
   if (IS_UNDEFINED(x)) return 'undefined';
+  if (IS_SYMBOL(x)) throw %MakeTypeError('symbol_to_string', []);
   return (IS_NULL(x)) ? 'null' : %ToString(%DefaultString(x));
 }
 
 
 // ES6 symbols
 function ToName(x) {
   return IS_SYMBOL(x) ? x : %ToString(x);
 }
 
 
 // ECMA-262, section 9.9, page 36.
 function ToObject(x) {
   if (IS_STRING(x)) return new $String(x);
-  if (IS_SYMBOL(x)) return new $Symbol(x);
   if (IS_NUMBER(x)) return new $Number(x);
   if (IS_BOOLEAN(x)) return new $Boolean(x);
+  if (IS_SYMBOL(x)) return %NewSymbolWrapper(x);
   if (IS_NULL_OR_UNDEFINED(x) && !IS_UNDETECTABLE(x)) {
     throw %MakeTypeError('undefined_or_null_to_object', []);
   }
   return x;
 }
 
 
 // ECMA-262, section 9.4, page 34.
 function ToInteger(x) {
   if (%_IsSmi(x)) return x;
@@ skipping 84 matching lines @@
   return i;
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));