Use a private own symbol instead of a hidden property for hash codes

src/collection.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, shared, exports) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 52 matching lines @@
   hash = ~hash + (hash << 15);  // hash = (hash << 15) - hash - 1;
   hash = hash ^ (hash >>> 12);
   hash = hash + (hash << 2);
   hash = hash ^ (hash >>> 4);
   hash = (hash * 2057) | 0;  // hash = (hash + (hash << 3)) + (hash << 11);
   hash = hash ^ (hash >>> 16);
   return hash;
 }
 %SetInlineBuiltinFlag(ComputeIntegerHash);
 
+var hash_code_symbol = GLOBAL_PRIVATE("hash_code_symbol");
 
 function GetHash(key) {
   if (%_IsSmi(key)) {
     return ComputeIntegerHash(key, 0);
   }
   if (IS_STRING(key)) {
     var field = %_StringGetRawHashField(key);
     if ((field & 1 /* Name::kHashNotComputedMask */) === 0) {
       return field >>> 2 /* Name::kHashShift */;
     }
   }
+  if (IS_SPEC_OBJECT(key)) {

[adamk, 2015/05/14 15:01:27]

You might need a TODO here for handling proxies appropriately.

Also, will this get the wrong value for the JSGlobalProxy?

[Erik Corry, 2015/05/14 15:42:19]

Probably.  What's the deal with the JSGlobalProxy?

[Toon Verwaest, 2015/05/15 12:24:10]

Due to split-object the global proxy points to the current global object, which
is a single object from the POV of the user. The global proxy represents an
iframe, whereas the global object represents a page in the iframe. If the iframe
navigates, the page changes, and hence the link from the global proxy to the
global object.

Access to the global proxy always relays the access to the global object. So if
you do window[hash_code_symbol], you'll get the hash-code from the current page.
That doesn't remain stable across navigation.

After navigation you won't be able to retrieve values associated with the iframe
anymore (unless there's a hash collision between the 2 pages).

+    var hash = key[hash_code_symbol];

[adamk, 2015/05/14 15:01:27]

We've been using a GET_PRIVATE() for this as a matter of style.

+    if (hash == void 0) {

[adamk, 2015/05/14 15:01:27]

IS_UNDEFINED(hash)

+      hash = $intrandom() | 0;
+      key[hash_code_symbol] = hash;

[adamk, 2015/05/14 15:01:27]

SET_PRIVATE()

+    }
+    return hash;
+  }
   return %GenericHash(key);
 }
 %SetInlineBuiltinFlag(GetHash);
 
 
 // -------------------------------------------------------------------
 // Harmony Set
 
 function SetConstructor(iterable) {
   if (!%_IsConstructCall()) {
@@ skipping 337 matching lines @@
 $installFunctions(GlobalMap.prototype, DONT_ENUM, [
   "get", MapGet,
   "set", MapSet,
   "has", MapHas,
   "delete", MapDelete,
   "clear", MapClearJS,
   "forEach", MapForEach
 ]);
 
 })