[es6] silence access-check failure for well-known symbol properties

src/objects.cc

 // Copyright 2013 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.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 976 matching lines @@
     if (it->state() == LookupIterator::ACCESSOR) {
       return GetPropertyWithAccessor(it, SLOPPY);
     }
     DCHECK_EQ(LookupIterator::INTERCEPTOR, it->state());
     bool done;
     Handle<Object> result;
     ASSIGN_RETURN_ON_EXCEPTION(it->isolate(), result,
                                GetPropertyWithInterceptor(it, &done), Object);
     if (done) return result;
   }
+  if (!it->IsElement()) {

[Toon Verwaest, 2015/10/02 08:05:27]

Rather than if (!it->IsElement()) etc, you can just use
Handle<Name> name = it->GetName();
if (name->IsSymbol() && Symbol::cast(*name)->is_well_known_symbol()) {
  return it->factory()->undefined_value();
}

[caitp (gmail), 2015/10/02 10:01:15]

GetName() converts elements to strings, which isn't needed, but name() has a
DCHECK(!IsElement()). So, it seemed better to avoid the allocation, from my pov.

I can change it if people prefer that

[Toon Verwaest, 2015/10/02 10:07:01]

That is possibly true. It could already have been cached. Adding IsElement()
only avoids this possible cost (in an exceptional path that's not performance
sensitive), but does introduce extra unnecessary complexity here.

[caitp (gmail), 2015/10/02 10:41:56]

Done.

+    Handle<Name> name = it->name();
+    if (name->IsSymbol() &&
+        Handle<Symbol>::cast(name)->is_well_known_symbol()) {
+      RETURN_EXCEPTION_IF_SCHEDULED_EXCEPTION(it->isolate(), Object);

[Toon Verwaest, 2015/10/02 08:05:27]

I don't see why this statement (RETURN_EX..) is needed.

[caitp (gmail), 2015/10/02 10:01:15]

I guess it isn't really needed, will remove

[caitp (gmail), 2015/10/02 10:41:56]

Done.

+      return it->factory()->undefined_value();
+    }
+  }
   it->isolate()->ReportFailedAccessCheck(checked);
   RETURN_EXCEPTION_IF_SCHEDULED_EXCEPTION(it->isolate(), Object);
   return it->factory()->undefined_value();
 }
 
 
 Maybe<PropertyAttributes> JSObject::GetPropertyAttributesWithFailedAccessCheck(
     LookupIterator* it) {
   Handle<JSObject> checked = it->GetHolder<JSObject>();
   while (AllCanRead(it)) {
@@ skipping 15807 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8