[builtins] take slow path in IsConcatSpreadable if proxy in prototype

src/builtins.cc

 // 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.
 
 #include "src/builtins.h"
 
 #include "src/api-arguments.h"
 #include "src/api-natives.h"
 #include "src/api.h"
 #include "src/base/ieee754.h"
@@ skipping 1162 matching lines @@
     case FAST_STRING_WRAPPER_ELEMENTS:
     case SLOW_STRING_WRAPPER_ELEMENTS:
       // |array| is guaranteed to be an array or typed array.
       UNREACHABLE();
       break;
   }
   visitor->increase_index_offset(length);
   return true;
 }
 
+static bool HasProxyInPrototype(Isolate* isolate, JSReceiver* receiver) {
+  DisallowHeapAllocation no_heap;
+  for (PrototypeIterator iter(isolate, receiver, kStartAtReceiver,
+                              PrototypeIterator::END_AT_NON_HIDDEN);

[neis, 2016/07/11 09:25:19]

This must be END_AT_NULL.

[caitp, 2016/07/11 11:12:08]

I have no idea why it's not END_AT_NULL, I could have sworn I didn't add this
parameter o_O. Will fix in the next patch.

+       !iter.IsAtEnd(); iter.AdvanceIgnoringProxies()) {
+    if (iter.GetCurrent<Object>()->IsJSProxy()) return true;
+  }
+  return false;
+}
+
 static Maybe<bool> IsConcatSpreadable(Isolate* isolate, Handle<Object> obj) {
   HandleScope handle_scope(isolate);
   if (!obj->IsJSReceiver()) return Just(false);
-  if (!isolate->IsIsConcatSpreadableLookupChainIntact()) {
+  if (!isolate->IsIsConcatSpreadableLookupChainIntact() ||
+      HasProxyInPrototype(isolate, JSReceiver::cast(*obj))) {

[neis, 2016/07/11 09:25:19]

I think it makes sense to move the proxy check into
IsIsConcatSpreadableLookupChainIntact.

[caitp, 2016/07/11 11:12:08]

Acknowledged, however this would change the prototype of
IsIsConcatSpreadableLookupChainIntact, which might get messy

     // Slow path if @@isConcatSpreadable has been used.
     Handle<Symbol> key(isolate->factory()->is_concat_spreadable_symbol());
     Handle<Object> value;
     MaybeHandle<Object> maybeValue =
         i::Runtime::GetObjectProperty(isolate, obj, key);
     if (!maybeValue.ToHandle(&value)) return Nothing<bool>();
     if (!value->IsUndefined(isolate)) return Just(value->BooleanValue());
   }
   return Object::IsArray(obj);
 }
@@ skipping 5540 matching lines @@
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 #undef DEFINE_BUILTIN_ACCESSOR_T
 #undef DEFINE_BUILTIN_ACCESSOR_S
 #undef DEFINE_BUILTIN_ACCESSOR_H
 
 }  // namespace internal
 }  // namespace v8