Make __proto__ a real JavaScript accessor property.

src/runtime.cc

 // Copyright 2012 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 1099 matching lines @@
       isolate->ReportFailedAccessCheck(JSObject::cast(obj), v8::ACCESS_GET);
       return isolate->heap()->undefined_value();
     }
     obj = obj->GetPrototype(isolate);
   } while (obj->IsJSObject() &&
            JSObject::cast(obj)->map()->is_hidden_prototype());
   return obj;
 }
 
 
+static inline Object* GetPrototypeSkipHiddenPrototypes(Isolate* isolate,
+                                                       Object* receiver) {
+  Object* current = receiver->GetPrototype(isolate);
+  while (current->IsJSObject() &&
+         JSObject::cast(current)->map()->is_hidden_prototype()) {
+    current = current->GetPrototype(isolate);
+  }
+  return current;
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetPrototype) {
   NoHandleAllocation ha(isolate);
   ASSERT(args.length() == 2);
-  CONVERT_ARG_CHECKED(JSReceiver, input_obj, 0);
+  CONVERT_ARG_CHECKED(JSObject, input_obj, 0);
   CONVERT_ARG_CHECKED(Object, prototype, 1);
+  if (FLAG_harmony_observation && input_obj->map()->is_observed()) {
+    HandleScope scope(isolate);
+    Handle<JSObject> receiver(input_obj);
+    Handle<Object> value(prototype, isolate);
+    Handle<Object> old_value(
+        GetPrototypeSkipHiddenPrototypes(isolate, *receiver), isolate);
+
+    MaybeObject* result = receiver->SetPrototype(*value, true);
+    Handle<Object> hresult;
+    if (!result->ToHandle(&hresult, isolate)) return result;
+
+    Handle<Object> new_value(
+        GetPrototypeSkipHiddenPrototypes(isolate, *receiver), isolate);
+    if (!new_value->SameValue(*old_value)) {
+      JSObject::EnqueueChangeRecord(receiver, "prototype",
+                                    isolate->factory()->proto_string(),
+                                    old_value);
+    }
+    return *hresult;
+  }
   return input_obj->SetPrototype(prototype, true);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_IsInPrototypeChain) {
   NoHandleAllocation ha(isolate);
   ASSERT(args.length() == 2);
   // See ECMA-262, section 15.3.5.3, page 88 (steps 5 - 8).
   Object* O = args[0];
   Object* V = args[1];
@@ skipping 3109 matching lines @@
 
   // Special case for callback properties.
   if (result.IsPropertyCallbacks()) {
     Object* callback = result.GetCallbackObject();
     // To be compatible with Safari we do not change the value on API objects
     // in Object.defineProperty(). Firefox disagrees here, and actually changes
     // the value.
     if (callback->IsAccessorInfo()) {
       return isolate->heap()->undefined_value();
     }
-    // TODO(mstarzinger): The __proto__ property should actually be a real
-    // JavaScript accessor instead of a foreign callback. But for now we just
-    // avoid changing the writability and configurability attribute of this
-    // property.
-    Handle<Name> proto_string = isolate->factory()->proto_string();
-    if (callback->IsForeign() && proto_string->Equals(*name)) {
-      attr = static_cast<PropertyAttributes>(attr & ~(READ_ONLY | DONT_DELETE));
-    }
     // Avoid redefining foreign callback as data property, just use the stored
     // setter to update the value instead.
     // TODO(mstarzinger): So far this only works if property attributes don't
     // change, this should be fixed once we cleanup the underlying code.
     if (callback->IsForeign() && result.GetAttributes() == attr) {
       return js_object->SetPropertyWithCallback(callback,
                                                 *name,
                                                 *obj_value,
                                                 result.holder(),
                                                 kStrictMode);
@@ skipping 7888 matching lines @@
   }
   return JSArray::cast(result)->SetContent(instances);
 }
 
 
 // Find the effective prototype object as returned by __proto__.
 // args[0]: the object to find the prototype for.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugGetPrototype) {
   NoHandleAllocation ha(isolate);
   ASSERT(args.length() == 1);
-
   CONVERT_ARG_CHECKED(JSObject, obj, 0);
-
-  // Use the __proto__ accessor.
-  return Accessors::ObjectPrototype.getter(obj, NULL);
+  return GetPrototypeSkipHiddenPrototypes(isolate, obj);
 }
 
 
 // Patches script source (should be called upon BeforeCompile event).
 RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugSetScriptSource) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
 
   CONVERT_ARG_HANDLE_CHECKED(JSValue, script_wrapper, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, source, 1);
@@ skipping 966 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal