Make __proto__ a real JavaScript accessor property.

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index d9dc09651e65d7654ef1ee2e9193dc8a2d47f38b..adabbc24f8130a77e272ac4527729d387677945c 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -61,7 +61,7 @@ function InstallFunctions(object, attributes, functions) {
 }
 
 
-// Helper function to install a getter only property.
+// Helper function to install a getter-only accessor property.
 function InstallGetter(object, name, getter) {
   %FunctionSetName(getter, name);
   %FunctionRemovePrototype(getter);
@@ -70,6 +70,18 @@ function InstallGetter(object, name, getter) {
 }
 
 
+// Helper function to install a getter/setter accessor property.
+function InstallGetterSetter(object, name, getter, setter) {
+  %FunctionSetName(getter, name);
+  %FunctionSetName(setter, name);
+  %FunctionRemovePrototype(getter);
+  %FunctionRemovePrototype(setter);
+  %DefineOrRedefineAccessorProperty(object, name, getter, setter, DONT_ENUM);
+  %SetNativeFlag(getter);
+  %SetNativeFlag(setter);
+}
+
+
 // Prevents changes to the prototype of a built-in function.
 // The "prototype" property of the function object is made non-configurable,
 // and the prototype object is made non-extensible. The latter prevents
@@ -394,8 +406,10 @@ function FromPropertyDescriptor(desc) {
              configurable: desc.isConfigurable() };
   }
   // Must be an AccessorDescriptor then. We never return a generic descriptor.
-  return { get: desc.getGet(),
-           set: desc.getSet(),
+  return { get: desc.getGet() === ObjectGetProto ? ObjectPoisonProto

[rossberg, 2013/04/04 09:58:43]

I don't think there is a need (or the intention) to poison the getter as well,
since you can always get a prototype with Object.getPrototypeOf anyway.

[Michael Starzinger, 2013/04/04 11:52:19]

Done.

+                                                 : desc.getGet(),
+           set: desc.getSet() === ObjectSetProto ? ObjectPoisonProto
+                                                 : desc.getSet(),
            enumerable: desc.isEnumerable(),
            configurable: desc.isConfigurable() };
 }
@@ -1326,6 +1340,24 @@ function ObjectIs(obj1, obj2) {
 }
 
 
+// Harmony __proto__ getter.
+function ObjectGetProto() {
+  return %GetPrototype(this);
+}
+
+
+// Harmony __proto__ setter.
+function ObjectSetProto(obj) {
+  return %SetPrototype(this, obj);
+}
+
+
+// Harmony __proto__ poison pill.
+function ObjectPoisonProto() {
+  throw MakeTypeError("proto_poison_pill", []);
+}
+
+
 %SetCode($Object, function(x) {
   if (%_IsConstructCall()) {
     if (x == null) return this;
@@ -1336,14 +1368,18 @@ function ObjectIs(obj1, obj2) {
   }
 });
 
-%SetExpectedNumberOfProperties($Object, 4);
 
 // ----------------------------------------------------------------------------
 // Object
 
 function SetUpObject() {
   %CheckIsBootstrapping();
-  // Set Up non-enumerable functions on the Object.prototype object.
+
+  %FunctionSetName(ObjectPoisonProto, "__proto__");
+  %FunctionRemovePrototype(ObjectPoisonProto);
+  %SetExpectedNumberOfProperties($Object, 4);
+
+  // Set up non-enumerable functions on the Object.prototype object.
   InstallFunctions($Object.prototype, DONT_ENUM, $Array(
     "toString", ObjectToString,
     "toLocaleString", ObjectToLocaleString,
@@ -1356,6 +1392,10 @@ function SetUpObject() {
     "__defineSetter__", ObjectDefineSetter,
     "__lookupSetter__", ObjectLookupSetter
   ));
+  InstallGetterSetter($Object.prototype, "__proto__",
+                      ObjectGetProto, ObjectSetProto);
+
+  // Set up non-enumerable functions in the Object object.
   InstallFunctions($Object, DONT_ENUM, $Array(
     "keys", ObjectKeys,
     "create", ObjectCreate,