Introduce a BuiltinsConstructStub that sets up new.target and does a [[call]] per ES6 9.3.2

src/js/promise.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, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 43 matching lines @@
 
   return {
     __proto__: null,
     resolve: resolve,
     reject: reject
   };
 }
 
 
 var GlobalPromise = function Promise(resolver) {
-  if (resolver === promiseRawSymbol) return;
-  if (!%_IsConstructCall()) throw MakeTypeError(kNotAPromise, this);
+  if (resolver === promiseRawSymbol) {
+    return %NewObject(GlobalPromise, new.target);
+  }
+  if (IS_UNDEFINED(new.target)) throw MakeTypeError(kNotAPromise, this);

[Igor Sheludko, 2015/11/19 09:30:53]

Perhaps this should be done even before checking resolver.

[Toon Verwaest, 2015/11/19 09:39:53]

%NewObject internally will check that new.target is a JSReceiver (and
constructable) in debug mode. That should be fine...

   if (!IS_CALLABLE(resolver))
     throw MakeTypeError(kResolverNotAFunction, resolver);
-  var promise = PromiseInit(this);
+
+  var promise = PromiseInit(%NewObject(GlobalPromise, new.target));
+
   try {
     %DebugPushPromise(promise, Promise, resolver);
     var callbacks = CreateResolvingFunctions(promise);
     resolver(callbacks.resolve, callbacks.reject);
   } catch (e) {
     PromiseReject(promise, e);
   } finally {
     %DebugPopPromise();
   }
+
+  return promise;
 }
 
 // Core functionality.
 
 function PromiseSet(promise, status, value, onResolve, onReject) {
   SET_PRIVATE(promise, promiseStatusSymbol, status);
   SET_PRIVATE(promise, promiseValueSymbol, value);
   SET_PRIVATE(promise, promiseOnResolveSymbol, onResolve);
   SET_PRIVATE(promise, promiseOnRejectSymbol, onReject);
   if (DEBUG_IS_ACTIVE) {
@@ skipping 379 matching lines @@
 // This allows extras to create promises quickly without building extra
 // resolve/reject closures, and allows them to later resolve and reject any
 // promise without having to hold on to those closures forever.
 utils.InstallFunctions(extrasUtils, 0, [
   "createPromise", PromiseCreate,
   "resolvePromise", PromiseResolve,
   "rejectPromise", PromiseReject
 ]);
 
 })