[promise] Spec compliance fixes for async/await

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 368 matching lines @@
     return promiseCapability.promise;
   }
 }
 
 // Shortcut Promise.reject and Promise.resolve() implementations, used by
 // Async Functions implementation.
 function PromiseCreateRejected(r) {
   return %_Call(PromiseReject, GlobalPromise, r);
 }
 
-function PromiseCreateResolved(x) {
-  return %_Call(PromiseResolve, GlobalPromise, x);
+function PromiseCreateResolved(value) {
+  if (IsPromise(value)) {
+    return value;

[caitp, 2016/08/05 00:43:43]

looks great. Should we do something similar for PromiseCreateRejected? I haven't
checked

[Dan Ehrenberg, 2016/08/05 01:22:36]

I don't think we need to optimize for the reject case, and it's not needed from
a correctness perspective because rejecting a Promise doesn't collapse/chain in
any particular way.

+  } else {
+    var promise = PromiseInit(new GlobalPromise(promiseRawSymbol));
+    var resolveResult = ResolvePromise(promise, value);
+    return promise;
+  }
 }
 
 function PerformPromiseThen(promise, onResolve, onReject, resultCapability) {
   if (!IS_CALLABLE(onResolve)) onResolve = PromiseIdResolveHandler;
   if (!IS_CALLABLE(onReject)) onReject = PromiseIdRejectHandler;
 
   var status = GET_PRIVATE(promise, promiseStateSymbol);
   switch (status) {
     case kPending:
       PromiseAttachCallbacks(promise, resultCapability, onResolve, onReject);
@@ skipping 221 matching lines @@
   "createPromise", PromiseCreate,
   "resolvePromise", ResolvePromise,
   "rejectPromise", RejectPromise
 ]);
 
 // TODO(v8:4567): Allow experimental natives to remove function prototype
 [PromiseChain, PromiseDefer, PromiseAccept].forEach(
     fn => %FunctionRemovePrototype(fn));
 
 utils.Export(function(to) {
-  to.IsPromise = IsPromise;
-
   to.PromiseChain = PromiseChain;
   to.PromiseDefer = PromiseDefer;
   to.PromiseAccept = PromiseAccept;
 
   to.PromiseCreateRejected = PromiseCreateRejected;
   to.PromiseCreateResolved = PromiseCreateResolved;
   to.PromiseThen = PromiseThen;
 
   to.GlobalPromise = GlobalPromise;
   to.NewPromiseCapability = NewPromiseCapability;
   to.PerformPromiseThen = PerformPromiseThen;
 });
 
 })