[esnext] prototype runtime implementation for async functions

src/js/promise.js

Index: src/js/promise.js
diff --git a/src/js/promise.js b/src/js/promise.js
index bcf826a10151d48a498d40e72f418805a5022f18..03f43cd13faa57ef02be8dbbc725bdae23307298 100644
--- a/src/js/promise.js
+++ b/src/js/promise.js
@@ -25,10 +25,13 @@ var promiseStatusSymbol = utils.ImportNow("promise_status_symbol");
 var promiseValueSymbol = utils.ImportNow("promise_value_symbol");
 var SpeciesConstructor;
 var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
-
+var AsyncFunctionNext;
+var AsyncFunctionThrow;
 utils.Import(function(from) {
   MakeTypeError = from.MakeTypeError;
   SpeciesConstructor = from.SpeciesConstructor;
+  AsyncFunctionNext = from.AsyncFunctionNext;
+  AsyncFunctionThrow = from.AsyncFunctionThrow;
 });
 
 // -------------------------------------------------------------------
@@ -268,6 +271,19 @@ function PromiseRejected(r) {
   }
 }
 
+// Shortcut Promise.reject and Promise.resolve() implementations, used by
+// Async Functions implementation.
+function PromiseCreateRejected(r) {
+  var promise = PromiseCreateAndSet(-1, r);
+  %PromiseRejectEvent(promise, r, false);
+  return promise;
+}
+
+function PromiseCreateResolved(x) {
+  if (IsPromise(x) && x.constructor === GlobalPromise) return x;
+  return PromiseCreateAndSet(+1, x);
+}
+
 // Multi-unwrapped chaining with thenable coercion.
 
 function PromiseThen(onResolve, onReject) {
@@ -424,6 +440,25 @@ function PromiseHasUserDefinedRejectHandler() {
   return PromiseHasUserDefinedRejectHandlerRecursive(this);
 };
 
+// TODO(caitp): move me to a new file =)
+function AsyncFunctionResume(generator, sentValue, resumeFunc) {
+  try {
+    var result = resumeFunc(generator, sentValue);
+    if (result.done) return PromiseCreateResolved(result.value);
+  } catch (error) {
+    return PromiseCreateRejected(error);
+  }
+
+  %GlobalPrint("await...\n");
+  return %_Call(PromiseThen, PromiseCreateResolved(result.value),
+      function(value) { %GlobalPrint("resume normal...\n"); return AsyncFunctionResume(generator, value, AsyncFunctionNext); },

[caitp (gmail), 2016/04/16 18:33:03]

phantom edits from some debugging =)

+      function(error) { %GlobalPrint("resume throw...\n"); return AsyncFunctionResume(generator, error, AsyncFunctionThrow); });
+}
+
+function AsyncFunctionStart(generator) {
+  return AsyncFunctionResume(generator, UNDEFINED, AsyncFunctionNext);
+}
+
 // -------------------------------------------------------------------
 // Install exported functions.
 
@@ -451,6 +486,9 @@ utils.InstallFunctions(GlobalPromise.prototype, DONT_ENUM, [
   "promise_reject", PromiseReject,
   "promise_resolve", PromiseResolve,
   "promise_then", PromiseThen,
+  "promise_create_rejected", PromiseCreateRejected,
+  "promise_create_resolved", PromiseCreateResolved,
+  "async_function_start", AsyncFunctionStart
 ]);
 
 // This allows extras to create promises quickly without building extra