Bug 1379525 - Part 1: Await on the value before yielding or returning inside async generator.

Tag #1287

4 files changed, 344 insertions, 258 deletions

diff --git a/js/src/builtin/Promise.cpp b/js/src/builtin/Promise.cpp
index 6bb2d61d7..62c5eb429 100644
--- a/js/src/builtin/Promise.cpp
+++ b/js/src/builtin/Promise.cpp
@@ -36,18 +36,30 @@ MillisecondsSinceStartup()
 enum PromiseHandler {
     PromiseHandlerIdentity = 0,
     PromiseHandlerThrower,
-    PromiseHandlerAsyncFunctionAwaitFulfilled,
-    PromiseHandlerAsyncFunctionAwaitRejected,
-    PromiseHandlerAsyncGeneratorAwaitFulfilled,
-    PromiseHandlerAsyncGeneratorAwaitRejected,
-
-    // Async Iteration proposal 6.1.1.2.1.
-    // Async iterator handlers take the resolved value and create new iterator
-    // objects.  To do so it needs to forward whether the iterator is done. In
-    // spec, this is achieved via the [[Done]] internal slot. We enumerate both
-    // true and false cases here.
-    PromiseHandlerAsyncIteratorValueUnwrapDone,
-    PromiseHandlerAsyncIteratorValueUnwrapNotDone,
+
+    // ES 2018 draft 25.5.5.4-5.
+    PromiseHandlerAsyncFunctionAwaitedFulfilled,
+    PromiseHandlerAsyncFunctionAwaitedRejected,
+
+    // Async Iteration proposal 4.1.
+    PromiseHandlerAsyncGeneratorAwaitedFulfilled,
+    PromiseHandlerAsyncGeneratorAwaitedRejected,
+
+    // Async Iteration proposal 11.4.3.5.1-2.
+    PromiseHandlerAsyncGeneratorResumeNextReturnFulfilled,
+    PromiseHandlerAsyncGeneratorResumeNextReturnRejected,
+
+    // Async Iteration proposal 11.4.3.7 steps 8.c-e.
+    PromiseHandlerAsyncGeneratorYieldReturnAwaitedFulfilled,
+    PromiseHandlerAsyncGeneratorYieldReturnAwaitedRejected,
+
+    // Async Iteration proposal 11.1.3.2.5.
+    // Async-from-Sync iterator handlers take the resolved value and create new
+    // iterator objects.  To do so it needs to forward whether the iterator is
+    // done. In spec, this is achieved via the [[Done]] internal slot. We
+    // enumerate both true and false cases here.
+    PromiseHandlerAsyncFromSyncIteratorValueUnwrapDone,
+    PromiseHandlerAsyncFromSyncIteratorValueUnwrapNotDone,
 };
 
 enum ResolutionMode {
@@ -197,8 +209,8 @@ enum ReactionRecordSlots {
 #define REACTION_FLAG_RESOLVED                  0x1
 #define REACTION_FLAG_FULFILLED                 0x2
 #define REACTION_FLAG_IGNORE_DEFAULT_RESOLUTION 0x4
-#define REACTION_FLAG_ASYNC_FUNCTION_AWAIT      0x8
-#define REACTION_FLAG_ASYNC_GENERATOR_AWAIT     0x10
+#define REACTION_FLAG_ASYNC_FUNCTION            0x8
+#define REACTION_FLAG_ASYNC_GENERATOR           0x10
 
 // ES2016, 25.4.1.2.
 class PromiseReactionRecord : public NativeObject
@@ -225,28 +237,28 @@ class PromiseReactionRecord : public NativeObject
             flags |= REACTION_FLAG_FULFILLED;
         setFixedSlot(ReactionRecordSlot_Flags, Int32Value(flags));
     }
-    void setIsAsyncFunctionAwait() {
+    void setIsAsyncFunction() {
         int32_t flags = this->flags();
-        flags |= REACTION_FLAG_ASYNC_FUNCTION_AWAIT;
+        flags |= REACTION_FLAG_ASYNC_FUNCTION;
         setFixedSlot(ReactionRecordSlot_Flags, Int32Value(flags));
     }
-    bool isAsyncFunctionAwait() {
+    bool isAsyncFunction() {
         int32_t flags = this->flags();
-        return flags & REACTION_FLAG_ASYNC_FUNCTION_AWAIT;
+        return flags & REACTION_FLAG_ASYNC_FUNCTION;
     }
-    void setIsAsyncGeneratorAwait(Handle<AsyncGeneratorObject*> asyncGenObj) {
+    void setIsAsyncGenerator(Handle<AsyncGeneratorObject*> asyncGenObj) {
         int32_t flags = this->flags();
-        flags |= REACTION_FLAG_ASYNC_GENERATOR_AWAIT;
+        flags |= REACTION_FLAG_ASYNC_GENERATOR;
         setFixedSlot(ReactionRecordSlot_Flags, Int32Value(flags));
 
         setFixedSlot(ReactionRecordSlot_Generator, ObjectValue(*asyncGenObj));
     }
-    bool isAsyncGeneratorAwait() {
+    bool isAsyncGenerator() {
         int32_t flags = this->flags();
-        return flags & REACTION_FLAG_ASYNC_GENERATOR_AWAIT;
+        return flags & REACTION_FLAG_ASYNC_GENERATOR;
     }
     AsyncGeneratorObject* asyncGenerator() {
-        MOZ_ASSERT(isAsyncGeneratorAwait());
+        MOZ_ASSERT(isAsyncGenerator());
         return &getFixedSlot(ReactionRecordSlot_Generator).toObject()
                                                           .as<AsyncGeneratorObject>();
     }
@@ -848,10 +860,10 @@ TriggerPromiseReactions(JSContext* cx, HandleValue reactionsVal, JS::PromiseStat
 }
 
 static MOZ_MUST_USE bool
-AsyncFunctionAwaitPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord*> reaction,
-                                     MutableHandleValue rval)
+AsyncFunctionPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord*> reaction,
+                                MutableHandleValue rval)
 {
-    MOZ_ASSERT(reaction->isAsyncFunctionAwait());
+    MOZ_ASSERT(reaction->isAsyncFunction());
 
     RootedValue handlerVal(cx, reaction->handler());
     RootedValue argument(cx, reaction->handlerArg());
@@ -859,15 +871,14 @@ AsyncFunctionAwaitPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord
     RootedValue generatorVal(cx, resultPromise->getFixedSlot(PromiseSlot_AwaitGenerator));
 
     int32_t handlerNum = int32_t(handlerVal.toNumber());
-    MOZ_ASSERT(handlerNum == PromiseHandlerAsyncFunctionAwaitFulfilled ||
-               handlerNum == PromiseHandlerAsyncFunctionAwaitRejected);
 
     // Await's handlers don't return a value, nor throw exception.
     // They fail only on OOM.
-    if (handlerNum == PromiseHandlerAsyncFunctionAwaitFulfilled) {
+    if (handlerNum == PromiseHandlerAsyncFunctionAwaitedFulfilled) {
         if (!AsyncFunctionAwaitedFulfilled(cx, resultPromise, generatorVal, argument))
             return false;
     } else {
+        MOZ_ASSERT(handlerNum == PromiseHandlerAsyncFunctionAwaitedRejected);
         if (!AsyncFunctionAwaitedRejected(cx, resultPromise, generatorVal, argument))
             return false;
     }
@@ -877,27 +888,48 @@ AsyncFunctionAwaitPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord
 }
 
 static MOZ_MUST_USE bool
-AsyncGeneratorAwaitPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord*> reaction,
-                                      MutableHandleValue rval)
+AsyncGeneratorPromiseReactionJob(JSContext* cx, Handle<PromiseReactionRecord*> reaction,
+                                 MutableHandleValue rval)
 {
-    MOZ_ASSERT(reaction->isAsyncGeneratorAwait());
+    MOZ_ASSERT(reaction->isAsyncGenerator());
 
     RootedValue handlerVal(cx, reaction->handler());
     RootedValue argument(cx, reaction->handlerArg());
     Rooted<AsyncGeneratorObject*> asyncGenObj(cx, reaction->asyncGenerator());
 
     int32_t handlerNum = int32_t(handlerVal.toNumber());
-    MOZ_ASSERT(handlerNum == PromiseHandlerAsyncGeneratorAwaitFulfilled ||
-               handlerNum == PromiseHandlerAsyncGeneratorAwaitRejected);
 
     // Await's handlers don't return a value, nor throw exception.
     // They fail only on OOM.
-    if (handlerNum == PromiseHandlerAsyncGeneratorAwaitFulfilled) {
+    if (handlerNum == PromiseHandlerAsyncGeneratorAwaitedFulfilled) {
+        // 4.1.1.
         if (!AsyncGeneratorAwaitedFulfilled(cx, asyncGenObj, argument))
             return false;
-    } else {
+    } else if (handlerNum == PromiseHandlerAsyncGeneratorAwaitedRejected) {
+        // 4.1.2.
         if (!AsyncGeneratorAwaitedRejected(cx, asyncGenObj, argument))
             return false;
+    } else if (handlerNum == PromiseHandlerAsyncGeneratorResumeNextReturnFulfilled) {
+        asyncGenObj->setCompleted();
+        // 11.4.3.5.1 step 1.
+        if (!AsyncGeneratorResolve(cx, asyncGenObj, argument, true))
+            return false;
+    } else if (handlerNum == PromiseHandlerAsyncGeneratorResumeNextReturnRejected) {
+        asyncGenObj->setCompleted();
+        // 11.4.3.5.2 step 1.
+        if (!AsyncGeneratorReject(cx, asyncGenObj, argument))
+            return false;
+    } else if (handlerNum == PromiseHandlerAsyncGeneratorYieldReturnAwaitedFulfilled) {
+        asyncGenObj->setExecuting();
+        // 11.4.3.7 steps 8.d-e.
+        if (!AsyncGeneratorYieldReturnAwaitedFulfilled(cx, asyncGenObj, argument))
+            return false;
+    } else {
+        MOZ_ASSERT(handlerNum == PromiseHandlerAsyncGeneratorYieldReturnAwaitedRejected);
+        asyncGenObj->setExecuting();
+        // 11.4.3.7 step 8.c.
+        if (!AsyncGeneratorYieldReturnAwaitedRejected(cx, asyncGenObj, argument))
+            return false;
     }
 
     rval.setUndefined();
@@ -947,10 +979,10 @@ PromiseReactionJob(JSContext* cx, unsigned argc, Value* vp)
 
     // Steps 1-2.
     Rooted<PromiseReactionRecord*> reaction(cx, &reactionObj->as<PromiseReactionRecord>());
-    if (reaction->isAsyncFunctionAwait())
-        return AsyncFunctionAwaitPromiseReactionJob(cx, reaction, args.rval());
-    if (reaction->isAsyncGeneratorAwait())
-        return AsyncGeneratorAwaitPromiseReactionJob(cx, reaction, args.rval());
+    if (reaction->isAsyncFunction())
+        return AsyncFunctionPromiseReactionJob(cx, reaction, args.rval());
+    if (reaction->isAsyncGenerator())
+        return AsyncGeneratorPromiseReactionJob(cx, reaction, args.rval());
 
     // Step 3.
     RootedValue handlerVal(cx, reaction->handler());
@@ -972,11 +1004,11 @@ PromiseReactionJob(JSContext* cx, unsigned argc, Value* vp)
             resolutionMode = RejectMode;
             handlerResult = argument;
         } else {
-            MOZ_ASSERT(handlerNum == PromiseHandlerAsyncIteratorValueUnwrapDone ||
-                       handlerNum == PromiseHandlerAsyncIteratorValueUnwrapNotDone);
+            MOZ_ASSERT(handlerNum == PromiseHandlerAsyncFromSyncIteratorValueUnwrapDone ||
+                       handlerNum == PromiseHandlerAsyncFromSyncIteratorValueUnwrapNotDone);
 
-            bool done = handlerNum == PromiseHandlerAsyncIteratorValueUnwrapDone;
-            // Async Iteration proposal 6.1.1.2.1 step 1.
+            bool done = handlerNum == PromiseHandlerAsyncFromSyncIteratorValueUnwrapDone;
+            // Async Iteration proposal 11.1.3.2.5 step 1.
             RootedObject resultObj(cx, CreateIterResultObject(cx, argument, done));
             if (!resultObj)
                 return false;
@@ -2214,7 +2246,7 @@ static MOZ_MUST_USE bool PerformPromiseThenWithReaction(JSContext* cx,
 // Some async/await functions are implemented here instead of
 // js/src/builtin/AsyncFunction.cpp, to call Promise internal functions.
 
-// Async Functions proposal 1.1.8 and 1.2.14 step 1.
+// ES 2018 draft 14.6.11 and 14.7.14 step 1.
 MOZ_MUST_USE PromiseObject*
 js::CreatePromiseObjectForAsync(JSContext* cx, HandleValue generatorVal)
 {
@@ -2228,7 +2260,7 @@ js::CreatePromiseObjectForAsync(JSContext* cx, HandleValue generatorVal)
     return promise;
 }
 
-// Async Functions proposal 2.2 steps 3.f, 3.g.
+// ES 2018 draft 25.5.5.2 steps 3.f, 3.g.
 MOZ_MUST_USE bool
 js::AsyncFunctionThrown(JSContext* cx, Handle<PromiseObject*> resultPromise)
 {
@@ -2244,7 +2276,7 @@ js::AsyncFunctionThrown(JSContext* cx, Handle<PromiseObject*> resultPromise)
     return true;
 }
 
-// Async Functions proposal 2.2 steps 3.d-e, 3.g.
+// ES 2018 draft 25.5.5.2 steps 3.d-e, 3.g.
 MOZ_MUST_USE bool
 js::AsyncFunctionReturned(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleValue value)
 {
@@ -2256,28 +2288,27 @@ js::AsyncFunctionReturned(JSContext* cx, Handle<PromiseObject*> resultPromise, H
     return true;
 }
 
-// Async Functions proposal 2.3 steps 2-8.
-MOZ_MUST_USE bool
-js::AsyncFunctionAwait(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleValue value)
+// Helper function that performs the equivalent steps as
+// Async Iteration proposal 4.1 Await steps 2-3, 6-9 or similar.
+template <typename T>
+static MOZ_MUST_USE bool
+InternalAwait(JSContext* cx, HandleValue value, HandleObject resultPromise,
+              HandleValue onFulfilled, HandleValue onRejected, T extraStep)
 {
     // Step 2.
     Rooted<PromiseObject*> promise(cx, CreatePromiseObjectWithoutResolutionFunctions(cx));
     if (!promise)
         return false;
 
-    // Steps 3.
+    // Step 3.
     if (!ResolvePromiseInternal(cx, promise, value))
         return false;
 
-    // Steps 4-5.
-    RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncFunctionAwaitFulfilled));
-    RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncFunctionAwaitRejected));
-
     RootedObject incumbentGlobal(cx);
     if (!GetObjectFromIncumbentGlobal(cx, &incumbentGlobal))
         return false;
 
-    // Steps 6-7.
+    // Steps 7-8.
     Rooted<PromiseReactionRecord*> reaction(cx, NewReactionRecord(cx, resultPromise,
                                                                   onFulfilled, onRejected,
                                                                   nullptr, nullptr,
@@ -2285,53 +2316,47 @@ js::AsyncFunctionAwait(JSContext* cx, Handle<PromiseObject*> resultPromise, Hand
     if (!reaction)
         return false;
 
-    reaction->setIsAsyncFunctionAwait();
+    // Step 6.
+    extraStep(reaction);
 
-    // Step 8.
+    // Step 9.
     return PerformPromiseThenWithReaction(cx, promise, reaction);
 }
 
-// Async Iteration proposal 5.1 steps 2-9.
+// ES 2018 draft 25.5.5.3 steps 2-10.
 MOZ_MUST_USE bool
-js::AsyncGeneratorAwait(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                        HandleValue value)
+js::AsyncFunctionAwait(JSContext* cx, Handle<PromiseObject*> resultPromise, HandleValue value)
 {
-    // Step 2.
-    Rooted<PromiseObject*> promise(cx, CreatePromiseObjectWithoutResolutionFunctions(cx));
-    if (!promise)
-        return false;
-
-    // Steps 3.
-    if (!ResolvePromiseInternal(cx, promise, value))
-        return false;
-
     // Steps 4-5.
-    RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncGeneratorAwaitFulfilled));
-    RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncGeneratorAwaitRejected));
-
-    RootedObject incumbentGlobal(cx);
-    if (!GetObjectFromIncumbentGlobal(cx, &incumbentGlobal))
-        return false;
+    RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncFunctionAwaitedFulfilled));
+    RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncFunctionAwaitedRejected));
 
-    // Step 6 (skipped).
-
-    // Steps 7-8.
-    Rooted<PromiseReactionRecord*> reaction(cx, NewReactionRecord(cx, nullptr,
-                                                                  onFulfilled, onRejected,
-                                                                  nullptr, nullptr,
-                                                                  incumbentGlobal));
-    if (!reaction)
-        return false;
+    // Steps 2-3, 6-10.
+    auto extra = [](Handle<PromiseReactionRecord*> reaction) {
+        reaction->setIsAsyncFunction();
+    };
+    return InternalAwait(cx, value, resultPromise, onFulfilled, onRejected, extra);
+}
 
-    reaction->setIsAsyncGeneratorAwait(asyncGenObj);
+// Async Iteration proposal 4.1 Await steps 2-9.
+MOZ_MUST_USE bool
+js::AsyncGeneratorAwait(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
+                        HandleValue value)
+{
+    // Steps 4-5.
+    RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncGeneratorAwaitedFulfilled));
+    RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncGeneratorAwaitedRejected));
 
-    // Step 9.
-    return PerformPromiseThenWithReaction(cx, promise, reaction);
+    // Steps 2-3, 6-9.
+    auto extra = [&](Handle<PromiseReactionRecord*> reaction) {
+        reaction->setIsAsyncGenerator(asyncGenObj);
+    };
+    return InternalAwait(cx, value, nullptr, onFulfilled, onRejected, extra);
 }
 
-// Async Iteration proposal 6.1.3.2.1 %AsyncFromSyncIteratorPrototype%.next
-// Async Iteration proposal 6.1.3.2.2 %AsyncFromSyncIteratorPrototype%.return
-// Async Iteration proposal 6.1.3.2.3 %AsyncFromSyncIteratorPrototype%.throw
+// Async Iteration proposal 11.1.3.2.1 %AsyncFromSyncIteratorPrototype%.next
+// Async Iteration proposal 11.1.3.2.2 %AsyncFromSyncIteratorPrototype%.return
+// Async Iteration proposal 11.1.3.2.3 %AsyncFromSyncIteratorPrototype%.throw
 bool
 js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind completionKind)
 {
@@ -2368,11 +2393,11 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
     RootedValue resultVal(cx);
     RootedValue func(cx);
     if (completionKind == CompletionKind::Normal) {
-        // 6.1.3.2.1 steps 5-6 (partially).
+        // 11.1.3.2.1 steps 5-6 (partially).
         if (!GetProperty(cx, iter, iter, cx->names().next, &func))
             return AbruptRejectPromise(cx, args, resultPromise, nullptr);
     } else if (completionKind == CompletionKind::Return) {
-        // 6.1.3.2.2 steps 5-6.
+        // 11.1.3.2.2 steps 5-6.
         if (!GetProperty(cx, iter, iter, cx->names().return_, &func))
             return AbruptRejectPromise(cx, args, resultPromise, nullptr);
 
@@ -2394,7 +2419,7 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
             return true;
         }
     } else {
-        // 6.1.3.2.3 steps 5-6.
+        // 11.1.3.2.3 steps 5-6.
         MOZ_ASSERT(completionKind == CompletionKind::Throw);
         if (!GetProperty(cx, iter, iter, cx->names().throw_, &func))
             return AbruptRejectPromise(cx, args, resultPromise, nullptr);
@@ -2411,16 +2436,16 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
         }
     }
 
-    // 6.1.3.2.1 steps 5-6 (partially).
-    // 6.1.3.2.2, 6.1.3.2.3 steps 8-9.
+    // 11.1.3.2.1 steps 5-6 (partially).
+    // 11.1.3.2.2, 11.1.3.2.3 steps 8-9.
     RootedValue iterVal(cx, ObjectValue(*iter));
     FixedInvokeArgs<1> args2(cx);
     args2[0].set(args.get(0));
     if (!js::Call(cx, func, iterVal, args2, &resultVal))
         return AbruptRejectPromise(cx, args, resultPromise, nullptr);
 
-    // 6.1.3.2.1 steps 5-6 (partially).
-    // 6.1.3.2.2, 6.1.3.2.3 steps 10.
+    // 11.1.3.2.1 steps 5-6 (partially).
+    // 11.1.3.2.2, 11.1.3.2.3 steps 10.
     if (!resultVal.isObject()) {
         CheckIsObjectKind kind;
         switch (completionKind) {
@@ -2440,8 +2465,8 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
 
     RootedObject resultObj(cx, &resultVal.toObject());
 
-    // Following step numbers are for 6.1.3.2.1.
-    // For 6.1.3.2.2 and 6.1.3.2.3, steps 7-16 corresponds to steps 11-20.
+    // Following step numbers are for 11.1.3.2.1.
+    // For 11.1.3.2.2 and 11.1.3.2.3, steps 7-16 corresponds to steps 11-20.
 
     // Steps 7-8.
     RootedValue doneVal(cx);
@@ -2454,33 +2479,15 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
     if (!GetProperty(cx, resultObj, resultObj, cx->names().value, &value))
         return AbruptRejectPromise(cx, args, resultPromise, nullptr);
 
-    // Step 11.
-    Rooted<PromiseObject*> promise(cx, CreatePromiseObjectWithoutResolutionFunctions(cx));
-    if (!promise)
-        return false;
-
-    // Step 12.
-    if (!ResolvePromiseInternal(cx, promise, value))
-        return false;
-
     // Steps 13-14.
     RootedValue onFulfilled(cx, Int32Value(done
-                                           ? PromiseHandlerAsyncIteratorValueUnwrapDone
-                                           : PromiseHandlerAsyncIteratorValueUnwrapNotDone));
+                                           ? PromiseHandlerAsyncFromSyncIteratorValueUnwrapDone
+                                           : PromiseHandlerAsyncFromSyncIteratorValueUnwrapNotDone));
 
-    RootedObject incumbentGlobal(cx);
-    if (!GetObjectFromIncumbentGlobal(cx, &incumbentGlobal))
-        return false;
-
-    // Step 15.
-    Rooted<PromiseReactionRecord*> reaction(cx, NewReactionRecord(cx, resultPromise, onFulfilled,
-                                                                  UndefinedHandleValue,
-                                                                  nullptr, nullptr,
-                                                                  incumbentGlobal));
-    if (!reaction)
-        return false;
-
-    if (!PerformPromiseThenWithReaction(cx, promise, reaction))
+    // Steps 11-12, 15.
+    auto extra = [](Handle<PromiseReactionRecord*> reaction) {
+    };
+    if (!InternalAwait(cx, value, resultPromise, onFulfilled, UndefinedHandleValue, extra))
         return false;
 
     // Step 16.
@@ -2488,7 +2495,10 @@ js::AsyncFromSyncIteratorMethod(JSContext* cx, CallArgs& args, CompletionKind co
     return true;
 }
 
-// Async Iteration proposal 6.4.3.3.
+static MOZ_MUST_USE bool
+AsyncGeneratorResumeNext(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj);
+
+// Async Iteration proposal 11.4.3.3.
 MOZ_MUST_USE bool
 js::AsyncGeneratorResolve(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                           HandleValue value, bool done)
@@ -2508,43 +2518,25 @@ js::AsyncGeneratorResolve(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenO
     RootedObject resultPromise(cx, request->promise());
 
     // Step 6.
-    Rooted<PromiseObject*> promise(cx, CreatePromiseObjectWithoutResolutionFunctions(cx));
-    if (!promise)
-        return false;
-
-    // Step 7.
-    if (!ResolvePromiseInternal(cx, promise, value))
-        return false;
-
-    // Steps 8-9.
-    RootedValue onFulfilled(cx, Int32Value(done
-                                           ? PromiseHandlerAsyncIteratorValueUnwrapDone
-                                           : PromiseHandlerAsyncIteratorValueUnwrapNotDone));
-
-    RootedObject incumbentGlobal(cx);
-    if (!GetObjectFromIncumbentGlobal(cx, &incumbentGlobal))
+    RootedObject resultObj(cx, CreateIterResultObject(cx, value, done));
+    if (!resultObj)
         return false;
 
-    // Step 10.
-    Rooted<PromiseReactionRecord*> reaction(cx, NewReactionRecord(cx, resultPromise, onFulfilled,
-                                                                  UndefinedHandleValue,
-                                                                  nullptr, nullptr,
-                                                                  incumbentGlobal));
-    if (!reaction)
-        return false;
+    RootedValue resultValue(cx, ObjectValue(*resultObj));
 
-    if (!PerformPromiseThenWithReaction(cx, promise, reaction))
+    // Step 7.
+    if (!ResolvePromiseInternal(cx, resultPromise, resultValue))
         return false;
 
-    // Step 11.
+    // Step 8.
     if (!AsyncGeneratorResumeNext(cx, asyncGenObj))
         return false;
 
-    // Step 12.
+    // Step 9.
     return true;
 }
 
-// Async Iteration proposal 6.4.3.4.
+// Async Iteration proposal 11.4.3.4.
 MOZ_MUST_USE bool
 js::AsyncGeneratorReject(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                          HandleValue exception)
@@ -2575,7 +2567,98 @@ js::AsyncGeneratorReject(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenOb
     return true;
 }
 
-// Async Iteration proposal 6.4.3.6.
+// Async Iteration proposal 11.4.3.5.
+static MOZ_MUST_USE bool
+AsyncGeneratorResumeNext(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj)
+{
+    // Step 1 (implicit).
+
+    // Steps 2-3.
+    MOZ_ASSERT(!asyncGenObj->isExecuting());
+
+    // Step 4.
+    if (asyncGenObj->isAwaitingYieldReturn() || asyncGenObj->isAwaitingReturn())
+        return true;
+
+    // Steps 5-6.
+    if (asyncGenObj->isQueueEmpty())
+        return true;
+
+    // Steps 7-8.
+    Rooted<AsyncGeneratorRequest*> request(
+        cx, AsyncGeneratorObject::peekRequest(cx, asyncGenObj));
+    if (!request)
+        return false;
+
+    // Step 9.
+    CompletionKind completionKind = request->completionKind();
+
+    // Step 10.
+    if (completionKind != CompletionKind::Normal) {
+        // Step 10.a.
+        if (asyncGenObj->isSuspendedStart())
+            asyncGenObj->setCompleted();
+
+        // Step 10.b.
+        if (asyncGenObj->isCompleted()) {
+            RootedValue value(cx, request->completionValue());
+
+            // Step 10.b.i.
+            if (completionKind == CompletionKind::Return) {
+                // Steps 10.b.i.1.
+                asyncGenObj->setAwaitingReturn();
+
+                // Steps 10.b.i.4-6 (reordered).
+                RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncGeneratorResumeNextReturnFulfilled));
+                RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncGeneratorResumeNextReturnRejected));
+
+                // Steps 10.b.i.2-3, 7-10.
+                auto extra = [&](Handle<PromiseReactionRecord*> reaction) {
+                    reaction->setIsAsyncGenerator(asyncGenObj);
+                };
+                return InternalAwait(cx, value, nullptr, onFulfilled, onRejected, extra);
+            }
+
+            // Step 10.b.ii.1.
+            MOZ_ASSERT(completionKind == CompletionKind::Throw);
+
+            // Steps 10.b.ii.2-3.
+            return AsyncGeneratorReject(cx, asyncGenObj, value);
+        }
+    } else if (asyncGenObj->isCompleted()) {
+        // Step 11.
+        return AsyncGeneratorResolve(cx, asyncGenObj, UndefinedHandleValue, true);
+    }
+
+    // Step 12.
+    MOZ_ASSERT(asyncGenObj->isSuspendedStart() || asyncGenObj->isSuspendedYield());
+
+    // Step 16 (reordered).
+    asyncGenObj->setExecuting();
+
+    RootedValue argument(cx, request->completionValue());
+
+    if (completionKind == CompletionKind::Return) {
+        // 11.4.3.7 AsyncGeneratorYield step 8.b-e.
+        // Since we don't have the place that handles return from yield
+        // inside the generator, handle the case here, with extra state
+        // State_AwaitingYieldReturn.
+        asyncGenObj->setAwaitingYieldReturn();
+
+        RootedValue onFulfilled(cx, Int32Value(PromiseHandlerAsyncGeneratorYieldReturnAwaitedFulfilled));
+        RootedValue onRejected(cx, Int32Value(PromiseHandlerAsyncGeneratorYieldReturnAwaitedRejected));
+
+        auto extra = [&](Handle<PromiseReactionRecord*> reaction) {
+            reaction->setIsAsyncGenerator(asyncGenObj);
+        };
+        return InternalAwait(cx, argument, nullptr, onFulfilled, onRejected, extra);
+    }
+
+    // Steps 13-15, 17-21.
+    return AsyncGeneratorResume(cx, asyncGenObj, completionKind, argument);
+}
+
+// Async Iteration proposal 11.4.3.6.
 MOZ_MUST_USE bool
 js::AsyncGeneratorEnqueue(JSContext* cx, HandleValue asyncGenVal,
                           CompletionKind completionKind, HandleValue completionValue,
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index f629c86e5..4710ab8e6 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -8578,6 +8578,13 @@ BytecodeEmitter::emitReturn(ParseNode* pn)
     if (ParseNode* pn2 = pn->pn_kid) {
         if (!emitTree(pn2))
             return false;
+
+        bool isAsyncGenerator = sc->asFunctionBox()->isAsync() &&
+                                sc->asFunctionBox()->isStarGenerator();
+        if (isAsyncGenerator) {
+            if (!emitAwait())
+                return false;
+        }
     } else {
         /* No explicit return value provided */
         if (!emit1(JSOP_UNDEFINED))
@@ -8690,6 +8697,14 @@ BytecodeEmitter::emitYield(ParseNode* pn)
         if (!emit1(JSOP_UNDEFINED))
             return false;
     }
+
+    // 11.4.3.7 AsyncGeneratorYield step 5.
+    bool isAsyncGenerator = sc->asFunctionBox()->isAsync();
+    if (isAsyncGenerator) {
+        if (!emitAwait())                                 // RESULT
+            return false;
+    }
+
     if (needsIteratorResult) {
         if (!emitFinishIteratorResult(false))
             return false;
@@ -8762,6 +8777,12 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter)
 
     MOZ_ASSERT(this->stackDepth == startDepth);
 
+    // 11.4.3.7 AsyncGeneratorYield step 5.
+    if (isAsyncGenerator) {
+        if (!emitAwait())                                 // ITER RESULT
+            return false;
+    }
+
     // Load the generator object.
     if (!emitGetDotGenerator())                           // ITER RESULT GENOBJ
         return false;
@@ -8910,10 +8931,6 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter)
         return false;
     if (!emitAtomOp(cx->names().value, JSOP_GETPROP))     // ITER OLDRESULT FTYPE FVALUE VALUE
         return false;
-    if (isAsyncGenerator) {
-        if (!emitAwait())                                 // ITER OLDRESULT FTYPE FVALUE VALUE
-            return false;
-    }
     if (!emitPrepareIteratorResult())                     // ITER OLDRESULT FTYPE FVALUE VALUE RESULT
         return false;
     if (!emit1(JSOP_SWAP))                                // ITER OLDRESULT FTYPE FVALUE RESULT VALUE
@@ -9006,11 +9023,6 @@ BytecodeEmitter::emitYieldStar(ParseNode* iter)
     if (!emitAtomOp(cx->names().value, JSOP_GETPROP))            // VALUE
         return false;
 
-    if (isAsyncGenerator) {
-        if (!emitAwait())                                        // VALUE
-            return false;
-    }
-
     MOZ_ASSERT(this->stackDepth == startDepth - 1);
 
     return true;
diff --git a/js/src/vm/AsyncIteration.cpp b/js/src/vm/AsyncIteration.cpp
index 74f6389c1..256f247b0 100644
--- a/js/src/vm/AsyncIteration.cpp
+++ b/js/src/vm/AsyncIteration.cpp
@@ -26,7 +26,7 @@ using namespace js::gc;
 #define UNWRAPPED_ASYNC_WRAPPED_SLOT 1
 #define WRAPPED_ASYNC_UNWRAPPED_SLOT 0
 
-// Async Iteration proposal 2.3.10 Runtime Semantics: EvaluateBody.
+// Async Iteration proposal 8.3.10 Runtime Semantics: EvaluateBody.
 static bool
 WrappedAsyncGenerator(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -128,11 +128,7 @@ js::GetUnwrappedAsyncGenerator(JSFunction* wrapped)
     return unwrapped;
 }
 
-static MOZ_MUST_USE bool
-AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                     CompletionKind completionKind, HandleValue argument);
-
-// Async Iteration proposal 5.1.1 Await Fulfilled Functions.
+// Async Iteration proposal 4.1.1 Await Fulfilled Functions.
 MOZ_MUST_USE bool
 js::AsyncGeneratorAwaitedFulfilled(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                                    HandleValue value)
@@ -140,7 +136,7 @@ js::AsyncGeneratorAwaitedFulfilled(JSContext* cx, Handle<AsyncGeneratorObject*>
     return AsyncGeneratorResume(cx, asyncGenObj, CompletionKind::Normal, value);
 }
 
-// Async Iteration proposal 5.1.2 Await Rejected Functions.
+// Async Iteration proposal 4.1.2 Await Rejected Functions.
 MOZ_MUST_USE bool
 js::AsyncGeneratorAwaitedRejected(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                                   HandleValue reason)
@@ -148,12 +144,30 @@ js::AsyncGeneratorAwaitedRejected(JSContext* cx, Handle<AsyncGeneratorObject*> a
     return AsyncGeneratorResume(cx, asyncGenObj, CompletionKind::Throw, reason);
 }
 
+// Async Iteration proposal 11.4.3.7 step 8.d-e.
+MOZ_MUST_USE bool
+js::AsyncGeneratorYieldReturnAwaitedFulfilled(JSContext* cx,
+                                              Handle<AsyncGeneratorObject*> asyncGenObj,
+                                              HandleValue value)
+{
+    return AsyncGeneratorResume(cx, asyncGenObj, CompletionKind::Return, value);
+}
+
+// Async Iteration proposal 11.4.3.7 step 8.d-e.
+MOZ_MUST_USE bool
+js::AsyncGeneratorYieldReturnAwaitedRejected(JSContext* cx,
+                                             Handle<AsyncGeneratorObject*> asyncGenObj,
+                                             HandleValue reason)
+{
+    return AsyncGeneratorResume(cx, asyncGenObj, CompletionKind::Throw, reason);
+}
+
 const Class AsyncFromSyncIteratorObject::class_ = {
     "AsyncFromSyncIteratorObject",
     JSCLASS_HAS_RESERVED_SLOTS(AsyncFromSyncIteratorObject::Slots)
 };
 
-// Async Iteration proposal 6.1.3.1.
+// Async Iteration proposal 11.1.3.1.
 JSObject*
 js::CreateAsyncFromSyncIterator(JSContext* cx, HandleObject iter)
 {
@@ -164,7 +178,7 @@ js::CreateAsyncFromSyncIterator(JSContext* cx, HandleObject iter)
     return AsyncFromSyncIteratorObject::create(cx, iter);
 }
 
-// Async Iteration proposal 6.1.3.1 steps 2-4.
+// Async Iteration proposal 11.1.3.1 steps 2-4.
 /* static */ JSObject*
 AsyncFromSyncIteratorObject::create(JSContext* cx, HandleObject iter)
 {
@@ -187,7 +201,7 @@ AsyncFromSyncIteratorObject::create(JSContext* cx, HandleObject iter)
     return asyncIter;
 }
 
-// Async Iteration proposal 6.1.3.2.1 %AsyncFromSyncIteratorPrototype%.next.
+// Async Iteration proposal 11.1.3.2.1 %AsyncFromSyncIteratorPrototype%.next.
 static bool
 AsyncFromSyncIteratorNext(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -195,7 +209,7 @@ AsyncFromSyncIteratorNext(JSContext* cx, unsigned argc, Value* vp)
     return AsyncFromSyncIteratorMethod(cx, args, CompletionKind::Normal);
 }
 
-// Async Iteration proposal 6.1.3.2.2 %AsyncFromSyncIteratorPrototype%.return.
+// Async Iteration proposal 11.1.3.2.2 %AsyncFromSyncIteratorPrototype%.return.
 static bool
 AsyncFromSyncIteratorReturn(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -203,7 +217,7 @@ AsyncFromSyncIteratorReturn(JSContext* cx, unsigned argc, Value* vp)
     return AsyncFromSyncIteratorMethod(cx, args, CompletionKind::Return);
 }
 
-// Async Iteration proposal 6.1.3.2.3 %AsyncFromSyncIteratorPrototype%.throw.
+// Async Iteration proposal 11.1.3.2.3 %AsyncFromSyncIteratorPrototype%.throw.
 static bool
 AsyncFromSyncIteratorThrow(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -211,7 +225,7 @@ AsyncFromSyncIteratorThrow(JSContext* cx, unsigned argc, Value* vp)
     return AsyncFromSyncIteratorMethod(cx, args, CompletionKind::Throw);
 }
 
-// Async Iteration proposal 6.4.1.2 AsyncGenerator.prototype.next.
+// Async Iteration proposal 11.4.1.2 AsyncGenerator.prototype.next.
 static bool
 AsyncGeneratorNext(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -222,7 +236,7 @@ AsyncGeneratorNext(JSContext* cx, unsigned argc, Value* vp)
                                  args.rval());
 }
 
-// Async Iteration proposal 6.4.1.3 AsyncGenerator.prototype.return.
+// Async Iteration proposal 11.4.1.3 AsyncGenerator.prototype.return.
 static bool
 AsyncGeneratorReturn(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -233,7 +247,7 @@ AsyncGeneratorReturn(JSContext* cx, unsigned argc, Value* vp)
                                  args.rval());
 }
 
-// Async Iteration proposal 6.4.1.4 AsyncGenerator.prototype.throw.
+// Async Iteration proposal 11.4.1.4 AsyncGenerator.prototype.throw.
 static bool
 AsyncGeneratorThrow(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -371,7 +385,7 @@ const Class AsyncGeneratorRequest::class_ = {
     JSCLASS_HAS_RESERVED_SLOTS(AsyncGeneratorRequest::Slots)
 };
 
-// Async Iteration proposal 6.4.3.1.
+// Async Iteration proposal 11.4.3.1.
 /* static */ AsyncGeneratorRequest*
 AsyncGeneratorRequest::create(JSContext* cx, CompletionKind completionKind_,
                               HandleValue completionValue_, HandleObject promise_)
@@ -387,7 +401,7 @@ AsyncGeneratorRequest::create(JSContext* cx, CompletionKind completionKind_,
     return request;
 }
 
-// Async Iteration proposal 6.4.3.2 steps 5.d-g.
+// Async Iteration proposal 11.4.3.2 AsyncGeneratorStart steps 5.d-g.
 static MOZ_MUST_USE bool
 AsyncGeneratorReturned(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
                        HandleValue value)
@@ -402,7 +416,7 @@ AsyncGeneratorReturned(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
     return AsyncGeneratorResolve(cx, asyncGenObj, value, true);
 }
 
-// Async Iteration proposal 6.4.3.2 steps 5.d, f.
+// Async Iteration proposal 11.4.3.2 AsyncGeneratorStart steps 5.d, f.
 static MOZ_MUST_USE bool
 AsyncGeneratorThrown(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj)
 {
@@ -422,85 +436,33 @@ AsyncGeneratorThrown(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj)
     return AsyncGeneratorReject(cx, asyncGenObj, value);
 }
 
-// Async Iteration proposal 6.4.3.5.
-MOZ_MUST_USE bool
-js::AsyncGeneratorResumeNext(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj)
-{
-    // Step 1 (implicit).
-
-    // Steps 2-3.
-    MOZ_ASSERT(!asyncGenObj->isExecuting());
-
-    // Steps 4-5.
-    if (asyncGenObj->isQueueEmpty())
-        return true;
-
-    // Steps 6-7.
-    Rooted<AsyncGeneratorRequest*> request(
-        cx, AsyncGeneratorObject::peekRequest(cx, asyncGenObj));
-    if (!request)
-        return false;
-
-    // Step 8.
-    CompletionKind completionKind = request->completionKind();
-
-    // Step 9.
-    if (completionKind != CompletionKind::Normal) {
-        // Step 9.a.
-        if (asyncGenObj->isSuspendedStart())
-            asyncGenObj->setCompleted();
-
-        // Step 9.b.
-        if (asyncGenObj->isCompleted()) {
-            // Step 9.b.i.
-            RootedValue value(cx, request->completionValue());
-            if (completionKind == CompletionKind::Return)
-                return AsyncGeneratorResolve(cx, asyncGenObj, value, true);
-            // Step 9.b.ii.
-            return AsyncGeneratorReject(cx, asyncGenObj, value);
-        }
-    } else if (asyncGenObj->isCompleted()) {
-        // Step 10.
-        return AsyncGeneratorResolve(cx, asyncGenObj, UndefinedHandleValue, true);
-    }
-
-    // Step 11.
-    MOZ_ASSERT(asyncGenObj->isSuspendedStart() || asyncGenObj->isSuspendedYield());
-
-    // Step 15 (reordered).
-    asyncGenObj->setExecuting();
-
-    RootedValue argument(cx, request->completionValue());
-
-    // Steps 12-14, 16-20.
-    return AsyncGeneratorResume(cx, asyncGenObj, completionKind, argument);
-}
-
-// Async Iteration proposal 6.2.1.3 (partially).
+// Async Iteration proposal 11.4.3.7 (partially).
 // Most steps are done in generator.
 static MOZ_MUST_USE bool
-AsyncGeneratorYield(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                    HandleValue value)
+AsyncGeneratorYield(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj, HandleValue value)
 {
-    // Step 5.
+    // Step 5 is done in bytecode.
+
+    // Step 6.
     asyncGenObj->setSuspendedYield();
 
-    // Step 8.
+    // Step 9.
     return AsyncGeneratorResolve(cx, asyncGenObj, value, false);
 }
 
-// Async Iteration proposal 6.4.3.5 steps 12-14, 16-20.
-// Async Iteration proposal 6.2.1.2 step 10.
-// Async Iteration proposal 6.4.3.2 step 5.f-g.
-// Async Iteration proposal 5.1 steps 2-9.
+// Async Iteration proposal 4.1 Await steps 2-9.
+// Async Iteration proposal 8.2.1 yield* steps 6.a.vii, 6.b.ii.7, 6.c.ix.
+// Async Iteration proposal 11.4.3.2 AsyncGeneratorStart step 5.f-g.
+// Async Iteration proposal 11.4.3.5 AsyncGeneratorResumeNext
+//   steps 12-14, 16-20.
 // Execution context switching is handled in generator.
-static MOZ_MUST_USE bool
-AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                     CompletionKind completionKind, HandleValue argument)
+MOZ_MUST_USE bool
+js::AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
+                         CompletionKind completionKind, HandleValue argument)
 {
     RootedValue generatorVal(cx, asyncGenObj->generatorVal());
 
-    // 6.4.3.5 steps 12-14, 16-20.
+    // 11.4.3.5 steps 12-14, 16-20.
     HandlePropertyName funName = completionKind == CompletionKind::Normal
                                  ? cx->names().StarGeneratorNext
                                  : completionKind == CompletionKind::Throw
@@ -510,10 +472,11 @@ AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
     args[0].set(argument);
     RootedValue result(cx);
     if (!CallSelfHostedFunction(cx, funName, generatorVal, args, &result)) {
-        // 6.4.3.2 step 5.d, f.
+        // 11.4.3.2 step 5.d, f.
         return AsyncGeneratorThrown(cx, asyncGenObj);
     }
 
+    // 4.1 steps 2-9.
     if (asyncGenObj->generatorObj()->isAfterAwait())
         return AsyncGeneratorAwait(cx, asyncGenObj, result);
 
@@ -525,8 +488,10 @@ AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
     // object and it's not observable.
     // For yield*, it's done on a possibly user-provided result object, and
     // it's observable.
+    //
+    // Note that IteratorComplete steps in 8.2.1 are done in bytecode.
 
-    // 2.2.1 yield* steps 6.a.vii, 6.b.ii.7, 6.c.ix.
+    // 8.2.1 yield* steps 6.a.vii, 6.b.ii.7, 6.c.ix.
     RootedObject resultObj(cx, &result.toObject());
     RootedValue value(cx);
 
@@ -536,7 +501,7 @@ AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
     if (asyncGenObj->generatorObj()->isAfterYield())
         return AsyncGeneratorYield(cx, asyncGenObj, value);
 
-    // 6.4.3.2 step 5.d-g.
+    // 11.4.3.2 step 5.d-g.
     return AsyncGeneratorReturned(cx, asyncGenObj, value);
 }
 
@@ -565,14 +530,14 @@ GlobalObject::initAsyncGenerators(JSContext* cx, Handle<GlobalObject*> global)
     if (global->getReservedSlot(ASYNC_ITERATOR_PROTO).isObject())
         return true;
 
-    // Async Iteration proposal 6.1.2 %AsyncIteratorPrototype%.
+    // Async Iteration proposal 11.1.2 %AsyncIteratorPrototype%.
     RootedObject asyncIterProto(cx, GlobalObject::createBlankPrototype<PlainObject>(cx, global));
     if (!asyncIterProto)
         return false;
     if (!DefinePropertiesAndFunctions(cx, asyncIterProto, nullptr, async_iterator_proto_methods))
         return false;
 
-    // Async Iteration proposal 6.1.3.2 %AsyncFromSyncIteratorPrototype%.
+    // Async Iteration proposal 11.1.3.2 %AsyncFromSyncIteratorPrototype%.
     RootedObject asyncFromSyncIterProto(
         cx, GlobalObject::createBlankPrototypeInheriting(cx, global, &PlainObject::class_,
                                                          asyncIterProto));
@@ -585,7 +550,7 @@ GlobalObject::initAsyncGenerators(JSContext* cx, Handle<GlobalObject*> global)
         return false;
     }
 
-    // Async Iteration proposal 6.4.1 %AsyncGeneratorPrototype%.
+    // Async Iteration proposal 11.4.1 %AsyncGeneratorPrototype%.
     RootedObject asyncGenProto(
         cx, GlobalObject::createBlankPrototypeInheriting(cx, global, &PlainObject::class_,
                                                          asyncIterProto));
@@ -597,7 +562,7 @@ GlobalObject::initAsyncGenerators(JSContext* cx, Handle<GlobalObject*> global)
         return false;
     }
 
-    // Async Iteration proposal 6.3.3 %AsyncGenerator%.
+    // Async Iteration proposal 11.3.3 %AsyncGenerator%.
     RootedObject asyncGenerator(cx, NewSingletonObjectWithFunctionPrototype(cx, global));
     if (!asyncGenerator)
         return false;
@@ -616,7 +581,7 @@ GlobalObject::initAsyncGenerators(JSContext* cx, Handle<GlobalObject*> global)
     RootedObject proto(cx, &function.toObject());
     RootedAtom name(cx, cx->names().AsyncGeneratorFunction);
 
-    // Async Iteration proposal 6.3.2 %AsyncGeneratorFunction%.
+    // Async Iteration proposal 11.3.2 %AsyncGeneratorFunction%.
     RootedObject asyncGenFunction(
         cx, NewFunctionWithProto(cx, AsyncGeneratorConstructor, 1, JSFunction::NATIVE_CTOR,
                                  nullptr, name, proto, gc::AllocKind::FUNCTION, SingletonObject));
diff --git a/js/src/vm/AsyncIteration.h b/js/src/vm/AsyncIteration.h
index 974c209a0..58c43131b 100644
--- a/js/src/vm/AsyncIteration.h
+++ b/js/src/vm/AsyncIteration.h
@@ -38,11 +38,18 @@ GetUnwrappedAsyncGenerator(JSFunction* wrapped);
 
 MOZ_MUST_USE bool
 AsyncGeneratorAwaitedFulfilled(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                              HandleValue value);
-
+                               HandleValue value);
 MOZ_MUST_USE bool
 AsyncGeneratorAwaitedRejected(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
-                             HandleValue reason);
+                              HandleValue reason);
+MOZ_MUST_USE bool
+AsyncGeneratorYieldReturnAwaitedFulfilled(JSContext* cx,
+                                          Handle<AsyncGeneratorObject*> asyncGenObj,
+                                          HandleValue value);
+MOZ_MUST_USE bool
+AsyncGeneratorYieldReturnAwaitedRejected(JSContext* cx,
+                                         Handle<AsyncGeneratorObject*> asyncGenObj,
+                                         HandleValue reason);
 
 class AsyncGeneratorRequest : public NativeObject
 {
@@ -97,6 +104,12 @@ class AsyncGeneratorObject : public NativeObject
         State_SuspendedStart,
         State_SuspendedYield,
         State_Executing,
+        // State_AwaitingYieldReturn corresponds to the case that
+        // AsyncGenerator#return is called while State_Executing,
+        // just like the case that AsyncGenerator#return is called
+        // while State_Completed.
+        State_AwaitingYieldReturn,
+        State_AwaitingReturn,
         State_Completed
     };
 
@@ -155,6 +168,12 @@ class AsyncGeneratorObject : public NativeObject
     bool isExecuting() const {
         return state() == State_Executing;
     }
+    bool isAwaitingYieldReturn() const {
+        return state() == State_AwaitingYieldReturn;
+    }
+    bool isAwaitingReturn() const {
+        return state() == State_AwaitingReturn;
+    }
     bool isCompleted() const {
         return state() == State_Completed;
     }
@@ -168,6 +187,12 @@ class AsyncGeneratorObject : public NativeObject
     void setExecuting() {
         setState(State_Executing);
     }
+    void setAwaitingYieldReturn() {
+        setState(State_AwaitingYieldReturn);
+    }
+    void setAwaitingReturn() {
+        setState(State_AwaitingReturn);
+    }
     void setCompleted() {
         setState(State_Completed);
     }
@@ -223,7 +248,8 @@ class AsyncFromSyncIteratorObject : public NativeObject
 };
 
 MOZ_MUST_USE bool
-AsyncGeneratorResumeNext(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj);
+AsyncGeneratorResume(JSContext* cx, Handle<AsyncGeneratorObject*> asyncGenObj,
+                     CompletionKind completionKind, HandleValue argument);
 
 } // namespace js