Make async iterator return() and next() more like async generators

Previously, we would only set the async iterator's "ongoing promise" to null when the async iterator next steps succeeded. This meant that calling return() after a failed next() would not call the async iterator return steps, thus potentially preventing the cleanup of any associated resources. This changes the spec to reset the ongoing promise after the async iterator next steps complete, regardless of whether they succeed or fail.

Author: domenic

index.bs

@@ -12543,23 +12543,29 @@ The \[[Prototype]] [=internal slot=] of an [=asynchronous iterator prototype obj
                 1.  Let |value| be |next|, [=converted to an ECMAScript value=].
                 1.  Return [=!=] [$CreateIterResultObject$](|value|, <emu-val>false</emu-val>).
         1.  Let |onFulfilled| be [=!=] [$CreateBuiltinFunction$](|fulfillSteps|, « »).
-        1.  Perform [=!=] [$PerformPromiseThen$](|nextPromise|, |onFulfilled|,
-            <emu-val>undefined</emu-val>, |nextPromiseCapability|).
+        1.  Let |rejectSteps| be the following steps, given |reason|:
+            1.  Set |object|'s [=default asynchronous iterator object/ongoing promise=] to
+                null.
+            1.  Set |object|'s [=default asynchronous iterator object/is finished=] to true.
+            1.  [=ECMAScript/Throw=] |reason|.
+        1.  Let |onRejected| be [=!=] [$CreateBuiltinFunction$](|rejectSteps|, « »).
+        1.  Perform [=!=] [$PerformPromiseThen$](|nextPromise|, |onFulfilled|, |onRejected|,
+            |nextPromiseCapability|).
         1.  Return |nextPromiseCapability|.\[[Promise]].
 
-    1.  Let |promise| be |object|'s [=default asynchronous iterator object/ongoing promise=].
+    1.  Let |ongoingPromise| be |object|'s [=default asynchronous iterator object/ongoing promise=].
 
-    1.  If |promise| is not null, then:
+    1.  If |ongoingPromise| is not null, then:
         1.  Let |afterOngoingPromiseCapability| be [=!=] [$NewPromiseCapability$]({{%Promise%}}).
-        1.  Let |onFulfilled| be [=!=] [$CreateBuiltinFunction$](|nextSteps|, « »).
-        1.  Perform [=!=] [$PerformPromiseThen$](|promise|, |onFulfilled|,
-            <emu-val>undefined</emu-val>, |afterOngoingPromiseCapability|).
+        1.  Let |onSettled| be [=!=] [$CreateBuiltinFunction$](|nextSteps|, « »).
+        1.  Perform [=!=] [$PerformPromiseThen$](|ongoingPromise|, |onSettled|, |onSettled|,
+            |afterOngoingPromiseCapability|).
         1.  Set |object|'s [=default asynchronous iterator object/ongoing promise=] to
             |afterOngoingPromiseCapability|.\[[Promise]].
 
     1.  Otherwise:
-        1.  Run |nextSteps| and set |object|'s
-            [=default asynchronous iterator object/ongoing promise=] to the result.
+        1.  Set |object|'s [=default asynchronous iterator object/ongoing promise=] to the result of
+            running |nextSteps|.
 
     1.  Return |object|'s [=default asynchronous iterator object/ongoing promise=].
 </div>
@@ -12599,31 +12605,38 @@ The \[[Prototype]] [=internal slot=] of an [=asynchronous iterator prototype obj
             <emu-val>undefined</emu-val>, « |error| »).
         1.  Return |returnPromiseCapability|.\[[Promise]].
 
-    1.  If |object|'s [=default asynchronous iterator object/ongoing promise=] is not null, then:
-        1.  Let |error| be a new {{ECMAScript/TypeError}}.
-        1.  Perform [=!=] [$Call$](|returnPromiseCapability|.\[[Reject]],
-            <emu-val>undefined</emu-val>, « |error| »).
-        1.  Return |returnPromiseCapability|.\[[Promise]].
+    1.  Let |returnSteps| be the following steps:
+        1.  Let |returnPromiseCapability| be [=!=] [$NewPromiseCapability$]({{%Promise%}}).
+        1.  If |object|'s [=default asynchronous iterator object/is finished=] is true, then:
+            1.  Let |result| be [$CreateIterResultObject$](|value|, <emu-val>true</emu-val>).
+            1.  Perform [=!=] [$Call$](|returnPromiseCapability|.\[[Resolve]],
+                <emu-val>undefined</emu-val>, « |result| »).
+            1.  Return |returnPromiseCapability|.\[[Promise]].
+        1.  Set |object|'s [=default asynchronous iterator object/is finished=] to true.
+        1.  Return the result of running the [=asynchronous iterator return=] algorithm for
+            |interface|, given |object|'s [=default asynchronous iterator object/target=], |object|,
+            and |value|.
 
-    1.  If |object|'s [=default asynchronous iterator object/is finished=] is true, then:
-        1.  Let |result| be [=!=] [$CreateIterResultObject$](|value|,
-            <emu-val>true</emu-val>).
-        1.  Perform [=!=] [$Call$](|returnPromiseCapability|.\[[Resolve]],
-            <emu-val>undefined</emu-val>, « |result| »).
-        1.  Return |returnPromiseCapability|.\[[Promise]].
+    1.  Let |returnStepsPromise| be null.
 
-    1.  Set |object|'s [=default asynchronous iterator object/is finished=] to true.
+    1.  Let |ongoingPromise| be |object|'s [=default asynchronous iterator object/ongoing promise=].
 
-    1.  Let |returnPromise| be the result of running the [=asynchronous iterator return=] algorithm
-        for |interface|, given |object|'s [=default asynchronous iterator object/target=],
-        |object|, and |value|.
+    1.  If |ongoingPromise| is not null, then:
+        1.  Let |afterOngoingPromiseCapability| be [=!=] [$NewPromiseCapability$]({{%Promise%}}).
+        1.  Let |onSettled| be [=!=] [$CreateBuiltinFunction$](|returnSteps|, « »).
+        1.  Perform [=!=] [$PerformPromiseThen$](|ongoingPromise|, |onSettled|, |onSettled|,
+            |afterOngoingPromiseCapability|).
+        1.  Set |returnStepsPromise| to |afterOngoingPromiseCapability|.\[[Promise]].
+
+    1.  Otherwise:
+        1.  Set |returnStepsPromise| to the result of running |returnSteps|.
 
     1.  Let |fulfillSteps| be the following steps:
         1.  Return [=!=] [$CreateIterResultObject$](|value|, <emu-val>true</emu-val>).
 
     1.  Let |onFulfilled| be [=!=] [$CreateBuiltinFunction$](|fulfillSteps|, « »).
 
-    1.  Perform [=!=] [$PerformPromiseThen$](|returnPromise|, |onFulfilled|,
+    1.  Perform [=!=] [$PerformPromiseThen$](|returnStepsPromise|, |onFulfilled|,
         <emu-val>undefined</emu-val>, |returnPromiseCapability|).
 
     1.  Return |returnPromiseCapability|.\[[Promise]].