Implement changes for "avoid mostly-redundant await in async `yield…

…*`" (#3619)

test/language/statements/async-generator/yield-star-promise-not-unwrapped.js

@@ -0,0 +1,41 @@
+// Copyright (C) 2022 Kevin Gibbons. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-generator-function-definitions-runtime-semantics-evaluation
+description: >
+  `yield*` in an async generator does not await promises returned by a manually implemented async iterator.
+flags: [async]
+features: [async-iteration]
+---*/
+
+var innerPromise = Promise.resolve("unwrapped value");
+
+var asyncIter = {
+  [Symbol.asyncIterator]() {
+    return this;
+  },
+  next() {
+    return {
+      done: false,
+      value: innerPromise,
+    };
+  },
+  get return() {
+    throw new Test262Error(".return should not be accessed");
+  },
+  get throw() {
+    throw new Test262Error(".throw should not be accessed");
+  },
+};
+
+async function* f() {
+  yield* asyncIter;
+}
+
+f()
+  .next()
+  .then(v => {
+    assert.sameValue(v.value, innerPromise, "yield* should not unwrap promises from manually-implemented async iterators");
+  })
+  .then($DONE, $DONE)

test/language/statements/async-generator/yield-star-return-then-getter-ticks.js

@@ -6,7 +6,7 @@ esid: sec-generator-function-definitions-runtime-semantics-evaluation
 description: >
   Return resumption value is awaited upon and hence is treated as a thenable.
 info: |
-  14.4.14 Runtime Semantics: Evaluation
+  15.5.5 Runtime Semantics: Evaluation
     YieldExpression : yield* AssignmentExpression
 
     ...
@@ -27,46 +27,49 @@ info: |
           2. Return Completion(received).
         ...
 
-  25.5.3.7 AsyncGeneratorYield ( value )
+  27.6.3.8 AsyncGeneratorYield ( value )
     ...
-    5. Set value to ? Await(value).
-    ...
-    8. Set the code evaluation state of genContext such that when evaluation is resumed with a
-       Completion resumptionValue the following steps will be performed:
-      ...
-      b. Let awaited be Await(resumptionValue.[[Value]]).
+    12. If queue is not empty, then
       ...
-      e. Return Completion { [[Type]]: return, [[Value]]: awaited.[[Value]], [[Target]]: empty }.
+    13. Else,
       ...
+      c. Set the code evaluation state of genContext such that when evaluation is resumed with a
+       Completion resumptionValue the following steps will be performed:
+        i. Return ? AsyncGeneratorUnwrapYieldResumption(resumptionValue).
+
+  27.6.3.7 AsyncGeneratorUnwrapYieldResumption ( resumptionValue  )
+    ...
+    2. Let awaited be Completion(Await(resumptionValue.[[Value]])).
+    ...
 
   6.2.3.1 Await
     ...
     2. Let promise be ? PromiseResolve(%Promise%, « value »).
     ...
 
-  25.6.4.5.1 PromiseResolve ( C, x )
+  27.2.4.7.1 PromiseResolve ( C, x )
     ...
-    3. Let promiseCapability be ? NewPromiseCapability(C).
-    4. Perform ? Call(promiseCapability.[[Resolve]], undefined, « x »).
+    2. Let promiseCapability be ? NewPromiseCapability(C).
+    3. Perform ? Call(promiseCapability.[[Resolve]], undefined, « x »).
     ...
 
-  25.6.1.5 NewPromiseCapability ( C )
+  27.2.1.5 NewPromiseCapability ( C )
     ...
     7. Let promise be ? Construct(C, « executor »).
     ...
 
-  25.6.3.1 Promise ( executor )
+  27.2.3.1 Promise ( executor )
     ...
     8. Let resolvingFunctions be CreateResolvingFunctions(promise).
     ...
 
-  25.6.1.3 CreateResolvingFunctions ( promise )
+  27.2.1.3 CreateResolvingFunctions ( promise )
     ...
     2. Let stepsResolve be the algorithm steps defined in Promise Resolve Functions (25.6.1.3.2).
     3. Let resolve be CreateBuiltinFunction(stepsResolve, « [[Promise]], [[AlreadyResolved]] »).
     ...
 
-  25.6.1.3.2 Promise Resolve Functions
+  27.2.1.3.2 Promise Resolve Functions
     ...
     9. Let then be Get(resolution, "then").
     ...
@@ -82,14 +85,11 @@ var expected = [
   // `Await(innerResult)` promise resolved.
   "tick 1",
 
-  // `Await(value)` promise resolved.
-  "tick 2",
-
   // "then" of `resumptionValue.[[Value]]` accessed.
   "get then",
 
   // `Await(resumptionValue.[[Value]])` promise resolved.
-  "tick 3",
+  "tick 2",
 
   // Get iterator "return" method.
   "get return",
@@ -98,7 +98,7 @@ var expected = [
   "get then",
 
   // `Await(received.[[Value]])` promise resolved.
-  "tick 4",
+  "tick 3",
 ];
 
 var actual = [];
@@ -127,7 +127,6 @@ Promise.resolve(0)
   .then(() => actual.push("tick 1"))
   .then(() => actual.push("tick 2"))
   .then(() => actual.push("tick 3"))
-  .then(() => actual.push("tick 4"))
   .then(() => {
     assert.compareArray(actual, expected, "Ticks for return with thenable getter");
 }).then($DONE, $DONE);