[async-iteration] implement spec change to [Async-from-Sync Iterator]

A really slight change in behaviour introduced by
https://github.com/tc39/proposal-async-iteration/commit/395b2e3b2f5acb62f9fae11c5e189423d4af50e6

Just swaps the order that properties are loaded from an iterator result
object in the various Async-from-Sync Iterator methods.

Fixes for the test262 tests have been submitted already (https://github.com/tc39/test262/pull/961).

BUG=v8:5855, v8:6242
R=littledan@chromium.org, jwolfe@igalia.com,

Change-Id: I1ff0e1b7758c126d02aec27d67ceeb15b91c06cf
Reviewed-on: https://chromium-review.googlesource.com/474087Reviewed-by: Daniel Ehrenberg <littledan@chromium.org>
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#44572}

src/builtins/builtins-async-iterator-gen.cc

@@ -160,26 +160,26 @@ std::pair<Node*, Node*> AsyncFromSyncBuiltinsAssembler::LoadIteratorResult(
 
   BIND(&if_fastpath);
   {
+    var_done.Bind(LoadObjectField(iter_result, JSIteratorResult::kDoneOffset));
     var_value.Bind(
         LoadObjectField(iter_result, JSIteratorResult::kValueOffset));
-    var_done.Bind(LoadObjectField(iter_result, JSIteratorResult::kDoneOffset));
     Goto(&merge);
   }
 
   BIND(&if_slowpath);
   {
-    // Let nextValue be IteratorValue(nextResult).
-    // IfAbruptRejectPromise(nextValue, promiseCapability).
-    Node* const value =
-        GetProperty(context, iter_result, factory()->value_string());
-    GotoIfException(value, if_exception, var_exception);
-
     // Let nextDone be IteratorComplete(nextResult).
     // IfAbruptRejectPromise(nextDone, promiseCapability).
     Node* const done =
         GetProperty(context, iter_result, factory()->done_string());
     GotoIfException(done, if_exception, var_exception);
 
+    // Let nextValue be IteratorValue(nextResult).
+    // IfAbruptRejectPromise(nextValue, promiseCapability).
+    Node* const value =
+        GetProperty(context, iter_result, factory()->value_string());
+    GotoIfException(value, if_exception, var_exception);
+
     var_value.Bind(value);
     var_done.Bind(done);
     Goto(&merge);

test/mjsunit/harmony/async-from-sync-iterator.js

@@ -668,3 +668,95 @@ if (testFailed) {
   assertThrowsAsync(() => extractedReturn.call(undefined), TypeError);
   assertThrowsAsync(() => extractedReturn.call(1), TypeError);
 })();
+
+(function AsyncFromSyncIteratorOrdering() {
+  let i = 0;
+  let log = [];
+  function r(value, done) {
+    let number = (++i);
+    return {
+      get value() {
+        log.push("get iterResult #" + number + ".value");
+        return {
+          get then() {
+            log.push("get nextValue#" + number + ".then");
+            return (r) => {
+              log.push("call nextValue#" + number + ".then");
+              r(value);
+            }
+          }
+        };
+      },
+      get done() {
+        log.push("get iterResult #" + number + ".done");
+        return done;
+      }
+    };
+  }
+  var results = [r("value1", false), r("value2", false), r("value3", true),
+                 r("value4", false)];
+
+  var iter = {
+    get [Symbol.asyncIterator]() {
+      log.push("get syncIterable[@@asyncIterator]");
+      return null;
+    },
+
+    get [Symbol.iterator]() {
+      log.push("get syncIterable[@@iterator]");
+      return (...args) => {
+        log.push("call syncIterable[@@iterator](" + args.join(", ") + ")");
+        return this;
+      }
+    },
+    next_: 0,
+    get next() {
+      log.push("get syncIterable.next");
+      let i = this.next_++;
+      return (...args) => {
+        log.push("call syncIterable.next(" + args.join(", ") + ")");
+        return results[i];
+      }
+    }
+  };
+
+  async function iterate(iterable) {
+    log.push("before");
+    for await (let x of iterable) {
+      log.push("got value " + x);
+    }
+    log.push("after");
+
+    return log;
+  }
+
+  iterate(iter).then(log => {
+    assertEquals([
+      "before",
+      "get syncIterable[@@asyncIterator]",
+      "get syncIterable[@@iterator]",
+      "call syncIterable[@@iterator]()",
+      "get syncIterable.next",
+      "call syncIterable.next()",
+      "get iterResult #1.done",
+      "get iterResult #1.value",
+      "get nextValue#1.then",
+      "call nextValue#1.then",
+      "got value value1",
+      "get syncIterable.next",
+      "call syncIterable.next()",
+      "get iterResult #2.done",
+      "get iterResult #2.value",
+      "get nextValue#2.then",
+      "call nextValue#2.then",
+      "got value value2",
+      "get syncIterable.next",
+      "call syncIterable.next()",
+      "get iterResult #3.done",
+      "get iterResult #3.value",
+      "get nextValue#3.then",
+      "call nextValue#3.then",
+      "after"
+    ], log)
+  }).catch(x => %AbortJS(String(x)));
+})();

test/test262/test262.status

@@ -451,6 +451,32 @@
   'language/statements/class/async-gen-method-yield-star-async-return': [FAIL],
   'language/statements/class/async-gen-method-yield-star-async-throw': [FAIL],
 
+  # https://bugs.chromium.org/p/v8/issues/detail?id=6242
+  'language/expressions/async-generator/named-yield-star-sync-next': [FAIL],
+  'language/expressions/async-generator/named-yield-star-sync-return': [FAIL],
+  'language/expressions/async-generator/named-yield-star-sync-throw': [FAIL],
+  'language/expressions/async-generator/yield-star-sync-next': [FAIL],
+  'language/expressions/async-generator/yield-star-sync-return': [FAIL],
+  'language/expressions/async-generator/yield-star-sync-throw': [FAIL],
+  'language/expressions/class/async-gen-method-static-yield-star-sync-next': [FAIL],
+  'language/expressions/class/async-gen-method-static-yield-star-sync-return': [FAIL],
+  'language/expressions/class/async-gen-method-static-yield-star-sync-throw': [FAIL],
+  'language/expressions/class/async-gen-method-yield-star-sync-next': [FAIL],
+  'language/expressions/class/async-gen-method-yield-star-sync-return': [FAIL],
+  'language/expressions/class/async-gen-method-yield-star-sync-throw': [FAIL],
+  'language/expressions/object/method-definition/async-gen-yield-star-sync-next': [FAIL],
+  'language/expressions/object/method-definition/async-gen-yield-star-sync-return': [FAIL],
+  'language/expressions/object/method-definition/async-gen-yield-star-sync-throw': [FAIL],
+  'language/statements/async-generator/yield-star-sync-next': [FAIL],
+  'language/statements/async-generator/yield-star-sync-return': [FAIL],
+  'language/statements/async-generator/yield-star-sync-throw': [FAIL],
+  'language/statements/class/async-gen-method-static-yield-star-sync-next': [FAIL],
+  'language/statements/class/async-gen-method-static-yield-star-sync-return': [FAIL],
+  'language/statements/class/async-gen-method-static-yield-star-sync-throw': [FAIL],
+  'language/statements/class/async-gen-method-yield-star-sync-next': [FAIL],
+  'language/statements/class/async-gen-method-yield-star-sync-return': [FAIL],
+  'language/statements/class/async-gen-method-yield-star-sync-throw': [FAIL],
+
   # SharedArrayBuffer tests that require flags
   'built-ins/SharedArrayBuffer/*': ['--harmony-sharedarraybuffer'],
   'built-ins/Atomics/*': ['--harmony-sharedarraybuffer'],