From b449e99118cbfa820943394531055bfb243a7743 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Mon, 8 Apr 2024 12:42:29 +0000
Subject: [PATCH] [dart2wasm] Fix async* transformation of nested async*
 functions
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With nested `async*` functions, the state of whether we're in an
`async*` function should be restored as the previous state after leaving
the nested function, instead of as `false`.

Fixes #55397.

Change-Id: I5f2a964847ae34e98584f3adad6df7857b81e474
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/361600
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
---
 pkg/dart2wasm/lib/transformers.dart   |  5 +++--
 tests/language/async/nested_test.dart | 31 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 tests/language/async/nested_test.dart

diff --git a/pkg/dart2wasm/lib/transformers.dart b/pkg/dart2wasm/lib/transformers.dart
index 51a3994f6bf..b2b6788f9f8 100644
--- a/pkg/dart2wasm/lib/transformers.dart
+++ b/pkg/dart2wasm/lib/transformers.dart
@@ -679,13 +679,14 @@ class _WasmTransformer extends Transformer {
 
   @override
   TreeNode visitFunctionNode(FunctionNode functionNode) {
+    final previousEnclosing = _enclosingIsAsyncStar;
     if (functionNode.dartAsyncMarker == AsyncMarker.AsyncStar) {
       _enclosingIsAsyncStar = true;
       functionNode = _lowerAsyncStar(functionNode) as FunctionNode;
-      _enclosingIsAsyncStar = false;
+      _enclosingIsAsyncStar = previousEnclosing;
       return super.visitFunctionNode(functionNode);
     } else {
-      bool previousEnclosing = _enclosingIsAsyncStar;
+      _enclosingIsAsyncStar = false;
       TreeNode result = super.visitFunctionNode(functionNode);
       _enclosingIsAsyncStar = previousEnclosing;
       return result;
diff --git a/tests/language/async/nested_test.dart b/tests/language/async/nested_test.dart
new file mode 100644
index 00000000000..d5c398c8fdc
--- /dev/null
+++ b/tests/language/async/nested_test.dart
@@ -0,0 +1,31 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+
+Stream<String> stream() async* {
+  yield 'a';
+  yield 'b';
+}
+
+Stream<String> expandedStream() async* {
+  final expanded = stream().asyncExpand((s) async* {
+    yield 'before';
+    yield s;
+    yield 'after';
+  });
+
+  yield* expanded;
+}
+
+test() async {
+  Expect.listEquals(['before', 'a', 'after', 'before', 'b', 'after'],
+      await expandedStream().toList());
+}
+
+void main() {
+  asyncStart();
+  test().then((_) => asyncEnd());
+}