[ddc] Fix async rewrite ignoring new ScopedId variables.

The async rewriter was ignoring these variables since they were only used for non-user variables that didn't need to be captured. Now that we use these ScopedIds for user variables we need to capture some of them. "userDefined" specifies if the variable should be captured.

Change-Id: I2dbb86e1834982b59883a3d107612ee8f8e2284a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/400662
Commit-Queue: Nate Biggs <[email protected]>
Reviewed-by: Nicholas Shahan <[email protected]>

Author: natebiggs

pkg/dev_compiler/lib/src/compiler/js_names.dart

@@ -33,15 +33,20 @@ abstract class FixedNames {
 class ScopedId extends Identifier {
   final int _id;
 
+  /// If true, this variable can be used across different async scopes and must
+  /// therefore be specially captured.
+  final bool needsCapture;
+
   @override
   ScopedId withSourceInformation(dynamic sourceInformation) =>
       ScopedId.from(this)..sourceInformation = sourceInformation;
 
   static int _idCounter = 0;
 
-  ScopedId(super.name) : _id = _idCounter++;
+  ScopedId(super.name, {this.needsCapture = false}) : _id = _idCounter++;
   ScopedId.from(ScopedId other)
       : _id = other._id,
+        needsCapture = other.needsCapture,
         super(other.name);
 
   @override

pkg/dev_compiler/lib/src/compiler/rewrite_async.dart

@@ -3258,14 +3258,14 @@ class _ScopeCollector extends js_ast.VariableDeclarationVisitor {
 
   @override
   void declare(js_ast.Identifier node) {
-    if (node is ScopedId) return;
+    if (node is ScopedId && !node.needsCapture) return;
     _currentScope.declare(node, inClosure || skipHoisting);
     registerUsed(node);
   }
 
   @override
   void visitIdentifier(js_ast.Identifier node) {
-    if (node is ScopedId) return;
+    if (node is ScopedId && !node.needsCapture) return;
     registerUsed(node);
   }
 

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -1035,8 +1035,9 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
   static js_ast.Identifier _emitIdentifier(String name) =>
       js_ast.Identifier(js_ast.toJSIdentifier(name));
 
-  static js_ast.ScopedId _emitScopedId(String name) =>
-      js_ast.ScopedId(js_ast.toJSIdentifier(name));
+  static js_ast.ScopedId _emitScopedId(String name,
+          {bool needsCapture = false}) =>
+      js_ast.ScopedId(js_ast.toJSIdentifier(name), needsCapture: needsCapture);
 
   js_ast.Statement _emitClassDeclaration(Class c) {
     var className = _emitTopLevelNameNoExternalInterop(c);
@@ -4988,7 +4989,8 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
       // See https://github.com/dart-lang/sdk/issues/55918
       name = extractLocalNameFromLateLoweredLocal(name);
     }
-    return js_ast.ScopedId.from(_variableTempIds[v] ??= _emitScopedId(name));
+    return js_ast.ScopedId.from(
+        _variableTempIds[v] ??= _emitScopedId(name, needsCapture: true));
   }
 
   /// Emits the declaration of a variable.

pkg/dev_compiler/lib/src/kernel/compiler_new.dart

@@ -1204,8 +1204,9 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
   static js_ast.Identifier _emitIdentifier(String name) =>
       js_ast.Identifier(js_ast.toJSIdentifier(name));
 
-  static js_ast.ScopedId _emitScopedId(String name) =>
-      js_ast.ScopedId(js_ast.toJSIdentifier(name));
+  static js_ast.ScopedId _emitScopedId(String name,
+          {bool needsCapture = false}) =>
+      js_ast.ScopedId(js_ast.toJSIdentifier(name), needsCapture: needsCapture);
 
   js_ast.Statement _emitClassDeclaration(Class c) {
     var className = _emitTopLevelNameNoExternalInterop(c);
@@ -5308,7 +5309,8 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
       // See https://github.com/dart-lang/sdk/issues/55918
       name = extractLocalNameFromLateLoweredLocal(name);
     }
-    return js_ast.ScopedId.from(_variableTempIds[v] ??= _emitScopedId(name));
+    return js_ast.ScopedId.from(
+        _variableTempIds[v] ??= _emitScopedId(name, needsCapture: true));
   }
 
   /// Emits the declaration of a variable.

tests/web/async_loop_scope_capture_test.dart

@@ -0,0 +1,29 @@
+// 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:expect/async_helper.dart';
+import 'package:expect/expect.dart';
+
+int global = -1;
+
+Future<void> staticAsyncLoopFunction(String value) async {
+  Function? f;
+  for (var i in [1, 2, 3]) {
+    print(value);
+    final myLocal = await 'my local value';
+    f ??= () {
+      // This should capture the value from the first loop iteration.
+      global = i;
+      return myLocal;
+    };
+  }
+  f!();
+}
+
+void main() async {
+  asyncStart();
+  await staticAsyncLoopFunction('foo');
+  Expect.equals(global, 1);
+  asyncEnd();
+}