Add variable support for new DDC async lowering (#2471)

* Add variable support for new DDC async lowering.

---------

Co-authored-by: Nate Biggs <natebiggs@google.com>

dwds/lib/src/debugging/dart_scope.dart

@@ -28,6 +28,9 @@ final ddcTemporaryTypeVariableRegExp = RegExp(r'^__t[\$\w*]+$');
 final previousDdcTemporaryVariableRegExp =
     RegExp(r'^(t[0-9]+\$?[0-9]*|__t[\$\w*]+)$');
 
+const ddcAsyncScope = 'asyncScope';
+const ddcCapturedAsyncScope = 'capturedAsyncScope';
+
 /// Find the visible Dart variables from a JS Scope Chain, coming from the
 /// scopeChain attribute of a Chrome CallFrame corresponding to [frame].
 ///
@@ -70,6 +73,46 @@ Future<List<Property>> visibleVariables({
     );
   }
 
+  // DDC's async lowering hoists variable declarations into scope objects. We
+  // create one scope object per Dart scope (skipping scopes containing no
+  // declarations). If a Dart scope is captured by a Dart closure the
+  // JS scope object will also be captured by the compiled JS closure.
+  //
+  // For debugging purposes we unpack these scope objects into the set of
+  // available properties to recreate the Dart context at any given point.
+
+  final capturedAsyncScopes = [
+    ...allProperties
+        .where((p) => p.name?.startsWith(ddcCapturedAsyncScope) ?? false),
+  ];
+
+  if (capturedAsyncScopes.isNotEmpty) {
+    // If we are in a local function within an async function, we should use the
+    // available captured scopes. These will contain all the variables captured
+    // by the closure. We only close over variables used within the closure.
+    for (final scopeObject in capturedAsyncScopes) {
+      final scopeObjectId = scopeObject.value?.objectId;
+      if (scopeObjectId == null) continue;
+      final scopeProperties = await inspector.getProperties(scopeObjectId);
+      allProperties.addAll(scopeProperties);
+      allProperties.remove(scopeObject);
+    }
+  } else {
+    // Otherwise we are in the async function body itself. Unpack the available
+    // async scopes. Scopes we have not entered may already have a scope object
+    // declared but the object will not have any values in it yet.
+    final asyncScopes = [
+      ...allProperties.where((p) => p.name?.startsWith(ddcAsyncScope) ?? false),
+    ];
+    for (final scopeObject in asyncScopes) {
+      final scopeObjectId = scopeObject.value?.objectId;
+      if (scopeObjectId == null) continue;
+      final scopeProperties = await inspector.getProperties(scopeObjectId);
+      allProperties.addAll(scopeProperties);
+      allProperties.remove(scopeObject);
+    }
+  }
+
   allProperties.removeWhere((property) {
     final value = property.value;
     if (value == null) return true;

dwds/test/variable_scope_test.dart

@@ -187,30 +187,64 @@ void main() {
       expect(variableNames, containsAll(['formal']));
     });
 
-    test(
-      'variables in function',
-      () async {
-        stack = await breakAt('nestedFunction', mainScript);
-        final variables = getFrameVariables(stack.frames!.first);
-        await expectDartVariables(variables);
-
-        final variableNames = variables.keys.toList()..sort();
-        expect(
-          variableNames,
-          containsAll([
-            'aClass',
-            'another',
-            'intLocalInMain',
-            'local',
-            'localThatsNull',
-            'nestedFunction',
-            'parameter',
-            'testClass',
-          ]),
-        );
-      },
-      skip: 'See https://github.com/dart-lang/webdev/issues/2469',
-    );
+    test('variables in static async function', () async {
+      stack = await breakAt('staticAsyncFunction', mainScript);
+      final variables = getFrameVariables(stack.frames!.first);
+      await expectDartVariables(variables);
+
+      final variableNames = variables.keys.toList()..sort();
+      final variableValues =
+          variableNames.map((name) => variables[name]?.valueAsString).toList();
+      expect(
+        variableNames,
+        containsAll(['myLocal', 'value']),
+      );
+      expect(
+        variableValues,
+        containsAll(['a local value', 'arg1']),
+      );
+    });
+
+    test('variables in static async loop function', () async {
+      stack = await breakAt('staticAsyncLoopFunction', mainScript);
+      final variables = getFrameVariables(stack.frames!.first);
+      await expectDartVariables(variables);
+
+      final variableNames = variables.keys.toList()..sort();
+      final variableValues =
+          variableNames.map((name) => variables[name]?.valueAsString).toList();
+      expect(
+        variableNames,
+        containsAll(['i', 'myLocal', 'value']),
+      );
+      // Ensure the loop variable, i, is captued correctly. The value from the
+      // first iteration should be captured by the saved closure.
+      expect(
+        variableValues,
+        containsAll(['1', 'my local value', 'arg2']),
+      );
+    });
+
+    test('variables in function', () async {
+      stack = await breakAt('nestedFunction', mainScript);
+      final variables = getFrameVariables(stack.frames!.first);
+      await expectDartVariables(variables);
+
+      final variableNames = variables.keys.toList()..sort();
+      expect(
+        variableNames,
+        containsAll([
+          'aClass',
+          'another',
+          'intLocalInMain',
+          'local',
+          'localThatsNull',
+          'nestedFunction',
+          'parameter',
+          'testClass',
+        ]),
+      );
+    });
 
     test('variables in closure nested in method', () async {
       stack = await breakAt('nestedClosure', mainScript);

fixtures/_testSound/example/scopes/main.dart

@@ -25,6 +25,25 @@ void staticFunction(int formal) {
   print(formal); // Breakpoint: staticFunction
 }
 
+void staticAsyncFunction(String value) async {
+  var myLocal = await 'a local value';
+  print(value); // Breakpoint: staticAsyncFunction
+}
+
+void staticAsyncLoopFunction(String value) async {
+  Function? f;
+  for (var i in [1, 2, 3]) {
+    print(i);
+    var myLocal = await 'my local value';
+    f ??= () {
+      print(value);
+      print(i);
+      return myLocal; // Breakpoint: staticAsyncLoopFunction
+    };
+  }
+  f!();
+}
+
 void main() async {
   print('Initial print from scopes app');
   var local = 'local in main';
@@ -52,6 +71,8 @@ void main() async {
     var closureLocal;
     libraryPublicFinal.printCount();
     staticFunction(1);
+    staticAsyncFunction('arg1');
+    staticAsyncLoopFunction('arg2');
     print('ticking... $ticks (the answer is $intLocalInMain)');
     print(nestedFunction('$ticks ${testClass.message}', Timer));
     print(localThatsNull);