always adds alert label for alert dialog in Android (#65973)

packages/flutter/lib/src/material/dialog.dart

@@ -413,9 +413,11 @@ class AlertDialog extends StatelessWidget {
   /// The semantic label of the dialog used by accessibility frameworks to
   /// announce screen transitions when the dialog is opened and closed.
   ///
-  /// If this label is not provided, a semantic label will be inferred from the
-  /// [title] if it is not null.  If there is no title, the label will be taken
-  /// from [MaterialLocalizations.alertDialogLabel].
+  /// In iOS, if this label is not provided, a semantic label will be inferred
+  /// from the [title] if it is not null.
+  ///
+  /// In Android, if this label is not provided, the dialog will use the
+  /// [MaterialLocalizations.alertDialogLabel] as its label.
   ///
   /// See also:
   ///
@@ -455,18 +457,15 @@ class AlertDialog extends StatelessWidget {
     final DialogTheme dialogTheme = DialogTheme.of(context);
 
     String label = semanticLabel;
-    if (title == null) {
-      switch (theme.platform) {
-        case TargetPlatform.iOS:
-        case TargetPlatform.macOS:
-          label = semanticLabel;
-          break;
-        case TargetPlatform.android:
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.windows:
-          label = semanticLabel ?? MaterialLocalizations.of(context)?.alertDialogLabel;
-      }
+    switch (theme.platform) {
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        break;
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        label ??= MaterialLocalizations.of(context)?.alertDialogLabel;
     }
 
     // The paddingScaleFactor is used to adjust the padding of Dialog's
@@ -491,7 +490,7 @@ class AlertDialog extends StatelessWidget {
           style: titleTextStyle ?? dialogTheme.titleTextStyle ?? theme.textTheme.headline6,
           child: Semantics(
             child: title,
-            namesRoute: true,
+            namesRoute: label == null,
             container: true,
           ),
         ),
@@ -569,6 +568,8 @@ class AlertDialog extends StatelessWidget {
 
     if (label != null)
       dialogChild = Semantics(
+        scopesRoute: true,
+        explicitChildNodes: true,
         namesRoute: true,
         label: label,
         child: dialogChild,

packages/flutter/test/material/dialog_test.dart

@@ -1275,10 +1275,12 @@ void main() {
         ));
   });
 
-  testWidgets('Dialog widget contains route semantics from title', (WidgetTester tester) async {
+  testWidgets('AlertDialog widget contains route semantics from title for iOS', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
+
     await tester.pumpWidget(
       MaterialApp(
+        theme: ThemeData(platform: TargetPlatform.iOS),
         home: Material(
           child: Builder(
             builder: (BuildContext context) {
@@ -1321,6 +1323,62 @@ void main() {
     semantics.dispose();
   });
 
+    testWidgets('AlertDialog widget always contains alert route semantics for android', (WidgetTester tester) async {
+    final SemanticsTester semantics = SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(platform: TargetPlatform.android),
+        home: Material(
+          child: Builder(
+            builder: (BuildContext context) {
+              return Center(
+                child: ElevatedButton(
+                  child: const Text('X'),
+                  onPressed: () {
+                    showDialog<void>(
+                      context: context,
+                      builder: (BuildContext context) {
+                        return const AlertDialog(
+                          title: Text('Title'),
+                          content: Text('Y'),
+                          actions: <Widget>[],
+                        );
+                      },
+                    );
+                  },
+                ),
+              );
+            },
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, isNot(includesNodeWith(
+      label: 'Title',
+      flags: <SemanticsFlag>[SemanticsFlag.namesRoute],
+    )));
+    expect(semantics, isNot(includesNodeWith(
+      label: 'Alert',
+      flags: <SemanticsFlag>[SemanticsFlag.namesRoute, SemanticsFlag.scopesRoute],
+    )));
+
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+    // It does not use 'Title' as route semantics
+    expect(semantics, isNot(includesNodeWith(
+      label: 'Title',
+      flags: <SemanticsFlag>[SemanticsFlag.namesRoute],
+    )));
+    expect(semantics, includesNodeWith(
+      label: 'Alert',
+      flags: <SemanticsFlag>[SemanticsFlag.namesRoute, SemanticsFlag.scopesRoute],
+    ));
+
+    semantics.dispose();
+  });
+
   testWidgets('Dismissible.confirmDismiss defers to an AlertDialog', (WidgetTester tester) async {
     final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
     final List<int> dismissedItems = <int>[];