Add semantic routing to CupertinoAlertDialog (#21583)

Fixes #21250

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

@@ -10,6 +10,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
+import 'localizations.dart';
 import 'scrollbar.dart';
 
 // TODO(abarth): These constants probably belong somewhere more general.
@@ -218,6 +219,8 @@ class CupertinoAlertDialog extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final CupertinoLocalizations localizations = CupertinoLocalizations.of(context)
+                                              ?? const DefaultCupertinoLocalizations();
     final bool isInAccessibilityMode = _isInAccessibilityMode(context);
     final double textScaleFactor = MediaQuery.of(context).textScaleFactor;
     return new MediaQuery(
@@ -235,9 +238,15 @@ class CupertinoAlertDialog extends StatelessWidget {
                   : _kCupertinoDialogWidth,
               child: new CupertinoPopupSurface(
                 isSurfacePainted: false,
-                child: new _CupertinoDialogRenderWidget(
-                  contentSection: _buildContent(),
-                  actionsSection: _buildActions(),
+                child: new Semantics(
+                  namesRoute: true,
+                  scopesRoute: true,
+                  explicitChildNodes: true,
+                  label: localizations.alertDialogLabel,
+                  child: new _CupertinoDialogRenderWidget(
+                    contentSection: _buildContent(),
+                    actionsSection: _buildActions(),
+                  ),
                 ),
               ),
             ),
@@ -949,18 +958,21 @@ class _PressableActionButtonState extends State<_PressableActionButton> {
   Widget build(BuildContext context) {
     return new _ActionButtonParentDataWidget(
       isPressed: _isPressed,
-      // TODO(mattcarroll): Button press dynamics need overhaul for iOS: https://github.com/flutter/flutter/issues/19786
-      child: new GestureDetector(
-        behavior: HitTestBehavior.opaque,
-        onTapDown: (TapDownDetails details) => setState(() {
-          _isPressed = true;
-        }),
-        onTapUp: (TapUpDetails details) => setState(() {
-          _isPressed = false;
-        }),
-        // TODO(mattcarroll): Cancel is currently triggered when user moves past slop instead of off button: https://github.com/flutter/flutter/issues/19783
-        onTapCancel: () => setState(() => _isPressed = false),
-        child: widget.child,
+      child: new MergeSemantics(
+        // TODO(mattcarroll): Button press dynamics need overhaul for iOS: https://github.com/flutter/flutter/issues/19786
+        child: new GestureDetector(
+          excludeFromSemantics: true,
+          behavior: HitTestBehavior.opaque,
+          onTapDown: (TapDownDetails details) => setState(() {
+            _isPressed = true;
+          }),
+          onTapUp: (TapUpDetails details) => setState(() {
+            _isPressed = false;
+          }),
+          // TODO(mattcarroll): Cancel is currently triggered when user moves past slop instead of off button: https://github.com/flutter/flutter/issues/19783
+          onTapCancel: () => setState(() => _isPressed = false),
+          child: widget.child,
+        ),
       ),
     );
   }
@@ -1091,12 +1103,16 @@ class CupertinoDialogAction extends StatelessWidget {
             constraints: new BoxConstraints(
               maxWidth: fontSizeRatio * (dialogWidth - (2 * padding)),
             ),
-            child: new DefaultTextStyle(
-              style: textStyle,
-              textAlign: TextAlign.center,
-              overflow: TextOverflow.ellipsis,
-              maxLines: 1,
-              child: content,
+            child: new Semantics(
+              button: true,
+              onTap: onPressed,
+              child: new DefaultTextStyle(
+                style: textStyle,
+                textAlign: TextAlign.center,
+                overflow: TextOverflow.ellipsis,
+                maxLines: 1,
+                child: content,
+              ),
             ),
           ),
         ),
@@ -1149,6 +1165,7 @@ class CupertinoDialogAction extends StatelessWidget {
         );
 
     return new GestureDetector(
+      excludeFromSemantics: true,
       onTap: onPressed,
       behavior: HitTestBehavior.opaque,
       child: new ConstrainedBox(

packages/flutter/lib/src/cupertino/localizations.dart

@@ -80,6 +80,9 @@ abstract class CupertinoLocalizations {
   /// The abbreviation for post meridiem (after noon) shown in the time picker.
   String get postMeridiemAbbreviation;
 
+  /// The term used by the system to announce dialog alerts.
+  String get alertDialogLabel;
+
   /// Hour that is shown in [CupertinoCountdownTimerPicker] corresponding to
   /// the given hour value.
   ///
@@ -232,6 +235,9 @@ class DefaultCupertinoLocalizations implements CupertinoLocalizations {
   @override
   String get postMeridiemAbbreviation => 'PM';
 
+  @override
+  String get alertDialogLabel => 'Alert';
+
   @override
   String timerPickerHour(int hour) => hour.toString();
 

packages/flutter/test/cupertino/dialog_test.dart

@@ -10,6 +10,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
+import '../widgets/semantics_tester.dart';
 
 void main() {
   testWidgets('Alert dialog control test', (WidgetTester tester) async {
@@ -63,6 +64,68 @@ void main() {
     expect(widget.style.color.alpha, lessThan(255));
   });
 
+  testWidgets('Has semantic annotations', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+    await tester.pumpWidget(MaterialApp(home: const Material(
+      child: CupertinoAlertDialog(
+        title: Text('The Title'),
+        content: Text('Content'),
+        actions: <Widget>[
+          CupertinoDialogAction(child: Text('Cancel')),
+          CupertinoDialogAction(child: Text('OK')),
+        ],
+      )
+    )));
+
+    expect(
+      semantics,
+      hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics(
+            children: <TestSemantics>[
+              new TestSemantics(
+                flags: <SemanticsFlag>[SemanticsFlag.scopesRoute],
+                children: <TestSemantics>[
+                  new TestSemantics(
+                    flags: <SemanticsFlag>[SemanticsFlag.scopesRoute, SemanticsFlag.namesRoute],
+                    label: 'Alert',
+                    children: <TestSemantics>[
+                      new TestSemantics(
+                        children: <TestSemantics>[
+                          new TestSemantics(label: 'The Title'),
+                          new TestSemantics(label: 'Content'),
+                        ],
+                      ),
+                      new TestSemantics(
+                        children: <TestSemantics>[
+                          new TestSemantics(
+                            flags: <SemanticsFlag>[SemanticsFlag.isButton],
+                            label: 'Cancel',
+                          ),
+                          new TestSemantics(
+                            flags: <SemanticsFlag>[SemanticsFlag.isButton],
+                            label: 'OK',
+                          ),
+                        ],
+                      ),
+                    ],
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ],
+      ),
+      ignoreId: true,
+      ignoreRect: true,
+      ignoreTransform: true,
+    )
+  );
+
+    semantics.dispose();
+  });
+
   testWidgets('Dialog default action styles', (WidgetTester tester) async {
     await tester.pumpWidget(boilerplate(const CupertinoDialogAction(
       isDefaultAction: true,