Allow for cupertino modal popups to be dismissed with semantics (#48915)

examples/flutter_gallery/lib/demo/cupertino/cupertino_picker_demo.dart

@@ -108,6 +108,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
       onTap: () async {
         await showCupertinoModalPopup<void>(
           context: context,
+          semanticsDismissible: true,
           builder: (BuildContext context) {
             return _BottomPicker(
               child: CupertinoPicker(
@@ -144,6 +145,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
       onTap: () {
         showCupertinoModalPopup<void>(
           context: context,
+          semanticsDismissible: true,
           builder: (BuildContext context) {
             return _BottomPicker(
               child: CupertinoTimerPicker(
@@ -176,6 +178,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
       onTap: () {
         showCupertinoModalPopup<void>(
           context: context,
+          semanticsDismissible: true,
           builder: (BuildContext context) {
             return _BottomPicker(
               child: CupertinoDatePicker(
@@ -207,6 +210,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
       onTap: () {
         showCupertinoModalPopup<void>(
           context: context,
+          semanticsDismissible: true,
           builder: (BuildContext context) {
             return _BottomPicker(
               child: CupertinoDatePicker(
@@ -238,6 +242,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
       onTap: () {
         showCupertinoModalPopup<void>(
           context: context,
+          semanticsDismissible: true,
           builder: (BuildContext context) {
             return _BottomPicker(
               child: CupertinoDatePicker(

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

@@ -35,7 +35,8 @@ const double _kOverAndUnderCenterOpacity = 0.447;
 /// that child the initially selected child.
 ///
 /// Can be used with [showCupertinoModalPopup] to display the picker modally at the
-/// bottom of the screen.
+/// bottom of the screen. When calling [showCupertinoModalPopup], be sure to set
+/// `semanticsDismissible` to true to enable dismissing the modal via semantics.
 ///
 /// Sizes itself to its parent. All children are sized to the same size based
 /// on [itemExtent].

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

@@ -792,14 +792,18 @@ class _CupertinoModalPopupRoute<T> extends PopupRoute<T> {
     this.barrierColor,
     this.barrierLabel,
     this.builder,
+    bool semanticsDismissible,
     ImageFilter filter,
     RouteSettings settings,
   }) : super(
          filter: filter,
          settings: settings,
-       );
+       ) {
+    _semanticsDismissible = semanticsDismissible;
+  }
 
   final WidgetBuilder builder;
+  bool _semanticsDismissible;
 
   @override
   final String barrierLabel;
@@ -811,7 +815,7 @@ class _CupertinoModalPopupRoute<T> extends PopupRoute<T> {
   bool get barrierDismissible => true;
 
   @override
-  bool get semanticsDismissible => false;
+  bool get semanticsDismissible => _semanticsDismissible ?? false;
 
   @override
   Duration get transitionDuration => _kModalPopupTransitionDuration;
@@ -871,6 +875,9 @@ class _CupertinoModalPopupRoute<T> extends PopupRoute<T> {
 /// popup to the [Navigator] furthest from or nearest to the given `context`. It
 /// is `false` by default.
 ///
+/// The `semanticsDismissble` argument is used to determine whether the
+/// semantics of the modal barrier are included in the semantics tree.
+///
 /// The `builder` argument typically builds a [CupertinoActionSheet] widget.
 /// Content below the widget is dimmed with a [ModalBarrier]. The widget built
 /// by the `builder` does not share a context with the location that
@@ -891,6 +898,7 @@ Future<T> showCupertinoModalPopup<T>({
   @required WidgetBuilder builder,
   ImageFilter filter,
   bool useRootNavigator = true,
+  bool semanticsDismissible,
 }) {
   assert(useRootNavigator != null);
   return Navigator.of(context, rootNavigator: useRootNavigator).push(
@@ -899,6 +907,7 @@ Future<T> showCupertinoModalPopup<T>({
       barrierLabel: 'Dismiss',
       builder: builder,
       filter: filter,
+      semanticsDismissible: semanticsDismissible,
     ),
   );
 }

packages/flutter/test/cupertino/route_test.dart

@@ -3,11 +3,14 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import 'package:mockito/mockito.dart';
 
+import '../widgets/semantics_tester.dart';
+
 void main() {
   MockNavigatorObserver navigatorObserver;
 
@@ -1052,6 +1055,75 @@ void main() {
     expect(rootObserver.dialogCount, 0);
     expect(nestedObserver.dialogCount, 1);
   });
+
+  testWidgets('showCupertinoModalPopup does not allow for semantics dismiss by default', (WidgetTester tester) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    final SemanticsTester semantics = SemanticsTester(tester);
+    await tester.pumpWidget(CupertinoApp(
+      home: Navigator(
+        onGenerateRoute: (RouteSettings settings) {
+          return PageRouteBuilder<dynamic>(
+            pageBuilder: (BuildContext context, Animation<double> _, Animation<double> __) {
+              return GestureDetector(
+                onTap: () async {
+                  await showCupertinoModalPopup<void>(
+                    context: context,
+                    builder: (BuildContext context) => const SizedBox(),
+                  );
+                },
+                child: const Text('tap'),
+              );
+            },
+          );
+        },
+      ),
+    ));
+
+    // Push the route.
+    await tester.tap(find.text('tap'));
+    await tester.pumpAndSettle();
+
+    expect(semantics, isNot(includesNodeWith(
+      actions: <SemanticsAction>[SemanticsAction.tap],
+      label: 'Dismiss',
+    )));
+    debugDefaultTargetPlatformOverride = null;
+  });
+
+  testWidgets('showCupertinoModalPopup allows for semantics dismiss when set', (WidgetTester tester) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    final SemanticsTester semantics = SemanticsTester(tester);
+    await tester.pumpWidget(CupertinoApp(
+      home: Navigator(
+        onGenerateRoute: (RouteSettings settings) {
+          return PageRouteBuilder<dynamic>(
+            pageBuilder: (BuildContext context, Animation<double> _, Animation<double> __) {
+              return GestureDetector(
+                onTap: () async {
+                  await showCupertinoModalPopup<void>(
+                    context: context,
+                    semanticsDismissible: true,
+                    builder: (BuildContext context) => const SizedBox(),
+                  );
+                },
+                child: const Text('tap'),
+              );
+            },
+          );
+        },
+      ),
+    ));
+
+    // Push the route.
+    await tester.tap(find.text('tap'));
+    await tester.pumpAndSettle();
+
+    expect(semantics, includesNodeWith(
+      actions: <SemanticsAction>[SemanticsAction.tap],
+      label: 'Dismiss',
+    ));
+    debugDefaultTargetPlatformOverride = null;
+  });
 }
 
 class MockNavigatorObserver extends Mock implements NavigatorObserver {}