Make sure modal BottomSheets routes are identified as dialog routes (#21075)

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

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
@@ -141,6 +142,7 @@ class _BottomSheetState extends State<BottomSheet> {
       onVerticalDragUpdate: _handleDragUpdate,
       onVerticalDragEnd: _handleDragEnd,
       child: bottomSheet,
+      excludeFromSemantics: true,
     );
   }
 }
@@ -190,20 +192,43 @@ class _ModalBottomSheet<T> extends StatefulWidget {
 class _ModalBottomSheetState<T> extends State<_ModalBottomSheet<T>> {
   @override
   Widget build(BuildContext context) {
+    final MediaQueryData mediaQuery = MediaQuery.of(context);
+    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
+    String routeLabel;
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.iOS:
+        routeLabel = '';
+        break;
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        routeLabel = localizations.dialogLabel;
+        break;
+    }
+
     return new GestureDetector(
+      excludeFromSemantics: true,
       onTap: () => Navigator.pop(context),
       child: new AnimatedBuilder(
         animation: widget.route.animation,
         builder: (BuildContext context, Widget child) {
-          return new ClipRect(
-            child: new CustomSingleChildLayout(
-              delegate: new _ModalBottomSheetLayout(widget.route.animation.value),
-              child: new BottomSheet(
-                animationController: widget.route._animationController,
-                onClosing: () => Navigator.pop(context),
-                builder: widget.route.builder
-              )
-            )
+          // Disable the initial animation when accessible navigation is on so
+          // that the semantics are added to the tree at the correct time.
+          final double animationValue = mediaQuery.accessibleNavigation ? 1.0 : widget.route.animation.value;
+          return new Semantics(
+            scopesRoute: true,
+            namesRoute: true,
+            label: routeLabel,
+            explicitChildNodes: true,
+            child: new ClipRect(
+              child: new CustomSingleChildLayout(
+                delegate: new _ModalBottomSheetLayout(animationValue),
+                child: new BottomSheet(
+                  animationController: widget.route._animationController,
+                  onClosing: () => Navigator.pop(context),
+                  builder: widget.route.builder,
+                ),
+              ),
+            ),
           );
         }
       )

packages/flutter/test/material/modal_bottom_sheet_test.dart

@@ -7,6 +7,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter/gestures.dart';
 
+import '../widgets/semantics_tester.dart';
+
 void main() {
   testWidgets('Verify that a tap dismisses a modal BottomSheet', (WidgetTester tester) async {
     BuildContext savedContext;
@@ -203,4 +205,50 @@ void main() {
       const EdgeInsets.only(left: 50.0, right: 50.0, bottom: 50.0),
     );
   });
+
+  testWidgets('modal BottomSheet has semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+    final GlobalKey<ScaffoldState> scaffoldKey = new GlobalKey<ScaffoldState>();
+
+    await tester.pumpWidget(new MaterialApp(
+      home: new Scaffold(
+        key: scaffoldKey,
+        body: const Center(child: Text('body'))
+      )
+    ));
+
+
+    showModalBottomSheet<void>(context: scaffoldKey.currentContext, builder: (BuildContext context) {
+      return new Container(
+        child: const Text('BottomSheet')
+      );
+    });
+
+    await tester.pump(); // bottom sheet show animation starts
+    await tester.pump(const Duration(seconds: 1)); // animation done
+
+    expect(semantics, hasSemantics(new TestSemantics.root(
+      children: <TestSemantics>[
+        new TestSemantics.rootChild(
+          children: <TestSemantics>[
+            new TestSemantics(
+              label: 'Dialog',
+              textDirection: TextDirection.ltr,
+              flags: <SemanticsFlag>[
+                SemanticsFlag.scopesRoute,
+                SemanticsFlag.namesRoute,
+              ],
+              children: <TestSemantics>[
+                new TestSemantics(
+                  label: 'BottomSheet',
+                  textDirection: TextDirection.ltr,
+                ),
+              ],
+            ),
+          ],
+        ),
+      ],
+    ), ignoreTransform: true, ignoreRect: true, ignoreId: true));
+    semantics.dispose();
+  });
 }