Add an isButton flag to the Semantic widget,use it for MaterialButton (#12657)

https://github.com/flutter/flutter/issues/11992

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

@@ -330,7 +330,7 @@ class _MaterialButtonState extends State<MaterialButton> {
           child: new Center(
             widthFactor: 1.0,
             heightFactor: 1.0,
-            child: widget.child
+            child: new Semantics(button: true, child: widget.child),
           )
         )
       )

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -3175,6 +3175,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     bool explicitChildNodes,
     bool checked,
     bool selected,
+    bool button,
     String label,
     TextDirection textDirection,
   }) : assert(container != null),
@@ -3182,6 +3183,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
        _explicitChildNodes = explicitChildNodes,
        _checked = checked,
        _selected = selected,
+       _button = button,
        _label = label,
        _textDirection = textDirection,
        super(child);
@@ -3260,6 +3262,17 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     markNeedsSemanticsUpdate(onlyLocalUpdates: (value != null) == hadValue);
   }
 
+  /// If non-null, sets the [SemanticsNode.isButton] semantic to the given value.
+  bool get button => _button;
+  bool _button;
+  set button(bool value) {
+    if (button == value)
+      return;
+    final bool hadValue = button != null;
+    _button = value;
+    markNeedsSemanticsUpdate(onlyLocalUpdates: (value != null) == hadValue);
+  }
+
   /// If non-null, sets the [SemanticsNode.textDirection] semantic to the given value.
   ///
   /// This must not be null if [label] is not null.
@@ -3286,6 +3299,8 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
       config.label = label;
     if (textDirection != null)
       config.textDirection = textDirection;
+    if (button != null)
+      config.isButton = button;
   }
 }
 

packages/flutter/lib/src/rendering/semantics.dart

@@ -680,6 +680,7 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
       properties.add(new FlagProperty('isChecked', value: _hasFlag(SemanticsFlags.isChecked), ifTrue: 'checked', ifFalse: 'unchecked'));
     properties.add(new FlagProperty('isSelected', value: _hasFlag(SemanticsFlags.isSelected), ifTrue: 'selected'));
     properties.add(new StringProperty('label', _label, defaultValue: ''));
+    properties.add(new FlagProperty('isButton', value: _hasFlag(SemanticsFlags.isButton), ifTrue: 'button'));
     properties.add(new EnumProperty<TextDirection>('textDirection', _textDirection, defaultValue: null));
   }
 
@@ -1045,6 +1046,11 @@ class SemanticsConfiguration {
     _setFlag(SemanticsFlags.isChecked, value);
   }
 
+  /// Whether the owning [RenderObject] is a button (true) or not (false).
+  set isButton(bool value) {
+    _setFlag(SemanticsFlags.isButton, value);
+  }
+
   // TAGS
 
   Iterable<SemanticsTag> get tagsForChildren => _tagsForChildren;

packages/flutter/lib/src/widgets/basic.dart

@@ -4451,6 +4451,7 @@ class Semantics extends SingleChildRenderObjectWidget {
     this.explicitChildNodes: false,
     this.checked,
     this.selected,
+    this.button,
     this.label,
     this.textDirection,
   }) : assert(container != null),
@@ -4491,6 +4492,12 @@ class Semantics extends SingleChildRenderObjectWidget {
   /// all other tabs are unselected.
   final bool selected;
 
+  /// If non-null, indicates that this subtree represents a button.
+  ///
+  /// TalkBack/VoiceOver provides users with the hint "button" when a button
+  /// is focused.
+  final bool button;
+
   /// Provides a textual description of the widget.
   ///
   /// If a label is provided, there must either by an ambient [Directionality]
@@ -4514,6 +4521,7 @@ class Semantics extends SingleChildRenderObjectWidget {
       checked: checked,
       selected: selected,
       label: label,
+      button: button,
       textDirection: _getTextDirection(context),
     );
   }

packages/flutter/test/material/buttons_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' show SemanticsFlags;
+
 import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
@@ -31,14 +33,49 @@ void main() {
       new TestSemantics.root(
         children: <TestSemantics>[
           new TestSemantics.rootChild(
-            id: 1,
             actions: SemanticsAction.tap.index,
             label: 'ABC',
             rect: new Rect.fromLTRB(0.0, 0.0, 88.0, 36.0),
-            transform: new Matrix4.translationValues(356.0, 282.0, 0.0)
+            transform: new Matrix4.translationValues(356.0, 282.0, 0.0),
+            flags: SemanticsFlags.isButton.index,
+          )
+        ],
+      ),
+      ignoreId: true,
+    ));
+
+    semantics.dispose();
+  });
+
+  testWidgets('Does RaisedButton contribute semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Material(
+          child: new Center(
+            child: new RaisedButton(
+              onPressed: () { },
+              child: const Text('ABC')
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics.rootChild(
+            actions: SemanticsAction.tap.index,
+            label: 'ABC',
+            rect: new Rect.fromLTRB(0.0, 0.0, 88.0, 36.0),
+            transform: new Matrix4.translationValues(356.0, 282.0, 0.0),
+            flags: SemanticsFlags.isButton.index,
           )
         ]
-      )
+      ),
+      ignoreId: true,
     ));
 
     semantics.dispose();

packages/flutter/test/material/card_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' show SemanticsFlags;
+
 import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
@@ -47,6 +49,7 @@ void main() {
                 label: 'Button',
                 textDirection: TextDirection.ltr,
                 actions: SemanticsAction.tap.index,
+                flags: SemanticsFlags.isButton.index,
               ),
             ],
           ),

packages/flutter/test/rendering/semantics_test.dart

@@ -198,7 +198,7 @@ void main() {
 
     expect(
       minimalProperties.toStringDeep(minLevel: DiagnosticLevel.hidden),
-      'SemanticsNode#16(owner: null, isPartOfNodeMerging: false, Rect.fromLTRB(0.0, 0.0, 0.0, 0.0), wasAffectedByClip: false, actions: [], isSelected: false, label: "", textDirection: null)\n',
+      'SemanticsNode#16(owner: null, isPartOfNodeMerging: false, Rect.fromLTRB(0.0, 0.0, 0.0, 0.0), wasAffectedByClip: false, actions: [], isSelected: false, label: "", isButton: false, textDirection: null)\n',
     );
 
     final SemanticsConfiguration config = new SemanticsConfiguration()
@@ -208,6 +208,7 @@ void main() {
       ..addAction(SemanticsAction.showOnScreen, () { })
       ..isChecked = false
       ..isSelected = true
+      ..isButton = true
       ..label = 'Use all the properties'
       ..textDirection = TextDirection.rtl;
     final SemanticsNode allProperties = new SemanticsNode()
@@ -217,11 +218,11 @@ void main() {
       ..updateWith(config: config, childrenInInversePaintOrder: null);
     expect(
       allProperties.toStringDeep(),
-      'SemanticsNode#17(STALE, owner: null, leaf merge, Rect.fromLTRB(60.0, 20.0, 80.0, 50.0), clipped, actions: [longPress, scrollUp, showOnScreen], unchecked, selected, label: "Use all the properties", textDirection: rtl)\n',
+      'SemanticsNode#17(STALE, owner: null, leaf merge, Rect.fromLTRB(60.0, 20.0, 80.0, 50.0), clipped, actions: [longPress, scrollUp, showOnScreen], unchecked, selected, label: "Use all the properties", button, textDirection: rtl)\n',
     );
     expect(
       allProperties.getSemanticsData().toString(),
-      'SemanticsData(Rect.fromLTRB(50.0, 10.0, 70.0, 40.0), [1.0,0.0,0.0,10.0; 0.0,1.0,0.0,10.0; 0.0,0.0,1.0,0.0; 0.0,0.0,0.0,1.0], actions: [longPress, scrollUp, showOnScreen], flags: [hasCheckedState, isSelected], label: "Use all the properties", textDirection: rtl)',
+      'SemanticsData(Rect.fromLTRB(50.0, 10.0, 70.0, 40.0), [1.0,0.0,0.0,10.0; 0.0,1.0,0.0,10.0; 0.0,0.0,1.0,0.0; 0.0,0.0,0.0,1.0], actions: [longPress, scrollUp, showOnScreen], flags: [hasCheckedState, isSelected, isButton], label: "Use all the properties", textDirection: rtl)',
     );
 
     final SemanticsNode scaled = new SemanticsNode()