Remove semantics boundary from gesture detector AND MORE (#13983)

`RenderSemanticsGestureHandler` is no longer a semantics boundary, which allows us to correctly mark disabled buttons as disabled without having their semantics size and semantics node id change unexpectedly.

Fixes https://github.com/flutter/flutter/issues/12589.
Fixes https://github.com/flutter/flutter/issues/11991.
See also https://github.com/flutter/flutter/issues/11993.

This change also required some refactoring to how we deal with `twoPaneSemantics` scrolling as it previously relied on `RenderSemanticsGestureHandler` being a semantics boundary. This should also make the underlying logic easier to understand.

In addition, the following minor changes are included in this PR:
* Removal of orphaned and unused `SemanticsConfiguration.isMergingDescendantsIntoOneNode`.
* Logic optimizations for `markNeedsSemanticsUpdate` .
* Fix for edge case where `MergeSemantics` failed to merge semantics.
* Use of emojis to better indicate leaf merging in the printed semantics tree.
* Better assert message for adding invisible child semantics nodes.
* Make some semantics tests robuster by not relying on creation order of SemanticsNode ids across test boundaries.

Fixes https://github.com/flutter/flutter/issues/13943.

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

@@ -332,7 +332,7 @@ class _MaterialButtonState extends State<MaterialButton> {
           child: new Center(
             widthFactor: 1.0,
             heightFactor: 1.0,
-            child: new Semantics(button: true, child: widget.child),
+            child: widget.child,
           )
         )
       )
@@ -352,12 +352,17 @@ class _MaterialButtonState extends State<MaterialButton> {
         child: contents
       );
     }
-    return new ConstrainedBox(
+    return new Semantics(
+      container: true,
+      button: true,
+      enabled: widget.enabled,
+      child: new ConstrainedBox(
         constraints: new BoxConstraints(
           minWidth: widget.minWidth ?? buttonTheme.minWidth,
           minHeight: height,
         ),
         child: contents
+      ),
     );
   }
 }

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

@@ -2243,7 +2243,7 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
     // RenderObject are still up-to date. Therefore, we will later only rebuild
     // the semantics subtree starting at th identified semantics boundary.
 
-    final bool wasSemanticsBoundary = _cachedSemanticsConfiguration?.isSemanticBoundary == true;
+    final bool wasSemanticsBoundary = _semantics != null && _cachedSemanticsConfiguration?.isSemanticBoundary == true;
     _cachedSemanticsConfiguration = null;
     bool isEffectiveSemanticsBoundary = _semanticsConfiguration.isSemanticBoundary && wasSemanticsBoundary;
     RenderObject node = this;
@@ -2254,7 +2254,6 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
       node._needsSemanticsUpdate = true;
 
       node = node.parent;
-      node._cachedSemanticsConfiguration = null;
       isEffectiveSemanticsBoundary = node._semanticsConfiguration.isSemanticBoundary;
       if (isEffectiveSemanticsBoundary && node._semantics == null) {
         // We have reached a semantics boundary that doesn't own a semantics node.
@@ -2274,10 +2273,6 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
       owner._nodesNeedingSemantics.remove(this);
     }
     if (!node._needsSemanticsUpdate) {
-      if (node != this) {
-        // Reset for `this` happened above already.
-        node._cachedSemanticsConfiguration = null;
-      }
       node._needsSemanticsUpdate = true;
       if (owner != null) {
         assert(node._semanticsConfiguration.isSemanticBoundary || node.parent is! RenderObject);

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

@@ -2565,37 +2565,6 @@ class RenderSemanticsGestureHandler extends RenderProxyBox {
        _onVerticalDragUpdate = onVerticalDragUpdate,
        super(child);
 
-  /// When a [SemanticsNode] that is a direct child of this object's
-  /// [SemanticsNode] is tagged with [excludeFromScrolling] it will not be
-  /// part of the scrolling area for semantic purposes.
-  ///
-  /// This behavior is only active if the [SemanticsNode] of this
-  /// [RenderSemanticsGestureHandler] is tagged with [useTwoPaneSemantics].
-  /// Otherwise, the [excludeFromScrolling] tag is ignored.
-  ///
-  /// As an example, a [RenderSliver] that stays on the screen within a
-  /// [Scrollable] even though the user has scrolled past it (e.g. a pinned app
-  /// bar) can tag its [SemanticsNode] with [excludeFromScrolling] to indicate
-  /// that it should no longer be considered for semantic actions related to
-  /// scrolling.
-  static const SemanticsTag excludeFromScrolling = const SemanticsTag('RenderSemanticsGestureHandler.excludeFromScrolling');
-
-  /// If the [SemanticsNode] of this [RenderSemanticsGestureHandler] is tagged
-  /// with [useTwoPaneSemantics], two semantics nodes will be used to represent
-  /// this render object in the semantics tree.
-  ///
-  /// Two semantics nodes are necessary to exclude certain child nodes (via the
-  /// [excludeFromScrolling] tag) from the scrollable area for semantic
-  /// purposes.
-  ///
-  /// If this tag is used, the first "outer" semantics node is the regular node
-  /// of this object. The second "inner" node is introduced as a child to that
-  /// node. All scrollable children become children of the inner node, which has
-  /// the semantic scrolling logic enabled. All children that have been
-  /// excluded from scrolling with [excludeFromScrolling] are turned into
-  /// children of the outer node.
-  static const SemanticsTag useTwoPaneSemantics = const SemanticsTag('RenderSemanticsGestureHandler.twoPane');
-
   /// If non-null, the set of actions to allow. Other actions will be omitted,
   /// even if their callback is provided.
   ///
@@ -2673,24 +2642,10 @@ class RenderSemanticsGestureHandler extends RenderProxyBox {
   /// leftwards drag.
   double scrollFactor;
 
-  bool get _hasHandlers {
-    return onTap != null
-        || onLongPress != null
-        || onHorizontalDragUpdate != null
-        || onVerticalDragUpdate != null;
-  }
-
   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
 
-    config.isSemanticBoundary = _hasHandlers;
-
-    // TODO(goderbauer): this needs to be set even when there is only potential
-    //    for this to become a scroll view.
-    config.explicitChildNodes = onHorizontalDragUpdate != null
-        || onVerticalDragUpdate != null;
-
     if (onTap != null && _isValidAction(SemanticsAction.tap))
       config.onTap = onTap;
     if (onLongPress != null && _isValidAction(SemanticsAction.longPress))
@@ -2713,42 +2668,6 @@ class RenderSemanticsGestureHandler extends RenderProxyBox {
     return validActions == null || validActions.contains(action);
   }
 
-  SemanticsNode _innerNode;
-  SemanticsNode _annotatedNode;
-
-  /// Sends a [SemanticsEvent] in the context of the [SemanticsNode] that is
-  /// annotated with this object's semantics information.
-  void sendSemanticsEvent(SemanticsEvent event) {
-    _annotatedNode?.sendEvent(event);
-  }
-
-  @override
-  void assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) {
-    if (children.isEmpty || !children.first.isTagged(useTwoPaneSemantics)) {
-      _annotatedNode = node;
-      super.assembleSemanticsNode(node, config, children);
-      return;
-    }
-
-    _innerNode ??= new SemanticsNode(showOnScreen: showOnScreen);
-    _innerNode
-      ..isMergedIntoParent = node.isPartOfNodeMerging
-      ..rect = Offset.zero & node.rect.size;
-    _annotatedNode = _innerNode;
-
-    final List<SemanticsNode> excluded = <SemanticsNode>[_innerNode];
-    final List<SemanticsNode> included = <SemanticsNode>[];
-    for (SemanticsNode child in children) {
-      assert(child.isTagged(useTwoPaneSemantics));
-      if (child.isTagged(excludeFromScrolling))
-        excluded.add(child);
-      else
-        included.add(child);
-    }
-    node.updateWith(config: null, childrenInInversePaintOrder: excluded);
-    _innerNode.updateWith(config: config, childrenInInversePaintOrder: included);
-  }
-
   void _performSemanticScrollLeft() {
     if (onHorizontalDragUpdate != null) {
       final double primaryDelta = size.width * -scrollFactor;

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

@@ -14,8 +14,8 @@ import 'package:vector_math/vector_math_64.dart';
 import 'binding.dart';
 import 'box.dart';
 import 'object.dart';
-import 'proxy_box.dart';
 import 'sliver.dart';
+import 'viewport.dart';
 import 'viewport_offset.dart';
 
 /// A base class for slivers that have a [RenderBox] child which scrolls
@@ -225,7 +225,7 @@ abstract class RenderSliverPersistentHeader extends RenderSliver with RenderObje
     super.describeSemanticsConfiguration(config);
 
     if (_excludeFromSemanticsScrolling)
-      config.addTagForChildren(RenderSemanticsGestureHandler.excludeFromScrolling);
+      config.addTagForChildren(RenderViewport.excludeFromScrolling);
   }
 
   @override

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

@@ -12,7 +12,6 @@ import 'package:vector_math/vector_math_64.dart';
 import 'binding.dart';
 import 'box.dart';
 import 'object.dart';
-import 'proxy_box.dart';
 import 'sliver.dart';
 import 'viewport_offset.dart';
 
@@ -91,12 +90,11 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
        _crossAxisDirection = crossAxisDirection,
        _offset = offset;
 
-
   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
 
-    config.addTagForChildren(RenderSemanticsGestureHandler.useTwoPaneSemantics);
+    config.addTagForChildren(RenderViewport.useTwoPaneSemantics);
   }
 
   @override
@@ -746,6 +744,36 @@ class RenderViewport extends RenderViewportBase<SliverPhysicalContainerParentDat
       _center = firstChild;
   }
 
+  /// If a [RenderAbstractViewport] overrides
+  /// [RenderObject.describeSemanticsConfiguration] to add the [SemanticsTag]
+  /// [useTwoPaneSemantics] to its [SemanticsConfiguration], two semantics nodes
+  /// will be used to represent the viewport with its associated scrolling
+  /// actions in the semantics tree.
+  ///
+  /// Two semantics nodes (an inner and an outer node) are necessary to exclude
+  /// certain child nodes (via the [excludeFromScrolling] tag) from the
+  /// scrollable area for semantic purposes: The [SemanticsNode]s of children
+  /// that should be excluded from scrolling will be attached to the outer node.
+  /// The semantic scrolling actions and the [SemanticsNode]s of scrollable
+  /// children will be attached to the inner node, which itself is a child of
+  /// the outer node.
+  static const SemanticsTag useTwoPaneSemantics = const SemanticsTag('RenderViewport.twoPane');
+
+  /// When a top-level [SemanticsNode] below a [RenderAbstractViewport] is
+  /// tagged with [excludeFromScrolling] it will not be part of the scrolling
+  /// area for semantic purposes.
+  ///
+  /// This behavior is only active if the [RenderAbstractViewport]
+  /// tagged its [SemanticsConfiguration] with [useTwoPaneSemantics].
+  /// Otherwise, the [excludeFromScrolling] tag is ignored.
+  ///
+  /// As an example, a [RenderSliver] that stays on the screen within a
+  /// [Scrollable] even though the user has scrolled past it (e.g. a pinned app
+  /// bar) can tag its [SemanticsNode] with [excludeFromScrolling] to indicate
+  /// that it should no longer be considered for semantic actions related to
+  /// scrolling.
+  static const SemanticsTag excludeFromScrolling = const SemanticsTag('RenderViewport.excludeFromScrolling');
+
   @override
   void setupParentData(RenderObject child) {
     if (child.parentData is! SliverPhysicalContainerParentData)

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

@@ -654,6 +654,7 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
           );
         }
       }
+      assert(!newChildren.any((SemanticsNode node) => node.isMergedIntoParent) || isPartOfNodeMerging);
 
       _debugPreviousSnapshot = new List<SemanticsNode>.from(newChildren);
 
@@ -677,7 +678,7 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
     }
     if (newChildren != null) {
       for (SemanticsNode child in newChildren) {
-        assert(!child.isInvisible, 'Child with id ${child.id} is invisible and should not be added to tree.');
+        assert(!child.isInvisible, '$child is invisible and should not be added as child of $this.');
         child._dead = false;
       }
     }
@@ -1072,7 +1073,8 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
       hideOwner = inDirtyNodes;
     }
     properties.add(new DiagnosticsProperty<SemanticsOwner>('owner', owner, level: hideOwner ? DiagnosticLevel.hidden : DiagnosticLevel.info));
-    properties.add(new FlagProperty('isPartOfNodeMerging', value: isPartOfNodeMerging, ifTrue: 'leaf merge'));
+    properties.add(new FlagProperty('isMergedIntoParent', value: isMergedIntoParent, ifTrue: 'merged up ⬆️'));
+    properties.add(new FlagProperty('mergeAllDescendantsIntoThisNode', value: mergeAllDescendantsIntoThisNode, ifTrue: 'merge boundary ⛔️'));
     final Offset offset = transform != null ? MatrixUtils.getAsTranslation(transform) : null;
     if (offset != null) {
       properties.add(new DiagnosticsProperty<Rect>('rect', rect.shift(offset), showName: false));
@@ -1344,7 +1346,7 @@ class SemanticsConfiguration {
   bool get isSemanticBoundary => _isSemanticBoundary;
   bool _isSemanticBoundary = false;
   set isSemanticBoundary(bool value) {
-    assert(!isMergingDescendantsIntoOneNode || value);
+    assert(!isMergingSemanticsOfDescendants || value);
     _isSemanticBoundary = value;
   }
 
@@ -1380,20 +1382,6 @@ class SemanticsConfiguration {
   /// determine if a node is previous to this one.
   bool isBlockingSemanticsOfPreviouslyPaintedNodes = false;
 
-  /// Whether the semantics information of all descendants should be merged
-  /// into the owning [RenderObject] semantics node.
-  ///
-  /// When this is set to true the [SemanticsNode] of the owning [RenderObject]
-  /// will not have any children.
-  ///
-  /// Setting this to true requires that [isSemanticBoundary] is also true.
-  bool get isMergingDescendantsIntoOneNode => _isMergingDescendantsIntoOneNode;
-  bool _isMergingDescendantsIntoOneNode = false;
-  set isMergingDescendantsIntoOneNode(bool value) {
-    assert(isSemanticBoundary);
-    _isMergingDescendantsIntoOneNode = value;
-  }
-
   // SEMANTIC ANNOTATIONS
   // These will end up on [SemanticNode]s generated from
   // [SemanticsConfiguration]s.
@@ -1645,9 +1633,12 @@ class SemanticsConfiguration {
   /// If set to true, the descendants of the owning [RenderObject]'s
   /// [SemanticsNode] will merge their semantic information into the
   /// [SemanticsNode] representing the owning [RenderObject].
+  ///
+  /// Setting this to true requires that [isSemanticBoundary] is also true.
   bool get isMergingSemanticsOfDescendants => _isMergingSemanticsOfDescendants;
   bool _isMergingSemanticsOfDescendants = false;
   set isMergingSemanticsOfDescendants(bool value) {
+    assert(isSemanticBoundary);
     _isMergingSemanticsOfDescendants = value;
     _hasBeenAnnotated = true;
   }
@@ -1910,9 +1901,11 @@ class SemanticsConfiguration {
   /// Returns an exact copy of this configuration.
   SemanticsConfiguration copy() {
     return new SemanticsConfiguration()
-      ..isSemanticBoundary = isSemanticBoundary
+      .._isSemanticBoundary = _isSemanticBoundary
       ..explicitChildNodes = explicitChildNodes
+      ..isBlockingSemanticsOfPreviouslyPaintedNodes = isBlockingSemanticsOfPreviouslyPaintedNodes
       .._hasBeenAnnotated = _hasBeenAnnotated
+      .._isMergingSemanticsOfDescendants = _isMergingSemanticsOfDescendants
       .._textDirection = _textDirection
       .._label = _label
       .._increasedValue = _increasedValue
@@ -1920,6 +1913,7 @@ class SemanticsConfiguration {
       .._decreasedValue = _decreasedValue
       .._hint = _hint
       .._flags = _flags
+      .._tagsForChildren = _tagsForChildren
       .._actionsAsBits = _actionsAsBits
       .._actions.addAll(_actions);
   }

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

@@ -570,21 +570,6 @@ class RawGestureDetectorState extends State<RawGestureDetector> {
     }
   }
 
-  /// Sends a [SemanticsEvent] in the context of the [SemanticsNode] that is
-  /// annotated with this object's semantics information.
-  ///
-  /// The event can be interpreted by assistive technologies to provide
-  /// additional feedback to the user about the state of the UI.
-  ///
-  /// The event will not be sent if [RawGestureDetector.excludeFromSemantics] is
-  /// set to true.
-  void sendSemanticsEvent(SemanticsEvent event) {
-    if (!widget.excludeFromSemantics) {
-      final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject();
-      semanticsGestureHandler.sendSemanticsEvent(event);
-    }
-  }
-
   @override
   void dispose() {
     for (GestureRecognizer recognizer in _recognizers.values)

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

@@ -281,7 +281,8 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
     if (_semanticsScrollEventScheduled)
       return;
     SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
-      _gestureDetectorKey.currentState?.sendSemanticsEvent(new ScrollCompletedSemanticsEvent(
+      final _RenderExcludableScrollSemantics render = _excludableScrollSemanticsKey.currentContext?.findRenderObject();
+      render?.sendSemanticsEvent(new ScrollCompletedSemanticsEvent(
         axis: position.axis,
         pixels: position.pixels,
         minScrollExtent: position.minScrollExtent,
@@ -332,7 +333,9 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
   }
 
 
-  // SEMANTICS ACTIONS
+  // SEMANTICS
+
+  final GlobalKey _excludableScrollSemanticsKey = new GlobalKey();
 
   @override
   @protected
@@ -487,10 +490,14 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
   Widget build(BuildContext context) {
     assert(position != null);
     // TODO(ianh): Having all these global keys is sad.
-    final Widget result = new RawGestureDetector(
+    final Widget result = new _ExcludableScrollSemantics(
+      key: _excludableScrollSemanticsKey,
+      child: new RawGestureDetector(
         key: _gestureDetectorKey,
         gestures: _gestureRecognizers,
         behavior: HitTestBehavior.opaque,
+        child: new Semantics(
+          explicitChildNodes: true,
           child: new IgnorePointer(
             key: _ignorePointerKey,
             ignoring: _shouldIgnorePointer,
@@ -501,6 +508,8 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
               child: widget.viewportBuilder(context, position),
             ),
           ),
+        ),
+      ),
     );
     return _configuration.buildViewportChrome(context, result, widget.axisDirection);
   }
@@ -511,3 +520,70 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
     description.add(new DiagnosticsProperty<ScrollPosition>('position', position));
   }
 }
+
+/// With [_ExcludableScrollSemantics] certain child [SemanticsNode]s can be
+/// excluded from the scrollable area for semantics purposes.
+///
+/// Nodes, that are to be excluded, have to be tagged with
+/// [RenderViewport.excludeFromScrolling] and the [RenderAbstractViewport] in
+/// use has to add the [RenderViewport.useTwoPaneSemantics] tag to its
+/// [SemanticsConfiguration] by overriding
+/// [RenderObject.describeSemanticsConfiguration].
+///
+/// If the tag [RenderViewport.useTwoPaneSemantics] is present on the viewport,
+/// two semantics nodes will be used to represent the [Scrollable]: The outer
+/// node will contain all children, that are excluded from scrolling. The inner
+/// node, which is annotated with the scrolling actions, will house the
+/// scrollable children.
+class _ExcludableScrollSemantics extends SingleChildRenderObjectWidget {
+  const _ExcludableScrollSemantics({ Key key, Widget child }) : super(key: key, child: child);
+
+  @override
+  _RenderExcludableScrollSemantics createRenderObject(BuildContext context) => new _RenderExcludableScrollSemantics();
+}
+
+class _RenderExcludableScrollSemantics extends RenderProxyBox {
+  _RenderExcludableScrollSemantics({ RenderBox child }) : super(child);
+
+  @override
+  void describeSemanticsConfiguration(SemanticsConfiguration config) {
+    super.describeSemanticsConfiguration(config);
+    config.isSemanticBoundary = true;
+  }
+
+  SemanticsNode _innerNode;
+  SemanticsNode _annotatedNode;
+
+  @override
+  void assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) {
+    if (children.isEmpty || !children.first.isTagged(RenderViewport.useTwoPaneSemantics)) {
+      _annotatedNode = node;
+      super.assembleSemanticsNode(node, config, children);
+      return;
+    }
+
+    _innerNode ??= new SemanticsNode(showOnScreen: showOnScreen);
+    _innerNode
+      ..isMergedIntoParent = node.isPartOfNodeMerging
+      ..rect = Offset.zero & node.rect.size;
+    _annotatedNode = _innerNode;
+
+    final List<SemanticsNode> excluded = <SemanticsNode>[_innerNode];
+    final List<SemanticsNode> included = <SemanticsNode>[];
+    for (SemanticsNode child in children) {
+      assert(child.isTagged(RenderViewport.useTwoPaneSemantics));
+      if (child.isTagged(RenderViewport.excludeFromScrolling))
+        excluded.add(child);
+      else
+        included.add(child);
+    }
+    node.updateWith(config: null, childrenInInversePaintOrder: excluded);
+    _innerNode.updateWith(config: config, childrenInInversePaintOrder: included);
+  }
+
+  /// Sends a [SemanticsEvent] in the context of the [SemanticsNode] that is
+  /// annotated with this object's semantics information.
+  void sendSemanticsEvent(SemanticsEvent event) {
+    _annotatedNode?.sendEvent(event);
+  }
+}

packages/flutter/test/material/buttons_test.dart

@@ -13,6 +13,10 @@ import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 void main() {
+  setUp(() {
+    debugResetSemanticsIdCounter();
+  });
+
   testWidgets('Does FlatButton contribute semantics', (WidgetTester tester) async {
     final SemanticsTester semantics = new SemanticsTester(tester);
     await tester.pumpWidget(
@@ -33,11 +37,17 @@ void main() {
       new TestSemantics.root(
         children: <TestSemantics>[
           new TestSemantics.rootChild(
-            actions: SemanticsAction.tap.index,
+            actions: <SemanticsAction>[
+              SemanticsAction.tap,
+            ],
             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: SemanticsFlag.isButton.index,
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+              SemanticsFlag.isEnabled,
+            ],
           )
         ],
       ),
@@ -67,11 +77,17 @@ void main() {
       new TestSemantics.root(
         children: <TestSemantics>[
           new TestSemantics.rootChild(
-            actions: SemanticsAction.tap.index,
+            actions: <SemanticsAction>[
+              SemanticsAction.tap,
+            ],
             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: SemanticsFlag.isButton.index,
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+              SemanticsFlag.isEnabled,
+            ],
           )
         ]
       ),
@@ -248,4 +264,83 @@ void main() {
     await gesture.up();
   });
 
+  testWidgets('Disabled MaterialButton has same semantic size as enabled and exposes disabled semantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    final Rect expectedButtonSize = new Rect.fromLTRB(0.0, 0.0, 116.0, 36.0);
+    // Button is in center of screen
+    final Matrix4 expectedButtonTransform = new Matrix4.identity()
+      ..translate(
+        TestSemantics.fullScreen.width / 2 - expectedButtonSize.width /2,
+        TestSemantics.fullScreen.height / 2 - expectedButtonSize.height /2,
+      );
+
+    // enabled button
+    await tester.pumpWidget(new Directionality(
+      textDirection: TextDirection.ltr,
+      child: new Material(
+        child: new Center(
+          child: new MaterialButton(
+            child: const Text('Button'),
+            onPressed: () { /* to make sure the button is enabled */ },
+          ),
+        ),
+      ),
+    ));
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics.rootChild(
+            id: 1,
+            rect: expectedButtonSize,
+            transform: expectedButtonTransform,
+            label: 'Button',
+            actions: <SemanticsAction>[
+              SemanticsAction.tap,
+            ],
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+              SemanticsFlag.isEnabled,
+            ],
+          ),
+        ],
+      ),
+    ));
+
+    // disabled button
+    await tester.pumpWidget(const Directionality(
+      textDirection: TextDirection.ltr,
+      child: const Material(
+        child: const Center(
+          child: const MaterialButton(
+            child: const Text('Button'),
+            onPressed: null, // button is disabled
+          ),
+        ),
+      ),
+    ));
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics.rootChild(
+            id: 1,
+            rect: expectedButtonSize,
+            transform: expectedButtonTransform,
+            label: 'Button',
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+            ],
+          ),
+        ],
+      ),
+    ));
+
+
+    semantics.dispose();
+  });
+
 }

packages/flutter/test/material/card_test.dart

@@ -48,8 +48,14 @@ void main() {
                 id: 2,
                 label: 'Button',
                 textDirection: TextDirection.ltr,
-                actions: SemanticsAction.tap.index,
-                flags: SemanticsFlag.isButton.index,
+                actions: <SemanticsAction>[
+                  SemanticsAction.tap,
+                ],
+                flags: <SemanticsFlag>[
+                  SemanticsFlag.isButton,
+                  SemanticsFlag.hasEnabledState,
+                  SemanticsFlag.isEnabled,
+                ],
               ),
             ],
           ),

packages/flutter/test/material/control_list_tile_test.dart

@@ -94,11 +94,11 @@ void main() {
         ],
       ),
     ));
+
     // This test verifies that the label and the control get merged.
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 1,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: null,
           flags: <SemanticsFlag>[
@@ -111,7 +111,6 @@ void main() {
           label: 'aaa\nAAA',
         ),
         new TestSemantics.rootChild(
-          id: 4,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 56.0, 0.0),
           flags: <SemanticsFlag>[
@@ -124,7 +123,6 @@ void main() {
           label: 'bbb\nBBB',
         ),
         new TestSemantics.rootChild(
-          id: 7,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 112.0, 0.0),
           flags: <SemanticsFlag>[
@@ -136,7 +134,7 @@ void main() {
           label: 'CCC\nccc',
         ),
       ],
-    )));
+    ), ignoreId: true));
   });
 
 }

packages/flutter/test/material/date_picker_test.dart

@@ -585,13 +585,21 @@ void _tests() {
             textDirection: TextDirection.ltr,
           ),
           new TestSemantics(
-            flags: <SemanticsFlag>[SemanticsFlag.isButton],
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+              SemanticsFlag.isEnabled,
+            ],
             actions: <SemanticsAction>[SemanticsAction.tap],
             label: r'CANCEL',
             textDirection: TextDirection.ltr,
           ),
           new TestSemantics(
-            flags: <SemanticsFlag>[SemanticsFlag.isButton],
+            flags: <SemanticsFlag>[
+              SemanticsFlag.isButton,
+              SemanticsFlag.hasEnabledState,
+              SemanticsFlag.isEnabled,
+            ],
             actions: <SemanticsAction>[SemanticsAction.tap],
             label: r'OK',
             textDirection: TextDirection.ltr,

packages/flutter/test/material/tabs_test.dart

@@ -165,6 +165,10 @@ class TestScrollPhysics extends ScrollPhysics {
 }
 
 void main() {
+  setUp(() {
+    debugResetSemanticsIdCounter();
+  });
+
   testWidgets('TabBar tap selects tab', (WidgetTester tester) async {
     final List<String> tabs = <String>['A', 'B', 'C'];
 
@@ -1213,6 +1217,10 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 2,
+              rect: TestSemantics.fullScreen,
+              children: <TestSemantics>[
+                new TestSemantics(
+                  id: 3,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'TAB #0\nTab 1 of 2',
@@ -1220,12 +1228,14 @@ void main() {
                   transform: new Matrix4.translationValues(0.0, 276.0, 0.0),
                 ),
                 new TestSemantics(
-              id: 3,
+                  id: 4,
                   actions: SemanticsAction.tap.index,
                   label: 'TAB #1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),
                   transform: new Matrix4.translationValues(108.0, 276.0, 0.0),
                 ),
+              ]
+            )
           ],
         ),
       ],
@@ -1458,11 +1468,15 @@ void main() {
     final TestSemantics expectedSemantics = new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 23,
+          id: 1,
+          rect: TestSemantics.fullScreen,
+          children: <TestSemantics>[
+            new TestSemantics(
+              id: 2,
               rect: TestSemantics.fullScreen,
               children: <TestSemantics>[
                 new TestSemantics(
-              id: 24,
+                  id: 3,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'Semantics override 0\nTab 1 of 2',
@@ -1470,12 +1484,14 @@ void main() {
                   transform: new Matrix4.translationValues(0.0, 276.0, 0.0),
                 ),
                 new TestSemantics(
-              id: 25,
+                  id: 4,
                   actions: SemanticsAction.tap.index,
                   label: 'Semantics override 1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),
                   transform: new Matrix4.translationValues(108.0, 276.0, 0.0),
                 ),
+              ]
+            )
           ],
         ),
       ],

packages/flutter/test/semantics/semantics_test.dart

@@ -11,6 +11,10 @@ import '../rendering/rendering_tester.dart';
 
 
 void main() {
+  setUp(() {
+    debugResetSemanticsIdCounter();
+  });
+
   group('SemanticsNode', () {
     const SemanticsTag tag1 = const SemanticsTag('Tag One');
     const SemanticsTag tag2 = const SemanticsTag('Tag Two');
@@ -45,6 +49,7 @@ void main() {
       tags.add(tag3);
 
       final SemanticsConfiguration config = new SemanticsConfiguration()
+        ..isSemanticBoundary = true
         ..isMergingSemanticsOfDescendants = true;
 
       node.updateWith(
@@ -121,9 +126,9 @@ void main() {
 
     expect(
       root.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversal),
-      'SemanticsNode#8(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
-      '├SemanticsNode#6(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n'
-      '└SemanticsNode#7(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n',
+      'SemanticsNode#3(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
+      '├SemanticsNode#1(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n'
+      '└SemanticsNode#2(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n',
     );
   });
 
@@ -140,16 +145,16 @@ void main() {
     );
     expect(
       root.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversal),
-      'SemanticsNode#11(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 20.0, 5.0))\n'
-      '├SemanticsNode#10(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
-      '└SemanticsNode#9(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n',
+      'SemanticsNode#3(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 20.0, 5.0))\n'
+      '├SemanticsNode#2(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
+      '└SemanticsNode#1(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n',
     );
 
     expect(
       root.toStringDeep(childOrder: DebugSemanticsDumpOrder.inverseHitTest),
-      'SemanticsNode#11(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 20.0, 5.0))\n'
-      '├SemanticsNode#9(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n'
-      '└SemanticsNode#10(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n',
+      'SemanticsNode#3(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 20.0, 5.0))\n'
+      '├SemanticsNode#1(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n'
+      '└SemanticsNode#2(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n',
     );
 
     final SemanticsNode child3 = new SemanticsNode()
@@ -173,22 +178,22 @@ void main() {
 
     expect(
       rootComplex.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversal),
-      'SemanticsNode#15(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 25.0, 5.0))\n'
-      '├SemanticsNode#12(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
-      '│├SemanticsNode#14(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n'
-      '│└SemanticsNode#13(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n'
-      '├SemanticsNode#10(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
-      '└SemanticsNode#9(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n',
+      'SemanticsNode#7(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 25.0, 5.0))\n'
+      '├SemanticsNode#4(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
+      '│├SemanticsNode#6(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n'
+      '│└SemanticsNode#5(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n'
+      '├SemanticsNode#2(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
+      '└SemanticsNode#1(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n',
     );
 
     expect(
       rootComplex.toStringDeep(childOrder: DebugSemanticsDumpOrder.inverseHitTest),
-      'SemanticsNode#15(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 25.0, 5.0))\n'
-      '├SemanticsNode#9(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n'
-      '├SemanticsNode#10(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
-      '└SemanticsNode#12(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
-      ' ├SemanticsNode#13(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n'
-      ' └SemanticsNode#14(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n',
+      'SemanticsNode#7(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 25.0, 5.0))\n'
+      '├SemanticsNode#1(STALE, owner: null, Rect.fromLTRB(15.0, 0.0, 20.0, 5.0))\n'
+      '├SemanticsNode#2(STALE, owner: null, Rect.fromLTRB(10.0, 0.0, 15.0, 5.0))\n'
+      '└SemanticsNode#4(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 10.0, 5.0))\n'
+      ' ├SemanticsNode#5(STALE, owner: null, Rect.fromLTRB(5.0, 0.0, 10.0, 5.0))\n'
+      ' └SemanticsNode#6(STALE, owner: null, Rect.fromLTRB(0.0, 0.0, 5.0, 5.0))\n',
     );
   });
 
@@ -196,15 +201,16 @@ void main() {
     final SemanticsNode minimalProperties = new SemanticsNode();
     expect(
       minimalProperties.toStringDeep(),
-      'SemanticsNode#16(Rect.fromLTRB(0.0, 0.0, 0.0, 0.0))\n',
+      'SemanticsNode#1(Rect.fromLTRB(0.0, 0.0, 0.0, 0.0))\n',
     );
 
     expect(
       minimalProperties.toStringDeep(minLevel: DiagnosticLevel.hidden),
-      'SemanticsNode#16(owner: null, isPartOfNodeMerging: false, Rect.fromLTRB(0.0, 0.0, 0.0, 0.0), actions: [], isSelected: false, isFocused: false, isButton: false, isTextField: false, label: "", value: "", increasedValue: "", decreasedValue: "", hint: "", textDirection: null)\n'
+      'SemanticsNode#1(owner: null, isMergedIntoParent: false, mergeAllDescendantsIntoThisNode: false, Rect.fromLTRB(0.0, 0.0, 0.0, 0.0), actions: [], isSelected: false, isFocused: false, isButton: false, isTextField: false, label: "", value: "", increasedValue: "", decreasedValue: "", hint: "", textDirection: null)\n'
     );
 
     final SemanticsConfiguration config = new SemanticsConfiguration()
+      ..isSemanticBoundary = true
       ..isMergingSemanticsOfDescendants = true
       ..onScrollUp = () { }
       ..onLongPress = () { }
@@ -220,7 +226,7 @@ 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), actions: [longPress, scrollUp, showOnScreen], unchecked, selected, button, label: "Use all the properties", textDirection: rtl)\n',
+      'SemanticsNode#2(STALE, owner: null, merge boundary ⛔️, Rect.fromLTRB(60.0, 20.0, 80.0, 50.0), actions: [longPress, scrollUp, showOnScreen], unchecked, selected, button, label: "Use all the properties", textDirection: rtl)\n',
     );
     expect(
       allProperties.getSemanticsData().toString(),
@@ -232,7 +238,7 @@ void main() {
       ..transform = new Matrix4.diagonal3(new Vector3(10.0, 10.0, 1.0));
     expect(
       scaled.toStringDeep(),
-      'SemanticsNode#18(STALE, owner: null, Rect.fromLTRB(50.0, 10.0, 70.0, 40.0) scaled by 10.0x)\n',
+      'SemanticsNode#3(STALE, owner: null, Rect.fromLTRB(50.0, 10.0, 70.0, 40.0) scaled by 10.0x)\n',
     );
     expect(
       scaled.getSemanticsData().toString(),
@@ -251,7 +257,6 @@ void main() {
     expect(config.isSelected, isFalse);
     expect(config.isBlockingSemanticsOfPreviouslyPaintedNodes, isFalse);
     expect(config.isFocused, isFalse);
-    expect(config.isMergingDescendantsIntoOneNode, isFalse);
     expect(config.isTextField, isFalse);
 
     expect(config.onShowOnScreen, isNull);
@@ -274,7 +279,6 @@ void main() {
     config.isSelected = true;
     config.isBlockingSemanticsOfPreviouslyPaintedNodes = true;
     config.isFocused = true;
-    config.isMergingDescendantsIntoOneNode = true;
     config.isTextField = true;
 
     final VoidCallback onShowOnScreen = () { };
@@ -309,7 +313,6 @@ void main() {
     expect(config.isSelected, isTrue);
     expect(config.isBlockingSemanticsOfPreviouslyPaintedNodes, isTrue);
     expect(config.isFocused, isTrue);
-    expect(config.isMergingDescendantsIntoOneNode, isTrue);
     expect(config.isTextField, isTrue);
 
     expect(config.onShowOnScreen, same(onShowOnScreen));

packages/flutter/test/widgets/keep_alive_test.dart

@@ -220,6 +220,12 @@ void main() {
       '       │ diagnosis: insufficient data to draw conclusion (less than five\n'
       '       │   repaints)\n'
       '       │\n'
+      '       └─child: _RenderExcludableScrollSemantics#00000\n'
+      '         │ parentData: <none> (can use size)\n'
+      '         │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
+      '         │ semantic boundary\n'
+      '         │ size: Size(800.0, 600.0)\n'
+      '         │\n'
       '         └─child: RenderSemanticsGestureHandler#00000\n'
       '           │ parentData: <none> (can use size)\n'
       '           │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
@@ -233,6 +239,11 @@ void main() {
       '             │ behavior: opaque\n'
       '             │ listeners: down\n'
       '             │\n'
+      '             └─child: RenderSemanticsAnnotations#00000\n'
+      '               │ parentData: <none> (can use size)\n'
+      '               │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
+      '               │ size: Size(800.0, 600.0)\n'
+      '               │\n'
       '               └─child: RenderIgnorePointer#00000\n'
       '                 │ parentData: <none> (can use size)\n'
       '                 │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
@@ -324,6 +335,12 @@ void main() {
       '       │ diagnosis: insufficient data to draw conclusion (less than five\n'
       '       │   repaints)\n'
       '       │\n'
+      '       └─child: _RenderExcludableScrollSemantics#00000\n'
+      '         │ parentData: <none> (can use size)\n'
+      '         │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
+      '         │ semantic boundary\n'
+      '         │ size: Size(800.0, 600.0)\n'
+      '         │\n'
       '         └─child: RenderSemanticsGestureHandler#00000\n'
       '           │ parentData: <none> (can use size)\n'
       '           │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
@@ -337,6 +354,11 @@ void main() {
       '             │ behavior: opaque\n'
       '             │ listeners: down\n'
       '             │\n'
+      '             └─child: RenderSemanticsAnnotations#00000\n'
+      '               │ parentData: <none> (can use size)\n'
+      '               │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
+      '               │ size: Size(800.0, 600.0)\n'
+      '               │\n'
       '               └─child: RenderIgnorePointer#00000\n'
       '                 │ parentData: <none> (can use size)\n'
       '                 │ constraints: BoxConstraints(w=800.0, h=600.0)\n'

packages/flutter/test/widgets/modal_barrier_test.dart

@@ -110,7 +110,6 @@ void main() {
     final TestSemantics expectedSemantics = new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
           rect: TestSemantics.fullScreen,
           actions: SemanticsAction.tap.index,
           label: 'Dismiss',
@@ -118,7 +117,7 @@ void main() {
         ),
       ]
     );
-    expect(semantics, hasSemantics(expectedSemantics));
+    expect(semantics, hasSemantics(expectedSemantics, ignoreId: true));
 
     semantics.dispose();
     debugDefaultTargetPlatformOverride = null;

packages/flutter/test/widgets/semantics_merge_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 SemanticsFlag;
+
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -10,6 +12,10 @@ import 'package:flutter_test/flutter_test.dart';
 import 'semantics_tester.dart';
 
 void main() {
+  setUp(() {
+    debugResetSemanticsIdCounter();
+  });
+
   testWidgets('MergeSemantics', (WidgetTester tester) async {
     final SemanticsTester semantics = new SemanticsTester(tester);
 
@@ -19,8 +25,14 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Row(
           children: <Widget>[
-            const Text('test1'),
-            const Text('test2'),
+            new Semantics(
+              container: true,
+              child: const Text('test1'),
+            ),
+            new Semantics(
+              container: true,
+              child: const Text('test2'),
+            ),
           ],
         ),
       ),
@@ -44,8 +56,14 @@ void main() {
         child: new MergeSemantics(
           child: new Row(
             children: <Widget>[
-              const Text('test1'),
-              const Text('test2'),
+              new Semantics(
+                container: true,
+                child: const Text('test1'),
+              ),
+              new Semantics(
+                container: true,
+                child: const Text('test2'),
+              ),
             ],
           ),
         ),
@@ -71,19 +89,70 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Row(
           children: <Widget>[
-            const Text('test1'),
-            const Text('test2'),
+            new Semantics(
+              container: true,
+              child: const Text('test1'),
+            ),
+            new Semantics(
+              container: true,
+              child: const Text('test2'),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics.rootChild(id: 6, label: 'test1'),
+          new TestSemantics.rootChild(id: 7, label: 'test2'),
+        ],
+      ),
+      ignoreRect: true,
+      ignoreTransform: true,
+    ));
+
+    semantics.dispose();
+  });
+
+  testWidgets('MergeSemantics works if other nodes are implicitly merged into its node', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new MergeSemantics(
+          child: new Semantics(
+            selected: true, // this is implicitly merged into the MergeSemantics node
+            child: new Row(
+              children: <Widget>[
+                new Semantics(
+                  container: true,
+                  child: const Text('test1'),
+                ),
+                new Semantics(
+                  container: true,
+                  child: const Text('test2'),
+                ),
               ],
             ),
           ),
+        ),
+      ),
     );
 
     expect(semantics, hasSemantics(
       new TestSemantics.root(
           children: <TestSemantics>[
-          new TestSemantics.rootChild(id: 4, label: 'test1'),
-          new TestSemantics.rootChild(id: 5, label: 'test2'),
+            new TestSemantics.rootChild(
+              id: 1,
+              flags: <SemanticsFlag>[
+                SemanticsFlag.isSelected,
               ],
+              label: 'test1\ntest2',
+            ),
+          ]
       ),
       ignoreRect: true,
       ignoreTransform: true,

packages/flutter/test/widgets/sliver_semantics_test.dart

@@ -51,7 +51,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 5,
@@ -89,7 +89,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 5,
@@ -112,7 +112,7 @@ void main() {
               new TestSemantics(
                 id: 4,
                 label: 'Semantics Test with Slivers',
-                tags: <SemanticsTag>[RenderSemanticsGestureHandler.excludeFromScrolling],
+                tags: <SemanticsTag>[RenderViewport.excludeFromScrolling],
               ),
             ],
           )
@@ -132,7 +132,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 5,
@@ -203,7 +203,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 7,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 10,
@@ -257,7 +257,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 11,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 17,
@@ -339,7 +339,7 @@ void main() {
           new TestSemantics.rootChild(
             id: 18,
             rect: TestSemantics.fullScreen,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 23,
@@ -371,7 +371,7 @@ void main() {
               new TestSemantics(
                 id: 22,
                 rect: new Rect.fromLTRB(0.0, 0.0, 120.0, 20.0),
-                tags: <SemanticsTag>[RenderSemanticsGestureHandler.excludeFromScrolling],
+                tags: <SemanticsTag>[RenderViewport.excludeFromScrolling],
                 label: 'AppBar',
               ),
             ],
@@ -422,7 +422,7 @@ void main() {
           new TestSemantics.rootChild(
             id: 24,
             rect: TestSemantics.fullScreen,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 29,
@@ -454,7 +454,7 @@ void main() {
               new TestSemantics(
                 id: 28,
                 rect: new Rect.fromLTRB(0.0, 0.0, 120.0, 20.0),
-                tags: <SemanticsTag>[RenderSemanticsGestureHandler.excludeFromScrolling],
+                tags: <SemanticsTag>[RenderViewport.excludeFromScrolling],
                 label: 'AppBar'
               ),
             ],
@@ -507,7 +507,7 @@ void main() {
           new TestSemantics.rootChild(
             id: 30,
             rect: TestSemantics.fullScreen,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 35,
@@ -540,7 +540,7 @@ void main() {
                 id: 34,
                 rect: new Rect.fromLTRB(0.0, 0.0, 120.0, 20.0),
                 transform: new Matrix4.translation(new Vector3(0.0, 544.0, 0.0)),
-                tags: <SemanticsTag>[RenderSemanticsGestureHandler.excludeFromScrolling],
+                tags: <SemanticsTag>[RenderViewport.excludeFromScrolling],
                 label: 'AppBar'
               ),
             ],
@@ -592,7 +592,7 @@ void main() {
           new TestSemantics.rootChild(
             id: 36,
             rect: TestSemantics.fullScreen,
-            tags: <SemanticsTag>[RenderSemanticsGestureHandler.useTwoPaneSemantics],
+            tags: <SemanticsTag>[RenderViewport.useTwoPaneSemantics],
             children: <TestSemantics>[
               new TestSemantics(
                 id: 41,
@@ -625,7 +625,7 @@ void main() {
                 id: 40,
                 rect: new Rect.fromLTRB(0.0, 0.0, 120.0, 20.0),
                 transform: new Matrix4.translation(new Vector3(0.0, 544.0, 0.0)),
-                tags: <SemanticsTag>[RenderSemanticsGestureHandler.excludeFromScrolling],
+                tags: <SemanticsTag>[RenderViewport.excludeFromScrolling],
                 label: 'AppBar'
               ),
             ],