a11y traversal: sort locally; use new sorting algorithm (#16253)

New a11y traversal:

- sort direct sibling SemanticsNodes only
- use new sorting algorithm
- implement RTL
- test semantics in traversal order by default
- add AppBar traversal test
- breaking: remove nextNodeId/previousNodeId from the framework
- breaking: remove DebugSemanticsDumpOrder.geometricOrder

examples/stocks/lib/stock_home.dart

@@ -130,7 +130,7 @@ class StockHomeState extends State<StockHome> {
                 debugDumpApp();
                 debugDumpRenderTree();
                 debugDumpLayerTree();
-                debugDumpSemanticsTree(DebugSemanticsDumpOrder.geometricOrder);
+                debugDumpSemanticsTree(DebugSemanticsDumpOrder.traversalOrder);
               } catch (e, stack) {
                 debugPrint('Exception while dumping app:\n$e\n$stack');
               }

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

@@ -482,10 +482,14 @@ class _AppBarState extends State<AppBar> {
       );
     }
 
-    return new Material(
-      color: widget.backgroundColor ?? themeData.primaryColor,
-      elevation: widget.elevation,
-      child: appBar,
+    return new Semantics(
+      container: true,
+      explicitChildNodes: true,
+      child: new Material(
+        color: widget.backgroundColor ?? themeData.primaryColor,
+        elevation: widget.elevation,
+        child: appBar,
+      ),
     );
   }
 }

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

@@ -485,41 +485,45 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
         backgroundColor = _backgroundColor;
         break;
     }
-    return new Stack(
-      children: <Widget>[
-        new Positioned.fill(
-          child: new Material( // Casts shadow.
-            elevation: 8.0,
-            color: backgroundColor,
+    return new Semantics(
+      container: true,
+      explicitChildNodes: true,
+      child: new Stack(
+        children: <Widget>[
+          new Positioned.fill(
+            child: new Material( // Casts shadow.
+              elevation: 8.0,
+              color: backgroundColor,
+            ),
           ),
-        ),
-        new ConstrainedBox(
-          constraints: new BoxConstraints(minHeight: kBottomNavigationBarHeight + additionalBottomPadding),
-          child: new Stack(
-            children: <Widget>[
-              new Positioned.fill(
-                child: new CustomPaint(
-                  painter: new _RadialPainter(
-                    circles: _circles.toList(),
-                    textDirection: Directionality.of(context),
+          new ConstrainedBox(
+            constraints: new BoxConstraints(minHeight: kBottomNavigationBarHeight + additionalBottomPadding),
+            child: new Stack(
+              children: <Widget>[
+                new Positioned.fill(
+                  child: new CustomPaint(
+                    painter: new _RadialPainter(
+                      circles: _circles.toList(),
+                      textDirection: Directionality.of(context),
+                    ),
                   ),
                 ),
-              ),
-              new Material( // Splashes.
-                type: MaterialType.transparency,
-                child: new Padding(
-                  padding: new EdgeInsets.only(bottom: additionalBottomPadding),
-                  child: new MediaQuery.removePadding(
-                    context: context,
-                    removeBottom: true,
-                    child: _createContainer(_createTiles()),
+                new Material( // Splashes.
+                  type: MaterialType.transparency,
+                  child: new Padding(
+                    padding: new EdgeInsets.only(bottom: additionalBottomPadding),
+                    child: new MediaQuery.removePadding(
+                      context: context,
+                      removeBottom: true,
+                      child: _createContainer(_createTiles()),
+                    ),
                   ),
                 ),
-              ),
-            ],
+              ],
+            ),
           ),
-        ),
-      ],
+        ],
+      ),
     );
   }
 }

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

@@ -641,30 +641,39 @@ class _MonthPickerState extends State<MonthPicker> {
       height: _kMaxDayPickerHeight,
       child: new Stack(
         children: <Widget>[
-          new PageView.builder(
-            key: new ValueKey<DateTime>(widget.selectedDate),
-            controller: _dayPickerController,
-            scrollDirection: Axis.horizontal,
-            itemCount: _monthDelta(widget.firstDate, widget.lastDate) + 1,
-            itemBuilder: _buildItems,
-            onPageChanged: _handleMonthPageChanged,
+          new Semantics(
+            sortKey: _MonthPickerSortKey.calendar,
+            child: new PageView.builder(
+              key: new ValueKey<DateTime>(widget.selectedDate),
+              controller: _dayPickerController,
+              scrollDirection: Axis.horizontal,
+              itemCount: _monthDelta(widget.firstDate, widget.lastDate) + 1,
+              itemBuilder: _buildItems,
+              onPageChanged: _handleMonthPageChanged,
+            ),
           ),
           new PositionedDirectional(
             top: 0.0,
             start: 8.0,
-            child: new IconButton(
-              icon: const Icon(Icons.chevron_left),
-              tooltip: _isDisplayingFirstMonth ? null : '${localizations.previousMonthTooltip} ${localizations.formatMonthYear(_previousMonthDate)}',
-              onPressed: _isDisplayingFirstMonth ? null : _handlePreviousMonth,
+            child: new Semantics(
+              sortKey: _MonthPickerSortKey.previousMonth,
+              child: new IconButton(
+                icon: const Icon(Icons.chevron_left),
+                tooltip: _isDisplayingFirstMonth ? null : '${localizations.previousMonthTooltip} ${localizations.formatMonthYear(_previousMonthDate)}',
+                onPressed: _isDisplayingFirstMonth ? null : _handlePreviousMonth,
+              ),
             ),
           ),
           new PositionedDirectional(
             top: 0.0,
             end: 8.0,
-            child: new IconButton(
-              icon: const Icon(Icons.chevron_right),
-              tooltip: _isDisplayingLastMonth ? null : '${localizations.nextMonthTooltip} ${localizations.formatMonthYear(_nextMonthDate)}',
-              onPressed: _isDisplayingLastMonth ? null : _handleNextMonth,
+            child: new Semantics(
+              sortKey: _MonthPickerSortKey.nextMonth,
+              child: new IconButton(
+                icon: const Icon(Icons.chevron_right),
+                tooltip: _isDisplayingLastMonth ? null : '${localizations.nextMonthTooltip} ${localizations.formatMonthYear(_nextMonthDate)}',
+                onPressed: _isDisplayingLastMonth ? null : _handleNextMonth,
+              ),
             ),
           ),
         ],
@@ -680,6 +689,16 @@ class _MonthPickerState extends State<MonthPicker> {
   }
 }
 
+// Defines semantic traversal order of the top-level widgets inside the month
+// picker.
+class _MonthPickerSortKey extends OrdinalSortKey {
+  static const _MonthPickerSortKey previousMonth = const _MonthPickerSortKey(1.0);
+  static const _MonthPickerSortKey nextMonth = const _MonthPickerSortKey(2.0);
+  static const _MonthPickerSortKey calendar = const _MonthPickerSortKey(3.0);
+
+  const _MonthPickerSortKey(double order) : super(order);
+}
+
 /// A scrollable list of years to allow picking a year.
 ///
 /// The year picker widget is rarely used directly. Instead, consider using

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

@@ -101,8 +101,8 @@ abstract class RendererBinding extends BindingBase with ServicesBinding, Schedul
     );
 
     registerSignalServiceExtension(
-      name: 'debugDumpSemanticsTreeInGeometricOrder',
-      callback: () { debugDumpSemanticsTree(DebugSemanticsDumpOrder.geometricOrder); return debugPrintDone; }
+      name: 'debugDumpSemanticsTreeInTraversalOrder',
+      callback: () { debugDumpSemanticsTree(DebugSemanticsDumpOrder.traversalOrder); return debugPrintDone; }
     );
 
     registerSignalServiceExtension(

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

@@ -602,7 +602,7 @@ class _WidgetsAppState extends State<WidgetsApp> implements WidgetsBindingObserv
     if (widget.onGenerateTitle != null) {
       title = new Builder(
         // This Builder exists to provide a context below the Localizations widget.
-        // The onGenerateCallback() can refer to Localizations via its context
+        // The onGenerateTitle callback can refer to Localizations via its context
         // parameter.
         builder: (BuildContext context) {
           final String title = widget.onGenerateTitle(context);

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

@@ -65,11 +65,11 @@ class ModalBarrier extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     assert(!dismissible || semanticsLabel == null || debugCheckHasDirectionality(context));
-    final bool semanticsDismissable = dismissible && defaultTargetPlatform != TargetPlatform.android;
+    final bool semanticsDismissible = dismissible && defaultTargetPlatform != TargetPlatform.android;
     return new BlockSemantics(
       child: new ExcludeSemantics(
         // On Android, the back button is used to dismiss a modal.
-        excluding: !semanticsDismissable,
+        excluding: !semanticsDismissible,
         child: new GestureDetector(
           onTapDown: (TapDownDetails details) {
             if (dismissible)
@@ -77,8 +77,8 @@ class ModalBarrier extends StatelessWidget {
           },
           behavior: HitTestBehavior.opaque,
           child: new Semantics(
-            label: semanticsDismissable ? semanticsLabel : null,
-            textDirection: semanticsDismissable && semanticsLabel != null ? Directionality.of(context) : null,
+            label: semanticsDismissible ? semanticsLabel : null,
+            textDirection: semanticsDismissible && semanticsLabel != null ? Directionality.of(context) : null,
             child: new ConstrainedBox(
               constraints: const BoxConstraints.expand(),
               child: color == null ? null : new DecoratedBox(

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

@@ -102,8 +102,10 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   ///    create scroll positions and initialize this property.
   final bool keepScrollOffset;
 
-  /// A label that is used in the [toString] output. Intended to aid with
-  /// identifying animation controller instances in debug output.
+  /// A label that is used in the [toString] output.
+  ///
+  /// Intended to aid with identifying animation controller instances in debug
+  /// output.
   final String debugLabel;
 
   @override
@@ -123,10 +125,9 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   double _viewportDimension;
 
   /// Whether [viewportDimension], [minScrollExtent], [maxScrollExtent],
-  /// [outOfRange], and [atEdge] are available yet.
+  /// [outOfRange], and [atEdge] are available.
   ///
-  /// Set to true just before the first time that [applyNewDimensions] is
-  /// called.
+  /// Set to true just before the first time [applyNewDimensions] is called.
   bool get haveDimensions => _haveDimensions;
   bool _haveDimensions = false;
 

packages/flutter/test/cupertino/button_test.dart

@@ -2,8 +2,6 @@
 // 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/rendering.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/scheduler.dart';

packages/flutter/test/foundation/service_extensions_test.dart

@@ -193,11 +193,11 @@ void main() {
     console.clear();
   });
 
-  test('Service extensions - debugDumpSemanticsTreeInGeometricOrder', () async {
+  test('Service extensions - debugDumpSemanticsTreeInTraversalOrder', () async {
     Map<String, dynamic> result;
 
     await binding.doFrame();
-    result = await binding.testExtension('debugDumpSemanticsTreeInGeometricOrder', <String, String>{});
+    result = await binding.testExtension('debugDumpSemanticsTreeInTraversalOrder', <String, String>{});
     expect(result, <String, String>{});
     expect(console, <String>['Semantics not collected.']);
     console.clear();

packages/flutter/test/material/app_bar_test.dart

@@ -7,6 +7,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../widgets/semantics_tester.dart';
+
 Widget buildSliverAppBarApp({ bool floating, bool pinned, double expandedHeight, bool snap: false }) {
   return new Localizations(
     locale: const Locale('en', 'US'),
@@ -65,6 +67,10 @@ double appBarBottom(WidgetTester tester) => tester.getBottomLeft(find.byType(App
 double tabBarHeight(WidgetTester tester) => tester.getSize(find.byType(TabBar)).height;
 
 void main() {
+  setUp(() {
+    debugResetSemanticsIdCounter();
+  });
+
   testWidgets('AppBar centers title on iOS', (WidgetTester tester) async {
     await tester.pumpWidget(
       new MaterialApp(
@@ -1182,4 +1188,155 @@ void main() {
     expect(tester.getRect(find.byKey(leadingKey)), new Rect.fromLTRB(800.0 - 56.0, 100.0, 800.0, 100.0 + 56.0));
     expect(tester.getRect(find.byKey(trailingKey)), new Rect.fromLTRB(4.0, 100.0, 400.0 + 4.0, 100.0 + 56.0));
   });
+
+  testWidgets('SliverAppBar provides correct semantics in LTR', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        home: new Center(
+          child: new AppBar(
+            leading: const Text('Leading'),
+            title: const Text('Title'),
+            actions: const <Widget>[
+              const Text('Action 1'),
+              const Text('Action 2'),
+              const Text('Action 3'),
+            ],
+            bottom: const PreferredSize(
+              preferredSize: const Size(0.0, kToolbarHeight),
+              child: const Text('Bottom'),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics(
+            flags: <SemanticsFlag>[SemanticsFlag.scopesRoute],
+            children: <TestSemantics>[
+              new TestSemantics(
+                children: <TestSemantics>[
+                  new TestSemantics(
+                    label: 'Leading',
+                    textDirection: TextDirection.ltr,
+                  ),
+                  new TestSemantics(
+                    flags: <SemanticsFlag>[SemanticsFlag.namesRoute],
+                    label: 'Title',
+                    textDirection: TextDirection.ltr,
+                  ),
+                  new TestSemantics(
+                    label: 'Action 1',
+                    textDirection: TextDirection.ltr,
+                  ),
+                  new TestSemantics(
+                    label: 'Action 2',
+                    textDirection: TextDirection.ltr,
+                  ),
+                  new TestSemantics(
+                    label: 'Action 3',
+                    textDirection: TextDirection.ltr,
+                  ),
+                  new TestSemantics(
+                    label: 'Bottom',
+                    textDirection: TextDirection.ltr,
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ],
+      ),
+      ignoreRect: true,
+      ignoreTransform: true,
+      ignoreId: true,
+    ));
+
+    semantics.dispose();
+  });
+
+  testWidgets('SliverAppBar provides correct semantics in RTL', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        home: new Semantics(
+          textDirection: TextDirection.rtl,
+          child: new Directionality(
+            textDirection: TextDirection.rtl,
+            child: new Center(
+              child: new AppBar(
+                leading: const Text('Leading'),
+                title: const Text('Title'),
+                actions: const <Widget>[
+                  const Text('Action 1'),
+                  const Text('Action 2'),
+                  const Text('Action 3'),
+                ],
+                bottom: const PreferredSize(
+                  preferredSize: const Size(0.0, kToolbarHeight),
+                  child: const Text('Bottom'),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics(
+            flags: <SemanticsFlag>[SemanticsFlag.scopesRoute],
+            children: <TestSemantics>[
+              new TestSemantics(
+                textDirection: TextDirection.rtl,
+                children: <TestSemantics>[
+                  new TestSemantics(
+                    children: <TestSemantics>[
+                      new TestSemantics(
+                        label: 'Leading',
+                        textDirection: TextDirection.rtl,
+                      ),
+                      new TestSemantics(
+                        flags: <SemanticsFlag>[SemanticsFlag.namesRoute],
+                        label: 'Title',
+                        textDirection: TextDirection.rtl,
+                      ),
+                      new TestSemantics(
+                        label: 'Action 1',
+                        textDirection: TextDirection.rtl,
+                      ),
+                      new TestSemantics(
+                        label: 'Action 2',
+                        textDirection: TextDirection.rtl,
+                      ),
+                      new TestSemantics(
+                        label: 'Action 3',
+                        textDirection: TextDirection.rtl,
+                      ),
+                      new TestSemantics(
+                        label: 'Bottom',
+                        textDirection: TextDirection.rtl,
+                      ),
+                    ],
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ],
+      ),
+      ignoreRect: true,
+      ignoreTransform: true,
+      ignoreId: true,
+    ));
+
+    semantics.dispose();
+  });
 }

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -512,32 +512,31 @@ void main() {
       ),
     );
 
-    // TODO(goderbauer): traversal order is incorrect, https://github.com/flutter/flutter/issues/14375
     final TestSemantics expected = new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics(
           id: 1,
-          flags: <SemanticsFlag>[SemanticsFlag.isSelected],
-          actions: <SemanticsAction>[SemanticsAction.tap],
-          label: 'AC\nTab 1 of 3',
-          textDirection: TextDirection.ltr,
-          previousNodeId: 3, // Should be 2
-        ),
-        new TestSemantics(
-          id: 2,
-          actions: <SemanticsAction>[SemanticsAction.tap],
-          label: 'Alarm\nTab 2 of 3',
-          textDirection: TextDirection.ltr,
-          nextNodeId: 3,
-          previousNodeId: -1, // Should be 1
-        ),
-        new TestSemantics(
-          id: 3,
-          actions: <SemanticsAction>[SemanticsAction.tap],
-          label: 'Hot Tub\nTab 3 of 3',
-          textDirection: TextDirection.ltr,
-          nextNodeId: 1, // Should be -1
-          previousNodeId: 2,
+          children: <TestSemantics>[
+            new TestSemantics(
+              id: 2,
+              flags: <SemanticsFlag>[SemanticsFlag.isSelected],
+              actions: <SemanticsAction>[SemanticsAction.tap],
+              label: 'AC\nTab 1 of 3',
+              textDirection: TextDirection.ltr,
+            ),
+            new TestSemantics(
+              id: 3,
+              actions: <SemanticsAction>[SemanticsAction.tap],
+              label: 'Alarm\nTab 2 of 3',
+              textDirection: TextDirection.ltr,
+            ),
+            new TestSemantics(
+              id: 4,
+              actions: <SemanticsAction>[SemanticsAction.tap],
+              label: 'Hot Tub\nTab 3 of 3',
+              textDirection: TextDirection.ltr,
+            ),
+          ],
         ),
       ],
     );

packages/flutter/test/material/buttons_test.dart

@@ -2,8 +2,6 @@
 // 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/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/material/card_test.dart

@@ -2,8 +2,6 @@
 // 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/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/material/control_list_tile_test.dart

@@ -2,8 +2,6 @@
 // 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_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -100,7 +98,6 @@ void main() {
       children: <TestSemantics>[
         new TestSemantics.rootChild(
           id: 1,
-          nextNodeId: 3,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: null,
           flags: <SemanticsFlag>[
@@ -114,8 +111,6 @@ void main() {
         ),
         new TestSemantics.rootChild(
           id: 3,
-          previousNodeId: 1,
-          nextNodeId: 5,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 56.0, 0.0),
           flags: <SemanticsFlag>[
@@ -129,7 +124,6 @@ void main() {
         ),
         new TestSemantics.rootChild(
           id: 5,
-          previousNodeId: 3,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 112.0, 0.0),
           flags: <SemanticsFlag>[

packages/flutter/test/material/list_tile_test.dart

@@ -2,8 +2,6 @@
 // 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_test/flutter_test.dart';

packages/flutter/test/material/outline_button_test.dart

@@ -2,8 +2,6 @@
 // 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_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';

packages/flutter/test/material/tabs_test.dart

@@ -2,8 +2,6 @@
 // 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, SemanticsAction;
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
@@ -1363,7 +1361,6 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 3,
-                  nextNodeId: 4,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'TAB #0\nTab 1 of 2',
@@ -1372,7 +1369,6 @@ void main() {
                 ),
                 new TestSemantics(
                   id: 4,
-                  previousNodeId: 3,
                   actions: SemanticsAction.tap.index,
                   label: 'TAB #1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),
@@ -1622,7 +1618,6 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 3,
-                  nextNodeId: 4,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'Semantics override 0\nTab 1 of 2',
@@ -1631,7 +1626,6 @@ void main() {
                 ),
                 new TestSemantics(
                   id: 4,
-                  previousNodeId: 3,
                   actions: SemanticsAction.tap.index,
                   label: 'Semantics override 1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),

packages/flutter/test/material/text_field_test.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:io' show Platform;
-import 'dart:ui' show SemanticsFlag;
 
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/material/user_accounts_drawer_header_test.dart

@@ -2,8 +2,6 @@
 // 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_test/flutter_test.dart';

packages/flutter/test/semantics/semantics_test.dart

@@ -125,7 +125,7 @@ void main() {
     expect(child2.transform, isNull);
 
     expect(
-      root.toStringDeep(childOrder: DebugSemanticsDumpOrder.geometricOrder),
+      root.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversalOrder),
       'SemanticsNode#3\n'
       ' │ STALE\n'
       ' │ owner: null\n'
@@ -143,18 +143,26 @@ void main() {
     );
   });
 
+  test('Incompatible OrdinalSortKey throw AssertionError when compared', () {
+    // Different types.
+    expect(() {
+      const OrdinalSortKey(0.0).compareTo(const CustomSortKey(0.0));
+    }, throwsAssertionError);
+
+    // Different names.
+    expect(() {
+      const OrdinalSortKey(0.0, name: 'a').compareTo(const OrdinalSortKey(0.0, name: 'b'));
+    }, throwsAssertionError);
+  });
+
   test('OrdinalSortKey compares correctly', () {
     const List<List<SemanticsSortKey>> tests = const <List<SemanticsSortKey>>[
       const <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(0.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(1.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(0.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(1.0)],
-      const <SemanticsSortKey>[const OrdinalSortKey(0.0), const CustomSortKey(1.0)],
-      const <SemanticsSortKey>[const OrdinalSortKey(0.0), const CustomSortKey(0.0)],
-      const <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)],
-      const <SemanticsSortKey>[const CustomSortKey(1.0), const OrdinalSortKey(0.0)],
     ];
-    final List<int> expectedResults = <int>[0, -1, 1, 0, 0, 0, 0, 0];
+    final List<int> expectedResults = <int>[0, -1, 1, 0];
     assert(tests.length == expectedResults.length);
     final List<int> results = <int>[];
     for (List<SemanticsSortKey> tuple in tests) {
@@ -163,31 +171,14 @@ void main() {
     expect(results, orderedEquals(expectedResults));
   });
 
-  test('SemanticsSortKey sorts correctly when assigned names', () {
-    const SemanticsSortKey order1g1 = const CustomSortKey(0.0, name: 'group 1');
-    const SemanticsSortKey order2g1 = const CustomSortKey(1.0, name: 'group 1');
-    const SemanticsSortKey order2g2 = const CustomSortKey(1.0, name: 'group 2');
-    const SemanticsSortKey order3g2 = const OrdinalSortKey(1.0, name: 'group 1');
-    // Keys in the same group compare.
-    expect(order1g1.compareTo(order2g1), equals(-1));
-    // Keys with different names compare equal.
-    expect(order1g1.compareTo(order2g2), equals(0));
-    // Keys with same names but different types compare equal.
-    expect(order1g1.compareTo(order3g2), equals(0));
-  });
-
   test('OrdinalSortKey compares correctly', () {
     const List<List<SemanticsSortKey>> tests = const <List<SemanticsSortKey>>[
       const <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(0.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(1.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(0.0)],
       const <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(1.0)],
-      const <SemanticsSortKey>[const OrdinalSortKey(0.0), const CustomSortKey(1.0)],
-      const <SemanticsSortKey>[const OrdinalSortKey(0.0), const CustomSortKey(0.0)],
-      const <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)],
-      const <SemanticsSortKey>[const CustomSortKey(1.0), const OrdinalSortKey(0.0)],
     ];
-    final List<int> expectedResults = <int>[0, -1, 1, 0, 0, 0, 0, 0];
+    final List<int> expectedResults = <int>[0, -1, 1, 0];
     assert(tests.length == expectedResults.length);
     final List<int> results = <int>[];
     for (List<SemanticsSortKey> tuple in tests) {
@@ -196,19 +187,6 @@ void main() {
     expect(results, orderedEquals(expectedResults));
   });
 
-  test('SemanticsSortKey sorts correctly when assigned names', () {
-    const SemanticsSortKey order1g1 = const CustomSortKey(0.0, name: 'group 1');
-    const SemanticsSortKey order2g1 = const CustomSortKey(1.0, name: 'group 1');
-    const SemanticsSortKey order2g2 = const CustomSortKey(1.0, name: 'group 2');
-    const SemanticsSortKey order3g2 = const OrdinalSortKey(1.0, name: 'group 1');
-    // Keys in the same group compare.
-    expect(order1g1.compareTo(order2g1), equals(-1));
-    // Keys with different names compare equal.
-    expect(order1g1.compareTo(order2g2), equals(0));
-    // Keys with same names but different types compare equal.
-    expect(order1g1.compareTo(order3g2), equals(0));
-  });
-
   test('toStringDeep respects childOrder parameter', () {
     final SemanticsNode child1 = new SemanticsNode()
       ..rect = new Rect.fromLTRB(15.0, 0.0, 20.0, 5.0);
@@ -221,21 +199,21 @@ void main() {
       childrenInInversePaintOrder: <SemanticsNode>[child1, child2],
     );
     expect(
-      root.toStringDeep(childOrder: DebugSemanticsDumpOrder.geometricOrder),
+      root.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversalOrder),
       'SemanticsNode#3\n'
       ' │ STALE\n'
       ' │ owner: null\n'
       ' │ Rect.fromLTRB(0.0, 0.0, 20.0, 5.0)\n'
       ' │\n'
-      ' ├─SemanticsNode#2\n'
+      ' ├─SemanticsNode#1\n'
       ' │   STALE\n'
       ' │   owner: null\n'
-      ' │   Rect.fromLTRB(10.0, 0.0, 15.0, 5.0)\n'
+      ' │   Rect.fromLTRB(15.0, 0.0, 20.0, 5.0)\n'
       ' │\n'
-      ' └─SemanticsNode#1\n'
+      ' └─SemanticsNode#2\n'
       '     STALE\n'
       '     owner: null\n'
-      '     Rect.fromLTRB(15.0, 0.0, 20.0, 5.0)\n'
+      '     Rect.fromLTRB(10.0, 0.0, 15.0, 5.0)\n'
     );
 
     expect(
@@ -276,36 +254,36 @@ void main() {
     );
 
     expect(
-      rootComplex.toStringDeep(childOrder: DebugSemanticsDumpOrder.geometricOrder),
+      rootComplex.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversalOrder),
       'SemanticsNode#7\n'
       ' │ STALE\n'
       ' │ owner: null\n'
       ' │ Rect.fromLTRB(0.0, 0.0, 25.0, 5.0)\n'
       ' │\n'
-      ' ├─SemanticsNode#4\n'
-      ' │ │ STALE\n'
-      ' │ │ owner: null\n'
-      ' │ │ Rect.fromLTRB(0.0, 0.0, 10.0, 5.0)\n'
-      ' │ │\n'
-      ' │ ├─SemanticsNode#6\n'
-      ' │ │   STALE\n'
-      ' │ │   owner: null\n'
-      ' │ │   Rect.fromLTRB(0.0, 0.0, 5.0, 5.0)\n'
-      ' │ │\n'
-      ' │ └─SemanticsNode#5\n'
-      ' │     STALE\n'
-      ' │     owner: null\n'
-      ' │     Rect.fromLTRB(5.0, 0.0, 10.0, 5.0)\n'
+      ' ├─SemanticsNode#1\n'
+      ' │   STALE\n'
+      ' │   owner: null\n'
+      ' │   Rect.fromLTRB(15.0, 0.0, 20.0, 5.0)\n'
       ' │\n'
       ' ├─SemanticsNode#2\n'
       ' │   STALE\n'
       ' │   owner: null\n'
       ' │   Rect.fromLTRB(10.0, 0.0, 15.0, 5.0)\n'
       ' │\n'
-      ' └─SemanticsNode#1\n'
-      '     STALE\n'
-      '     owner: null\n'
-      '     Rect.fromLTRB(15.0, 0.0, 20.0, 5.0)\n'
+      ' └─SemanticsNode#4\n'
+      '   │ STALE\n'
+      '   │ owner: null\n'
+      '   │ Rect.fromLTRB(0.0, 0.0, 10.0, 5.0)\n'
+      '   │\n'
+      '   ├─SemanticsNode#5\n'
+      '   │   STALE\n'
+      '   │   owner: null\n'
+      '   │   Rect.fromLTRB(5.0, 0.0, 10.0, 5.0)\n'
+      '   │\n'
+      '   └─SemanticsNode#6\n'
+      '       STALE\n'
+      '       owner: null\n'
+      '       Rect.fromLTRB(0.0, 0.0, 5.0, 5.0)\n'
     );
 
     expect(
@@ -368,8 +346,6 @@ void main() {
       '   decreasedValue: ""\n'
       '   hint: ""\n'
       '   textDirection: null\n'
-      '   nextNodeId: null\n'
-      '   previousNodeId: null\n'
       '   sortKey: null\n'
       '   scrollExtentMin: null\n'
       '   scrollPosition: null\n'

packages/flutter/test/widgets/custom_painter_test.dart

@@ -150,20 +150,16 @@ void _defineTests() {
             children: <TestSemantics>[
               new TestSemantics(
                 id: 3,
-                nextNodeId: 4,
-                previousNodeId: 2,
                 label: 'background',
                 rect: new Rect.fromLTRB(1.0, 1.0, 2.0, 2.0),
               ),
               new TestSemantics(
                 id: 2,
-                nextNodeId: 3,
                 label: 'Hello',
                 rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 600.0),
               ),
               new TestSemantics(
                 id: 4,
-                previousNodeId: 3,
                 label: 'foreground',
                 rect: new Rect.fromLTRB(1.0, 1.0, 2.0, 2.0),
               ),

packages/flutter/test/widgets/editable_text_test.dart

@@ -2,8 +2,6 @@
 // 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/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
@@ -600,8 +598,6 @@ void main() {
               flags: <SemanticsFlag>[SemanticsFlag.isTextField, SemanticsFlag.isObscured],
               value: expectedValue,
               textDirection: TextDirection.ltr,
-              nextNodeId: -1,
-              previousNodeId: -1,
             ),
           ],
         ),

packages/flutter/test/widgets/implicit_semantics_test.dart

@@ -2,8 +2,6 @@
 // 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/widgets.dart';
 import 'package:flutter/rendering.dart';
@@ -79,12 +77,10 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 2,
-                  nextNodeId: 3,
                   label: 'Michael Goderbauer',
                 ),
                 new TestSemantics(
                   id: 3,
-                  previousNodeId: 2,
                   label: 'goderbauer@google.com',
                 ),
               ],
@@ -235,20 +231,16 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 6,
-                  nextNodeId: 7,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 1',
                 ),
                 new TestSemantics(
                   id: 7,
-                  previousNodeId: 6,
-                  nextNodeId: 8,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 2',
                 ),
                 new TestSemantics(
                   id: 8,
-                  previousNodeId: 7,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 3',
                 ),

packages/flutter/test/widgets/semantics_1_test.dart

@@ -2,8 +2,6 @@
 // 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';
@@ -122,14 +120,12 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 2,
-              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
-              previousNodeId: 2,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
@@ -220,14 +216,12 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 4,
-              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
-              previousNodeId: 4,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,

packages/flutter/test/widgets/semantics_2_test.dart

@@ -2,8 +2,6 @@
 // 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';
@@ -58,14 +56,12 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 2,
-              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
-              previousNodeId: 2,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
@@ -156,14 +152,12 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 4,
-              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
-              previousNodeId: 4,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,

packages/flutter/test/widgets/semantics_3_test.dart

@@ -2,8 +2,6 @@
 // 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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/widgets/semantics_4_test.dart

@@ -2,8 +2,6 @@
 // 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/widgets.dart';
 import 'package:flutter/rendering.dart';
@@ -54,25 +52,21 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            nextNodeId: 2,
             label: 'L1',
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
-            previousNodeId: 1,
             label: 'L2',
             rect: TestSemantics.fullScreen,
             children: <TestSemantics>[
               new TestSemantics(
                 id: 3,
-                nextNodeId: 4,
                 flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
                 rect: TestSemantics.fullScreen,
               ),
               new TestSemantics(
                 id: 4,
-                previousNodeId: 3,
                 flags: SemanticsFlag.hasCheckedState.index,
                 rect: TestSemantics.fullScreen,
               ),
@@ -118,13 +112,11 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            nextNodeId: 2,
             label: 'L1',
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
-            previousNodeId: 1,
             label: 'L2',
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             rect: TestSemantics.fullScreen,

packages/flutter/test/widgets/semantics_5_test.dart

@@ -37,12 +37,10 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            nextNodeId: 2,
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
-            previousNodeId: 1,
             label: 'label',
             rect: TestSemantics.fullScreen,
           ),

packages/flutter/test/widgets/semantics_7_test.dart

@@ -2,8 +2,6 @@
 // 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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -56,7 +54,6 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            nextNodeId: 4,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -64,7 +61,6 @@ void main() {
           // IDs 2 and 3 are used up by the nodes that get merged in
           new TestSemantics.rootChild(
             id: 4,
-            previousNodeId: 1,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -114,7 +110,6 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
-            nextNodeId: 4,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -122,7 +117,6 @@ void main() {
           // IDs 2 and 3 are used up by the nodes that get merged in
           new TestSemantics.rootChild(
             id: 4,
-            previousNodeId: 1,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,

packages/flutter/test/widgets/semantics_8_test.dart

@@ -2,8 +2,6 @@
 // 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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/widgets/semantics_merge_test.dart

@@ -2,8 +2,6 @@
 // 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';
@@ -44,12 +42,10 @@ void main() {
           new TestSemantics.rootChild(
             id: 1,
             label: 'test1',
-            nextNodeId: 2,
           ),
           new TestSemantics.rootChild(
             id: 2,
             label: 'test2',
-            previousNodeId: 1,
           ),
         ],
       ),
@@ -113,8 +109,8 @@ void main() {
     expect(semantics, hasSemantics(
       new TestSemantics.root(
         children: <TestSemantics>[
-          new TestSemantics.rootChild(id: 6, label: 'test1', nextNodeId: 7),
-          new TestSemantics.rootChild(id: 7, label: 'test2', previousNodeId: 6),
+          new TestSemantics.rootChild(id: 6, label: 'test1'),
+          new TestSemantics.rootChild(id: 7, label: 'test2'),
         ],
       ),
       ignoreRect: true,

packages/flutter/test/widgets/semantics_test.dart

@@ -674,44 +674,36 @@ void main() {
           new TestSemantics(
             id: 1,
             children: <TestSemantics>[
-              new TestSemantics(
-                id: 2,
-                label: r'Label 1',
-                textDirection: TextDirection.ltr,
-                previousNodeId: 3,
-              ),
-              new TestSemantics(
-                id: 3,
-                label: r'Label 2',
-                textDirection: TextDirection.ltr,
-                nextNodeId: 2,
-                previousNodeId: 4,
-              ),
               new TestSemantics(
                 id: 4,
-                nextNodeId: 3,
                 children: <TestSemantics>[
                   new TestSemantics(
-                    id: 5,
-                    label: r'Label 3',
+                    id: 7,
+                    label: r'Label 5',
                     textDirection: TextDirection.ltr,
-                    previousNodeId: 6,
                   ),
                   new TestSemantics(
                     id: 6,
                     label: r'Label 4',
                     textDirection: TextDirection.ltr,
-                    nextNodeId: 5,
-                    previousNodeId: 7,
                   ),
                   new TestSemantics(
-                    id: 7,
-                    label: r'Label 5',
+                    id: 5,
+                    label: r'Label 3',
                     textDirection: TextDirection.ltr,
-                    nextNodeId: 6,
                   ),
                 ],
               ),
+              new TestSemantics(
+                id: 3,
+                label: r'Label 2',
+                textDirection: TextDirection.ltr,
+              ),
+              new TestSemantics(
+                id: 2,
+                label: r'Label 1',
+                textDirection: TextDirection.ltr,
+              ),
             ],
           ),
         ],
@@ -755,24 +747,20 @@ void main() {
     expect(semantics, hasSemantics(
       new TestSemantics.root(
         children: <TestSemantics>[
-          new TestSemantics(
-            id: 1,
-            label: r'Label 1',
-            textDirection: TextDirection.ltr,
-            previousNodeId: 3,
-          ),
           new TestSemantics(
             id: 2,
             label: r'Label 2',
             textDirection: TextDirection.ltr,
-            nextNodeId: 3,
           ),
           new TestSemantics(
             id: 3,
             label: r'Label 3',
             textDirection: TextDirection.ltr,
-            nextNodeId: 1,
-            previousNodeId: 2,
+          ),
+          new TestSemantics(
+            id: 1,
+            label: r'Label 1',
+            textDirection: TextDirection.ltr,
           ),
         ],
       ), ignoreTransform: true, ignoreRect: true));
@@ -818,22 +806,18 @@ void main() {
           new TestSemantics(
             label: r'Label 2',
             textDirection: TextDirection.ltr,
-            previousNodeId: 1,
           ),
           new TestSemantics(
             label: r'Label 3',
             textDirection: TextDirection.ltr,
-            previousNodeId: 2,
           ),
           new TestSemantics(
             label: r'Label 4',
             textDirection: TextDirection.ltr,
-            previousNodeId: 3,
           ),
           new TestSemantics(
             label: r'Label 5',
             textDirection: TextDirection.ltr,
-            previousNodeId: 4,
           ),
         ],
       ), ignoreTransform: true, ignoreRect: true, ignoreId: true),
@@ -879,12 +863,10 @@ void main() {
           new TestSemantics(
             label: r'Label 1',
             textDirection: TextDirection.ltr,
-            previousNodeId: 5,
           ),
           new TestSemantics(
             label: r'Label 2',
             textDirection: TextDirection.ltr,
-            previousNodeId: 1,
           ),
           new TestSemantics(
             label: r'Label 3',
@@ -893,12 +875,10 @@ void main() {
           new TestSemantics(
             label: r'Label 4',
             textDirection: TextDirection.ltr,
-            previousNodeId: 3,
           ),
           new TestSemantics(
             label: r'Label 5',
             textDirection: TextDirection.ltr,
-            previousNodeId: 4,
           ),
         ],
       ), ignoreTransform: true, ignoreRect: true, ignoreId: true),
@@ -986,23 +966,18 @@ void main() {
             ),
             new TestSemantics(
               flags: <SemanticsFlag>[SemanticsFlag.isButton],
-              previousNodeId: 5,
             ),
             new TestSemantics(
               flags: <SemanticsFlag>[SemanticsFlag.isButton],
-              previousNodeId: 6,
             ),
             new TestSemantics(
               flags: <SemanticsFlag>[SemanticsFlag.isButton],
-              previousNodeId: 3,
             ),
             new TestSemantics(
               flags: <SemanticsFlag>[SemanticsFlag.isButton],
-              previousNodeId: 4,
             ),
             new TestSemantics(
               flags: <SemanticsFlag>[SemanticsFlag.isButton],
-              previousNodeId: 1,
             ),
           ],
         ),

packages/flutter/test/widgets/semantics_tester_generateTestSemanticsExpressionForCurrentSemanticsTree_test.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:io';
-import 'dart:ui' show SemanticsFlag;
 
 import 'package:flutter/material.dart';
 import 'package:flutter/semantics.dart';
@@ -55,7 +54,7 @@ void _tests() {
     final SemanticsTester semantics = new SemanticsTester(tester);
     await pumpTestWidget(tester);
     final String code = semantics
-      .generateTestSemanticsExpressionForCurrentSemanticsTree()
+      .generateTestSemanticsExpressionForCurrentSemanticsTree(DebugSemanticsDumpOrder.inverseHitTest)
       .split('\n')
       .map((String line) => line.trim())
       .join('\n')
@@ -119,7 +118,6 @@ void _tests() {
                           tags: <SemanticsTag>[const SemanticsTag('RenderViewport.twoPane')],
                           label: 'Plain text',
                           textDirection: TextDirection.ltr,
-                          nextNodeId: 4,
                         ),
                         new TestSemantics(
                           id: 4,
@@ -132,7 +130,6 @@ void _tests() {
                           decreasedValue: 'test-decreasedValue',
                           hint: 'test-hint',
                           textDirection: TextDirection.rtl,
-                          previousNodeId: 3,
                         ),
                       ],
                     ),

packages/flutter_tools/lib/src/resident_runner.dart

@@ -195,9 +195,9 @@ class FlutterDevice {
       await view.uiIsolate.flutterDebugDumpLayerTree();
   }
 
-  Future<Null> debugDumpSemanticsTreeInGeometricOrder() async {
+  Future<Null> debugDumpSemanticsTreeInTraversalOrder() async {
     for (FlutterView view in views)
-      await view.uiIsolate.flutterDebugDumpSemanticsTreeInGeometricOrder();
+      await view.uiIsolate.flutterDebugDumpSemanticsTreeInTraversalOrder();
   }
 
   Future<Null> debugDumpSemanticsTreeInInverseHitTestOrder() async {
@@ -505,10 +505,10 @@ abstract class ResidentRunner {
       await device.debugDumpLayerTree();
   }
 
-  Future<Null> _debugDumpSemanticsTreeInGeometricOrder() async {
+  Future<Null> _debugDumpSemanticsTreeInTraversalOrder() async {
     await refreshViews();
     for (FlutterDevice device in flutterDevices)
-      await device.debugDumpSemanticsTreeInGeometricOrder();
+      await device.debugDumpSemanticsTreeInTraversalOrder();
   }
 
   Future<Null> _debugDumpSemanticsTreeInInverseHitTestOrder() async {
@@ -691,7 +691,7 @@ abstract class ResidentRunner {
       }
     } else if (character == 'S') {
       if (supportsServiceProtocol) {
-        await _debugDumpSemanticsTreeInGeometricOrder();
+        await _debugDumpSemanticsTreeInTraversalOrder();
         return true;
       }
     } else if (character == 'U') {
@@ -832,12 +832,12 @@ abstract class ResidentRunner {
       printStatus('You can dump the widget hierarchy of the app (debugDumpApp) by pressing "w".');
       printStatus('To dump the rendering tree of the app (debugDumpRenderTree), press "t".');
       if (isRunningDebug) {
-        printStatus('For layers (debugDumpLayerTree), use "L"; for accessibility (debugDumpSemantics), use "S" (for geometric order) or "U" (for inverse hit test order).');
+        printStatus('For layers (debugDumpLayerTree), use "L"; for accessibility (debugDumpSemantics), use "S" (for traversal order) or "U" (for inverse hit test order).');
         printStatus('To toggle the widget inspector (WidgetsApp.showWidgetInspectorOverride), press "i".');
         printStatus('To toggle the display of construction lines (debugPaintSizeEnabled), press "p".');
         printStatus('To simulate different operating systems, (defaultTargetPlatform), press "o".');
       } else {
-        printStatus('To dump the accessibility tree (debugDumpSemantics), press "S" (for geometric order) or "U" (for inverse hit test order).');
+        printStatus('To dump the accessibility tree (debugDumpSemantics), press "S" (for traversal order) or "U" (for inverse hit test order).');
       }
       printStatus('To display the performance overlay (WidgetsApp.showPerformanceOverlay), press "P".');
     }

packages/flutter_tools/lib/src/vmservice.dart

@@ -1201,8 +1201,8 @@ class Isolate extends ServiceObjectOwner {
     return invokeFlutterExtensionRpcRaw('ext.flutter.debugDumpLayerTree', timeout: kLongRequestTimeout);
   }
 
-  Future<Map<String, dynamic>> flutterDebugDumpSemanticsTreeInGeometricOrder() {
-    return invokeFlutterExtensionRpcRaw('ext.flutter.debugDumpSemanticsTreeInGeometricOrder', timeout: kLongRequestTimeout);
+  Future<Map<String, dynamic>> flutterDebugDumpSemanticsTreeInTraversalOrder() {
+    return invokeFlutterExtensionRpcRaw('ext.flutter.debugDumpSemanticsTreeInTraversalOrder', timeout: kLongRequestTimeout);
   }
 
   Future<Map<String, dynamic>> flutterDebugDumpSemanticsTreeInInverseHitTestOrder() {