Add support for setting the heading level for web semantics (flutter#97894) (flutter#41435)

victorgalo · web-flow · commit 11a32d43e3f6 · 2024-06-04T23:11:17.000Z
This change adds a new property in Semantics widget that would take an integer value corresponding to the heading levels defined by the ARIA heading role. This is necessary in order to get proper accessibility and usability in a website for users who rely on screen readers and other assistive technologies. Issue fixed by this PR: flutter#97894 Framework part: flutter#125771
diff --git a/ci/licenses_golden/licenses_flutter b/ci/licenses_golden/licenses_flutter
@@ -43347,6 +43347,7 @@ ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/accessibility.dart
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/checkable.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/dialog.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/focusable.dart + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/heading.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/image.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/incrementable.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/web_ui/lib/src/engine/semantics/label_and_value.dart + ../../../flutter/LICENSE
@@ -46218,6 +46219,7 @@ FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/accessibility.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/checkable.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/dialog.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/focusable.dart
+FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/heading.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/image.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/incrementable.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/semantics/label_and_value.dart
diff --git a/lib/ui/fixtures/ui_test.dart b/lib/ui/fixtures/ui_test.dart
@@ -231,7 +231,9 @@ void sendSemanticsUpdate() {
     transform: transform,
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
-    additionalActions: additionalActions);
+    additionalActions: additionalActions,
+    headingLevel: 0,
+  );
   _semanticsUpdate(builder.build());
 }
 
diff --git a/lib/ui/semantics.dart b/lib/ui/semantics.dart
@@ -841,6 +841,18 @@ abstract class SemanticsUpdateBuilder {
   /// z-direction starting at `elevation`. Basically, in the z-direction the
   /// node starts at `elevation` above the parent and ends at `elevation` +
   /// `thickness` above the parent.
+  ///
+  /// The `headingLevel` describes that this node is a heading and the hierarchy
+  /// level this node represents as a heading. A value of 0 indicates that this
+  /// node is not a heading. A value of 1 or greater indicates that this node is
+  /// a heading at the specified level. The valid value range is from 1 to 6,
+  /// inclusive. This attribute is only used for Web platform, and it will have
+  /// no effect on other platforms.
+  ///
+  /// See also:
+  ///
+  ///  * https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/heading_role
+  ///  * https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-level
   void updateNode({
     required int id,
     required int flags,
@@ -875,6 +887,7 @@ abstract class SemanticsUpdateBuilder {
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
+    int headingLevel = 0,
   });
 
   /// Update the custom semantics action associated with the given `id`.
@@ -945,8 +958,13 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
+    int headingLevel = 0,
   }) {
     assert(_matrix4IsValid(transform));
+    assert (
+      headingLevel >= 0 && headingLevel <= 6,
+      'Heading level must be between 1 and 6, or 0 to indicate that this node is not a heading.'
+    );
     _updateNode(
       id,
       flags,
@@ -984,6 +1002,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
       childrenInTraversalOrder,
       childrenInHitTestOrder,
       additionalActions,
+      headingLevel,
     );
   }
   @Native<
@@ -1024,7 +1043,8 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
           Handle,
           Handle,
           Handle,
-          Handle)>(symbol: 'SemanticsUpdateBuilder::updateNode')
+          Handle,
+          Int32)>(symbol: 'SemanticsUpdateBuilder::updateNode')
   external void _updateNode(
       int id,
       int flags,
@@ -1061,7 +1081,8 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
       Float64List transform,
       Int32List childrenInTraversalOrder,
       Int32List childrenInHitTestOrder,
-      Int32List additionalActions);
+      Int32List additionalActions,
+      int headingLevel);
 
   @override
   void updateCustomAction({required int id, String? label, String? hint, int overrideId = -1}) {
diff --git a/lib/ui/semantics/semantics_node.h b/lib/ui/semantics/semantics_node.h
@@ -143,6 +143,7 @@ struct SemanticsNode {
   std::vector<int32_t> childrenInTraversalOrder;
   std::vector<int32_t> childrenInHitTestOrder;
   std::vector<int32_t> customAccessibilityActions;
+  int32_t headingLevel = 0;
 };
 
 // Contains semantic nodes that need to be updated.
diff --git a/lib/ui/semantics/semantics_update_builder.cc b/lib/ui/semantics/semantics_update_builder.cc
@@ -66,7 +66,8 @@ void SemanticsUpdateBuilder::updateNode(
     const tonic::Float64List& transform,
     const tonic::Int32List& childrenInTraversalOrder,
     const tonic::Int32List& childrenInHitTestOrder,
-    const tonic::Int32List& localContextActions) {
+    const tonic::Int32List& localContextActions,
+    int headingLevel) {
   FML_CHECK(scrollChildren == 0 ||
             (scrollChildren > 0 && childrenInHitTestOrder.data()))
       << "Semantics update contained scrollChildren but did not have "
@@ -118,6 +119,8 @@ void SemanticsUpdateBuilder::updateNode(
       localContextActions.data(),
       localContextActions.data() + localContextActions.num_elements());
   nodes_[id] = node;
+
+  node.headingLevel = headingLevel;
 }
 
 void SemanticsUpdateBuilder::updateCustomAction(int id,
diff --git a/lib/ui/semantics/semantics_update_builder.h b/lib/ui/semantics/semantics_update_builder.h
@@ -65,7 +65,8 @@ class SemanticsUpdateBuilder
       const tonic::Float64List& transform,
       const tonic::Int32List& childrenInTraversalOrder,
       const tonic::Int32List& childrenInHitTestOrder,
-      const tonic::Int32List& customAccessibilityActions);
+      const tonic::Int32List& customAccessibilityActions,
+      int headingLevel);
 
   void updateCustomAction(int id,
                           std::string label,
diff --git a/lib/web_ui/lib/semantics.dart b/lib/web_ui/lib/semantics.dart
@@ -286,6 +286,7 @@ class SemanticsUpdateBuilder {
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
+    int headingLevel = 0,
   }) {
     if (transform.length != 16) {
       throw ArgumentError('transform argument must have 16 entries.');
@@ -324,6 +325,7 @@ class SemanticsUpdateBuilder {
       childrenInHitTestOrder: childrenInHitTestOrder,
       additionalActions: additionalActions,
       platformViewId: platformViewId,
+      headingLevel: headingLevel,
     ));
   }
 
diff --git a/lib/web_ui/lib/src/engine.dart b/lib/web_ui/lib/src/engine.dart
@@ -146,6 +146,7 @@ export 'engine/semantics/accessibility.dart';
 export 'engine/semantics/checkable.dart';
 export 'engine/semantics/dialog.dart';
 export 'engine/semantics/focusable.dart';
+export 'engine/semantics/heading.dart';
 export 'engine/semantics/image.dart';
 export 'engine/semantics/incrementable.dart';
 export 'engine/semantics/label_and_value.dart';
diff --git a/lib/web_ui/lib/src/engine/semantics.dart b/lib/web_ui/lib/src/engine/semantics.dart
@@ -5,6 +5,7 @@
 export 'semantics/accessibility.dart';
 export 'semantics/checkable.dart';
 export 'semantics/focusable.dart';
+export 'semantics/heading.dart';
 export 'semantics/image.dart';
 export 'semantics/incrementable.dart';
 export 'semantics/label_and_value.dart';
diff --git a/lib/web_ui/lib/src/engine/semantics/heading.dart b/lib/web_ui/lib/src/engine/semantics/heading.dart
@@ -0,0 +1,37 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import '../dom.dart';
+import 'semantics.dart';
+
+/// Renders semantics objects as headings with the corresponding
+/// level (h1 ... h6).
+class Heading extends PrimaryRoleManager {
+  Heading(SemanticsObject semanticsObject)
+      : super.blank(PrimaryRole.heading, semanticsObject) {
+        addHeadingRole();
+      }
+
+  @override
+  void update() {
+    super.update();
+
+    if (!semanticsObject.isHeadingLevelDirty) {
+      return;
+    }
+
+    addHeadingLevel(semanticsObject.headingLevel);
+  }
+
+  @override
+  bool focusAsRouteDefault() => focusable?.focusAsRouteDefault() ?? false;
+
+  void addHeadingRole() {
+    setAriaRole('heading');
+  }
+
+  void addHeadingLevel(int headingLevel) {
+    semanticsObject.element.setAttribute('aria-level', headingLevel);
+  }
+}
diff --git a/lib/web_ui/lib/src/engine/semantics/semantics.dart b/lib/web_ui/lib/src/engine/semantics/semantics.dart
@@ -22,6 +22,7 @@ import 'accessibility.dart';
 import 'checkable.dart';
 import 'dialog.dart';
 import 'focusable.dart';
+import 'heading.dart';
 import 'image.dart';
 import 'incrementable.dart';
 import 'label_and_value.dart';
@@ -232,6 +233,7 @@ class SemanticsNodeUpdate {
     required this.childrenInTraversalOrder,
     required this.childrenInHitTestOrder,
     required this.additionalActions,
+    required this.headingLevel,
   });
 
   /// See [ui.SemanticsUpdateBuilder.updateNode].
@@ -332,6 +334,9 @@ class SemanticsNodeUpdate {
 
   /// See [ui.SemanticsUpdateBuilder.updateNode].
   final double thickness;
+
+  /// See [ui.SemanticsUpdateBuilder.updateNode].
+  final int headingLevel;
 }
 
 /// Identifies [PrimaryRoleManager] implementations.
@@ -354,6 +359,10 @@ enum PrimaryRole {
   /// A control that has a checked state, such as a check box or a radio button.
   checkable,
 
+  /// Adds the "heading" ARIA role to the node. The attribute "aria-level" is
+  /// also assigned.
+  heading,
+
   /// Visual only element.
   image,
 
@@ -1097,6 +1106,19 @@ class SemanticsObject {
     _dirtyFields |= _platformViewIdIndex;
   }
 
+  /// See [ui.SemanticsUpdateBuilder.updateNode].
+  int get headingLevel => _headingLevel;
+  int _headingLevel = 0;
+
+  static const int _headingLevelIndex = 1 << 24;
+
+  /// Whether the [headingLevel] field has been updated but has not been
+  /// applied to the DOM yet.
+  bool get isHeadingLevelDirty => _isDirty(_headingLevelIndex);
+  void _markHeadingLevelDirty() {
+    _dirtyFields |= _headingLevelIndex;
+  }
+
   /// A unique permanent identifier of the semantics node in the tree.
   final int id;
 
@@ -1201,6 +1223,9 @@ class SemanticsObject {
   /// Whether this object represents an editable text field.
   bool get isTextField => hasFlag(ui.SemanticsFlag.isTextField);
 
+  /// Whether this object represents a heading element.
+  bool get isHeading => headingLevel != 0;
+
     /// Whether this object represents an editable text field.
   bool get isLink => hasFlag(ui.SemanticsFlag.isLink);
 
@@ -1358,6 +1383,11 @@ class SemanticsObject {
       _markTooltipDirty();
     }
 
+    if (_headingLevel != update.headingLevel) {
+      _headingLevel = update.headingLevel;
+      _markHeadingLevelDirty();
+    }
+
     if (_textDirection != update.textDirection) {
       _textDirection = update.textDirection;
       _markTextDirectionDirty();
@@ -1591,6 +1621,8 @@ class SemanticsObject {
     // The most specific role should take precedence.
     if (isPlatformView) {
       return PrimaryRole.platformView;
+    } else if (isHeading) {
+      return PrimaryRole.heading;
     } else if (isTextField) {
       return PrimaryRole.textField;
     } else if (isIncrementable) {
@@ -1623,6 +1655,7 @@ class SemanticsObject {
       PrimaryRole.image => ImageRoleManager(this),
       PrimaryRole.platformView => PlatformViewRoleManager(this),
       PrimaryRole.link => Link(this),
+      PrimaryRole.heading => Heading(this),
       PrimaryRole.generic => GenericRole(this),
     };
   }
diff --git a/lib/web_ui/test/engine/semantics/semantics_test.dart b/lib/web_ui/test/engine/semantics/semantics_test.dart
@@ -721,6 +721,27 @@ void _testHeader() {
     owner().updateSemantics(builder.build());
     expectSemanticsTree(owner(), '''
 <sem role="group" aria-label="Header of the page"><sem-c><sem></sem></sem-c></sem>
+''');
+
+    semantics().semanticsEnabled = false;
+  });
+
+  test('renders aria-level tag for headings with heading level', () {
+    semantics()
+      ..debugOverrideTimestampFunction(() => _testTime)
+      ..semanticsEnabled = true;
+
+    final ui.SemanticsUpdateBuilder builder = ui.SemanticsUpdateBuilder();
+    updateNode(
+      builder,
+      headingLevel: 2,
+      transform: Matrix4.identity().toFloat64(),
+      rect: const ui.Rect.fromLTRB(0, 0, 100, 50),
+    );
+
+    owner().updateSemantics(builder.build());
+    expectSemanticsTree(owner(), '''
+<sem aria-level="2" role="heading" style="filter: opacity(0%); color: rgba(0, 0, 0, 0)"></sem>
 ''');
 
     semantics().semanticsEnabled = false;
@@ -3557,6 +3578,7 @@ void updateNode(
   Int32List? childrenInTraversalOrder,
   Int32List? childrenInHitTestOrder,
   Int32List? additionalActions,
+  int headingLevel = 0,
 }) {
   transform ??= Float64List.fromList(Matrix4.identity().storage);
   childrenInTraversalOrder ??= Int32List(0);
@@ -3596,6 +3618,7 @@ void updateNode(
     childrenInTraversalOrder: childrenInTraversalOrder,
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
+    headingLevel: headingLevel,
   );
 }
 
diff --git a/lib/web_ui/test/engine/semantics/semantics_tester.dart b/lib/web_ui/test/engine/semantics/semantics_tester.dart
@@ -111,6 +111,7 @@ class SemanticsTester {
     Float64List? transform,
     Int32List? additionalActions,
     List<SemanticsNodeUpdate>? children,
+    int? headingLevel,
   }) {
     // Flags
     if (hasCheckedState ?? false) {
@@ -311,6 +312,7 @@ class SemanticsTester {
       childrenInTraversalOrder: childIds,
       childrenInHitTestOrder: childIds,
       additionalActions: additionalActions ?? Int32List(0),
+      headingLevel: headingLevel ?? 0,
     );
     _nodeUpdates.add(update);
     return update;
diff --git a/shell/platform/embedder/fixtures/main.dart b/shell/platform/embedder/fixtures/main.dart
@@ -178,6 +178,7 @@ Future<void> a11y_main() async {
       tooltip: 'tooltip',
       textDirection: TextDirection.ltr,
       additionalActions: Int32List(0),
+      headingLevel: 0
     )
     ..updateNode(
       id: 84,
@@ -213,6 +214,7 @@ Future<void> a11y_main() async {
       additionalActions: Int32List(0),
       childrenInHitTestOrder: Int32List(0),
       childrenInTraversalOrder: Int32List(0),
+      headingLevel: 0
     )
     ..updateNode(
       id: 96,
@@ -248,6 +250,7 @@ Future<void> a11y_main() async {
       tooltip: 'tooltip',
       textDirection: TextDirection.ltr,
       additionalActions: Int32List(0),
+      headingLevel: 0
     )
     ..updateNode(
       id: 128,
@@ -283,6 +286,7 @@ Future<void> a11y_main() async {
       textDirection: TextDirection.ltr,
       childrenInHitTestOrder: Int32List(0),
       childrenInTraversalOrder: Int32List(0),
+      headingLevel: 0
     )
     ..updateCustomAction(
       id: 21,
@@ -379,6 +383,7 @@ Future<void> a11y_string_attributes() async {
       tooltip: 'tooltip',
       textDirection: TextDirection.ltr,
       additionalActions: Int32List(0),
+      headingLevel: 0,
     );
 
   PlatformDispatcher.instance.views.first.updateSemantics(builder.build());
