Add Semantics Property linkUrl (#53507)

The new property allows the user to specify a URI for their semantics link node. It's plumbed through for both web and non-web engines, but it's only used in the web engine currently. It sets the `href` of the anchor element associated with semantics node.

This is going to unlock better semantics support in the Link widget on web ([PR](flutter/packages#6711)).

Framework counterpart: flutter/flutter#150639

Part of flutter/flutter#150263

Author: mdebbar

lib/ui/fixtures/ui_test.dart

@@ -233,6 +233,7 @@ void sendSemanticsUpdate() {
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
     headingLevel: 0,
+    linkUrl: '',
   );
   _semanticsUpdate(builder.build());
 }

lib/ui/semantics.dart

@@ -849,6 +849,9 @@ abstract class SemanticsUpdateBuilder {
   /// inclusive. This attribute is only used for Web platform, and it will have
   /// no effect on other platforms.
   ///
+  /// The `linkUrl` describes the URI that this node links to. If the node is
+  /// not a link, this should be an empty string.
+  ///
   /// See also:
   ///
   ///  * https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/heading_role
@@ -888,6 +891,7 @@ abstract class SemanticsUpdateBuilder {
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
     int headingLevel = 0,
+    String linkUrl = '',
   });
 
   /// Update the custom semantics action associated with the given `id`.
@@ -959,6 +963,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
     int headingLevel = 0,
+    String linkUrl = '',
   }) {
     assert(_matrix4IsValid(transform));
     assert (
@@ -1003,6 +1008,7 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
       childrenInHitTestOrder,
       additionalActions,
       headingLevel,
+      linkUrl,
     );
   }
   @Native<
@@ -1044,7 +1050,8 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
           Handle,
           Handle,
           Handle,
-          Int32)>(symbol: 'SemanticsUpdateBuilder::updateNode')
+          Int32,
+          Handle)>(symbol: 'SemanticsUpdateBuilder::updateNode')
   external void _updateNode(
       int id,
       int flags,
@@ -1082,7 +1089,8 @@ base class _NativeSemanticsUpdateBuilder extends NativeFieldWrapperClass1 implem
       Int32List childrenInTraversalOrder,
       Int32List childrenInHitTestOrder,
       Int32List additionalActions,
-      int headingLevel);
+      int headingLevel,
+      String linkUrl);
 
   @override
   void updateCustomAction({required int id, String? label, String? hint, int overrideId = -1}) {

lib/ui/semantics/semantics_node.h

@@ -144,6 +144,8 @@ struct SemanticsNode {
   std::vector<int32_t> childrenInHitTestOrder;
   std::vector<int32_t> customAccessibilityActions;
   int32_t headingLevel = 0;
+
+  std::string linkUrl;
 };
 
 // Contains semantic nodes that need to be updated.

lib/ui/semantics/semantics_update_builder.cc

@@ -67,7 +67,8 @@ void SemanticsUpdateBuilder::updateNode(
     const tonic::Int32List& childrenInTraversalOrder,
     const tonic::Int32List& childrenInHitTestOrder,
     const tonic::Int32List& localContextActions,
-    int headingLevel) {
+    int headingLevel,
+    std::string linkUrl) {
   FML_CHECK(scrollChildren == 0 ||
             (scrollChildren > 0 && childrenInHitTestOrder.data()))
       << "Semantics update contained scrollChildren but did not have "
@@ -121,6 +122,7 @@ void SemanticsUpdateBuilder::updateNode(
   nodes_[id] = node;
 
   node.headingLevel = headingLevel;
+  node.linkUrl = std::move(linkUrl);
 }
 
 void SemanticsUpdateBuilder::updateCustomAction(int id,

lib/ui/semantics/semantics_update_builder.h

@@ -66,7 +66,8 @@ class SemanticsUpdateBuilder
       const tonic::Int32List& childrenInTraversalOrder,
       const tonic::Int32List& childrenInHitTestOrder,
       const tonic::Int32List& customAccessibilityActions,
-      int headingLevel);
+      int headingLevel,
+      std::string linkUrl);
 
   void updateCustomAction(int id,
                           std::string label,

lib/web_ui/lib/semantics.dart

@@ -287,6 +287,7 @@ class SemanticsUpdateBuilder {
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
     int headingLevel = 0,
+    String? linkUrl,
   }) {
     if (transform.length != 16) {
       throw ArgumentError('transform argument must have 16 entries.');
@@ -326,6 +327,7 @@ class SemanticsUpdateBuilder {
       additionalActions: additionalActions,
       platformViewId: platformViewId,
       headingLevel: headingLevel,
+      linkUrl: linkUrl,
     ));
   }
 

lib/web_ui/lib/src/engine/semantics/link.dart

@@ -18,12 +18,23 @@ class Link extends PrimaryRoleManager {
   @override
   DomElement createElement() {
     final DomElement element = domDocument.createElement('a');
-    // TODO(mdebbar): Fill in the real link once the framework sends entire uri.
-    // https://github.com/flutter/flutter/issues/150263.
     element.style.display = 'block';
     return element;
   }
 
+  @override
+  void update() {
+    super.update();
+
+    if (semanticsObject.isLinkUrlDirty) {
+      if (semanticsObject.hasLinkUrl) {
+        element.setAttribute('href', semanticsObject.linkUrl!);
+      } else {
+        element.removeAttribute('href');
+      }
+    }
+  }
+
   @override
   bool focusAsRouteDefault() => focusable?.focusAsRouteDefault() ?? false;
 }

lib/web_ui/lib/src/engine/semantics/semantics.dart

@@ -234,6 +234,7 @@ class SemanticsNodeUpdate {
     required this.childrenInHitTestOrder,
     required this.additionalActions,
     required this.headingLevel,
+    this.linkUrl,
   });
 
   /// See [ui.SemanticsUpdateBuilder.updateNode].
@@ -337,6 +338,9 @@ class SemanticsNodeUpdate {
 
   /// See [ui.SemanticsUpdateBuilder.updateNode].
   final int headingLevel;
+
+  /// See [ui.SemanticsUpdateBuilder.updateNode].
+  final String? linkUrl;
 }
 
 /// Identifies [PrimaryRoleManager] implementations.
@@ -1146,6 +1150,22 @@ class SemanticsObject {
     _dirtyFields |= _identifierIndex;
   }
 
+  /// See [ui.SemanticsUpdateBuilder.updateNode].
+  String? get linkUrl => _linkUrl;
+  String? _linkUrl;
+
+  /// Whether this object contains a non-empty link URL.
+  bool get hasLinkUrl => _linkUrl != null && _linkUrl!.isNotEmpty;
+
+  static const int _linkUrlIndex = 1 << 26;
+
+  /// Whether the [linkUrl] field has been updated but has not been
+  /// applied to the DOM yet.
+  bool get isLinkUrlDirty => _isDirty(_linkUrlIndex);
+  void _markLinkUrlDirty() {
+    _dirtyFields |= _linkUrlIndex;
+  }
+
   /// A unique permanent identifier of the semantics node in the tree.
   final int id;
 
@@ -1445,6 +1465,11 @@ class SemanticsObject {
       _markPlatformViewIdDirty();
     }
 
+    if (_linkUrl != update.linkUrl) {
+      _linkUrl = update.linkUrl;
+      _markLinkUrlDirty();
+    }
+
     // Apply updates to the DOM.
     _updateRoles();
 

lib/web_ui/test/engine/semantics/semantics_test.dart

@@ -3603,6 +3603,28 @@ void _testLink() {
     expect(object.element.tagName.toLowerCase(), 'a');
     expect(object.element.hasAttribute('href'), isFalse);
   });
+
+  test('link nodes with linkUrl set the href attribute', () {
+    semantics()
+      ..debugOverrideTimestampFunction(() => _testTime)
+      ..semanticsEnabled = true;
+
+    SemanticsObject pumpSemantics() {
+      final SemanticsTester tester = SemanticsTester(owner());
+      tester.updateNode(
+        id: 0,
+        isLink: true,
+        linkUrl: 'https://flutter.dev',
+        rect: const ui.Rect.fromLTRB(0, 0, 100, 50),
+      );
+      tester.apply();
+      return tester.getSemanticsObject(0);
+    }
+
+    final SemanticsObject object = pumpSemantics();
+    expect(object.element.tagName.toLowerCase(), 'a');
+    expect(object.element.getAttribute('href'), 'https://flutter.dev');
+  });
 }
 
 /// A facade in front of [ui.SemanticsUpdateBuilder.updateNode] that
@@ -3645,6 +3667,7 @@ void updateNode(
   Int32List? childrenInHitTestOrder,
   Int32List? additionalActions,
   int headingLevel = 0,
+  String? linkUrl,
 }) {
   transform ??= Float64List.fromList(Matrix4.identity().storage);
   childrenInTraversalOrder ??= Int32List(0);
@@ -3685,6 +3708,7 @@ void updateNode(
     childrenInHitTestOrder: childrenInHitTestOrder,
     additionalActions: additionalActions,
     headingLevel: headingLevel,
+    linkUrl: linkUrl,
   );
 }
 

lib/web_ui/test/engine/semantics/semantics_tester.dart

@@ -112,6 +112,7 @@ class SemanticsTester {
     Int32List? additionalActions,
     List<SemanticsNodeUpdate>? children,
     int? headingLevel,
+    String? linkUrl,
   }) {
     // Flags
     if (hasCheckedState ?? false) {
@@ -313,6 +314,7 @@ class SemanticsTester {
       childrenInHitTestOrder: childIds,
       additionalActions: additionalActions ?? Int32List(0),
       headingLevel: headingLevel ?? 0,
+      linkUrl: linkUrl,
     );
     _nodeUpdates.add(update);
     return update;