Add web support for tooltip (flutter/engine#28966)

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

@@ -52,17 +52,24 @@ class LabelAndValue extends RoleManager {
   void update() {
     final bool hasValue = semanticsObject.hasValue;
     final bool hasLabel = semanticsObject.hasLabel;
+    final bool hasTooltip = semanticsObject.hasTooltip;
 
     // If the node is incrementable the value is reported to the browser via
     // the respective role manager. We do not need to also render it again here.
     final bool shouldDisplayValue = hasValue && !semanticsObject.isIncrementable;
 
-    if (!hasLabel && !shouldDisplayValue) {
+    if (!hasLabel && !shouldDisplayValue && !hasTooltip) {
       _cleanUpDom();
       return;
     }
 
     final StringBuffer combinedValue = StringBuffer();
+    if (hasTooltip) {
+      combinedValue.write(semanticsObject.tooltip);
+      if (hasLabel || shouldDisplayValue) {
+        combinedValue.write('\n');
+      }
+    }
     if (hasLabel) {
       combinedValue.write(semanticsObject.label);
       if (shouldDisplayValue) {

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

@@ -600,6 +600,22 @@ class SemanticsObject {
     _dirtyFields |= _additionalActionsIndex;
   }
 
+  /// See [ui.SemanticsUpdateBuilder.updateNode].
+  String? get tooltip => _tooltip;
+  String? _tooltip;
+
+  /// Whether this object contains a non-empty tooltip.
+  bool get hasTooltip => _tooltip != null && _tooltip!.isNotEmpty;
+
+  static const int _tooltipIndex = 1 << 22;
+
+  /// Whether the [tooltip] field has been updated but has not been
+  /// applied to the DOM yet.
+  bool get isTooltipDirty => _isDirty(_tooltipIndex);
+  void _markTooltipDirty() {
+    _dirtyFields |= _tooltipIndex;
+  }
+
   /// A unique permanent identifier of the semantics node in the tree.
   final int id;
 
@@ -812,6 +828,11 @@ class SemanticsObject {
       _markDecreasedValueDirty();
     }
 
+    if (_tooltip != update.tooltip) {
+      _tooltip = update.tooltip;
+      _markTooltipDirty();
+    }
+
     if (_textDirection != update.textDirection) {
       _textDirection = update.textDirection;
       _markTextDirectionDirty();
@@ -882,7 +903,7 @@ class SemanticsObject {
   /// Detects the roles that this semantics object corresponds to and manages
   /// the lifecycles of [SemanticsObjectRole] objects.
   void _updateRoles() {
-    _updateRole(Role.labelAndValue, (hasLabel || hasValue) && !isTextField && !isVisualOnly);
+    _updateRole(Role.labelAndValue, (hasLabel || hasValue || hasTooltip) && !isTextField && !isVisualOnly);
     _updateRole(Role.textField, isTextField);
 
     final bool shouldUseTappableRole =

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

@@ -131,7 +131,7 @@ void _testEngineSemanticsOwner() {
     expect(placeholder.isConnected, isFalse);
   });
 
-  void renderLabel(String label) {
+  void renderSemantics({String? label, String? tooltip}) {
     final ui.SemanticsUpdateBuilder builder = ui.SemanticsUpdateBuilder();
     updateNode(
       builder,
@@ -148,13 +148,18 @@ void _testEngineSemanticsOwner() {
       id: 1,
       actions: 0,
       flags: 0,
-      label: label,
+      label: label ?? '',
+      tooltip: tooltip ?? '',
       transform: Matrix4.identity().toFloat64(),
       rect: const ui.Rect.fromLTRB(0, 0, 20, 20),
     );
     semantics().updateSemantics(builder.build());
   }
 
+  void renderLabel(String label) {
+    renderSemantics(label: label);
+  }
+
   test('produces an aria-label', () async {
     semantics().semanticsEnabled = true;
 
@@ -202,6 +207,53 @@ void _testEngineSemanticsOwner() {
     semantics().semanticsEnabled = false;
   });
 
+  test('tooltip is part of label', () async {
+    semantics().semanticsEnabled = true;
+
+    // Create
+    renderSemantics(tooltip: 'tooltip');
+
+    final Map<int, SemanticsObject> tree = semantics().debugSemanticsTree!;
+    expect(tree.length, 2);
+    expect(tree[0]!.id, 0);
+    expect(tree[0]!.element.tagName.toLowerCase(), 'flt-semantics');
+    expect(tree[1]!.id, 1);
+    expect(tree[1]!.tooltip, 'tooltip');
+
+    expectSemanticsTree('''
+<sem style="$rootSemanticStyle">
+  <sem-c>
+    <sem aria-label="tooltip">
+      <sem-v>tooltip</sem-v>
+    </sem>
+  </sem-c>
+</sem>''');
+
+    // Update
+    renderSemantics(label: 'Hello', tooltip: 'tooltip');
+
+    expectSemanticsTree('''
+<sem style="$rootSemanticStyle">
+  <sem-c>
+    <sem aria-label="tooltip\nHello">
+      <sem-v>tooltip\nHello</sem-v>
+    </sem>
+  </sem-c>
+</sem>''');
+
+    // Remove
+    renderSemantics();
+
+    expectSemanticsTree('''
+<sem style="$rootSemanticStyle">
+  <sem-c>
+    <sem></sem>
+  </sem-c>
+</sem>''');
+
+    semantics().semanticsEnabled = false;
+  });
+
   test('clears semantics tree when disabled', () {
     expect(semantics().debugSemanticsTree, isEmpty);
     semantics().semanticsEnabled = true;