Label sources

Author: mdebbar

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

@@ -28,7 +28,10 @@ class Incrementable extends PrimaryRoleManager {
     // the one being focused on, but the internal `<input>` element.
     addLiveRegion();
     addRouteName();
-    addLabelAndValue(preferredRepresentation: LabelRepresentation.ariaLabel);
+    addLabelAndValue(
+      preferredRepresentation: LabelRepresentation.ariaLabel,
+      labelSources: _incrementableLabelSources,
+    );
 
     append(_element);
     _element.type = 'range';
@@ -60,6 +63,12 @@ class Incrementable extends PrimaryRoleManager {
     _focusManager.manage(semanticsObject.id, _element);
   }
 
+  // The incrementable role manager has custom reporting of the semantics value.
+  // We do not need to also render it as a label.
+  static final Set<LabelSource> _incrementableLabelSources = LabelAndValue
+      .allLabelSources
+      .difference(<LabelSource>{LabelSource.value});
+
   @override
   bool focusAsRouteDefault() {
     _element.focus();

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

@@ -425,14 +425,33 @@ final class SizedSpanRepresentation extends LabelRepresentationBehavior {
   DomElement get focusTarget => _domText;
 }
 
+/// The source of the label attribute for a semantic node.
+enum LabelSource {
+  /// The label is provided by the [SemanticsObject.label] property.
+  label,
+
+  /// The label is provided by the [SemanticsObject.value] property.
+  value,
+
+  /// The label is provided by the [SemanticsObject.hint] property.
+  hint,
+
+  /// The label is provided by the [SemanticsObject.tooltip] property.
+  tooltip,
+}
+
 /// Renders [SemanticsObject.label] and/or [SemanticsObject.value] to the semantics DOM.
 ///
 /// The value is not always rendered. Some semantics nodes correspond to
 /// interactive controls. In such case the value is reported via that element's
 /// `value` attribute rather than rendering it separately.
 class LabelAndValue extends RoleManager {
-  LabelAndValue(SemanticsObject semanticsObject, PrimaryRoleManager owner, { required this.preferredRepresentation })
-      : super(Role.labelAndValue, semanticsObject, owner);
+  LabelAndValue(
+    SemanticsObject semanticsObject,
+    PrimaryRoleManager owner, {
+    required this.preferredRepresentation,
+    this.labelSources = allLabelSources,
+  }) : super(Role.labelAndValue, semanticsObject, owner);
 
   /// The preferred representation of the label in the DOM.
   ///
@@ -443,6 +462,17 @@ class LabelAndValue extends RoleManager {
   /// instead.
   LabelRepresentation preferredRepresentation;
 
+  /// The sources of the label that are allowed to be used.
+  final Set<LabelSource> labelSources;
+
+  /// All possible sources of the label.
+  static const Set<LabelSource> allLabelSources = <LabelSource>{
+    LabelSource.label,
+    LabelSource.value,
+    LabelSource.hint,
+    LabelSource.tooltip,
+  };
+
   @override
   void update() {
     final String? computedLabel = _computeLabel();
@@ -477,20 +507,34 @@ class LabelAndValue extends RoleManager {
     return representation;
   }
 
+  String? get _label =>
+      labelSources.contains(LabelSource.label) && semanticsObject.hasLabel
+          ? semanticsObject.label
+          : null;
+
+  String? get _value =>
+      labelSources.contains(LabelSource.value) && semanticsObject.hasValue
+          ? semanticsObject.value
+          : null;
+
+  String? get _tooltip =>
+      labelSources.contains(LabelSource.tooltip) && semanticsObject.hasTooltip
+          ? semanticsObject.tooltip
+          : null;
+
+  String? get _hint =>
+      labelSources.contains(LabelSource.hint) ? semanticsObject.hint : null;
+
   /// Computes the final label to be assigned to the node.
   ///
   /// The label is a concatenation of tooltip, label, hint, and value, whichever
-  /// combination is present.
+  /// combination is present and allowed by [labelSources].
   String? _computeLabel() {
-    // 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 = !semanticsObject.isIncrementable && semanticsObject.hasValue;
-
     return computeDomSemanticsLabel(
-      tooltip: semanticsObject.hasTooltip ? semanticsObject.tooltip : null,
-      label: semanticsObject.hasLabel ? semanticsObject.label : null,
-      hint: semanticsObject.hint,
-      value: shouldDisplayValue ? semanticsObject.value : null,
+      tooltip: _tooltip,
+      label: _label,
+      hint: _hint,
+      value: _value,
     );
   }
 

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

@@ -11,10 +11,16 @@ class Link extends PrimaryRoleManager {
     PrimaryRole.link,
     semanticsObject,
     preferredLabelRepresentation: LabelRepresentation.domText,
+    labelSources: _linkLabelSources,
   ) {
     addTappable();
   }
 
+  // The semantics value is consumed by the [Link] role manager, so there's no
+  // need to also render it as a label.
+  static final Set<LabelSource> _linkLabelSources = LabelAndValue.allLabelSources
+      .difference(<LabelSource>{LabelSource.value});
+
   @override
   DomElement createElement() {
     final DomElement element = domDocument.createElement('a');

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

@@ -434,12 +434,20 @@ abstract class PrimaryRoleManager {
   ///
   /// If `labelRepresentation` is true, configures the [LabelAndValue] role with
   /// [LabelAndValue.labelRepresentation] set to true.
-  PrimaryRoleManager.withBasics(this.role, this.semanticsObject, { required LabelRepresentation preferredLabelRepresentation }) {
+  PrimaryRoleManager.withBasics(
+    this.role,
+    this.semanticsObject, {
+    required LabelRepresentation preferredLabelRepresentation,
+    Set<LabelSource> labelSources = LabelAndValue.allLabelSources,
+  }) {
     element = _initElement(createElement(), semanticsObject);
     addFocusManagement();
     addLiveRegion();
     addRouteName();
-    addLabelAndValue(preferredRepresentation: preferredLabelRepresentation);
+    addLabelAndValue(
+      preferredRepresentation: preferredLabelRepresentation,
+      labelSources: labelSources,
+    );
   }
 
   /// Initializes a blank role for a [semanticsObject].
@@ -566,8 +574,16 @@ abstract class PrimaryRoleManager {
   LabelAndValue? _labelAndValue;
 
   /// Adds generic label features.
-  void addLabelAndValue({ required LabelRepresentation preferredRepresentation }) {
-    addSecondaryRole(_labelAndValue = LabelAndValue(semanticsObject, this, preferredRepresentation: preferredRepresentation));
+  void addLabelAndValue({
+    required LabelRepresentation preferredRepresentation,
+    Set<LabelSource> labelSources = LabelAndValue.allLabelSources,
+  }) {
+    addSecondaryRole(_labelAndValue = LabelAndValue(
+      semanticsObject,
+      this,
+      preferredRepresentation: preferredRepresentation,
+      labelSources: labelSources,
+    ));
   }
 
   /// Adds generic functionality for handling taps and clicks.