Re-land Adding Link Semantics (flutter/engine#12972)

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

@@ -291,6 +291,7 @@ class SemanticsFlag {
   static const int _kIsMultilineIndex = 1 << 19;
   static const int _kIsReadOnlyIndex = 1 << 20;
   static const int _kIsFocusableIndex = 1 << 21;
+  static const int _kIsLinkIndex = 1 << 22;
 
   const SemanticsFlag._(this.index);
 
@@ -333,7 +334,7 @@ class SemanticsFlag {
 
   /// Whether the semantic node represents a button.
   ///
-  /// Platforms has special handling for buttons, for example Android's TalkBack
+  /// Platforms have special handling for buttons, for example Android's TalkBack
   /// and iOS's VoiceOver provides an additional hint when the focused object is
   /// a button.
   static const SemanticsFlag isButton = SemanticsFlag._(_kIsButtonIndex);
@@ -349,6 +350,13 @@ class SemanticsFlag {
   /// Only applicable when [isTextField] is true.
   static const SemanticsFlag isReadOnly = SemanticsFlag._(_kIsReadOnlyIndex);
 
+  /// Whether the semantic node is an interactive link.
+  ///
+  /// Platforms have special handling for links, for example iOS's VoiceOver
+  /// provides an additional hint when the focused object is a link, as well as
+  /// the ability to parse the links through another navigation menu.
+  static const SemanticsFlag isLink = SemanticsFlag._(_kIsLinkIndex);
+
   /// Whether the semantic node is able to hold the user's focus.
   ///
   /// The focused element is usually the current receiver of keyboard inputs.
@@ -528,6 +536,7 @@ class SemanticsFlag {
     _kHasImplicitScrollingIndex: hasImplicitScrolling,
     _kIsMultilineIndex: isMultiline,
     _kIsReadOnlyIndex: isReadOnly,
+    _kIsLinkIndex: isLink,
   };
 
   @override
@@ -575,6 +584,8 @@ class SemanticsFlag {
         return 'SemanticsFlag.isMultiline';
       case _kIsReadOnlyIndex:
         return 'SemanticsFlag.isReadOnly';
+      case _kIsLinkIndex:
+        return 'SemanticsFlag.isLink';
     }
     return null;
   }

engine/src/flutter/lib/ui/semantics/semantics_node.h

@@ -73,6 +73,7 @@ enum class SemanticsFlags : int32_t {
   // kIsMultiline = 1 << 19,
   kIsReadOnly = 1 << 20,
   kIsFocusable = 1 << 21,
+  kIsLink = 1 << 22,
 };
 
 const int kScrollableSemanticsFlags =

engine/src/flutter/shell/platform/android/io/flutter/view/AccessibilityBridge.java

@@ -591,7 +591,7 @@ public class AccessibilityBridge extends AccessibilityNodeProvider {
             }
         }
 
-        if (semanticsNode.hasFlag(Flag.IS_BUTTON)) {
+        if (semanticsNode.hasFlag(Flag.IS_BUTTON) || semanticsNode.hasFlag(Flag.IS_LINK)) {
             result.setClassName("android.widget.Button");
         }
         if (semanticsNode.hasFlag(Flag.IS_IMAGE)) {
@@ -1648,7 +1648,8 @@ public class AccessibilityBridge extends AccessibilityNodeProvider {
         // The Dart API defines the following flag but it isn't used in Android.
         // IS_MULTILINE(1 << 19);
         IS_READ_ONLY(1 << 20),
-        IS_FOCUSABLE(1 << 21);
+        IS_FOCUSABLE(1 << 21),
+        IS_LINK(1 << 22);
 
         final int value;
 

engine/src/flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm

@@ -407,6 +407,9 @@ flutter::SemanticsAction GetSemanticsActionForScrollDirection(
   if ([self node].HasFlag(flutter::SemanticsFlags::kIsLiveRegion)) {
     traits |= UIAccessibilityTraitUpdatesFrequently;
   }
+  if ([self node].HasFlag(flutter::SemanticsFlags::kIsLink)) {
+    traits |= UIAccessibilityTraitLink;
+  }
   return traits;
 }
 

engine/src/flutter/shell/platform/embedder/embedder.h

@@ -63,8 +63,7 @@ typedef enum {
 /// Must match the `SemanticsAction` enum in semantics.dart.
 typedef enum {
   /// The equivalent of a user briefly tapping the screen with the finger
-  /// without
-  /// moving it.
+  /// without moving it.
   kFlutterSemanticsActionTap = 1 << 0,
   /// The equivalent of a user pressing and holding the screen with the finger
   /// for a few seconds without moving it.
@@ -172,6 +171,8 @@ typedef enum {
   kFlutterSemanticsFlagIsReadOnly = 1 << 20,
   /// Whether the semantic node can hold the user's focus.
   kFlutterSemanticsFlagIsFocusable = 1 << 21,
+  /// Whether the semantics node represents a link.
+  kFlutterSemanticsFlagIsLink = 1 << 22,
 } FlutterSemanticsFlag;
 
 typedef enum {