add semantic label to image icon and exclude semantics from image widget (#19970)

packages/flutter/lib/src/widgets/image_icon.dart

@@ -26,7 +26,8 @@ class ImageIcon extends StatelessWidget {
   const ImageIcon(this.image, {
     Key key,
     this.size,
-    this.color
+    this.color,
+    this.semanticLabel,
   }) : super(key: key);
 
   /// The image to display as the icon.
@@ -53,14 +54,27 @@ class ImageIcon extends StatelessWidget {
   /// [IconTheme], if any.
   final Color color;
 
+  /// Semantic label for the icon.
+  ///
+  /// Announced in accessibility modes (e.g TalkBack/VoiceOver).
+  /// This label does not show in the UI.
+  ///
+  /// See also:
+  ///
+  ///  * [Semantics.label], which is set to [semanticLabel] in the underlying
+  ///    [Semantics] widget.
+  final String semanticLabel;
+
   @override
   Widget build(BuildContext context) {
     final IconThemeData iconTheme = IconTheme.of(context);
-
     final double iconSize = size ?? iconTheme.size;
 
     if (image == null)
-      return new SizedBox(width: iconSize, height: iconSize);
+      return new Semantics(
+        label: semanticLabel,
+        child: SizedBox(width: iconSize, height: iconSize)
+      );
 
     final double iconOpacity = iconTheme.opacity;
     Color iconColor = color ?? iconTheme.color;
@@ -68,13 +82,17 @@ class ImageIcon extends StatelessWidget {
     if (iconOpacity != null && iconOpacity != 1.0)
       iconColor = iconColor.withOpacity(iconColor.opacity * iconOpacity);
 
-    return new Image(
-      image: image,
-      width: iconSize,
-      height: iconSize,
-      color: iconColor,
-      fit: BoxFit.scaleDown,
-      alignment: Alignment.center,
+    return new Semantics(
+      label: semanticLabel,
+      child: Image(
+        image: image,
+        width: iconSize,
+        height: iconSize,
+        color: iconColor,
+        fit: BoxFit.scaleDown,
+        alignment: Alignment.center,
+        excludeFromSemantics: true,
+      ),
     );
   }
 

packages/flutter/test/widgets/image_icon_test.dart

@@ -96,4 +96,26 @@ void main() {
     final RenderBox renderObject = tester.renderObject(find.byType(ImageIcon));
     expect(renderObject.size, equals(const Size.square(24.0)));
   });
+
+  testWidgets('ImageIcon has semantics data', (WidgetTester tester) async {
+    final SemanticsHandle handle = tester.ensureSemantics();
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: const Center(
+          child: const IconTheme(
+            data: const IconThemeData(),
+            child: const ImageIcon(null, semanticLabel: 'test')
+          ),
+        ),
+      ),
+    );
+
+    expect(tester.getSemanticsData(find.byType(ImageIcon)), matchesSemanticsData(
+      label: 'test',
+      textDirection: TextDirection.ltr,
+    ));
+    handle.dispose();
+  });
+
 }