[a11y] Re-land Make sure RenderFractionalTranslation updates its semantics...

[a11y] Re-land Make sure RenderFractionalTranslation updates its semantics after the translation field is set (#49708)

Re-land Make sure RenderFractionalTranslation updates its semantics after the translation field is set

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -2472,6 +2472,7 @@ class RenderFractionalTranslation extends RenderProxyBox {
       return;
     _translation = value;
     markNeedsPaint();
+    markNeedsSemanticsUpdate();
   }
 
   @override

packages/flutter/test/rendering/proxy_box_test.dart

@@ -481,6 +481,18 @@ void main() {
       ..onHover = (_) {};
     // Passes if no error is thrown
   });
+
+  test('RenderFractionalTranslation updates its semantics after its translation value is set', () {
+    final _TestSemanticsUpdateRenderFractionalTranslation box = _TestSemanticsUpdateRenderFractionalTranslation(
+      translation: const Offset(0.5, 0.5),
+    );
+    layout(box, constraints: BoxConstraints.tight(const Size(200.0, 200.0)));
+    expect(box.markNeedsSemanticsUpdateCallCount, 1);
+    box.translation = const Offset(0.4, 0.4);
+    expect(box.markNeedsSemanticsUpdateCallCount, 2);
+    box.translation = const Offset(0.3, 0.3);
+    expect(box.markNeedsSemanticsUpdateCallCount, 3);
+  });
 }
 
 class _TestRectClipper extends CustomClipper<Rect> {
@@ -537,3 +549,18 @@ class _TestPathClipper extends CustomClipper<Path> {
   @override
   bool shouldReclip(_TestPathClipper oldClipper) => false;
 }
+
+class _TestSemanticsUpdateRenderFractionalTranslation extends RenderFractionalTranslation {
+  _TestSemanticsUpdateRenderFractionalTranslation({
+    @required Offset translation,
+    RenderBox child,
+  }) : super(translation: translation, child: child);
+
+  int markNeedsSemanticsUpdateCallCount = 0;
+
+  @override
+  void markNeedsSemanticsUpdate() {
+    markNeedsSemanticsUpdateCallCount++;
+    super.markNeedsSemanticsUpdate();
+  }
+}

packages/flutter/test/widgets/basic_test.dart

@@ -145,6 +145,69 @@ void main() {
       await tester.tap(find.byKey(key1));
       expect(_pointerDown, isTrue);
     });
+
+    testWidgets('semantics bounds are updated', (WidgetTester tester) async {
+      final GlobalKey fractionalTranslationKey = GlobalKey();
+      final GlobalKey textKey = GlobalKey();
+      Offset offset = const Offset(0.4, 0.4);
+
+      await tester.pumpWidget(
+          StatefulBuilder(
+            builder: (BuildContext context, StateSetter setState) {
+              return Directionality(
+                textDirection: TextDirection.ltr,
+                child: Center(
+                  child: Semantics(
+                    explicitChildNodes: true,
+                    child: FractionalTranslation(
+                      key: fractionalTranslationKey,
+                      translation: offset,
+                      transformHitTests: true,
+                      child: GestureDetector(
+                        onTap: () {
+                          setState(() {
+                            offset = const Offset(0.8, 0.8);
+                          });
+                        },
+                        child: SizedBox(
+                          width: 100.0,
+                          height: 100.0,
+                          child: Text(
+                            'foo',
+                            key: textKey,
+                          ),
+                        ),
+                      ),
+                    ),
+                  ),
+                ),
+              );
+            },
+          )
+      );
+
+      expect(
+        tester.getSemantics(find.byKey(textKey)).transform,
+        Matrix4(
+          3.0, 0.0, 0.0, 0.0,
+          0.0, 3.0, 0.0, 0.0,
+          0.0, 0.0, 1.0, 0.0,
+          1170.0, 870.0, 0.0, 1.0,
+        ),
+      );
+
+      await tester.tap(find.byKey(fractionalTranslationKey));
+      await tester.pump();
+      expect(
+        tester.getSemantics(find.byKey(textKey)).transform,
+        Matrix4(
+          3.0, 0.0, 0.0, 0.0,
+          0.0, 3.0, 0.0, 0.0,
+          0.0, 0.0, 1.0, 0.0,
+          1290.0, 990.0, 0.0, 1.0,
+        ),
+      );
+    });
   });
 
   group('Row', () {