Call `markNeedsPaint` when adding overlayChild to `Overlay` (#135941)

Fixes https://github.com/flutter/flutter/issues/134656

`_skipMarkNeesLayout` was meant to only skip `markNeedsLayout` calls. Re-painting is still needed when a child gets added/removed from the `Overlay`.

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

@@ -412,10 +412,8 @@ class MouseTracker extends ChangeNotifier {
     // hit-test order.
     final PointerExitEvent baseExitEvent = PointerExitEvent.fromMouseEvent(latestEvent);
     lastAnnotations.forEach((MouseTrackerAnnotation annotation, Matrix4 transform) {
-      if (!nextAnnotations.containsKey(annotation)) {
-        if (annotation.validForMouseTracker && annotation.onExit != null) {
-          annotation.onExit!(baseExitEvent.transformed(lastAnnotations[annotation]));
-        }
+      if (annotation.validForMouseTracker && !nextAnnotations.containsKey(annotation)) {
+        annotation.onExit?.call(baseExitEvent.transformed(lastAnnotations[annotation]));
       }
     });
 
@@ -426,8 +424,8 @@ class MouseTracker extends ChangeNotifier {
     ).toList();
     final PointerEnterEvent baseEnterEvent = PointerEnterEvent.fromMouseEvent(latestEvent);
     for (final MouseTrackerAnnotation annotation in enteringAnnotations.reversed) {
-      if (annotation.validForMouseTracker && annotation.onEnter != null) {
-        annotation.onEnter!(baseEnterEvent.transformed(nextAnnotations[annotation]));
+      if (annotation.validForMouseTracker) {
+        annotation.onEnter?.call(baseEnterEvent.transformed(nextAnnotations[annotation]));
       }
     }
   }

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

@@ -1032,6 +1032,10 @@ class _RenderTheater extends RenderBox with ContainerRenderObjectMixin<RenderBox
     assert(!_skipMarkNeedsLayout);
     _skipMarkNeedsLayout = true;
     adoptChild(child);
+    // The Overlay still needs repainting when a deferred child is added. Usually
+    // `markNeedsLayout` implies `markNeedsPaint`, but here `markNeedsLayout` is
+    // skipped when the `_skipMarkNeedsLayout` flag is set.
+    markNeedsPaint();
     _skipMarkNeedsLayout = false;
 
     // After adding `child` to the render tree, we want to make sure it will be
@@ -1045,6 +1049,9 @@ class _RenderTheater extends RenderBox with ContainerRenderObjectMixin<RenderBox
     assert(!_skipMarkNeedsLayout);
     _skipMarkNeedsLayout = true;
     dropChild(child);
+    // The Overlay still needs repainting when a deferred child is dropped. See
+    // the comment in `_addDeferredChild`.
+    markNeedsPaint();
     _skipMarkNeedsLayout = false;
   }
 

packages/flutter/test/widgets/overlay_portal_test.dart

@@ -777,6 +777,65 @@ void main() {
     verifyTreeIsClean();
   });
 
+  group('Adding/removing overlay child causes repaint', () {
+    // Regression test for https://github.com/flutter/flutter/issues/134656.
+    const Key childKey = Key('child');
+    final OverlayEntry overlayEntry = OverlayEntry(
+      builder: (BuildContext context) {
+        return RepaintBoundary(
+          child: OverlayPortal(
+            controller: controller1,
+            overlayChildBuilder: (BuildContext context) => const SizedBox(),
+            child: const SizedBox(key: childKey),
+          ),
+        );
+      },
+    );
+    final Widget widget = Directionality(
+      key: GlobalKey(debugLabel: 'key'),
+      textDirection: TextDirection.ltr,
+      child: Overlay(initialEntries: <OverlayEntry>[overlayEntry]),
+    );
+    tearDown(overlayEntry.remove);
+    tearDownAll(overlayEntry.dispose);
+
+    testWidgetsWithLeakTracking('Adding child', (WidgetTester tester) async {
+      controller1.hide();
+      await tester.pumpWidget(widget);
+
+      final RenderBox renderTheater = tester.renderObject<RenderBox>(find.byType(Overlay));
+      final RenderBox renderChild = tester.renderObject<RenderBox>(find.byKey(childKey));
+      assert(!renderTheater.debugNeedsPaint);
+      assert(!renderChild.debugNeedsPaint);
+
+      controller1.show();
+      await tester.pump(null, EnginePhase.layout);
+      expect(renderTheater.debugNeedsPaint, isTrue);
+      expect(renderChild.debugNeedsPaint, isFalse);
+
+      // Discard the dirty render tree.
+      await tester.pumpWidget(const SizedBox());
+    });
+
+    testWidgetsWithLeakTracking('Removing child', (WidgetTester tester) async {
+      controller1.show();
+      await tester.pumpWidget(widget);
+
+      final RenderBox renderTheater = tester.renderObject<RenderBox>(find.byType(Overlay));
+      final RenderBox renderChild = tester.renderObject<RenderBox>(find.byKey(childKey));
+      assert(!renderTheater.debugNeedsPaint);
+      assert(!renderChild.debugNeedsPaint);
+
+      controller1.hide();
+      await tester.pump(null, EnginePhase.layout);
+      expect(renderTheater.debugNeedsPaint, isTrue);
+      expect(renderChild.debugNeedsPaint, isFalse);
+
+      // Discard the dirty render tree.
+      await tester.pumpWidget(const SizedBox());
+    });
+  });
+
   testWidgetsWithLeakTracking('Adding/Removing OverlayPortal in LayoutBuilder during layout', (WidgetTester tester) async {
     final GlobalKey widgetKey = GlobalKey(debugLabel: 'widget');
     final GlobalKey overlayKey = GlobalKey(debugLabel: 'overlay');