Add rootOverlay flag to [Draggable], to put feedback on root [Overlay] (#67375)

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

@@ -124,6 +124,7 @@ class Draggable<T extends Object> extends StatefulWidget {
     this.onDragEnd,
     this.onDragCompleted,
     this.ignoringFeedbackSemantics = true,
+    this.rootOverlay = false,
   }) : assert(child != null),
        assert(feedback != null),
        assert(ignoringFeedbackSemantics != null),
@@ -261,6 +262,15 @@ class Draggable<T extends Object> extends StatefulWidget {
   /// the tree (i.e. [State.mounted] is true).
   final DragEndCallback? onDragEnd;
 
+  /// Whether the feedback widget will be put on the root [Overlay].
+  ///
+  /// When false, the feedback widget will be put on the closest [Overlay]. When
+  /// true, the [feedback] widget will be put on the farthest (aka root)
+  /// [Overlay].
+  ///
+  /// Defaults to false.
+  final bool rootOverlay;
+
   /// Creates a gesture recognizer that recognizes the start of the drag.
   ///
   /// Subclasses can override this function to customize when they start
@@ -390,7 +400,7 @@ class _DraggableState<T extends Object> extends State<Draggable<T>> {
       _activeCount += 1;
     });
     final _DragAvatar<T> avatar = _DragAvatar<T>(
-      overlayState: Overlay.of(context, debugRequiredFor: widget)!,
+      overlayState: Overlay.of(context, debugRequiredFor: widget, rootOverlay: widget.rootOverlay)!,
       data: widget.data,
       axis: widget.axis,
       initialPosition: position,
@@ -427,7 +437,7 @@ class _DraggableState<T extends Object> extends State<Draggable<T>> {
 
   @override
   Widget build(BuildContext context) {
-    assert(Overlay.of(context, debugRequiredFor: widget) != null);
+    assert(Overlay.of(context, debugRequiredFor: widget, rootOverlay: widget.rootOverlay) != null);
     final bool canDrag = widget.maxSimultaneousDrags == null ||
                          _activeCount < widget.maxSimultaneousDrags!;
     final bool showChild = _activeCount == 0 || widget.childWhenDragging == null;

packages/flutter/test/widgets/draggable_test.dart

@@ -2318,6 +2318,70 @@ void main() {
     await _testChildAnchorFeedbackPosition(tester: tester, left: 100.0, top: 100.0);
   });
 
+  testWidgets('Drag feedback is put on root overlay with [rootOverlay] flag', (WidgetTester tester) async {
+      final GlobalKey<NavigatorState> rootNavigatorKey = GlobalKey<NavigatorState>();
+      final GlobalKey<NavigatorState> childNavigatorKey = GlobalKey<NavigatorState>();
+      // Create a [MaterialApp], with a nested [Navigator], which has the
+      // [Draggable].
+      await tester.pumpWidget(MaterialApp(
+        navigatorKey: rootNavigatorKey,
+        home: Column(
+          children: <Widget>[
+            Container(
+              height: 200.0,
+              child: Navigator(
+                key: childNavigatorKey,
+                onGenerateRoute: (RouteSettings settings) {
+                  if (settings.name == '/') {
+                    return MaterialPageRoute<void>(
+                      settings: settings,
+                      builder: (BuildContext context) => const Draggable<int>(
+                        data: 1,
+                        child: Text('Source'),
+                        feedback: Text('Dragging'),
+                        rootOverlay: true,
+                      ),
+                    );
+                  }
+                  throw UnsupportedError('Unsupported route: $settings');
+                },
+              ),
+            ),
+            DragTarget<int>(
+              builder: (BuildContext context, List<int> data, List<dynamic> rejects) {
+                return Container(
+                    height: 300.0, child: const Center(child: Text('Target 1')),
+                );
+              },
+            ),
+          ],
+        ),
+      ));
+
+      final Offset firstLocation = tester.getCenter(find.text('Source'));
+      final TestGesture gesture =
+          await tester.startGesture(firstLocation, pointer: 7);
+      await tester.pump();
+
+      final Offset secondLocation = tester.getCenter(find.text('Target 1'));
+      await gesture.moveTo(secondLocation);
+      await tester.pump();
+
+      // Expect that the feedback widget is a descendant of the root overlay,
+      // but not a descendant of the child overlay.
+      expect(
+          find.descendant(
+            of: find.byType(Overlay).first,
+            matching: find.text('Dragging'),
+          ),
+          findsOneWidget);
+      expect(
+          find.descendant(
+            of: find.byType(Overlay).last,
+            matching: find.text('Dragging'),
+          ),
+          findsNothing);
+    });
 
   testWidgets('Drag and drop can contribute semantics', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);