Rebuild modal routes when the value of userGestureInProgress changes (#41150)

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

@@ -2239,10 +2239,25 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     route.dispose();
   }
 
+  int get _userGesturesInProgress => _userGesturesInProgressCount;
+  int _userGesturesInProgressCount = 0;
+  set _userGesturesInProgress(int value) {
+    _userGesturesInProgressCount = value;
+    userGestureInProgressNotifier.value = _userGesturesInProgress > 0;
+  }
+
   /// Whether a route is currently being manipulated by the user, e.g.
   /// as during an iOS back gesture.
-  bool get userGestureInProgress => _userGesturesInProgress > 0;
-  int _userGesturesInProgress = 0;
+  ///
+  /// See also:
+  ///
+  ///  * [userGestureInProgressNotifier], which notifies its listeners if
+  ///    the value of [userGestureInProgress] changes.
+  bool get userGestureInProgress => userGestureInProgressNotifier.value;
+
+  /// Notifies its listeners if the value of [userGestureInProgress] changes.
+  final ValueNotifier<bool> userGestureInProgressNotifier = ValueNotifier<bool>(false);
+
 
   /// The navigator is being controlled by a user gesture.
   ///

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

@@ -652,9 +652,18 @@ class _ModalScopeState<T> extends State<_ModalScope<T>> {
                     context,
                     widget.route.animation,
                     widget.route.secondaryAnimation,
-                    IgnorePointer(
-                      ignoring: widget.route.navigator.userGestureInProgress
-                        || widget.route.animation?.status == AnimationStatus.reverse,
+                    // This additional AnimatedBuilder is include because if the
+                    // value of the userGestureInProgressNotifier changes, it's
+                    // only necessary to rebuild the IgnorePointer widget.
+                    AnimatedBuilder(
+                      animation: widget.route.navigator.userGestureInProgressNotifier,
+                      builder: (BuildContext context, Widget child) {
+                        return IgnorePointer(
+                          ignoring: widget.route.navigator.userGestureInProgress
+                            || widget.route.animation?.status == AnimationStatus.reverse,
+                          child: child,
+                        );
+                      },
                       child: child,
                     ),
                   );

packages/flutter/test/material/page_test.dart

@@ -707,4 +707,76 @@ void main() {
     expect(tester.getTopLeft(find.byKey(pageScaffoldKey)), const Offset(400, 0));
     expect(tester.getTopLeft(find.byKey(homeScaffoldKey)).dx, lessThan(0));
   });
+
+  testWidgets('After a pop caused by a back-swipe, input reaches the exposed route', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/41024
+
+    final GlobalKey homeScaffoldKey = GlobalKey();
+    final GlobalKey pageScaffoldKey = GlobalKey();
+    int homeTapCount = 0;
+    int pageTapCount = 0;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(platform: TargetPlatform.iOS),
+        home: Scaffold(
+          key: homeScaffoldKey,
+          body: GestureDetector(
+            onTap: () {
+              homeTapCount += 1;
+            }
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.byKey(homeScaffoldKey));
+    expect(homeTapCount, 1);
+    expect(pageTapCount, 0);
+
+    final ValueNotifier<bool> notifier = Navigator.of(homeScaffoldKey.currentContext).userGestureInProgressNotifier;
+    expect(notifier.value, false);
+
+    Navigator.push<void>(homeScaffoldKey.currentContext, MaterialPageRoute<void>(
+      builder: (BuildContext context) {
+        return Scaffold(
+          key: pageScaffoldKey,
+          appBar: AppBar(title: const Text('Page')),
+          body: Padding(
+            padding: const EdgeInsets.all(16),
+            child: GestureDetector(
+              onTap: () {
+                pageTapCount += 1;
+              }
+            ),
+          ),
+        );
+      },
+    ));
+
+    await tester.pumpAndSettle();
+    await tester.tap(find.byKey(pageScaffoldKey));
+    expect(homeTapCount, 1);
+    expect(pageTapCount, 1);
+
+    // Trigger the basic iOS back-swipe dismiss transition. Drag the pushed
+    // "page" route more than halfway across the screen and then release it.
+
+    final TestGesture gesture = await tester.startGesture(const Offset(5, 300));
+    await gesture.moveBy(const Offset(500, 0));
+    await tester.pump();
+    expect(tester.getTopLeft(find.byKey(pageScaffoldKey)), const Offset(500, 0));
+    expect(tester.getTopLeft(find.byKey(homeScaffoldKey)).dx, lessThan(0));
+    expect(notifier.value, true);
+    await gesture.up();
+    await tester.pumpAndSettle();
+    expect(notifier.value, false);
+    expect(find.byKey(pageScaffoldKey), findsNothing);
+
+    // The back-swipe dismiss pop transition has finished and input on the
+    // home page still works.
+    await tester.tap(find.byKey(homeScaffoldKey));
+    expect(homeTapCount, 2);
+    expect(pageTapCount, 1);
+  });
 }