[go_router] Fix pages dropped when switching to an unloaded branch

packages/go_router/lib/src/route.dart

@@ -1476,8 +1476,67 @@ class StatefulNavigationShellState extends State<StatefulNavigationShell> with R
     if (matchList != null && matchList.isNotEmpty) {
       _router.restore(matchList);
     } else {
-      _router.go(widget._effectiveInitialBranchLocation(index));
+      final RouteMatchList? initialMatchList = _initialMatchListForBranch(index);
+      if (initialMatchList != null) {
+        _router.restore(initialMatchList);
+      } else {
+        _router.go(widget._effectiveInitialBranchLocation(index));
+      }
+    }
+  }
+
+  /// Builds the match list for the initial location of the branch at [index],
+  /// keeping the parts of the current match list that lie outside this shell
+  /// route.
+  ///
+  /// Switching to a branch without preserved state must not drop pages the
+  /// parent Navigators have below the shell route. This grafts the shell match
+  /// for the initial branch location into the current match list instead of
+  /// navigating from scratch. See
+  /// https://github.com/flutter/flutter/issues/188295.
+  RouteMatchList? _initialMatchListForBranch(int index) {
+    final RouteMatchList initialMatchList = _router.configuration.findMatch(
+      Uri.parse(widget._effectiveInitialBranchLocation(index)),
+    );
+    ShellRouteMatch? newShellMatch;
+    initialMatchList.visitRouteMatches((RouteMatchBase match) {
+      if (match is ShellRouteMatch && match.route == route) {
+        newShellMatch = match;
+        return false;
+      }
+      return true;
+    });
+    if (newShellMatch == null) {
+      return null;
+    }
+
+    List<RouteMatchBase> replaceShellMatch(List<RouteMatchBase> matches) {
+      return matches.map((RouteMatchBase match) {
+        if (match is ShellRouteMatch) {
+          if (match.route == route) {
+            return newShellMatch!;
+          }
+          return match.copyWith(matches: replaceShellMatch(match.matches));
+        }
+        return match;
+      }).toList();
     }
+
+    final RouteMatchList currentMatchList = _scopedMatchList(
+      widget.shellRouteContext.routeMatchList,
+    );
+    final List<RouteMatchBase> matches = replaceShellMatch(currentMatchList.matches);
+    return RouteMatchList(
+      matches: matches,
+      uri: initialMatchList.uri,
+      // The branch is navigated to as if by [GoRouter.go], which carries no
+      // extra. The object the outer location was given must not leak into it.
+      extra: initialMatchList.extra,
+      pathParameters: <String, String>{
+        ...currentMatchList.pathParameters,
+        ...initialMatchList.pathParameters,
+      },
+    );
   }
 
   @override

packages/go_router/pending_changelogs/change_2026_08_09_1786291908038.yaml

@@ -0,0 +1,3 @@
+changelog: |
+  - Fixes pages on parent navigators being dropped when switching to a not yet loaded branch of a `StatefulShellRoute`.
+version: patch

packages/go_router/test/go_router_test.dart

@@ -3211,6 +3211,112 @@ void main() {
       expect(matches.pathParameters['pid'], pid);
     });
 
+    testWidgets('StatefulShellRoute keeps parent navigator pages when switching '
+        'to an unloaded branch', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/188295
+      StatefulNavigationShell? routeState;
+      final routes = <RouteBase>[
+        GoRoute(
+          path: '/',
+          builder: (BuildContext context, GoRouterState state) => const Text('Home'),
+        ),
+        StatefulShellRoute.indexedStack(
+          builder:
+              (BuildContext context, GoRouterState state, StatefulNavigationShell navigationShell) {
+                routeState = navigationShell;
+                return navigationShell;
+              },
+          branches: <StatefulShellBranch>[
+            StatefulShellBranch(
+              routes: <RouteBase>[
+                GoRoute(
+                  path: '/a',
+                  builder: (BuildContext context, GoRouterState state) => const Text('Screen A'),
+                ),
+              ],
+            ),
+            StatefulShellBranch(
+              routes: <RouteBase>[
+                GoRoute(
+                  path: '/b',
+                  builder: (BuildContext context, GoRouterState state) => const Text('Screen B'),
+                ),
+              ],
+            ),
+          ],
+        ),
+      ];
+
+      final GoRouter router = await createRouter(routes, tester);
+      expect(find.text('Home'), findsOneWidget);
+
+      router.push('/a');
+      await tester.pumpAndSettle();
+      expect(find.text('Screen A'), findsOneWidget);
+      expect(router.canPop(), isTrue);
+
+      routeState!.goBranch(1);
+      await tester.pumpAndSettle();
+      expect(find.text('Screen B'), findsOneWidget);
+      expect(router.routerDelegate.currentConfiguration.uri.toString(), '/b');
+      expect(router.canPop(), isTrue);
+
+      router.pop();
+      await tester.pumpAndSettle();
+      expect(find.text('Home'), findsOneWidget);
+    });
+
+    testWidgets('StatefulShellRoute does not carry extra into an unloaded branch', (
+      WidgetTester tester,
+    ) async {
+      StatefulNavigationShell? routeState;
+      Object? extraOnB;
+      final routes = <RouteBase>[
+        StatefulShellRoute.indexedStack(
+          builder:
+              (BuildContext context, GoRouterState state, StatefulNavigationShell navigationShell) {
+                routeState = navigationShell;
+                return navigationShell;
+              },
+          branches: <StatefulShellBranch>[
+            StatefulShellBranch(
+              routes: <RouteBase>[
+                GoRoute(
+                  path: '/a',
+                  builder: (BuildContext context, GoRouterState state) => const Text('Screen A'),
+                ),
+              ],
+            ),
+            StatefulShellBranch(
+              routes: <RouteBase>[
+                GoRoute(
+                  path: '/b',
+                  builder: (BuildContext context, GoRouterState state) {
+                    extraOnB = state.extra;
+                    return const Text('Screen B');
+                  },
+                ),
+              ],
+            ),
+          ],
+        ),
+      ];
+
+      final GoRouter router = await createRouter(
+        routes,
+        tester,
+        initialLocation: '/a',
+        initialExtra: Object(),
+      );
+      expect(find.text('Screen A'), findsOneWidget);
+
+      routeState!.goBranch(1);
+      await tester.pumpAndSettle();
+      expect(find.text('Screen B'), findsOneWidget);
+      expect(extraOnB, isNull);
+      expect(router.routerDelegate.currentConfiguration.uri.toString(), '/b');
+    });
+
     testWidgets('StatefulShellRoute preserve extra when switching branch', (
       WidgetTester tester,
     ) async {