Navigation and routing

This skill owns app navigation with go_router. There is exactly ONE GoRouter for the app, defined in lib/routing/, and every screen is reachable by a URL. Navigation is a data structure (routes + a pure redirect), not a pile of imperative Navigator.push calls.

Read the reference for the task at hand:

• references/go-router-config.md — the single router, context.go vs context.push, path params vs state.extra, typed route helpers, errorBuilder/404.
• references/guards-and-redirects.md — pure redirect functions, the Riverpod refreshListenable, auth + onboarding gates, avoiding redirect loops.
• references/shells-and-deep-links.md — StatefulShellRoute.indexedStack for bottom-nav/rail shells, CustomTransitionPage, PopScope, and notification-payload → location mapping.

Run scripts/check_routing.sh before a PR.

Non-negotiable rules

1. Exactly ONE GoRouter, built in lib/routing/, wired once via MaterialApp.router in app.dart. Multiple routers fragment history, deep links, and back-button behaviour. The router is created behind a provider so guards can watch app state.
2. Deep-linkable identity lives in PATH PARAMS, never in state.extra. extra is a live Dart object: it is null on a cold start from a deep link and after process death / restoration. A screen that needs an id to rebuild must read it from state.pathParameters so the URL alone fully reconstructs the screen.
3. state.extra is ONLY an optional non-identity optimisation (a pre-fetched object to avoid a reload flash). The screen must still work — refetch by id — when extra is null.
4. Use context.go to replace the stack (declarative destinations, tabs, post-login home); use context.push to stack a screen you expect to pop back from (a detail, a modal flow). Mixing them wrong breaks the back button. Know which one every call site needs.
5. Guards are PURE redirect functions. redirect returns a new location String? (or null to allow) from GoRouterState + a snapshot of app state. No I/O, no navigation calls, no side effects inside redirect — it runs on every navigation and can run repeatedly.
6. Reactive guards use a refreshListenable, not polling. Bridge the Riverpod auth/onboarding provider to a Listenable; the router re-evaluates redirect whenever it fires. See state-management-riverpod.
7. Redirects must be loop-free. Always allow the destination the guard sends you TO (e.g. never redirect /sign-in back to /sign-in). Guard against A→B→A by checking the current location before redirecting.
8. Tab/branch shells use StatefulShellRoute.indexedStack. It preserves each branch's navigation stack and state across tab switches; a plain ShellRoute with an IndexedStack you wire by hand does not survive router rebuilds as cleanly. Switch branches with navigationShell.goBranch(index).
9. Custom transitions go through CustomTransitionPage and respect reduced motion. When the platform requests reduced motion, collapse to a no-op/fade. Read the flag from MediaQuery, resolve motion via the design system — see accessibility-as-code and design-system-structure.
10. Intercept back / unsaved changes with PopScope, not WillPopScope (removed). Set canPop: false and handle in onPopInvokedWithResult(bool didPop, T? result); only navigate away after the user confirms.
11. Provide an errorBuilder and a real 404/error route. An unmatched deep link must land on a designed error screen, never a red error box.
12. Never hold a BuildContext across an await before navigating. Capture GoRouter.of(context) (or the router) before the await, or guard with context.mounted after. See async-safety.
13. A feature does not build its own router. scaffold-feature-module registers a feature's GoRoute INTO this router's route list; features never instantiate GoRouter.

The single router

app.dart reads the router from a provider and hands it to MaterialApp.router. The router itself lives in routing/ and is the only place GoRouter(...) is constructed.

// routing/app_router.dart
final routerProvider = Provider<GoRouter>((ref) {
  // Bridge Riverpod auth state to a Listenable the router can watch.
  final refresh = ValueNotifier<int>(0);
  ref.onDispose(refresh.dispose);
  ref.listen(authNotifierProvider, (_, __) => refresh.value++);

  return GoRouter(
    initialLocation: Routes.home,
    refreshListenable: refresh,
    redirect: (context, state) => appRedirect(ref.read(authNotifierProvider), state),
    errorBuilder: (context, state) => ErrorScreen(error: state.error),
    routes: $appRoutes, // assembled from feature route lists
  );
});

// app.dart — the only MaterialApp.router
class MyApp extends ConsumerWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final router = ref.watch(routerProvider);
    return MaterialApp.router(
      routerConfig: router,
      theme: lightTheme,
      darkTheme: darkTheme,
      localizationsDelegates: AppLocalizations.localizationsDelegates,
      supportedLocales: AppLocalizations.supportedLocales,
    );
  }
}

Identity in the path, not in extra

// GOOD: id is in the URL — a cold-start deep link to /items/42 fully rebuilds.
GoRoute(
  path: '/items/:id',
  builder: (context, state) {
    final id = state.pathParameters['id']!; // always present
    // extra is an OPTIONAL fast-path; screen must work when it is null.
    final preloaded = state.extra as Item?;
    return ItemScreen(itemId: id, preloaded: preloaded);
  },
),

// BAD: identity smuggled through extra — null on cold start / after process death.
context.push('/item', extra: item); // no id in the URL => not deep-linkable

Typed route helpers (constants, not string soup)

Prefer small constant/builder classes so call sites never hand-concatenate paths. go_router_builder codegen is an OPTIONAL upgrade, not the default.

// routing/routes.dart
abstract final class Routes {
  static const home = '/';
  static const items = '/items';
  static String item(String id) => '/items/$id';
  static const signIn = '/sign-in';
}

// call site
context.push(Routes.item(item.id));

go vs push

context.go(Routes.home);          // replace whole stack: post-login, tab roots
context.push(Routes.item(id));    // stack a detail you'll pop back from
context.pop(result);              // return up, optionally with a result

Anti-patterns

• Two GoRouter instances, or a nested Navigator/MaterialApp inside a screen for "sub-navigation." Use nested routes / StatefulShellRoute.
• Passing a domain id through state.extra and reading extra! in build — crashes on cold start.
• I/O, ref.read of async work, or calling context.go INSIDE redirect. Redirect is pure and returns a location.
• A redirect that can bounce forever because it also redirects its own target.
• Mixing Navigator.pushNamed('/x') string routes with go_router — one navigation system only.
• WillPopScope (removed) instead of PopScope.
• Awaiting then using the same context to navigate without a mounted check.
• A feature package/folder constructing its own GoRouter.

Definition of done

• One GoRouter in lib/routing/, one MaterialApp.router in app.dart.
• Every screen reachable by a URL; every id-bearing screen reads its id from state.pathParameters.
• state.extra is only ever an optional optimisation; every such screen renders correctly with extra == null.
• Guards are pure redirect functions with a refreshListenable; no redirect loops.
• Tab shells use StatefulShellRoute.indexedStack; branch state survives tab switches.
• Transitions respect reduced motion; errorBuilder + 404 route present.
• PopScope guards unsaved changes; no BuildContext used across an await when navigating.
• scripts/check_routing.sh passes.

Related skills

• app-startup-and-bootstrap — owns main()/bootstrap() ordering and where MaterialApp.router is mounted.
• state-management-riverpod — the auth/onboarding providers the refreshListenable bridges.
• scaffold-feature-module — registers a feature GoRoute into this router.
• adaptive-layout — chooses NavigationRail vs BottomNavigationBar by width for the shell.
• accessibility-as-code — reduced-motion flag and semantics for navigation.
• design-system-structure — the reduced-motion token / resolveMotion helper for transitions.
• async-safety — BuildContext/mounted rules around awaited navigation.
• local-notifications-scheduler — the notification payload whose pure mapper produces a location.

References

• go_router package: https://pub.dev/packages/go_router
• go_router API docs: https://pub.dev/documentation/go_router/latest/
• Flutter navigation & routing: https://docs.flutter.dev/ui/navigation
• Deep linking: https://docs.flutter.dev/ui/navigation/deep-linking
• PopScope API: https://api.flutter.dev/flutter/widgets/PopScope-class.html