[go_router] feat: access GoRouter.of from redirect methods

[tomassasovsky]

This PR fixes being able to access the GoRouter instance from the context inside redirect methods.

It solves flutter/flutter#116855 (comment)

My use case for this is:

I'm building an extension package for navigation guards for go_router. Specifically, for type-safe generated routes. These guards are chainable and need to have the ability to block a route push/go. For this, I have the following method implemented:

  /// Block navigation by redirecting to current location
  void block({bool reevaluateOnChange = false}) {
    if (isResolved) return;
    final currentLocation =
        GoRouter.of(context).routerDelegate.currentConfiguration.fullPath;
    // Block by redirecting to current location
    _completer.complete(GuardResult.redirect(
      currentLocation,
      reevaluateOnChange: reevaluateOnChange,
    ));
  }

This method, however, needs this PR because it's ran on the redirect function of a GoRouteData.

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[gemini-code-assist]

Code Review

This pull request introduces a great feature to access GoRouter.of(context) from within redirect methods by using a Zone. The implementation is solid and the new tests cover the functionality well.

I have a couple of suggestions to improve the code quality:

• I've identified a duplicated constant across two files and suggest centralizing it to improve maintainability.
• There's some redundant logic in the new GoRouter.of method which can be simplified.

Please see my detailed comments. Overall, great work!

[stuartmorgan-g]

Thanks for the contribution! You haven’t checked off any of the items in the PR checklist above, so I’m assuming this is a work in progress and am marking it as a Draft. Please review the checklist, updating the PR as appropriate, and when that’s complete please feel free to mark the PR as ready for review.

[tomassasovsky]

Thanks @stuartmorgan-g! Just updated and marked as ready.

[chunhtai]

approach seems fine to me, just need some more error handling

[chunhtai]

Can you add a test that the error throw during the redirect can be caught by onException?

[tomassasovsky]

Added proper exception handling in the _redirect method to ensure redirect errors are gracefully converted to error RouteMatchList objects instead of crashing navigation.

What changed:

• Wrapped redirect calls in try-catch for sync exceptions
• Added .catchError() for async redirect exceptions
• Both paths convert exceptions to GoException and return error match lists

Why this matters:
This ensures that when a redirect throws an exception (like in the failing test), it gets properly handled by the onException callback instead of breaking the entire navigation flow. Previously, exceptions would bubble up and crash the router - now they're caught and transformed into proper error states that the router knows how to handle.

Works hand-in-hand with the configuration.dart fix to provide complete exception handling coverage throughout the redirect chain.