[go_router] fix PopScope.onPopInvokedWithResult getting called twice when popping a route if GoRouteData.onExit is not null

[techouse]

This pull request includes changes to the GoRouter package, focusing on improving the handling of route pop events and adding corresponding tests. The most important changes include modifying the GoRouterDelegate class to invoke the didPop method and adding comprehensive test cases to ensure the correct behavior of the PopScope widget.

The problem

PopScope.onPopInvokedWithResult is getting called twice when popping a route since v14.0.0 which introduced #6495.

The 1st time it's called from

https://github.com/flutter/flutter/blob/bb81a93d752690bc2889a713ec448359c9867f40/packages/flutter/lib/src/widgets/navigator.dart#L5586

The 2nd time it's called from

https://github.com/flutter/flutter/blob/bb81a93d752690bc2889a713ec448359c9867f40/packages/flutter/lib/src/widgets/navigator.dart#L3305

Before v14.0.0, the 2nd call doesn't happen.

Version	PopScope.onPopInvokedWithResult called
12.1.3	1x
13.2.4	1x
14.0.0	2x
14.8.1	2x

I pinned it down to GoRouteData.onExit

packages/packages/go_router/lib/src/route_data.dart

Line 69 in 2df1c3a

FutureOr<bool> onExit(BuildContext context, GoRouterState state) => true;

returning true by default (it can never be null.

Since I use go_router_builder all my routes extend from GoRouteData where GoRouteData.onExit always a callable and never null

packages/packages/go_router/lib/src/route_data.dart

Line 114 in 2df1c3a

FutureOr<bool> onExit(BuildContext context, GoRouterState state) =>

so

packages/packages/go_router/lib/src/delegate.dart

Line 139 in 2df1c3a

if (routeBase is! GoRoute || routeBase.onExit == null) {

is never executed, as it would be had I created my GoRoutes manually without onExit defined.

Fixes:

• Pop scope not working with the go_router initial routes  flutter#155441 (comment)
• [go_router] WillPopScope/PopScope doesn't trigger with back button navigation on root screens flutter#140869 (comment)

Improvements to route pop handling:

• packages/go_router/lib/src/delegate.dart: Modified the GoRouterDelegate class to call the didPop method when a route is popped.

Addition of test cases:

• packages/go_router/test/on_exit_on_pop_invoked_with_result_test.dart: Added new test cases to verify that the onPopInvokedWithResult callback in the PopScope widget is called only once when a route is popped. This includes tests for both standard routes and routes using GoRouteData.

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Footnotes

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[techouse]

@chunhtai Even though all the test pass, including the ones I specifically added to test this case, I am not 100% certain that this is the correct approach, however, I don't see another way, as GoRouteData.onExit is always a callable and never null, even though I don't explicitly declare it.

[chunhtai]

Change lgtm, but will need to fix version

[chunhtai]

looks like the ci is not happy

[techouse]

Change lgtm, but will need to fix version

The currently published version is 14.8.1, so I guess this one should be 14.8.2

[techouse]

looks like the ci is not happy

Yeah, I'm not sure why. 🫠

[chunhtai]

looks like some tests are failing https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8718793893833895121/+/u/Run_package_tests/Dart_unit_tests/stdout

[techouse]

looks like some tests are failing https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8718793893833895121/+/u/Run_package_tests/Dart_unit_tests/stdout

Oh, I see, the 1 test in the example directory is failing.

This basically points to a deeper problem. The onExit method is awaited and by the time it resolves the widget / screen is unmounted. Looks like I'll have to find a way to make GoRouteData.onExit truly null.

The only way I see this working is by changing ExitCallback from

packages/packages/go_router/lib/src/route.dart

Line 70 in 7fb1a4d

typedef ExitCallback = FutureOr<bool> Function(

to

typedef ExitCallback = FutureOr<bool>? Function(BuildContext context, GoRouterState state);

but that opens up another can of worms where onExit can return null.

This will probably need a go_router_builder patch as well, since I changed

packages/packages/go_router/lib/src/route_data.dart

Line 69 in 7fb1a4d

FutureOr<bool> onExit(BuildContext context, GoRouterState state) => true;

to

ExitCallback? get onExit => null;

and any override would have to be declared as

@override
ExitCallback? get onExit => (BuildContext context, GoRouterState state) {
  // stuff
  return true;
};

This quickly ballooned into a big task. 🫠

@chunhtai do you have any other suggestions perhaps?

[techouse]

Hi @chunhtai and @hannah-hyj

Would you mind taking another look at this PR?

The changes ended up being moderately substantial in the process of fixing the double onPopInvokedWithResult issue (especially around making onExit optional for GoRouteData). All the go_router tests are passing now, and the earlier failing example test highlighted a deeper onExit scenario that I’ll address in a separate PR for go_router_builder (to update its usage of the updated go_router version).

I’m committed to getting this fix landed and will follow up with the builder changes promptly.

Thank you both for your time and guidance! 

[techouse]

All tests passed, yay! 🎉

@chunhtai thank you for all the tips! 🙏

[chunhtai]

I think I know what is going on, the issue is that when onPopPage returns false, it still attempt to call the onPopInvokedWithResult callback. This is something that needs to be fixed in framework

[chunhtai]

I will put up an framework pr to fix this closing this one

[chunhtai]

pr flutter/flutter#168567