System order ambiguity time_system and event_update_system

[thmxv]

Bevy version

0.14.0 and git main branch most recent commit ca3d8e8

What you did

My app crashes because of a system order ambiguity.
My app has the following code to detect ambiguity:

fn main() {
    let mut app = App::new();
    app.configure_schedules(ScheduleBuildSettings {
        ambiguity_detection: LogLevel::Error,
        ..default()
    });
    ...
}

I reproduced this error/crash in bevy only by adding this code to the time/time.rs example.

What went wrong

thread 'main' panicked at crates/bevy_ecs/src/schedule/schedule.rs:383:33:
Error when initializing schedule First: Systems with conflicting access have indeterminate run order.
1 pairs of systems with conflicting data access have indeterminate execution order. Consider adding `before`, `after`, or `ambiguous_with` relationships between these:
 -- time_system (in set TimeSystem) and event_update_system (in set EventUpdates)
    conflict on: bevy_ecs::world::World

Additional information

My app does have this crash but with 2 pairs of systems, not just the one. This crash comes from a dependency of a dependency of my app: bevy_mod_raycast

2 pairs of systems with conflicting data access have indeterminate execution order. Consider adding `before`, `after`, or `ambiguous_with` relationships between these:
 -- time_system (in set TimeSystem) and event_update_system (in set EventUpdates)
    conflict on: bevy_ecs::world::World
 -- update_cursor_ray and event_update_system (in set EventUpdates)
    conflict on: bevy_ecs::world::World

The update_cursor_ray system comes from bevy_mod_raycast. But because event_update_system comes from Bevy and is common to the 2 pairs of systems, I do not know if I should report a similar issue there.

[alice-i-cecile]

I don't mind resolving the ambiguity either way: do you have a preference?

[thmxv]

I do not have any preference. I suppose the time_system and event_update_system are ambiguous but this is not a problem. In this case maybe using ambiguous_with() and not before() nor after() is the "correct" way. But I have no real knowledge of those systems and new to Bevy, so you sure know better than me what is better.

[alice-i-cecile]

Hmm yeah, I actually think that these two systems aren't actually ambiguous in meaningful ways, since the event system work won't touch time despite having world access. Yeah, marked as ambiguous with is the right approach here.

For the actual crash, you need an ordering in bevy_mod_raycast :)

[thmxv]

Thanks. To avoid the crash, I changed from LogLevel::Error to LogLevel::Warn, which only prints warning messages but do no crash the app. I will report the issue in bevy_mod_raycast.

[richchurcher]

As this issue is marked with trivial, I might take a stab at closing it 🤞