RunCriteria on State exit

[wilk10]

I'm trying to run a SystemSet on State exit with a RunCriteria. A simplified version of what i'm doing is the following:

use bevy::{ecs::schedule::ShouldRun, prelude::*};

fn main() {
    App::build()
        .add_plugins(MinimalPlugins)
        .add_state(MyState::S1)
        .add_system_set(
            SystemSet::on_enter(MyState::S1)
                .with_system(exit_state_1.system())
        )
        .add_system_set(
            SystemSet::on_exit(MyState::S1)
                .with_run_criteria(check.system())
                .with_system(success.system())
        )
        .run();
}

struct Marker;

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
enum MyState {
    S1,
    S2,
}

fn exit_state_1(mut commands: Commands, mut state: ResMut<State<MyState>>) {
    commands.spawn().insert(Marker);
    state.set(MyState::S2).unwrap();
}

fn check(marker: Query<&Marker>) -> ShouldRun {
    dbg!(marker.iter().count());
    match marker.single() {
        Ok(_) => {
            println!("running");
            ShouldRun::Yes
        },
        Err(_) => {
            println!("not running");
            ShouldRun::No
        },
    }
}

fn success(marker: Query<&Marker>) {
    if let Ok(_) = marker.single() {
        println!("hurray");
        panic!("terminate");
    }
}

This code loops indefinitely, printing:

[src/main.rs:33] marker.iter().count() = 0
not running

If i comment out the line that adds with_run_criteria, it behaves as expected, printing:

hurray
thread 'Compute Task Pool (1)' panicked at 'terminate', src/main.rs:48:9

If i add the following to the App:

        .add_system_set(
            SystemSet::on_enter(MyState::S2)
                .with_system(exit_state_2.system())
        )

which is:

fn exit_state_2(mut state: ResMut<State<MyState>>) {
    state.set(MyState::S1).unwrap();
}

and move the SystemSet with RunCriteria on MyState::S2, it hangs printing only once:

hurray
thread 'Compute Task Pool (1)' panicked at 'terminate', src/main.rs:48:9

What does this mean for the usage of RunCriteria? Is it only supposed be used on update? Are there some learning materials with slightly more advanced examples?

My real world usage in this case would be to despawn the current room and trigger the spawning of the next one only when the Player exits the room, while if NPCs exit the room, i want to do something else. But I also really like it to conditionally run systems based on certain conditions, just need to wrap my ahead around it and i guess avoid some footgun?

Thanks a lot!

(PS: i'm on 0.5, didn't try with main)

[wilk10]

ok i dug a bit more into it. I think the crux of the issue is that when building the SystemSet, with_run_criteria is called:

bevy/crates/bevy_ecs/src/schedule/system_set.rs

Lines 68 to 73 in 43d99bb

	pub fn on_exit<T>(s: T) -> SystemSet
	where
	T: Component + Debug + Clone + Eq + Hash,
	{
	Self::new().with_run_criteria(State::<T>::on_exit(s))
	}

but then when i add my own with_run_criteria, it is overwritten here:

bevy/crates/bevy_ecs/src/schedule/system_set.rs

Lines 99 to 102 in 43d99bb

	pub fn with_run_criteria<Marker>(mut self, run_criteria: impl IntoRunCriteria<Marker>) -> Self {
	self.run_criteria = Some(run_criteria.into());
	self
	}

to me looks like a bug..? I think i'll open an issue.

[wilk10]

opened: #2609

[wilk10]

Marking as answered. The linked issue has more details in it now.