RemovedComponents doesn't work in FixedUpdate

[mirsella]

hello

Bevy version

0.14.2

What you did

have a system remove a Component in an Update system.
use a RemovedComponents in a FixedUpdate system.

What went wrong

RemovedComponents.read() doesn't return any entities

Additional information

it works by just moving the system from FixedUpdate to Update

there has been an issue about events not working in FixedUpdate #7691 fixed in this PR #10077. someone has talked about it in the pr and issue. here is a comment about it in the pr #10077 (comment).

if making events like RemovedComponents works in FixedUpdate too much of a drawback, i think there should be a clear indication on the docs, and even better, a bevy warning about it, since now it just silently fails.

thanks

[alice-i-cecile]

I expect that the best way to solve / close this is actually via a rewrite to use observers, ala #13928. I would definitely suggest that for now as a workaround.

[mirsella]

i guess this can be used as reproduction:

use bevy::prelude::*;
fn main() {
    let mut app = App::new();
    app.add_plugins(DefaultPlugins)
        .add_systems(Startup, |mut commands: Commands| {
            (0..10).for_each(|_| {
                commands.spawn(Foo);
            })
        })
        .add_systems(
            Update,
            |mut commands: Commands, q_foo: Query<Entity, With<Foo>>| {
                if let Some(entity) = q_foo.iter().next() {
                    commands.entity(entity).despawn();
                }
            },
        )
        .add_systems(FixedUpdate, |rm: RemovedComponents<Foo>| {
            println!("count: {}", rm.len());
        })
        .run();
}

#[derive(Component)]
struct Foo;

when running the removedcomponents system with Update we get 10 times a count 1 but with FixedUpdate not all of them are shown (6 on my computer)