Panic despawning non-existent entity

I have setup using `For::each`, `Cond`, and a `Mutable` which can cause quill to get into trouble trying to despawn an entity. ``` 2024-08-17T12:18:19.750435Z WARN bevy_ecs::world: error[B0003]: Could not despawn entity Entity { index: 20, generation: 1 } because it doesn't exist in this World. See: https://bevyengine.org/learn/errors/#b0003 ``` I've tried to create a reduced example but could probably be simplified more. Removing either the Cond or the update of the mutable stops the panic from happening. I was able to bisect the issue to be starting from 479fc2aedfd5646abf88aa1f1dec7ee018829813 - Run the example - click the button - panic ``` //! Example of a simple UI layout #![feature(impl_trait_in_assoc_type)] #[path = "./common/lib.rs"] mod common; use bevy::prelude::*; use bevy_mod_picking::prelude::*; use bevy_quill::{Cond, Cx, Element, For, Mutable, QuillPlugin, View, ViewTemplate}; use common::*; fn main() { App::new() .add_plugins(( DefaultPlugins.set(ImagePlugin::default_nearest()), QuillPlugin, DefaultPickingPlugins, )) .init_resource::<Birds>() .observe(Birds::on_add) .observe(Birds::on_remove) .add_systems(Startup, (setup, setup_view_root, setup_birds)) .add_systems(Update, (close_on_esc, rotate)) .run(); } fn setup_view_root(mut commands: Commands) { commands.spawn(Reproduce.to_root()); } fn setup_birds(mut commands: Commands) { commands.spawn(Bird); } #[derive(Component)] struct Bird; #[derive(Resource, Default)] struct Birds(Vec<Entity>); impl Birds { pub fn on_add(trigger: Trigger<OnAdd, Bird>, mut birds: ResMut<Self>) { birds.0.push(trigger.entity()); } pub fn on_remove(trigger: Trigger<OnRemove, Bird>, mut birds: ResMut<Self>) { birds.0.retain(|&e| e != trigger.entity()); } } #[derive(Clone, PartialEq)] struct Reproduce; impl ViewTemplate for Reproduce { type View = impl View; fn create(&self, cx: &mut Cx) -> Self::View { let selected = cx.create_mutable::<Option<Entity>>(None); let birds = cx.use_resource::<Birds>().0.clone(); selected.update(cx, |mut selected: Mut<Option<Entity>>| { let new_selected = selected .filter(|s| birds.contains(s)) .or(birds.first().copied()); if new_selected != *selected { info!("Updating selected {:?}", new_selected); *selected = new_selected; } }); Element::<NodeBundle>::new().children(( For::each(birds, move |&item| SubComponent { item, selected }), Element::<ButtonBundle>::new() .insert_dyn( move |_| { On::<Pointer<Click>>::run( move |mut commands: Commands, birds: Query<Entity, With<Bird>>| { info!("Clicked"); for bird in &birds { commands.entity(bird).despawn(); } }, ) }, (), ) .children("Click me"), )) } } #[derive(Clone, PartialEq)] struct SubComponent { pub item: Entity, pub selected: Mutable<Option<Entity>>, } impl ViewTemplate for SubComponent { type View = impl View; fn create(&self, cx: &mut Cx) -> Self::View { let selected = self.selected.get(cx); Cond::new( selected.is_some(), Element::<NodeBundle>::new().children("Bird"), (), ) } } ```