Use of `SyncComponentPlugin` on `ExtractComponentPlugin` causes `RenderEntity` to be incorrectly despawned

[tychedelia]

Bevy version

Since 0.15.

What you did

use bevy::prelude::*;
use bevy_render::extract_component::{ExtractComponent, ExtractComponentPlugin};
use bevy_render::sync_world::RenderEntity;
use bevy_render::{Extract, RenderApp};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins((
            TestExtractPlugin,
            ExtractComponentPlugin::<ComponentA>::default(),
            ExtractComponentPlugin::<ComponentB>::default(),
        ))
        .add_systems(Startup, setup)
        .add_systems(Update, update)
        .run();
}

#[derive(Component, ExtractComponent, Clone)]
struct ComponentA;
#[derive(Component, ExtractComponent, Clone)]
struct ComponentB;

/// set up a simple 3D scene
fn setup(mut commands: Commands) {
    commands.spawn((ComponentA, ComponentB));
}

fn update(mut commands: Commands, mut query: Query<(Entity), With<ComponentB>>) {
    for (entity) in query.iter() {
        commands.entity(entity).remove::<ComponentA>();
        commands.entity(entity).insert(ComponentA);
    }
}

struct TestExtractPlugin;

impl Plugin for TestExtractPlugin {
    fn build(&self, app: &mut App) {
        let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app
            .add_systems(ExtractSchedule, extract);
    }
}

fn extract(query: Extract<Query<RenderEntity, With<ComponentB>>>) {
    for (entity) in query.iter() {
        println!("Render entity id: {:?}", entity);
    }
}

What went wrong

Adding ExtractComponentPlugin adds SyncComponentPlugin, which will cause the RenderEntity to be changed in entity_sync_system if the component is removed.

Unfortunately, this logic doesn't make sense, as it's possible for multiple components a main world entity to want to be extracted. Further, being removed doesn't mean that the main world entity necessarily needs to be de-synced from the render world, as it could be being extracted for other reasons. This leads to very confusing and hard to debug behavior and is generally just incorrect.

[RageCPP]

I'm learning bevy, so if I'm wrong, I hope you can correct me.
I don't think there's anything wrong with the design of the system itself, just whether it's better to write the code like this in this case (note: English is not my native language, so the expression may look strange

use bevy::{
prelude::*,
render::{
Extract, RenderApp,
extract_component::{ExtractComponent, ExtractComponentPlugin},
sync_world::RenderEntity,
},
};

fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_plugins((
TestExtractPlugin,
ExtractComponentPlugin::<ComponentC>::default(),
))
.add_systems(Startup, setup)
.add_systems(Update, update)
.run();
}

#[derive(Component, Clone, Default)]
struct ComponentA;
#[derive(Component, Clone, Default)]
struct ComponentB;

#[derive(Component, Clone, ExtractComponent)]
#[require(ComponentA, ComponentB)]
struct ComponentC;

/// set up a simple 3D scene
fn setup(mut commands: Commands) {
 commands.spawn(ComponentC);
}

fn update(mut commands: Commands, mut query: Query<(Entity), With<ComponentB>>) {
 for (entity) in query.iter() {
 commands.entity(entity).remove::<ComponentA>();
 commands.entity(entity).insert(ComponentA);
 }
}

struct TestExtractPlugin;

impl Plugin for TestExtractPlugin {
 fn build(&self, app: &mut App) {
 let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
 return;
 }; render_app.add_systems(ExtractSchedule, extract);
 }
}

fn extract(query: Extract<Query<RenderEntity, With<ComponentB>>>) {
 for (entity) in query.iter() {
 println!("Render entity id: {:?}", entity);
 }
}