Query::get and Query::get_component return different references

[greytdepression]

Bevy version

0.9
308e092

What you did

I ran the following snippet of code

use bevy::prelude::*;

fn main() {
    App::new()

        // We need a game loop for the problem to occur.
        .add_plugins(DefaultPlugins)

        // spawn some entities
        .insert_resource(MyEntities::default())
        .add_startup_system(spawn_entities)
        .add_system(query_system)
        .run();
}

#[derive(Default, Resource)]
struct MyEntities(Vec<Entity>);

#[derive(Debug, Component, PartialEq, Eq)]
struct IndexComponent(i32); // we use this component to check that we have the correct component

#[derive(Component)]
#[component(storage = "SparseSet")]
struct MySparseComponent;


fn spawn_entities(mut commands: Commands, mut my_entities: ResMut<MyEntities>) {
    (0..10)
        .for_each(|i|
            // spawn an entity, give it an `IndexComponent` with its number, and push it into `MyEntities`
            my_entities.0.push(commands.spawn(IndexComponent(i)).id())
        );
}


fn query_system(
    mut commands: Commands,
    my_entities: Res<MyEntities>,
    query: Query<&IndexComponent>,
    mut frame_counter: Local<usize>,
) {

    let mut last: Option<Entity> = None;

    for &entity in my_entities.0.iter() {
        let get = query.get(entity).unwrap();
        let get_comp = query.get_component::<IndexComponent>(entity).unwrap();

        // give the entity the sparse component
        commands.entity(entity)
            .insert(MySparseComponent);

        // remove the sparse component from the last entity
        if let Some(last) = last {
            commands.entity(last)
                .remove::<MySparseComponent>();
        }

        // this is where things go wrong
        if get != get_comp {
            dbg!(entity, get, get_comp);
            dbg!(*frame_counter);
            panic!("AAAA");
        }

        last = Some(entity);
    }

    // count what frame we are on
    *frame_counter += 1;
}

What went wrong

Here, get and get_comp should have the same value, which they do on the first frame, but not on the second.

Additional information

In this example MyEntities and IndexcComponent are just some scaffolding in order to demonstrate the problem. What is important is MySparseComponent and the fact that it is of storage type SparseSet.

I made a git repo containing this snippet for convenience.

[greytdepression]

I should add that this bug was introduced with bevy 0.9. I noticed it, because I have a similar system in my game which ran fine on bevy 0.8.1, but broke when I updated to 0.9.

[greytdepression]

One more thing, I just saw #6622 about duplicate components, and yes, my code would insert a duplicate component onto the last entity on the second frame. But the code panics before that and it didn't make a difference with or without, so I decided to go with the shorter code snippet and not remove explicitly remove MySparseComponent from the last entity.

[rparrett]

bisected to fe7ebd4

[james7132]

Was able to reproduce the bug.

Made the following changes to the example code:

        // this is where things go wrong
        dbg!(entity, get as *const IndexComponent, get_comp as *const IndexComponent);
        dbg!(*frame_counter);
        if get != get_comp {
            panic!("AAAA");
        }

... and got the following output:

[src/main.rs:60] entity = 0v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae500
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae500
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 1v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae504
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae504
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 2v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae508
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae508
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 3v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae50c
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae50c
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 4v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae510
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae510
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 5v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae514
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae514
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 6v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae518
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae518
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 7v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae51c
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae51c
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 8v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae520
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae520
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 9v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae524
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae524
[src/main.rs:61] *frame_counter = 0
[src/main.rs:60] entity = 0v0
[src/main.rs:60] get as *const IndexComponent = 0x00000285555ae508
[src/main.rs:60] get_comp as *const IndexComponent = 0x00000285555ae500
[src/main.rs:61] *frame_counter = 1

The returned pointer from Query::get seems to be incorrect.