Bevy: Panic in `Archetype::put_dynamic` when using `spawn` and `spawn_batch` in the same system

[w1th0utnam3]

Bevy version

Bevy master 43aac1a78480e196f9b8b29339a34d78bc44b663

Operating system & version

• Toolchain nightly-x86_64-pc-windows-msvc with rustc 1.49.0-nightly (9722952f0 2020-11-12)
• Windows 10 Build 19042.630

What you did

Spawn a single PbrComponents with commands.spawn, in the same system spawn many more PbrComponents with commands.spawn_batch

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .run();
}

fn setup(
    commands: &mut Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let unit_cube = meshes.add(Mesh::from(shape::Cube { size: 0.5 }));
    let material = materials.add(StandardMaterial {
        albedo: Color::rgb_linear(0.25, 0.25, 0.25),
        shaded: false,
        ..Default::default()
    });

    // Lambda to construct PbrComponents for a single cube
    let create_cube = |index: i32| -> PbrComponents {
        PbrComponents {
            mesh: unit_cube.clone(),
            material: material.clone(),
            transform: Transform {
                translation: Vec3::unit_x() * 2.0 * index as f32,
                ..Default::default()
            },
            ..Default::default()
        }
    };

    // Lambda to construct multiple cubes
    let create_n_cubes =
        |n: i32| -> Vec<PbrComponents> { (-n..n).map(create_cube).collect() };

    // Works if n is small (e.g. n=10), panics if n is larger (e.g. n=100)
    let n = 100;

    let grid_line = create_cube(0);
    let grid_line_batch = create_n_cubes(n);

    commands
        .spawn(Camera3dComponents {
            transform: Transform::from_matrix(Mat4::face_toward(
                Vec3::new(-3.0, 5.0, 8.0),
                Vec3::new(0.0, 0.0, 0.0),
                Vec3::new(0.0, 1.0, 0.0),
            )),
            ..Default::default()
        })
        // Does not panic if we comment out one of the following lines
        .spawn(grid_line)
        .spawn_batch(grid_line_batch);
}

What you expected to happen

Everything is spawned correctly.

What actually happened

Panics.

• Works if n (number of PbrComponents in the batch) is small (e.g. n=10), panics if n is larger (e.g. n=100)
• Does not panic if you remove either the spawn or the spawn_batch

The panic:

thread 'main' panicked at 'index out of bounds: the len is 138 but the index is 138', C:\Users\_\.cargo\git\checkouts\bevy-f7ffde730c324c74\43aac1a\crates\bevy_ecs\hecs\src\archetype.rs:428:13

The corresponding function: https://github.com/bevyengine/bevy/blob/43aac1a78480e196f9b8b29339a34d78bc44b663/crates/bevy_ecs/hecs/src/archetype.rs#L410-L439

[w1th0utnam3]

I worked around this issue for now by using a setup system that directly spawns using the &mut World. This doesn't cause the problem for me. So it's apparently related to the handling of Commands?

[Git0Shuai]

This should be fixed by #930

[memoryruins]

Tested the example before and after #930, and I can confirm it resolves the issue.
Thanks for the report @w1th0utnam3 and for the fix @Git0Shuai !