repro.rs

use bevy::prelude::*;

fn main() {
    App::build()
        .insert_resource(Msaa { samples: 4 })
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(spawn_child.system())
        .run();
}

struct TheParent;

/// set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands
        .spawn()
        .insert(GlobalTransform::default())
        .insert(Transform::from_scale(Vec3::splat(2.0)))
        .insert(TheParent);
    // .with_children(|_| ());

    // light
    commands.spawn_bundle(LightBundle {
        transform: Transform::from_xyz(4.0, 8.0, 4.0),
        ..Default::default()
    });
    // camera
    commands.spawn_bundle(PerspectiveCameraBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..Default::default()
    });
}

fn spawn_child(
    mut finished: Local<bool>,
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    parent: Query<Entity, With<TheParent>>,
) {
    if *finished {
        return;
    }
    *finished = true;

    let parent = parent.single().unwrap();
    let id = commands
        .spawn_bundle(PbrBundle {
            mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
            material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
            transform: Transform::from_xyz(0.0, 0.5, 0.0),
            ..Default::default()
        })
        .insert(Parent(parent))
        .id();
}