use bevy::ecs::entity::MapEntities;
use bevy::ecs::reflect::ReflectMapEntities;
use bevy::prelude::*;

#[derive(Default, Component, Reflect)]
#[reflect(Component)]
struct CompA;
#[derive(Component, Reflect)]
// #[reflect(Component)]             // OK
#[reflect(Component, MapEntities)]   // Breaks
struct CompB(pub Entity);

impl MapEntities for CompB {
  fn map_entities<M: EntityMapper>(&mut self, entity_mapper: &mut M) {
    self.0 = entity_mapper.map_entity(self.0);
  }
}

fn main() {
  let mut app = App::new();
  app.register_type::<CompA>().register_type::<CompB>();
  let world = app.world_mut();
  world
    .register_component_hooks::<CompA>()
    .on_add(|mut world, _, _| {
      world
        .commands()
        .spawn_empty();
    });
  world.spawn((CompB(Entity::PLACEHOLDER), CompA));

  let scene = DynamicScene::from_world(world);
  scene.write_to_world(world, &mut default()).unwrap();
}