`Entities::resolve_from_id` of freed entity makes `Entities::contains` return `true`

[urben1680]

Bevy version

0.16

What you did

I noticed this when I tried to check if an entity by index is currently in use.

I ran this test:

let mut world = World::new();
let entity_mut = world.spawn_empty();
let existing = entity_mut.id();
let entity_index = existing.index();
entity_mut.despawn();
let freed = world
    .entities()
    .resolve_from_id(entity_index)
    .expect("freed entities are still allocated");
assert_eq!(
    world.entities().contains(freed),
    false,
    "before: {existing}, freed: {freed}"
)

What went wrong

The test failed:

assertion `left == right` failed: before: 0v1, freed: 0v2
  left: true
 right: false
stack backtrace:

This is unexpected because resolve_from_id docs say:

Get the Entity with a given id, if it exists in this Entities collection Returns None if this Entity is outside of the range of currently reserved Entities

Note: This method may return Entities which are currently free Note that contains will correctly return false for freed entities, since it checks the generation

I would think contains works as a way of verifying if the entity of this index is freed. However this is only done by get as that method also checks the current archetype.

I am unsure what the issue is here, the docs or the implementation. But I think that contains should never return true for a freed entity no matter if the generation value has been increased by free or I took a good guess when using Entity::from_bits.