Fix the clippy failure

crates/bevy_ecs/src/world/identifier.rs

@@ -3,25 +3,26 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 // We use usize here because that is the largest `Atomic` we want to require
 /// A unique identifier for a [`super::World`].
+// Note that this *is* used by external crates as well as for internal safety checks
 pub struct WorldId(usize);
 
 /// The next [`WorldId`].
 static MAX_WORLD_ID: AtomicUsize = AtomicUsize::new(0);
 
 impl WorldId {
- /// Create a new, unique [`WorldId`]
+ /// Create a new, unique [`WorldId`]. Returns [`None`] if the supply of unique
+ /// [`WorldId`]s has been exhausted
  ///
- /// # Panics
- /// If [`usize::MAX`] [`WorldId`]s have been created
- // This could be kept crate private, but external crates may wish to create some for their tests
- pub fn new() -> Self {
- let id = MAX_WORLD_ID
+ /// Please note that the [`WorldId`]s created from this method are unique across
+ /// time - if a given [`WorldId`] is [`Drop`]ped its value still cannot be reused
+ pub fn new() -> Option<Self> {
+ MAX_WORLD_ID
  // We use `Relaxed` here since this atomic only needs to be consistent with itself
  .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |val| {
  val.checked_add(1)
  })
- .expect("More `bevy` `World`s have been created than is supported");
- WorldId(id)
+ .map(WorldId)
+  .ok()
  }
 }
 
@@ -33,6 +34,7 @@ mod tests {
  fn world_ids_unique() {
  let ids = std::iter::repeat_with(WorldId::new)
  .take(50)
+ .map(Option::unwrap)
  .collect::<Vec<_>>();
  for (i, &id1) in ids.iter().enumerate() {
  // For the first element, i is 0 - so skip 1

crates/bevy_ecs/src/world/mod.rs

@@ -51,7 +51,7 @@ pub struct World {
 impl Default for World {
  fn default() -> Self {
  Self {
- id: WorldId::new(),
+ id: WorldId::new().expect("More `bevy` `World`s have been created than is supported"),
  entities: Default::default(),
  components: Default::default(),
  archetypes: Default::default(),