From 3f65af876f82bc1b93dc3530c5912ba96bb69c62 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Sep 2021 13:15:44 +0100
Subject: [PATCH] Fix the clippy failure

---
 crates/bevy_ecs/src/world/identifier.rs | 18 ++++++++++--------
 crates/bevy_ecs/src/world/mod.rs        |  2 +-
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/crates/bevy_ecs/src/world/identifier.rs b/crates/bevy_ecs/src/world/identifier.rs
index e5f99ae6ed8cbf..6e2b8efc0f2220 100644
--- a/crates/bevy_ecs/src/world/identifier.rs
+++ b/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
diff --git a/crates/bevy_ecs/src/world/mod.rs b/crates/bevy_ecs/src/world/mod.rs
index 33633d62a6211b..25c775d499d96c 100644
--- a/crates/bevy_ecs/src/world/mod.rs
+++ b/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(),