Add/fix track_caller attribute on panicking entity accessor methods (#8951)

# Objective

`World::entity`, `World::entity_mut` and `Commands::entity` should be
marked with `track_caller` to display where (in user code) the call with
the invalid `Entity` was made. `Commands::entity` already has the
attibute, but it does nothing due to the call to `unwrap_or_else`.

## Solution

- Apply the `track_caller` attribute to the `World::entity_mut` and
`World::entity`.
- Remove the call to `unwrap_or_else` which makes the `track_caller`
attribute useless (because `unwrap_or_else` is not `track_caller`
itself). The avoid eager evaluation of the panicking branch it is never
inlined.

---------

Co-authored-by: Giacomo Stevanato <[email protected]>

Author: MrGunflame

crates/bevy_ecs/src/system/commands/mod.rs

@@ -307,11 +307,19 @@ impl<'w, 's> Commands<'w, 's> {
     #[inline]
     #[track_caller]
     pub fn entity<'a>(&'a mut self, entity: Entity) -> EntityCommands<'w, 's, 'a> {
-        self.get_entity(entity).unwrap_or_else(|| {
+        #[inline(never)]
+        #[cold]
+        #[track_caller]
+        fn panic_no_entity(entity: Entity) -> ! {
             panic!(
                 "Attempting to create an EntityCommands for entity {entity:?}, which doesn't exist.",
-            )
-        })
+            );
+        }
+
+        match self.get_entity(entity) {
+            Some(entity) => entity,
+            None => panic_no_entity(entity),
+        }
     }
 
     /// Returns the [`EntityCommands`] for the requested [`Entity`], if it exists.

crates/bevy_ecs/src/world/mod.rs

@@ -241,10 +241,19 @@ impl World {
     /// assert_eq!(position.x, 0.0);
     /// ```
     #[inline]
+    #[track_caller]
     pub fn entity(&self, entity: Entity) -> EntityRef {
-        // Lazily evaluate panic!() via unwrap_or_else() to avoid allocation unless failure
-        self.get_entity(entity)
-            .unwrap_or_else(|| panic!("Entity {entity:?} does not exist"))
+        #[inline(never)]
+        #[cold]
+        #[track_caller]
+        fn panic_no_entity(entity: Entity) -> ! {
+            panic!("Entity {entity:?} does not exist");
+        }
+
+        match self.get_entity(entity) {
+            Some(entity) => entity,
+            None => panic_no_entity(entity),
+        }
     }
 
     /// Retrieves an [`EntityMut`] that exposes read and write operations for the given `entity`.
@@ -267,10 +276,19 @@ impl World {
     /// position.x = 1.0;
     /// ```
     #[inline]
+    #[track_caller]
     pub fn entity_mut(&mut self, entity: Entity) -> EntityMut {
-        // Lazily evaluate panic!() via unwrap_or_else() to avoid allocation unless failure
-        self.get_entity_mut(entity)
-            .unwrap_or_else(|| panic!("Entity {entity:?} does not exist"))
+        #[inline(never)]
+        #[cold]
+        #[track_caller]
+        fn panic_no_entity(entity: Entity) -> ! {
+            panic!("Entity {entity:?} does not exist");
+        }
+
+        match self.get_entity_mut(entity) {
+            Some(entity) => entity,
+            None => panic_no_entity(entity),
+        }
     }
 
     /// Returns the components of an [`Entity`](crate::entity::Entity) through [`ComponentInfo`](crate::component::ComponentInfo).