Change event to event_key where it refers to an EventKey (#20060)

# Objective

The ECS code to do with Observers was recently refactored to use an
`EventKey` newtype. On reading through the PR, I was a bit confused that
sometimes a variable called `event` refers to an `Event` and sometimes
it refers to an `EventKey`. I think the code is clearer when `event`
refers to an `Event` and `event_key` refers to an `EventKey`.

## Solution

This PR renames some uses of `event` to `event_key`.

## Testing

- Did you test these changes? If so, how?

I ran `cargo run -p ci -- tests`

- Are there any parts that need more testing?

No

- How can other people (reviewers) test your changes? Is there anything
specific they need to know?

No.

- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?

Probably not relevant, but MacOS.

---------

Co-authored-by: Steve Alexander <steve.alexander@priva.com>

crates/bevy_ecs/src/event/registry.rs

@@ -12,7 +12,7 @@ struct RegisteredEvent {
     event_key: EventKey,
     // Required to flush the secondary buffer and drop events even if left unchanged.
     previously_updated: bool,
-    // SAFETY: The component ID and the function must be used to fetch the Events<T> resource
+    // SAFETY: The `EventKey`'s component ID and the function must be used to fetch the Events<T> resource
     // of the same type initialized in `register_event`, or improper type casts will occur.
     update: unsafe fn(MutUntyped),
 }

crates/bevy_ecs/src/observer/distributed_storage.rs

@@ -248,7 +248,7 @@ impl Observer {
                 world.commands().queue(move |world: &mut World| {
                     let entity = hook_context.entity;
                     if let Some(mut observe) = world.get_mut::<Observer>(entity) {
-                        if observe.descriptor.events.is_empty() {
+                        if observe.descriptor.event_keys.is_empty() {
                             return;
                         }
                         if observe.error_handler.is_none() {
@@ -286,13 +286,13 @@ impl Observer {
         self
     }
 
-    /// Observe the given `event`. This will cause the [`Observer`] to run whenever an event with the given [`ComponentId`]
+    /// Observe the given `event_key`. This will cause the [`Observer`] to run whenever an event with the given [`EventKey`]
     /// is triggered.
     /// # Safety
-    /// The type of the `event` [`EventKey`] _must_ match the actual value
+    /// The type of the `event_key` [`EventKey`] _must_ match the actual value
     /// of the event passed into the observer system.
-    pub unsafe fn with_event(mut self, event: EventKey) -> Self {
-        self.descriptor.events.push(event);
+    pub unsafe fn with_event_key(mut self, event_key: EventKey) -> Self {
+        self.descriptor.event_keys.push(event_key);
         self
     }
 
@@ -349,8 +349,8 @@ impl Component for Observer {
 /// This information is stored inside of the [`Observer`] component,
 #[derive(Default, Clone)]
 pub struct ObserverDescriptor {
-    /// The events the observer is watching.
-    pub(super) events: Vec<EventKey>,
+    /// The event keys the observer is watching.
+    pub(super) event_keys: Vec<EventKey>,
 
     /// The components the observer is watching.
     pub(super) components: Vec<ComponentId>,
@@ -360,12 +360,12 @@ pub struct ObserverDescriptor {
 }
 
 impl ObserverDescriptor {
-    /// Add the given `events` to the descriptor.
+    /// Add the given `event_keys` to the descriptor.
     /// # Safety
-    /// The type of each [`EventKey`] in `events` _must_ match the actual value
+    /// The type of each [`EventKey`] in `event_keys` _must_ match the actual value
     /// of the event passed into the observer.
-    pub unsafe fn with_events(mut self, events: Vec<EventKey>) -> Self {
-        self.events = events;
+    pub unsafe fn with_event_keys(mut self, event_keys: Vec<EventKey>) -> Self {
+        self.event_keys = event_keys;
         self
     }
 
@@ -381,9 +381,9 @@ impl ObserverDescriptor {
         self
     }
 
-    /// Returns the `events` that the observer is watching.
-    pub fn events(&self) -> &[EventKey] {
-        &self.events
+    /// Returns the `event_keys` that the observer is watching.
+    pub fn event_keys(&self) -> &[EventKey] {
+        &self.event_keys
     }
 
     /// Returns the `components` that the observer is watching.
@@ -416,7 +416,7 @@ fn hook_on_add<E: Event, B: Bundle, S: ObserverSystem<E, B>>(
             components.push(id);
         });
         if let Some(mut observer) = world.get_mut::<Observer>(entity) {
-            observer.descriptor.events.push(event_key);
+            observer.descriptor.event_keys.push(event_key);
             observer.descriptor.components.extend(components);
 
             let system: &mut dyn Any = observer.system.as_mut();

crates/bevy_ecs/src/observer/entity_cloning.rs

@@ -43,7 +43,7 @@ fn component_clone_observed_by(_source: &SourceComponent, ctx: &mut ComponentClo
                 .get_mut::<Observer>(observer_entity)
                 .expect("Source observer entity must have Observer");
             observer_state.descriptor.entities.push(target);
-            let event_keys = observer_state.descriptor.events.clone();
+            let event_keys = observer_state.descriptor.event_keys.clone();
             let components = observer_state.descriptor.components.clone();
             for event_key in event_keys {
                 let observers = world.observers.get_observers_mut(event_key);

crates/bevy_ecs/src/observer/mod.rs

@@ -379,7 +379,7 @@ impl World {
         };
         let descriptor = &observer_state.descriptor;
 
-        for &event_key in &descriptor.events {
+        for &event_key in &descriptor.event_keys {
             let cache = observers.get_observers_mut(event_key);
 
             if descriptor.components.is_empty() && descriptor.entities.is_empty() {
@@ -430,7 +430,7 @@ impl World {
         let archetypes = &mut self.archetypes;
         let observers = &mut self.observers;
 
-        for &event_key in &descriptor.events {
+        for &event_key in &descriptor.event_keys {
             let cache = observers.get_observers_mut(event_key);
             if descriptor.components.is_empty() && descriptor.entities.is_empty() {
                 cache.global_observers.remove(&entity);
@@ -741,7 +741,7 @@ mod tests {
                 Observer::new(|_: On<Add, A>, mut res: ResMut<Order>| {
                     res.observed("add/remove");
                 })
-                .with_event(on_remove)
+                .with_event_key(on_remove)
             },
         );
 
@@ -1015,7 +1015,7 @@ mod tests {
             Observer::with_dynamic_runner(|mut world, _trigger, _ptr, _propagate| {
                 world.resource_mut::<Order>().observed("event_a");
             })
-            .with_event(event_a)
+            .with_event_key(event_a)
         };
         world.spawn(observe);
 

crates/bevy_ecs/src/observer/system_param.rs

@@ -181,7 +181,7 @@ impl<'w, E, B: Bundle> DerefMut for On<'w, E, B> {
 pub struct ObserverTrigger {
     /// The [`Entity`] of the observer handling the trigger.
     pub observer: Entity,
-    /// The [`Event`] the trigger targeted.
+    /// The [`EventKey`] the trigger targeted.
     pub event_key: EventKey,
     /// The [`ComponentId`]s the trigger targeted.
     pub components: SmallVec<[ComponentId; 2]>,

crates/bevy_ecs/src/world/deferred_world.rs

@@ -781,18 +781,18 @@ impl<'w> DeferredWorld<'w> {
     /// Triggers all event observers for [`ComponentId`] in target.
     ///
     /// # Safety
-    /// Caller must ensure observers listening for `event` can accept ZST pointers
+    /// Caller must ensure observers listening for `event_key` can accept ZST pointers
     #[inline]
     pub(crate) unsafe fn trigger_observers(
         &mut self,
-        event: EventKey,
+        event_key: EventKey,
         target: Option<Entity>,
         components: impl Iterator<Item = ComponentId> + Clone,
         caller: MaybeLocation,
     ) {
         Observers::invoke::<_>(
             self.reborrow(),
-            event,
+            event_key,
             target,
             target,
             components,
@@ -805,11 +805,11 @@ impl<'w> DeferredWorld<'w> {
     /// Triggers all event observers for [`ComponentId`] in target.
     ///
     /// # Safety
-    /// Caller must ensure `E` is accessible as the type represented by `event`
+    /// Caller must ensure `E` is accessible as the type represented by `event_key`
     #[inline]
     pub(crate) unsafe fn trigger_observers_with_data<E, T>(
         &mut self,
-        event: EventKey,
+        event_key: EventKey,
         current_target: Option<Entity>,
         original_target: Option<Entity>,
         components: impl Iterator<Item = ComponentId> + Clone,
@@ -821,7 +821,7 @@ impl<'w> DeferredWorld<'w> {
     {
         Observers::invoke::<_>(
             self.reborrow(),
-            event,
+            event_key,
             current_target,
             original_target,
             components.clone(),
@@ -849,7 +849,7 @@ impl<'w> DeferredWorld<'w> {
             }
             Observers::invoke::<_>(
                 self.reborrow(),
-                event,
+                event_key,
                 Some(current_target),
                 original_target,
                 components.clone(),