Trigger::entity() only returns valid entities

crates/bevy_ecs/src/observer/mod.rs

@@ -55,11 +55,30 @@ impl<'w, E, B: Bundle> Trigger<'w, E, B> {
         Ptr::from(&self.event)
     }
 
-    /// Returns the entity that triggered the observer, could be [`Entity::PLACEHOLDER`].
+    /// Returns the entity that triggered the observer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the entity is [`Entity::PLACEHOLDER`].
+    /// Use [`Trigger::get_entity`] if you want to handle the case where the entity is a placeholder.
     pub fn entity(&self) -> Entity {
+        if self.trigger.entity == Entity::PLACEHOLDER {
+            panic!(
+                "called `Trigger::entity()` when the target entity was a `Entity::PLACEHOLDER`."
+            );
+        }
         self.trigger.entity
     }
 
+    /// Returns the entity that triggered the observer, if it's not a placeholder entity.
+    pub fn get_entity(&self) -> Option<Entity> {
+        if self.trigger.entity == Entity::PLACEHOLDER {
+            None
+        } else {
+            Some(self.trigger.entity)
+        }
+    }
+
     /// Enables or disables event propagation, allowing the same event to trigger observers on a chain of different entities.
     ///
     /// The path an event will propagate along is specified by its associated [`Traversal`] component. By default, events
@@ -665,7 +684,7 @@ mod tests {
             .spawn_empty()
             .observe(|_: Trigger<EventA>| panic!("Trigger routed to non-targeted entity."));
         world.observe(move |obs: Trigger<EventA>, mut res: ResMut<R>| {
-            assert_eq!(obs.entity(), Entity::PLACEHOLDER);
+            assert_eq!(obs.get_entity(), None);
             res.0 += 1;
         });
 
@@ -959,7 +978,11 @@ mod tests {
 
         world.observe(
             |trigger: Trigger<EventPropagating>, query: Query<&A>, mut res: ResMut<R>| {
-                if query.get(trigger.entity()).is_ok() {
+                if trigger
+                    .get_entity()
+                    .map(|entity| query.get(entity).is_ok())
+                    .unwrap_or_default()
+                {
                     res.0 += 1;
                 }
             },

crates/bevy_scene/src/scene_spawner.rs

@@ -576,7 +576,7 @@ mod tests {
             })
     }
 
-    fn observe_trigger(app: &mut App, scene_id: InstanceId, scene_entity: Entity) {
+    fn observe_trigger(app: &mut App, scene_id: InstanceId, scene_entity: Option<Entity>) {
         // Add observer
         app.world_mut().observe(
             move |trigger: Trigger<SceneInstanceReady>,
@@ -588,7 +588,7 @@ mod tests {
                     "`SceneInstanceReady` contains the wrong `InstanceId`"
                 );
                 assert_eq!(
-                    trigger.entity(),
+                    trigger.get_entity(),
                     scene_entity,
                     "`SceneInstanceReady` triggered on the wrong parent entity"
                 );
@@ -626,7 +626,7 @@ mod tests {
                 });
 
         // Check trigger.
-        observe_trigger(&mut app, scene_id, Entity::PLACEHOLDER);
+        observe_trigger(&mut app, scene_id, None);
     }
 
     #[test]
@@ -644,7 +644,7 @@ mod tests {
                 });
 
         // Check trigger.
-        observe_trigger(&mut app, scene_id, Entity::PLACEHOLDER);
+        observe_trigger(&mut app, scene_id, None);
     }
 
     #[test]
@@ -664,7 +664,7 @@ mod tests {
         );
 
         // Check trigger.
-        observe_trigger(&mut app, scene_id, scene_entity);
+        observe_trigger(&mut app, scene_id, Some(scene_entity));
     }
 
     #[test]
@@ -684,7 +684,7 @@ mod tests {
         );
 
         // Check trigger.
-        observe_trigger(&mut app, scene_id, scene_entity);
+        observe_trigger(&mut app, scene_id, Some(scene_entity));
     }
 
     #[test]

examples/ecs/observer_propagation.rs

@@ -78,8 +78,10 @@ fn attack_armor(entities: Query<Entity, With<Armor>>, mut commands: Commands) {
 }
 
 fn attack_hits(trigger: Trigger<Attack>, name: Query<&Name>) {
-    if let Ok(name) = name.get(trigger.entity()) {
-        info!("Attack hit {}", name);
+    if let Some(entity) = trigger.get_entity() {
+        if let Ok(name) = name.get(entity) {
+            info!("Attack hit {}", name);
+        }
     }
 }
 

examples/ecs/observers.rs

@@ -147,7 +147,9 @@ fn on_remove_mine(
 
 fn explode_mine(trigger: Trigger<Explode>, query: Query<&Mine>, mut commands: Commands) {
     // If a triggered event is targeting a specific entity you can access it with `.entity()`
-    let id = trigger.entity();
+    let Some(id) = trigger.get_entity() else {
+        return;
+    };
     let Some(mut entity) = commands.get_entity(id) else {
         return;
     };