Remove extra call to clear_trackers

crates/bevy_app/src/app.rs

@@ -916,9 +916,17 @@ impl Termination for AppExit {
 
 #[cfg(test)]
 mod tests {
-    use std::{marker::PhantomData, mem};
-
-    use bevy_ecs::{event::EventWriter, schedule::ScheduleLabel, system::Commands};
+    use std::{iter, marker::PhantomData, mem};
+
+    use bevy_ecs::{
+        component::Component,
+        entity::Entity,
+        event::EventWriter,
+        query::With,
+        removal_detection::RemovedComponents,
+        schedule::{IntoSystemConfigs, ScheduleLabel},
+        system::{Commands, Query},
+    };
 
     use crate::{App, AppExit, Plugin, Update};
 
@@ -1123,6 +1131,35 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_update_clears_trackers_once() {
+        #[derive(Component, Copy, Clone)]
+        struct Foo;
+
+        let mut app = App::new();
+        app.world_mut().spawn_batch(iter::repeat(Foo).take(5));
+
+        fn despawn_one_foo(mut commands: Commands, foos: Query<Entity, With<Foo>>) {
+            if let Some(e) = foos.iter().next() {
+                commands.entity(e).despawn();
+            };
+        }
+        fn check_despawns(mut removed_foos: RemovedComponents<Foo>) {
+            let mut despawn_count = 0;
+            for _ in removed_foos.read() {
+                despawn_count += 1;
+            }
+
+            assert_eq!(despawn_count, 2);
+        }
+
+        app.add_systems(Update, despawn_one_foo);
+        app.update(); // Frame 0
+        app.update(); // Frame 1
+        app.add_systems(Update, check_despawns.after(despawn_one_foo));
+        app.update(); // Should see despawns from frames 1 & 2, but not frame 0
+    }
+
     #[test]
     fn runner_returns_correct_exit_code() {
         fn raise_exits(mut exits: EventWriter<AppExit>) {

crates/bevy_app/src/sub_app.rs

@@ -429,8 +429,6 @@ impl SubApps {
             sub_app.extract(&mut self.main.world);
             sub_app.update();
         }
-
-        self.main.world.clear_trackers();
     }
 
     /// Returns an iterator over the sub-apps (starting with the main one).