Fix spawn tracking for spawn commands (#19351)

# Objective

See also
https://discord.com/channels/691052431525675048/1374187654425481266/1375553989185372292.

## Solution

Set spawn info in `Commands::spawn_empty`.
Also added a benchmark for `Commands::spawn`.

## Testing

See added test.

benches/benches/bevy_ecs/world/commands.rs

@@ -62,6 +62,31 @@ pub fn spawn_commands(criterion: &mut Criterion) {
     group.finish();
 }
 
+pub fn nonempty_spawn_commands(criterion: &mut Criterion) {
+    let mut group = criterion.benchmark_group("nonempty_spawn_commands");
+    group.warm_up_time(core::time::Duration::from_millis(500));
+    group.measurement_time(core::time::Duration::from_secs(4));
+
+    for entity_count in [100, 1_000, 10_000] {
+        group.bench_function(format!("{}_entities", entity_count), |bencher| {
+            let mut world = World::default();
+            let mut command_queue = CommandQueue::default();
+
+            bencher.iter(|| {
+                let mut commands = Commands::new(&mut command_queue, &world);
+                for i in 0..entity_count {
+                    if black_box(i % 2 == 0) {
+                        commands.spawn(A);
+                    }
+                }
+                command_queue.apply(&mut world);
+            });
+        });
+    }
+
+    group.finish();
+}
+
 #[derive(Default, Component)]
 struct Matrix([[f32; 4]; 4]);
 

benches/benches/bevy_ecs/world/mod.rs

@@ -17,6 +17,7 @@ criterion_group!(
     benches,
     empty_commands,
     spawn_commands,
+    nonempty_spawn_commands,
     insert_commands,
     fake_commands,
     zero_sized_commands,

crates/bevy_ecs/src/entity/mod.rs

@@ -943,6 +943,15 @@ impl Entities {
         meta.spawned_or_despawned = MaybeUninit::new(SpawnedOrDespawned { by, at });
     }
 
+    /// # Safety
+    ///  - `index` must be a valid entity index.
+    #[inline]
+    pub(crate) unsafe fn mark_spawn_despawn(&mut self, index: u32, by: MaybeLocation, at: Tick) {
+        // SAFETY: Caller guarantees that `index` a valid entity index
+        let meta = unsafe { self.meta.get_unchecked_mut(index as usize) };
+        meta.spawned_or_despawned = MaybeUninit::new(SpawnedOrDespawned { by, at });
+    }
+
     /// Increments the `generation` of a freed [`Entity`]. The next entity ID allocated with this
     /// `index` will count `generation` starting from the prior `generation` + the specified
     /// value + 1.

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

@@ -16,7 +16,7 @@ use core::marker::PhantomData;
 use crate::{
     self as bevy_ecs,
     bundle::{Bundle, InsertMode, NoBundleEffect},
-    change_detection::Mut,
+    change_detection::{MaybeLocation, Mut},
     component::{Component, ComponentId, Mutable},
     entity::{Entities, Entity, EntityClonerBuilder, EntityDoesNotExistError},
     error::{ignore, warn, BevyError, CommandWithEntity, ErrorContext, HandleError},
@@ -317,12 +317,24 @@ impl<'w, 's> Commands<'w, 's> {
     /// - [`spawn`](Self::spawn) to spawn an entity with components.
     /// - [`spawn_batch`](Self::spawn_batch) to spawn many entities
     ///   with the same combination of components.
+    #[track_caller]
     pub fn spawn_empty(&mut self) -> EntityCommands {
         let entity = self.entities.reserve_entity();
-        EntityCommands {
+        let mut entity_commands = EntityCommands {
             entity,
             commands: self.reborrow(),
+        };
+        let caller = MaybeLocation::caller();
+        entity_commands.queue(move |entity: EntityWorldMut| {
+            let index = entity.id().index();
+            let world = entity.into_world_mut();
+            let tick = world.change_tick();
+            // SAFETY: Entity has been flushed
+            unsafe {
+                world.entities_mut().mark_spawn_despawn(index, caller, tick);
             }
+        });
+        entity_commands
     }
 
     /// Spawns a new [`Entity`] with the given components
@@ -369,9 +381,35 @@ impl<'w, 's> Commands<'w, 's> {
     ///   with the same combination of components.
     #[track_caller]
     pub fn spawn<T: Bundle>(&mut self, bundle: T) -> EntityCommands {
-        let mut entity = self.spawn_empty();
+        let entity = self.entities.reserve_entity();
-        entity.insert(bundle);
+        let mut entity_commands = EntityCommands {
-        entity
+            entity,
+            commands: self.reborrow(),
+        };
+        let caller = MaybeLocation::caller();
+
+        entity_commands.queue(move |mut entity: EntityWorldMut| {
+            // Store metadata about the spawn operation.
+            // This is the same as in `spawn_empty`, but merged into
+            // the same command for better performance.
+            let index = entity.id().index();
+            entity.world_scope(|world| {
+                let tick = world.change_tick();
+                // SAFETY: Entity has been flushed
+                unsafe {
+                    world.entities_mut().mark_spawn_despawn(index, caller, tick);
+                }
+            });
+
+            entity.insert_with_caller(
+                bundle,
+                InsertMode::Replace,
+                caller,
+                crate::relationship::RelationshipHookMode::Run,
+            );
+        });
+        // entity_command::insert(bundle, InsertMode::Replace)
+        entity_commands
     }
 
     /// Returns the [`EntityCommands`] for the given [`Entity`].
@@ -2577,4 +2615,17 @@ mod tests {
         assert!(world.contains_resource::<W<i32>>());
         assert!(world.contains_resource::<W<f64>>());
     }
+
+    #[test]
+    fn track_spawn_ticks() {
+        let mut world = World::default();
+        world.increment_change_tick();
+        let expected = world.change_tick();
+        let id = world.commands().spawn_empty().id();
+        world.flush();
+        assert_eq!(
+            Some(expected),
+            world.entities().entity_get_spawned_or_despawned_at(id)
+        );
+    }
 }