Deprecate get_or_spawn (#15652)

# Objective

After merging retained rendering world #15320, we now have a good way of
creating a link between worlds (*HIYAA intensifies*). This means that
`get_or_spawn` is no longer necessary for that function. Entity should
be opaque as the warning above `get_or_spawn` says. This is also part of
#15459.

I'm deprecating `get_or_spawn_batch` in a different PR in order to keep
the PR small in size.

## Solution

Deprecate `get_or_spawn` and replace it with `get_entity` in most
contexts. If it's possible to query `&RenderEntity`, then the entity is
synced and `render_entity.id()` is initialized in the render world.

## Migration Guide

If you are given an `Entity` and you want to do something with it, use
`Commands.entity(...)` or `World.entity(...)`. If instead you want to
spawn something use `Commands.spawn(...)` or `World.spawn(...)`. If you
are not sure if an entity exists, you can always use `get_entity` and
match on the `Option<...>` that is returned.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

benches/benches/bevy_ecs/world/commands.rs

@@ -209,41 +209,3 @@ pub fn medium_sized_commands(criterion: &mut Criterion) {
 pub fn large_sized_commands(criterion: &mut Criterion) {
     sized_commands_impl::<SizedCommand<LargeStruct>>(criterion);
 }
-
-pub fn get_or_spawn(criterion: &mut Criterion) {
-    let mut group = criterion.benchmark_group("get_or_spawn");
-    group.warm_up_time(core::time::Duration::from_millis(500));
-    group.measurement_time(core::time::Duration::from_secs(4));
-
-    group.bench_function("individual", |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..10_000 {
-                commands
-                    .get_or_spawn(Entity::from_raw(i))
-                    .insert((Matrix::default(), Vec3::default()));
-            }
-            command_queue.apply(&mut world);
-        });
-    });
-
-    group.bench_function("batched", |bencher| {
-        let mut world = World::default();
-        let mut command_queue = CommandQueue::default();
-
-        bencher.iter(|| {
-            let mut commands = Commands::new(&mut command_queue, &world);
-            let mut values = Vec::with_capacity(10_000);
-            for i in 0..10_000 {
-                values.push((Entity::from_raw(i), (Matrix::default(), Vec3::default())));
-            }
-            commands.insert_or_spawn_batch(values);
-            command_queue.apply(&mut world);
-        });
-    });
-
-    group.finish();
-}

benches/benches/bevy_ecs/world/mod.rs

@@ -27,7 +27,6 @@ criterion_group!(
     zero_sized_commands,
     medium_sized_commands,
     large_sized_commands,
-    get_or_spawn,
     world_entity,
     world_get,
     world_query_get,

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -590,7 +590,8 @@ pub fn extract_camera_prepass_phase(
         live_entities.insert(entity);
 
         commands
-            .get_or_spawn(entity)
+            .get_entity(entity)
+            .expect("Camera entity wasn't synced.")
             .insert_if(DepthPrepass, || depth_prepass)
             .insert_if(NormalPrepass, || normal_prepass)
             .insert_if(MotionVectorPrepass, || motion_vector_prepass)

crates/bevy_core_pipeline/src/dof/mod.rs

@@ -830,14 +830,18 @@ fn extract_depth_of_field_settings(
             calculate_focal_length(depth_of_field.sensor_height, perspective_projection.fov);
 
         // Convert `DepthOfField` to `DepthOfFieldUniform`.
-        commands.get_or_spawn(entity).insert((
+        commands
+            .get_entity(entity)
+            .expect("Depth of field entity wasn't synced.")
+            .insert((
                 *depth_of_field,
                 DepthOfFieldUniform {
                     focal_distance: depth_of_field.focal_distance,
                     focal_length,
                     coc_scale_factor: focal_length * focal_length
                         / (depth_of_field.sensor_height * depth_of_field.aperture_f_stops),
-                max_circle_of_confusion_diameter: depth_of_field.max_circle_of_confusion_diameter,
+                    max_circle_of_confusion_diameter: depth_of_field
+                        .max_circle_of_confusion_diameter,
                     max_depth: depth_of_field.max_depth,
                     pad_a: 0,
                     pad_b: 0,

crates/bevy_core_pipeline/src/taa/mod.rs

@@ -375,7 +375,8 @@ fn extract_taa_settings(mut commands: Commands, mut main_world: ResMut<MainWorld
         let has_perspective_projection = matches!(camera_projection, Projection::Perspective(_));
         if camera.is_active && has_perspective_projection {
             commands
-                .get_or_spawn(entity.id())
+                .get_entity(entity.id())
+                .expect("Camera entity wasn't synced.")
                 .insert(taa_settings.clone());
             taa_settings.reset = false;
         }

crates/bevy_ecs/src/lib.rs

@@ -1616,107 +1616,6 @@ mod tests {
         assert_eq!(0, query_min_size![(&A, &B), Or<(Changed<A>, Changed<B>)>]);
     }
 
-    #[test]
-    fn reserve_entities_across_worlds() {
-        let mut world_a = World::default();
-        let mut world_b = World::default();
-
-        let e1 = world_a.spawn(A(1)).id();
-        let e2 = world_a.spawn(A(2)).id();
-        let e3 = world_a.entities().reserve_entity();
-        world_a.flush_entities();
-
-        let world_a_max_entities = world_a.entities().len();
-        world_b.entities.reserve_entities(world_a_max_entities);
-        world_b.entities.flush_as_invalid();
-
-        let e4 = world_b.spawn(A(4)).id();
-        assert_eq!(
-            e4,
-            Entity::from_raw(3),
-            "new entity is created immediately after world_a's max entity"
-        );
-        assert!(world_b.get::<A>(e1).is_none());
-        assert!(world_b.get_entity(e1).is_err());
-
-        assert!(world_b.get::<A>(e2).is_none());
-        assert!(world_b.get_entity(e2).is_err());
-
-        assert!(world_b.get::<A>(e3).is_none());
-        assert!(world_b.get_entity(e3).is_err());
-
-        world_b.get_or_spawn(e1).unwrap().insert(B(1));
-        assert_eq!(
-            world_b.get::<B>(e1),
-            Some(&B(1)),
-            "spawning into 'world_a' entities works"
-        );
-
-        world_b.get_or_spawn(e4).unwrap().insert(B(4));
-        assert_eq!(
-            world_b.get::<B>(e4),
-            Some(&B(4)),
-            "spawning into existing `world_b` entities works"
-        );
-        assert_eq!(
-            world_b.get::<A>(e4),
-            Some(&A(4)),
-            "spawning into existing `world_b` entities works"
-        );
-
-        let e4_mismatched_generation =
-            Entity::from_raw_and_generation(3, NonZero::<u32>::new(2).unwrap());
-        assert!(
-            world_b.get_or_spawn(e4_mismatched_generation).is_none(),
-            "attempting to spawn on top of an entity with a mismatched entity generation fails"
-        );
-        assert_eq!(
-            world_b.get::<B>(e4),
-            Some(&B(4)),
-            "failed mismatched spawn doesn't change existing entity"
-        );
-        assert_eq!(
-            world_b.get::<A>(e4),
-            Some(&A(4)),
-            "failed mismatched spawn doesn't change existing entity"
-        );
-
-        let high_non_existent_entity = Entity::from_raw(6);
-        world_b
-            .get_or_spawn(high_non_existent_entity)
-            .unwrap()
-            .insert(B(10));
-        assert_eq!(
-            world_b.get::<B>(high_non_existent_entity),
-            Some(&B(10)),
-            "inserting into newly allocated high / non-continuous entity id works"
-        );
-
-        let high_non_existent_but_reserved_entity = Entity::from_raw(5);
-        assert!(
-            world_b.get_entity(high_non_existent_but_reserved_entity).is_err(),
-            "entities between high-newly allocated entity and continuous block of existing entities don't exist"
-        );
-
-        let reserved_entities = vec![
-            world_b.entities().reserve_entity(),
-            world_b.entities().reserve_entity(),
-            world_b.entities().reserve_entity(),
-            world_b.entities().reserve_entity(),
-        ];
-
-        assert_eq!(
-            reserved_entities,
-            vec![
-                Entity::from_raw(5),
-                Entity::from_raw(4),
-                Entity::from_raw(7),
-                Entity::from_raw(8),
-            ],
-            "space between original entities and high entities is used for new entity ids"
-        );
-    }
-
     #[test]
     fn insert_or_spawn_batch() {
         let mut world = World::default();

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

@@ -325,8 +325,10 @@ impl<'w, 's> Commands<'w, 's> {
     /// [`Commands::spawn`]. This method should generally only be used for sharing entities across
     /// apps, and only when they have a scheme worked out to share an ID space (which doesn't happen
     /// by default).
+    #[deprecated(since = "0.15.0", note = "use Commands::spawn instead")]
     pub fn get_or_spawn(&mut self, entity: Entity) -> EntityCommands {
         self.queue(move |world: &mut World| {
+            #[allow(deprecated)]
             world.get_or_spawn(entity);
         });
         EntityCommands {

crates/bevy_ecs/src/world/mod.rs

@@ -944,6 +944,7 @@ impl World {
     /// This method should generally only be used for sharing entities across apps, and only when they have a
     /// scheme worked out to share an ID space (which doesn't happen by default).
     #[inline]
+    #[deprecated(since = "0.15.0", note = "use `World::spawn` instead")]
     pub fn get_or_spawn(&mut self, entity: Entity) -> Option<EntityWorldMut> {
         self.flush();
         match self.entities.alloc_at_without_replacement(entity) {

crates/bevy_pbr/src/cluster/mod.rs

@@ -554,7 +554,10 @@ pub fn extract_clusters(
             }
         }
 
-        commands.get_or_spawn(entity.id()).insert((
+        commands
+            .get_entity(entity.id())
+            .expect("Clusters entity wasn't synced.")
+            .insert((
                 ExtractedClusterableObjects { data },
                 ExtractedClusterConfig {
                     near: clusters.near,
@@ -617,7 +620,7 @@ pub fn prepare_clusters(
 
         view_clusters_bindings.write_buffers(render_device, &render_queue);
 
-        commands.get_or_spawn(entity).insert(view_clusters_bindings);
+        commands.entity(entity).insert(view_clusters_bindings);
     }
 }
 

crates/bevy_pbr/src/light_probe/mod.rs

@@ -386,7 +386,8 @@ fn gather_environment_map_uniform(
             EnvironmentMapUniform::default()
         };
         commands
-            .get_or_spawn(view_entity.id())
+            .get_entity(view_entity.id())
+            .expect("Environment map light entity wasn't synced.")
             .insert(environment_map_uniform);
     }
 }
@@ -440,11 +441,13 @@ fn gather_light_probes<C>(
         // Record the per-view light probes.
         if render_view_light_probes.is_empty() {
             commands
-                .get_or_spawn(entity)
+                .get_entity(entity)
+                .expect("View entity wasn't synced.")
                 .remove::<RenderViewLightProbes<C>>();
         } else {
             commands
-                .get_or_spawn(entity)
+                .get_entity(entity)
+                .expect("View entity wasn't synced.")
                 .insert(render_view_light_probes);
         }
     }

crates/bevy_pbr/src/prepass/mod.rs

@@ -585,7 +585,9 @@ pub fn extract_camera_previous_view_data(
     for (entity, camera, maybe_previous_view_data) in cameras_3d.iter() {
         if camera.is_active {
             let entity = entity.id();
-            let mut entity = commands.get_or_spawn(entity);
+            let mut entity = commands
+                .get_entity(entity)
+                .expect("Camera entity wasn't synced.");
 
             if let Some(previous_view_data) = maybe_previous_view_data {
                 entity.insert(previous_view_data.clone());

crates/bevy_pbr/src/render/light.rs

@@ -403,7 +403,10 @@ pub fn extract_lights(
             }
         }
 
-        commands.get_or_spawn(entity.id()).insert((
+        commands
+            .get_entity(entity.id())
+            .expect("Light entity wasn't synced.")
+            .insert((
                 ExtractedDirectionalLight {
                     color: directional_light.color.into(),
                     illuminance: directional_light.illuminance,

crates/bevy_pbr/src/ssao/mod.rs

@@ -537,7 +537,8 @@ fn extract_ssao_settings(
         }
         if camera.is_active {
             commands
-                .get_or_spawn(entity.id())
+                .get_entity(entity.id())
+                .expect("SSAO entity wasn't synced.")
                 .insert(ssao_settings.clone());
         }
     }

crates/bevy_pbr/src/volumetric_fog/render.rs

@@ -280,18 +280,25 @@ pub fn extract_volumetric_fog(
     }
 
     for (entity, volumetric_fog) in view_targets.iter() {
-        commands.get_or_spawn(entity.id()).insert(*volumetric_fog);
+        commands
+            .get_entity(entity.id())
+            .expect("Volumetric fog entity wasn't synced.")
+            .insert(*volumetric_fog);
     }
 
     for (entity, fog_volume, fog_transform) in fog_volumes.iter() {
         commands
-            .get_or_spawn(entity.id())
+            .get_entity(entity.id())
+            .expect("Fog volume entity wasn't synced.")
             .insert((*fog_volume).clone())
             .insert(*fog_transform);
     }
 
     for (entity, volumetric_light) in volumetric_lights.iter() {
-        commands.get_or_spawn(entity.id()).insert(*volumetric_light);
+        commands
+            .get_entity(entity.id())
+            .expect("Volumetric light entity wasn't synced.")
+            .insert(*volumetric_light);
     }
 }
 

crates/bevy_render/src/extract_param.rs

@@ -30,11 +30,13 @@ use core::ops::{Deref, DerefMut};
 /// ```
 /// use bevy_ecs::prelude::*;
 /// use bevy_render::Extract;
+/// use bevy_render::world_sync::RenderEntity;
 /// # #[derive(Component)]
+/// // Do make sure to sync the cloud entities before extracting them.
 /// # struct Cloud;
-/// fn extract_clouds(mut commands: Commands, clouds: Extract<Query<Entity, With<Cloud>>>) {
+/// fn extract_clouds(mut commands: Commands, clouds: Extract<Query<&RenderEntity, With<Cloud>>>) {
 ///     for cloud in &clouds {
-///         commands.get_or_spawn(cloud).insert(Cloud);
+///         commands.entity(cloud.id()).insert(Cloud);
 ///     }
 /// }
 /// ```

crates/bevy_ui/src/render/mod.rs

@@ -510,7 +510,9 @@ pub fn extract_default_ui_camera_view(
                     TemporaryRenderEntity,
                 ))
                 .id();
-            let mut entity_commands = commands.get_or_spawn(entity);
+            let mut entity_commands = commands
+                .get_entity(entity)
+                .expect("Camera entity wasn't synced.");
             entity_commands.insert(DefaultCameraView(default_camera_view));
             if let Some(ui_anti_alias) = ui_anti_alias {
                 entity_commands.insert(*ui_anti_alias);

examples/stress_tests/transform_hierarchy.rs

@@ -428,9 +428,7 @@ fn spawn_tree(
             cmd.id()
         };
 
-        commands
+        commands.entity(ents[parent_idx]).add_child(child_entity);
-            .get_or_spawn(ents[parent_idx])
-            .add_child(child_entity);
 
         ents.push(child_entity);
     }