Change ReflectMapEntities to operate on components before insertion

crates/bevy_ecs/src/entity/map_entities.rs

@@ -122,6 +122,19 @@ impl<T: EntityMapper> DynEntityMapper for T {
     }
 }
 
+/// Helper to construct an [`EntityMapper`] from a [`DynEntityMapper`].
+pub struct UnDynEntityMapper<'a>(pub &'a mut dyn DynEntityMapper);
+
+impl<'a> EntityMapper for UnDynEntityMapper<'a> {
+    fn map_entity(&mut self, entity: Entity) -> Entity {
+        self.0.dyn_map_entity(entity)
+    }
+
+    fn mappings(&self) -> impl Iterator<Item = (Entity, Entity)> {
+        self.0.dyn_mappings().into_iter()
+    }
+}
+
 impl EntityMapper for SceneEntityMapper<'_> {
     /// Returns the corresponding mapped entity or reserves a new dead entity ID in the current world if it is absent.
     fn map_entity(&mut self, entity: Entity) -> Entity {

crates/bevy_ecs/src/reflect/map_entities.rs

@@ -1,9 +1,11 @@
 use crate::{
     component::Component,
-    entity::{Entity, EntityHashMap, MapEntities, SceneEntityMapper},
+    entity::{
+        DynEntityMapper, Entity, EntityHashMap, MapEntities, SceneEntityMapper, UnDynEntityMapper,
+    },
     world::World,
 };
-use bevy_reflect::FromType;
+use bevy_reflect::{FromReflect, FromType, Reflect};
 
 /// For a specific type of component, this maps any fields with values of type [`Entity`] to a new world.
 /// Since a given `Entity` ID is only valid for the world it came from, when performing deserialization
@@ -12,63 +14,26 @@ use bevy_reflect::FromType;
 /// See [`SceneEntityMapper`] and [`MapEntities`] for more information.
 #[derive(Clone)]
 pub struct ReflectMapEntities {
-    map_all_entities: fn(&mut World, &mut SceneEntityMapper),
-    map_entities: fn(&mut World, &mut SceneEntityMapper, &[Entity]),
+    map_entities: fn(&mut dyn Reflect, &mut dyn DynEntityMapper),
 }
 
 impl ReflectMapEntities {
-    /// A general method for applying [`MapEntities`] behavior to all elements in an [`EntityHashMap<Entity>`].
+    /// A general method for applying [`MapEntities`] behavior to a reflected component.
     ///
     /// Be mindful in its usage: Works best in situations where the entities in the [`EntityHashMap<Entity>`] are newly
-    /// created, before systems have a chance to add new components. If some of the entities referred to
-    /// by the [`EntityHashMap<Entity>`] might already contain valid entity references, you should use [`map_entities`](Self::map_entities).
-    ///
-    /// An example of this: A scene can be loaded with `Parent` components, but then a `Parent` component can be added
-    /// to these entities after they have been loaded. If you reload the scene using [`map_all_entities`](Self::map_all_entities), those `Parent`
-    /// components with already valid entity references could be updated to point at something else entirely.
-    pub fn map_all_entities(&self, world: &mut World, entity_map: &mut EntityHashMap<Entity>) {
-        SceneEntityMapper::world_scope(entity_map, world, self.map_all_entities);
-    }
-
-    /// A general method for applying [`MapEntities`] behavior to elements in an [`EntityHashMap<Entity>`]. Unlike
-    /// [`map_all_entities`](Self::map_all_entities), this is applied to specific entities, not all values
-    /// in the [`EntityHashMap<Entity>`].
-    ///
-    /// This is useful mostly for when you need to be careful not to update components that already contain valid entity
-    /// values. See [`map_all_entities`](Self::map_all_entities) for more details.
-    pub fn map_entities(
-        &self,
-        world: &mut World,
-        entity_map: &mut EntityHashMap<Entity>,
-        entities: &[Entity],
-    ) {
-        SceneEntityMapper::world_scope(entity_map, world, |world, mapper| {
-            (self.map_entities)(world, mapper, entities);
-        });
+    /// created, before systems have a chance to add new components.
+    pub fn map_entities(&self, component: &mut dyn Reflect, mapper: &mut dyn DynEntityMapper) {
+        (self.map_entities)(component, mapper);
     }
 }
 
-impl<C: Component + MapEntities> FromType<C> for ReflectMapEntities {
+impl<C: Component + MapEntities + Reflect + FromReflect> FromType<C> for ReflectMapEntities {
     fn from_type() -> Self {
         ReflectMapEntities {
-            map_entities: |world, entity_mapper, entities| {
-                for &entity in entities {
-                    if let Some(mut component) = world.get_mut::<C>(entity) {
-                        component.map_entities(entity_mapper);
-                    }
-                }
-            },
-            map_all_entities: |world, entity_mapper| {
-                let entities = entity_mapper
-                    .get_map()
-                    .values()
-                    .copied()
-                    .collect::<Vec<Entity>>();
-                for entity in &entities {
-                    if let Some(mut component) = world.get_mut::<C>(*entity) {
-                        component.map_entities(entity_mapper);
-                    }
-                }
+            map_entities: |component, entity_mapper| {
+                let mut concrete = C::from_reflect(&*component).unwrap();
+                concrete.map_entities(&mut UnDynEntityMapper(entity_mapper));
+                component.apply(&concrete as _);
             },
         }
     }

crates/bevy_scene/src/dynamic_scene.rs

@@ -1,12 +1,11 @@
 use crate::{ron, DynamicSceneBuilder, Scene, SceneSpawnError};
-use bevy_ecs::entity::EntityHashMap;
+use bevy_ecs::entity::{EntityHashMap, SceneEntityMapper};
 use bevy_ecs::{
     entity::Entity,
     reflect::{AppTypeRegistry, ReflectComponent, ReflectMapEntities},
     world::World,
 };
 use bevy_reflect::{Reflect, TypePath, TypeRegistry};
-use bevy_utils::TypeIdMap;
 
 #[cfg(feature = "serialize")]
 use crate::serde::SceneSerializer;
@@ -71,23 +70,26 @@ impl DynamicScene {
     ) -> Result<(), SceneSpawnError> {
         let type_registry = type_registry.read();
 
-        // For each component types that reference other entities, we keep track
-        // of which entities in the scene use that component.
-        // This is so we can update the scene-internal references to references
-        // of the actual entities in the world.
-        let mut scene_mappings: TypeIdMap<Vec<Entity>> = Default::default();
-
+        // First ensure that every entity in the scene has a corresponding world
+        // entity in the entity map.
         for scene_entity in &self.entities {
             // Fetch the entity with the given entity id from the `entity_map`
             // or spawn a new entity with a transiently unique id if there is
             // no corresponding entry.
-            let entity = *entity_map
+            entity_map
                 .entry(scene_entity.entity)
                 .or_insert_with(|| world.spawn_empty().id());
-            let entity_mut = &mut world.entity_mut(entity);
+        }
+
+        for scene_entity in &self.entities {
+            // Fetch the entity with the given entity id from the `entity_map`.
+            let entity = *entity_map
+                .get(&scene_entity.entity)
+                .expect("should have previously spawned an empty entity");
 
             // Apply/ add each component to the given entity.
             for component in &scene_entity.components {
+                let mut component = component.clone_value();
                 let type_info = component.get_represented_type_info().ok_or_else(|| {
                     SceneSpawnError::NoRepresentedType {
                         type_path: component.reflect_type_path().to_string(),
@@ -105,29 +107,19 @@ impl DynamicScene {
                         }
                     })?;
 
-                // If this component references entities in the scene, track it
-                // so we can update it to the entity in the world.
-                if registration.data::<ReflectMapEntities>().is_some() {
-                    scene_mappings
-                        .entry(registration.type_id())
-                        .or_default()
-                        .push(entity);
+                // If this component references entities in the scene, update
+                // them to the entities in the world.
+                if let Some(map_entities) = registration.data::<ReflectMapEntities>() {
+                    SceneEntityMapper::world_scope(entity_map, world, |_, mapper| {
+                        map_entities.map_entities(&mut *component, mapper);
+                    });
                 }
 
-                // If the entity already has the given component attached,
-                // just apply the (possibly) new value, otherwise add the
-                // component to the entity.
-                reflect_component.apply_or_insert(entity_mut, &**component, &type_registry);
-            }
-        }
-
-        // Updates references to entities in the scene to entities in the world
-        for (type_id, entities) in scene_mappings.into_iter() {
-            let registration = type_registry.get(type_id).expect(
-                "we should be getting TypeId from this TypeRegistration in the first place",
-            );
-            if let Some(map_entities_reflect) = registration.data::<ReflectMapEntities>() {
-                map_entities_reflect.map_entities(world, entity_map, &entities);
+                reflect_component.apply_or_insert(
+                    &mut world.entity_mut(entity),
+                    &*component,
+                    &type_registry,
+                );
             }
         }
 

crates/bevy_scene/src/scene.rs

@@ -1,11 +1,11 @@
 use crate::{DynamicScene, SceneSpawnError};
 use bevy_asset::Asset;
-use bevy_ecs::entity::{Entity, EntityHashMap};
+use bevy_ecs::entity::{Entity, EntityHashMap, SceneEntityMapper};
 use bevy_ecs::{
     reflect::{AppTypeRegistry, ReflectComponent, ReflectMapEntities, ReflectResource},
     world::World,
 };
-use bevy_reflect::TypePath;
+use bevy_reflect::{Reflect, TypePath};
 
 /// To spawn a scene, you can use either:
 /// * [`SceneSpawner::spawn`](crate::SceneSpawner::spawn)
@@ -92,7 +92,7 @@ impl Scene {
 
         for archetype in self.world.archetypes().iter() {
             for scene_entity in archetype.entities() {
-                let entity = entity_map
+                let entity = *entity_map
                     .entry(scene_entity.id())
                     .or_insert_with(|| world.spawn_empty().id());
                 for component_id in archetype.components() {
@@ -102,35 +102,42 @@ impl Scene {
                         .get_info(component_id)
                         .expect("component_ids in archetypes should have ComponentInfo");
 
-                    let reflect_component = type_registry
+                    let registration = type_registry
                         .get(component_info.type_id().unwrap())
                         .ok_or_else(|| SceneSpawnError::UnregisteredType {
                             std_type_name: component_info.name().to_string(),
-                        })
-                        .and_then(|registration| {
-                            registration.data::<ReflectComponent>().ok_or_else(|| {
-                                SceneSpawnError::UnregisteredComponent {
-                                    type_path: registration.type_info().type_path().to_string(),
-                                }
-                            })
                         })?;
-                    reflect_component.copy(
-                        &self.world,
-                        world,
-                        scene_entity.id(),
-                        *entity,
+                    let reflect_component =
+                        registration.data::<ReflectComponent>().ok_or_else(|| {
+                            SceneSpawnError::UnregisteredComponent {
+                                type_path: registration.type_info().type_path().to_string(),
+                            }
+                        })?;
+
+                    let Some(mut component) = reflect_component
+                        .reflect(self.world.entity(scene_entity.id()))
+                        .map(Reflect::clone_value)
+                    else {
+                        continue;
+                    };
+
+                    // If this component references entities in the scene,
+                    // update them to the entities in the world.
+                    if let Some(map_entities) = registration.data::<ReflectMapEntities>() {
+                        SceneEntityMapper::world_scope(entity_map, world, |_, mapper| {
+                            map_entities.map_entities(&mut *component, mapper);
+                        });
+                    }
+
+                    reflect_component.apply_or_insert(
+                        &mut world.entity_mut(entity),
+                        &*component,
                         &type_registry,
                     );
                 }
             }
         }
 
-        for registration in type_registry.iter() {
-            if let Some(map_entities_reflect) = registration.data::<ReflectMapEntities>() {
-                map_entities_reflect.map_all_entities(world, entity_map);
-            }
-        }
-
         Ok(())
     }
 }