Components as entities (v2)

_release-content/migration-guides/components-as-entities.md

@@ -0,0 +1,36 @@
+---
+title: "Components as Entities"
+pull_requests: [24728]
+---
+
+- `ComponentId::new` now takes `Entity` as an argument instead of `usize`. For debugging, you can use `ComponentId::from_u32`.
+- `ComponentId::index` was removed in favor of implementing `ContainsEntity`, call `ComponentId::entity` to get the underlying entity.
+- `ComponentIdSet` is now an `EntityEquivalentHashSet` instead of a `FixedBitSet`.
+  - `ComponentIdSet::is_clear` has changed to `ComponentIdSet::is_empty`.
+  - `ComponentIdSet::difference` has changed to `-`, i.e.: `difference = set - other`.
+  - `ComponentIdSet::intersection` has changed to `&`, i.e.: `intersection = set & other`.
+  - `ComponentIdSet::union` has changed to `|`, i.e.: `union = set | other`.
+  - Other methods have remained the same.
+- `ComponentIds` has been removed. Instead of `ComponentIds`, `ComponentsRegistrator::new` now takes `EntityAllocator`, while `ComponentsQueuedRegistrator::new` now takes `RemoteAllocator`.
+- `Access` and `EcsAccessType` no longer derive `Hash`.
+- `ResourceEntities` was removed. The following methods have been removed with it: `World::resource_entities`, `EntityWorldMut::resource_entities`, `UnsafeWorldCell::resource_entities`. It can also no longer be used as a system param. If you need the entity linked with a `ComponentId`, simply call `component_id.entity()`.
+- The `component_id` field has been removed from the `IsResource` component, along with `IsResource::new` and `IsResource::resource_component_id`. If you need the `ComponentId` for a resource dynamically, you can simply query `Entity` alongside the resource you want and wrap it: `ComponentId::new(entity)`.
+
+In 0.19, you could attach components to a resource by simply calling `world.spawn((Res1, Comp1, Comp2))`. In 0.20, this no longer works as `Res1` needs to be on the resource entity allocated by `world.register_component<Res1>()`. In 0.20, adding components looks as follows:
+
+```rust
+let entity = world.register_component::<R>().entity();
+world.spawn_at(entity, (Res1, Comp1, Comp2));
+```
+
+Additionally, manually implementing `Resource` through
+
+```rust
+#[derive(Component, Default)]
+struct R;
+
+impl Resource for R {}
+```
+
+has become less viable, as now `Res` and `ResMut` panic when `IsResource` has not been made a required component for a resource.
+Use `#[derive(Resource)]` instead.

benches/benches/bevy_ecs/empty_archetypes.rs

@@ -156,6 +156,7 @@ fn add_archetypes(world: &mut World, count: u16) {
         if i & (1 << 15) != 0 {
             e.insert(A::<28>(1.0));
         }
+        e.despawn();
     }
 }
 
@@ -166,7 +167,6 @@ fn empty_archetypes(criterion: &mut Criterion) {
             schedule.add_systems(iter);
         });
         add_archetypes(&mut world, archetype_count);
-        world.clear_entities();
         let mut e = world.spawn_empty();
         e.insert(A::<0>(1.0));
         e.insert(A::<1>(1.0));
@@ -197,7 +197,6 @@ fn empty_archetypes(criterion: &mut Criterion) {
             schedule.add_systems(for_each);
         });
         add_archetypes(&mut world, archetype_count);
-        world.clear_entities();
         let mut e = world.spawn_empty();
         e.insert(A::<0>(1.0));
         e.insert(A::<1>(1.0));
@@ -228,7 +227,6 @@ fn empty_archetypes(criterion: &mut Criterion) {
             schedule.add_systems(par_for_each);
         });
         add_archetypes(&mut world, archetype_count);
-        world.clear_entities();
         let mut e = world.spawn_empty();
         e.insert(A::<0>(1.0));
         e.insert(A::<1>(1.0));

crates/bevy_dev_tools/src/inspection/component_inspection.rs

@@ -175,10 +175,9 @@ impl ComponentMetadataMap {
     pub fn generate(world: &World) -> Self {
         let mut map = HashMap::new();
 
-        for index in 0..world.components().num_registered() {
-            let component_id = ComponentId::new(index);
-            if let Ok(metadata) = ComponentTypeMetadata::new(world, component_id) {
-                map.insert(component_id, metadata);
+        for (id, _) in world.components().iter_registered() {
+            if let Ok(metadata) = ComponentTypeMetadata::new(world, id) {
+                map.insert(id, metadata);
             }
         }
 
@@ -209,12 +208,11 @@ impl ComponentMetadataMap {
 
     /// Adds entries for component types that are not yet in the map, leaving existing entries alone.
     pub fn update(&mut self, world: &World) {
-        for index in 0..world.components().num_registered() {
-            let component_id = ComponentId::new(index);
-            if !self.map.contains_key(&component_id)
-                && let Ok(metadata) = ComponentTypeMetadata::new(world, component_id)
+        for (id, _) in world.components().iter_registered() {
+            if !self.map.contains_key(&id)
+                && let Ok(metadata) = ComponentTypeMetadata::new(world, id)
             {
-                self.map.insert(component_id, metadata);
+                self.map.insert(id, metadata);
             }
         }
     }
@@ -449,7 +447,7 @@ mod tests {
     #[test]
     fn unregistered_component_id_returns_error() {
         let world = test_world();
-        let component_id = ComponentId::new(usize::MAX);
+        let component_id = ComponentId::from_u32(464149);
 
         let result = ComponentTypeMetadata::new(&world, component_id);
 

crates/bevy_dev_tools/src/inspection/world_summary.rs

@@ -2,7 +2,10 @@
 //!
 //! See [`WorldSummary`] for the output, and [`WorldSummaryExt`] to generate.
 
-use bevy_ecs::{archetype::ArchetypeId, component::ComponentId, system::Commands, world::World};
+use bevy_ecs::{
+    archetype::ArchetypeId, component::ComponentId, storage::SparseSetIndex, system::Commands,
+    world::World,
+};
 use bevy_log::info;
 use bevy_utils::{memory_size::MemorySize, prelude::DebugName};
 use core::{cmp::Reverse, fmt};
@@ -143,7 +146,7 @@ pub trait WorldSummaryExt {
 impl WorldSummaryExt for World {
     fn summarize(&self, settings: SummarySettings) -> WorldSummary {
         let total_entities = self.entities().count_spawned();
-        let total_send_resources = self.resource_entities().iter().count();
+        let total_send_resources = self.iter_resources().count();
         let total_non_send_resources = self.storages().non_sends.len();
         let total_archetypes = self.archetypes().len();
         let mut archetype_summaries: Vec<ArchetypeSummary> = self
@@ -161,7 +164,7 @@ impl WorldSummaryExt for World {
                             self.components()
                                 .get_name(*component_id)
                                 .unwrap_or_else(|| {
-                                    let component_index = component_id.index();
+                                    let component_index = component_id.sparse_set_index();
                                     DebugName::owned(format!("Component #{component_index}"))
                                 })
                         })

crates/bevy_dev_tools/src/schedule_data/serde.rs

@@ -129,11 +129,11 @@ impl AccessData {
         let writes = value.writes().as_finite_set();
 
         let (reads_inverted, reads) = match reads {
-            Some(reads) => (false, trace.get_indexes(reads.iter())),
+            Some(reads) => (false, trace.get_indexes(reads.iter().copied())),
             None => (true, vec![]),
         };
         let (writes_inverted, writes) = match writes {
-            Some(writes) => (false, trace.get_indexes(writes.iter())),
+            Some(writes) => (false, trace.get_indexes(writes.iter().copied())),
             None => (true, vec![]),
         };
 
@@ -142,7 +142,7 @@ impl AccessData {
             writes,
             reads_inverted,
             writes_inverted,
-            archetypal: trace.get_indexes(value.archetypal().iter()),
+            archetypal: trace.get_indexes(value.archetypal().iter().copied()),
         }
     }
 }
@@ -164,8 +164,8 @@ pub struct AccessFiltersData {
 impl AccessFiltersData {
     fn new(value: &bevy_ecs::query::AccessFilters, trace: &mut ComponentTrace) -> Self {
         Self {
-            with: trace.get_indexes(value.with().iter()),
-            without: trace.get_indexes(value.without().iter()),
+            with: trace.get_indexes(value.with().iter().copied()),
+            without: trace.get_indexes(value.without().iter().copied()),
         }
     }
 }

crates/bevy_ecs/macro_logic/src/component.rs

@@ -53,6 +53,8 @@ pub struct DeriveComponent {
     pub map_entities: Option<MapEntitiesAttributeKind>,
     /// Additional required component registrations that are added in `Component::register_required_components`
     pub additional_requires: Vec<TokenStream>,
+    /// Additional `on_insert` hook
+    pub additional_insert_hook: Option<TokenStream>,
 }
 
 impl DeriveComponent {
@@ -73,6 +75,7 @@ impl DeriveComponent {
             clone_behavior: None,
             map_entities: None,
             additional_requires: Vec::new(),
+            additional_insert_hook: None,
         };
 
         let mut require_paths = HashSet::new();
@@ -250,6 +253,10 @@ impl DeriveComponent {
         let mut on_despawn_path =
             Vec::from_iter(self.on_despawn.map(|path| path.to_token_stream(bevy_ecs)));
 
+        if let Some(extra_insert_hook) = self.additional_insert_hook {
+            on_insert_path.push(extra_insert_hook);
+        }
+
         if relationship.is_some() {
             on_insert_path.push(quote!(<Self as #bevy_ecs::relationship::Relationship>::on_insert));
             on_discard_path

crates/bevy_ecs/macros/src/resource.rs

@@ -1,5 +1,4 @@
 use bevy_ecs_macro_logic::component::{DeriveComponent, StorageAttribute, StorageTy};
-use bevy_macro_utils::fq_std::FQOption;
 use proc_macro2::TokenStream;
 use quote::quote;
 use syn::{DeriveInput, Path};
@@ -11,17 +10,12 @@ pub fn derive_resource(ast: &mut DeriveInput) -> TokenStream {
         Err(e) => return e.into_compile_error(),
     };
 
-    let struct_name = &ast.ident;
-    let (_, type_generics, _) = &ast.generics.split_for_impl();
+    // We add an extra insert hook to the resource
+    derive_component.additional_insert_hook = Some(quote!(#bevy_ecs::resource::on_resource_insert));
 
     // We add the component_id existence check here to avoid recursive init during required components initialization.
     derive_component.additional_requires.push(quote! {
-        let resource_component_id = if let #FQOption::Some(id) = required_components.components_registrator().component_id::<#struct_name #type_generics>() {
-            id
-        } else {
-            required_components.components_registrator().register_component::<#struct_name #type_generics>()
-        };
-        required_components.register_required::<#bevy_ecs::resource::IsResource>(move || #bevy_ecs::resource::IsResource::new(resource_component_id));
+        required_components.register_required::<#bevy_ecs::resource::IsResource>(|| #bevy_ecs::resource::IsResource);
     });
 
     let component_impl = match derive_component.impl_component(ast, &bevy_ecs, StorageTy::SparseSet)