System param config

crates/bevy_ecs/macros/src/lib.rs

@@ -425,12 +425,20 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
                 type State = #state_struct_name<#punctuated_generic_idents>;
                 type Item<'w, 's> = #struct_name #ty_generics;
 
-                fn init_state(world: &mut #path::world::World, system_meta: &mut #path::system::SystemMeta) -> Self::State {
+                fn default_state() -> Self::State {
                     #state_struct_name {
-                        state: <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::init_state(world, system_meta),
+                        state: <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::default_state()
                     }
                 }
 
+                fn configurate(state: &mut Self::State, config: &mut dyn core::any::Any) {
+                    <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::configurate(&mut state.state, config)
+                }
+
+                fn init_state(world: &mut #path::world::World, system_meta: &mut #path::system::SystemMeta, state: &mut Self::State) {
+                    <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::init_state(world, system_meta, &mut state.state);
+                }
+
                 unsafe fn new_archetype(state: &mut Self::State, archetype: &#path::archetype::Archetype, system_meta: &mut #path::system::SystemMeta) {
                     // SAFETY: The caller ensures that `archetype` is from the World the state was initialized from in `init_state`.
                     unsafe { <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::new_archetype(&mut state.state, archetype, system_meta) }

crates/bevy_ecs/src/component.rs

@@ -1049,6 +1049,11 @@ impl ComponentId {
         ComponentId(index)
     }
 
+    /// Returns an [`ComponentId`] with an invalid id, which _should_ never be assigned to.
+    pub const fn invalid() -> Self {
+        ComponentId(usize::MAX)
+    }
+
     /// Returns the index of the current component.
     #[inline]
     pub fn index(self) -> usize {

crates/bevy_ecs/src/removal_detection.rs

@@ -252,9 +252,10 @@ unsafe impl<'a> ReadOnlySystemParam for &'a RemovedComponentEvents {}
 // SAFETY: no component value access.
 unsafe impl<'a> SystemParam for &'a RemovedComponentEvents {
     type State = ();
+    fn default_state() {}
     type Item<'w, 's> = &'w RemovedComponentEvents;
 
-    fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
+    fn init_state(_world: &mut World, _system_meta: &mut SystemMeta, _state: &mut Self::State) {}
 
     #[inline]
     unsafe fn get_param<'w, 's>(

crates/bevy_ecs/src/system/adapter_system.rs

@@ -191,6 +191,10 @@ where
         self.system.initialize(world);
     }
 
+    fn configurate(&mut self, config: &mut dyn core::any::Any) {
+        self.system.configurate(config);
+    }
+
     #[inline]
     fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
         self.system.update_archetype_component_access(world);

crates/bevy_ecs/src/system/builder.rs

@@ -170,7 +170,9 @@ pub struct ParamBuilder;
 // SAFETY: Calls `SystemParam::init_state`
 unsafe impl<P: SystemParam> SystemParamBuilder<P> for ParamBuilder {
     fn build(self, world: &mut World, meta: &mut SystemMeta) -> P::State {
-        P::init_state(world, meta)
+        let mut state: P::State = P::default_state();
+        P::init_state(world, meta, &mut state);
+        state
     }
 }
 
@@ -212,10 +214,10 @@ impl ParamBuilder {
 unsafe impl<'w, 's, D: QueryData + 'static, F: QueryFilter + 'static>
     SystemParamBuilder<Query<'w, 's, D, F>> for QueryState<D, F>
 {
-    fn build(self, world: &mut World, system_meta: &mut SystemMeta) -> QueryState<D, F> {
+    fn build(self, world: &mut World, system_meta: &mut SystemMeta) -> Option<QueryState<D, F>> {
         self.validate_world(world.id());
         init_query_param(world, system_meta, &self);
-        self
+        Some(self)
     }
 }
 
@@ -291,12 +293,12 @@ unsafe impl<
         T: FnOnce(&mut QueryBuilder<D, F>),
     > SystemParamBuilder<Query<'w, 's, D, F>> for QueryParamBuilder<T>
 {
-    fn build(self, world: &mut World, system_meta: &mut SystemMeta) -> QueryState<D, F> {
+    fn build(self, world: &mut World, system_meta: &mut SystemMeta) -> Option<QueryState<D, F>> {
         let mut builder = QueryBuilder::new(world);
         (self.0)(&mut builder);
         let state = builder.build();
         init_query_param(world, system_meta, &state);
-        state
+        Some(state)
     }
 }
 
@@ -564,7 +566,7 @@ unsafe impl<'s, T: FromWorld + Send + 'static> SystemParamBuilder<Local<'s, T>>
         _world: &mut World,
         _meta: &mut SystemMeta,
     ) -> <Local<'s, T> as SystemParam>::State {
-        SyncCell::new(self.0)
+        Some(SyncCell::new(self.0))
     }
 }
 

crates/bevy_ecs/src/system/combinator.rs

@@ -221,6 +221,11 @@ where
             .extend(self.b.component_access_set().clone());
     }
 
+    fn configurate(&mut self, config: &mut dyn core::any::Any) {
+        self.a.configurate(config);
+        self.b.configurate(config);
+    }
+
     fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
         self.a.update_archetype_component_access(world);
         self.b.update_archetype_component_access(world);
@@ -459,6 +464,11 @@ where
             .extend(self.b.component_access_set().clone());
     }
 
+    fn configurate(&mut self, config: &mut dyn core::any::Any) {
+        self.a.configurate(config);
+        self.b.configurate(config);
+    }
+
     fn update_archetype_component_access(&mut self, world: UnsafeWorldCell) {
         self.a.update_archetype_component_access(world);
         self.b.update_archetype_component_access(world);

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

@@ -118,18 +118,24 @@ const _: () = {
     unsafe impl bevy_ecs::system::SystemParam for Commands<'_, '_> {
         type State = FetchState;
 
+        fn default_state() -> Self::State {
+            FetchState {
+                state: <__StructFieldsAlias<'static, 'static> as bevy_ecs::system::SystemParam>::default_state()
+            }
+        }
+
         type Item<'w, 's> = Commands<'w, 's>;
 
         fn init_state(
             world: &mut World,
             system_meta: &mut bevy_ecs::system::SystemMeta,
-        ) -> Self::State {
-            FetchState {
-                state: <__StructFieldsAlias<'_, '_> as bevy_ecs::system::SystemParam>::init_state(
-                    world,
-                    system_meta,
-                ),
-            }
+            state: &mut Self::State,
+        ) {
+            <__StructFieldsAlias<'_, '_> as bevy_ecs::system::SystemParam>::init_state(
+                world,
+                system_meta,
+                &mut state.state,
+            )
         }
 
         unsafe fn new_archetype(