Add Allows filter to bypass DefaultQueryFilters (#18192)

# Objective

Fixes #17803 

## Solution

- Add an `Allows<T>` `QueryFilter` that adds archetypal access for `T`
- Fix access merging to include archetypal from both sides

## Testing

- Added a case to the unit test for the application of
`DefaultQueryFilters`

Author: NiseVoid

crates/bevy_ecs/src/lib.rs

@@ -80,7 +80,7 @@ pub mod prelude {
         hierarchy::{ChildOf, ChildSpawner, ChildSpawnerCommands, Children},
         name::{Name, NameOrEntity},
         observer::{Observer, Trigger},
-        query::{Added, AnyOf, Changed, Has, Or, QueryBuilder, QueryState, With, Without},
+        query::{Added, Allows, AnyOf, Changed, Has, Or, QueryBuilder, QueryState, With, Without},
         related,
         relationship::RelationshipTarget,
         removal_detection::RemovedComponents,

crates/bevy_ecs/src/query/access.rs

@@ -257,9 +257,10 @@ impl<T: SparseSetIndex> Access<T> {
     /// This is for components whose values are not accessed (and thus will never cause conflicts),
     /// but whose presence in an archetype may affect query results.
     ///
-    /// Currently, this is only used for [`Has<T>`].
+    /// Currently, this is only used for [`Has<T>`] and [`Allows<T>`].
     ///
     /// [`Has<T>`]: crate::query::Has
+    /// [`Allows<T>`]: crate::query::filter::Allows
     pub fn add_archetypal(&mut self, index: T) {
         self.archetypal.grow_and_insert(index.sparse_set_index());
     }
@@ -499,6 +500,7 @@ impl<T: SparseSetIndex> Access<T> {
         self.resource_read_and_writes
             .union_with(&other.resource_read_and_writes);
         self.resource_writes.union_with(&other.resource_writes);
+        self.archetypal.union_with(&other.archetypal);
     }
 
     /// Returns `true` if the access and `other` can be active at the same time,

crates/bevy_ecs/src/query/filter.rs

@@ -555,6 +555,63 @@ all_tuples!(
     S
 );
 
+/// Allows a query to contain entities with the component `T`, bypassing [`DefaultQueryFilters`].
+///
+/// [`DefaultQueryFilters`]: crate::entity_disabling::DefaultQueryFilters
+pub struct Allows<T>(PhantomData<T>);
+
+/// SAFETY:
+/// `update_component_access` does not add any accesses.
+/// This is sound because [`QueryFilter::filter_fetch`] does not access any components.
+/// `update_component_access` adds an archetypal filter for `T`.
+/// This is sound because it doesn't affect the query
+unsafe impl<T: Component> WorldQuery for Allows<T> {
+    type Fetch<'w> = ();
+    type State = ComponentId;
+
+    fn shrink_fetch<'wlong: 'wshort, 'wshort>(_: Self::Fetch<'wlong>) -> Self::Fetch<'wshort> {}
+
+    #[inline]
+    unsafe fn init_fetch(_: UnsafeWorldCell, _: &ComponentId, _: Tick, _: Tick) {}
+
+    // Even if the component is sparse, this implementation doesn't do anything with it
+    const IS_DENSE: bool = true;
+
+    #[inline]
+    unsafe fn set_archetype(_: &mut (), _: &ComponentId, _: &Archetype, _: &Table) {}
+
+    #[inline]
+    unsafe fn set_table(_: &mut (), _: &ComponentId, _: &Table) {}
+
+    #[inline]
+    fn update_component_access(&id: &ComponentId, access: &mut FilteredAccess<ComponentId>) {
+        access.access_mut().add_archetypal(id);
+    }
+
+    fn init_state(world: &mut World) -> ComponentId {
+        world.register_component::<T>()
+    }
+
+    fn get_state(components: &Components) -> Option<Self::State> {
+        components.component_id::<T>()
+    }
+
+    fn matches_component_set(_: &ComponentId, _: &impl Fn(ComponentId) -> bool) -> bool {
+        // Allows<T> always matches
+        true
+    }
+}
+
+// SAFETY: WorldQuery impl performs no access at all
+unsafe impl<T: Component> QueryFilter for Allows<T> {
+    const IS_ARCHETYPAL: bool = true;
+
+    #[inline(always)]
+    unsafe fn filter_fetch(_: &mut Self::Fetch<'_>, _: Entity, _: TableRow) -> bool {
+        true
+    }
+}
+
 /// A filter on a component that only retains results the first time after they have been added.
 ///
 /// A common use for this filter is one-time initialization.

crates/bevy_ecs/src/query/state.rs

@@ -2315,6 +2315,10 @@ mod tests {
         let mut query = QueryState::<Has<C>>::new(&mut world);
         assert_eq!(3, query.iter(&world).count());
 
+        // Allows should bypass the filter entirely
+        let mut query = QueryState::<(), Allows<C>>::new(&mut world);
+        assert_eq!(3, query.iter(&world).count());
+
         // Other filters should still be respected
         let mut query = QueryState::<Has<C>, Without<B>>::new(&mut world);
         assert_eq!(1, query.iter(&world).count());