Separate Query filter access from fetch access during initial evaluation (#1977)

Fixes #1955 

See this comment for implementation details / motivation: https://github.com/bevyengine/bevy/issues/1955#issuecomment-823600886

crates/bevy_ecs/src/lib.rs

@@ -36,9 +36,11 @@ pub mod prelude {
 mod tests {
     use crate::{
         bundle::Bundle,
-        component::{Component, ComponentDescriptor, StorageType, TypeInfo},
+        component::{Component, ComponentDescriptor, ComponentId, StorageType, TypeInfo},
         entity::Entity,
-        query::{Added, ChangeTrackers, Changed, FilterFetch, With, Without, WorldQuery},
+        query::{
+            Added, ChangeTrackers, Changed, FilterFetch, FilteredAccess, With, Without, WorldQuery,
+        },
         world::{Mut, World},
     };
     use bevy_tasks::TaskPool;
@@ -1118,6 +1120,28 @@ mod tests {
         query.iter(&world_b);
     }
 
+    #[test]
+    fn query_filters_dont_collide_with_fetches() {
+        let mut world = World::new();
+        world.query_filtered::<&mut i32, Changed<i32>>();
+    }
+
+    #[test]
+    fn filtered_query_access() {
+        let mut world = World::new();
+        let query = world.query_filtered::<&mut i32, Changed<f64>>();
+
+        let mut expected = FilteredAccess::<ComponentId>::default();
+        let i32_id = world.components.get_id(TypeId::of::<i32>()).unwrap();
+        let f64_id = world.components.get_id(TypeId::of::<f64>()).unwrap();
+        expected.add_write(i32_id);
+        expected.add_read(f64_id);
+        assert!(
+            query.component_access.eq(&expected),
+            "ComponentId access from query fetch and query filter should be combined"
+        );
+    }
+
     #[test]
     #[should_panic]
     fn multiple_worlds_same_query_get() {

crates/bevy_ecs/src/query/access.rs

@@ -101,7 +101,7 @@ impl<T: SparseSetIndex> Access<T> {
     }
 }
 
-#[derive(Clone)]
+#[derive(Clone, Eq, PartialEq)]
 pub struct FilteredAccess<T: SparseSetIndex> {
     access: Access<T>,
     with: FixedBitSet,
@@ -152,6 +152,12 @@ impl<T: SparseSetIndex> FilteredAccess<T> {
                 || self.without.intersection(&other.with).next().is_some()
         }
     }
+
+    pub fn extend(&mut self, access: &FilteredAccess<T>) {
+        self.access.extend(&access.access);
+        self.with.union_with(&access.with);
+        self.without.union_with(&access.without);
+    }
 }
 
 pub struct FilteredAccessSet<T: SparseSetIndex> {
@@ -202,7 +208,7 @@ impl<T: SparseSetIndex> Default for FilteredAccessSet<T> {
 
 #[cfg(test)]
 mod tests {
-    use crate::query::Access;
+    use crate::query::{Access, FilteredAccess};
 
     #[test]
     fn access_get_conflicts() {
@@ -230,4 +236,28 @@ mod tests {
         assert_eq!(access_d.get_conflicts(&access_b), vec![]);
         assert_eq!(access_d.get_conflicts(&access_c), vec![0]);
     }
+
+    #[test]
+    fn filtered_access_extend() {
+        let mut access_a = FilteredAccess::<usize>::default();
+        access_a.add_read(0);
+        access_a.add_read(1);
+        access_a.add_with(2);
+
+        let mut access_b = FilteredAccess::<usize>::default();
+        access_b.add_read(0);
+        access_b.add_write(3);
+        access_b.add_without(4);
+
+        access_a.extend(&access_b);
+
+        let mut expected = FilteredAccess::<usize>::default();
+        expected.add_read(0);
+        expected.add_read(1);
+        expected.add_with(2);
+        expected.add_write(3);
+        expected.add_without(4);
+
+        assert!(access_a.eq(&expected));
+    }
 }

crates/bevy_ecs/src/query/state.rs

@@ -38,9 +38,20 @@ where
     pub fn new(world: &mut World) -> Self {
         let fetch_state = <Q::State as FetchState>::init(world);
         let filter_state = <F::State as FetchState>::init(world);
-        let mut component_access = Default::default();
+
+        let mut component_access = FilteredAccess::default();
         fetch_state.update_component_access(&mut component_access);
-        filter_state.update_component_access(&mut component_access);
+
+        // Use a temporary empty FilteredAccess for filters. This prevents them from conflicting with the
+        // main Query's `fetch_state` access. Filters are allowed to conflict with the main query fetch
+        // because they are evaluated *before* a specific reference is constructed.
+        let mut filter_component_access = FilteredAccess::default();
+        filter_state.update_component_access(&mut filter_component_access);
+
+        // Merge the temporary filter access with the main access. This ensures that filter access is
+        // properly considered in a global "cross-query" context (both within systems and across systems).
+        component_access.extend(&filter_component_access);
+
         let mut state = Self {
             world_id: world.id(),
             archetype_generation: ArchetypeGeneration::new(usize::MAX),