Failed attempt at a stateless query helper

crates/bevy_ecs/src/world/mod.rs

@@ -16,7 +16,7 @@ use crate::{
     event::Events,
     query::{FilterFetch, QueryState, WorldQuery},
     storage::{Column, SparseSet, Storages},
-    system::Resource,
+    system::{Query, Resource},
 };
 use std::{
     any::TypeId,
@@ -569,6 +569,27 @@ impl World {
         QueryState::new(self)
     }
 
+    /// Returns a [`Query`] for the given [`WorldQuery`]
+    ///
+    /// To access a [`Query`] at the same time as other parts of the [`World`],
+    /// consider using [`SystemState`](crate::system::SystemState) instead.
+    ///
+    /// ## Warning
+    /// This method is primarily intended for integration testing purposes.
+    /// No state is cached, or provided to be cached, which means:
+    ///  1. Overhead will be measurably higher.
+    ///  2. [`Added`](crate::query::Added) and [`Changed`](crate::query::Changed) query filters will be true for all compoenents.
+    #[inline]
+    pub fn query_stateless<Q: WorldQuery, F: WorldQuery>(&mut self) -> Query<Q, F>
+    where
+        F::Fetch: FilterFetch,
+    {
+        let query_state = QueryState::new(self);
+
+        // SAFE: we have unique mutable access to the world
+        unsafe { Query::new(self, &query_state, self.change_tick(), self.change_tick()) }
+    }
+
     /// Returns an iterator of entities that had components of type `T` removed
     /// since the last call to [`World::clear_trackers`].
     pub fn removed<T: Component>(&self) -> std::iter::Cloned<std::slice::Iter<'_, Entity>> {