Shorten the 'world lifetime returned from QueryLens::query().

crates/bevy_ecs/compile_fail/tests/ui/query_lens_lifetime_safety.rs

@@ -0,0 +1,24 @@
+use bevy_ecs::prelude::*;
+use bevy_ecs::system::SystemState;
+
+#[derive(Component, Eq, PartialEq, Debug)]
+struct Foo(u32);
+
+fn main() {
+    let mut world = World::default();
+    let e = world.spawn(Foo(10_u32)).id();
+
+    let mut system_state = SystemState::<Query<&mut Foo>>::new(&mut world);
+    {
+        let mut query = system_state.get_mut(&mut world);
+        let mut lens = query.as_query_lens();
+        dbg!("hi");
+        {
+            let mut data: Mut<Foo> = lens.query().get_inner(e).unwrap();
+            let mut data2: Mut<Foo> = lens.query().get_inner(e).unwrap();
+            //~^ E0499
+            assert_eq!(&mut *data, &mut *data2); // oops UB
+        }
+        dbg!("bye");
+    }
+}

crates/bevy_ecs/compile_fail/tests/ui/query_lens_lifetime_safety.stderr

@@ -0,0 +1,5 @@
+error[E0499]: cannot borrow `lens` as mutable more than once at a time
+  --> tests/ui\query_lens_lifetime_safety.rs:18:39
+   |
+17 |             let mut data: Mut<Foo> = lens.query().get_inner(e).unwrap();
+   |                                      ---- first mutable borrow occurs here

crates/bevy_ecs/src/system/query.rs

@@ -2097,7 +2097,21 @@ pub struct QueryLens<'w, Q: QueryData, F: QueryFilter = ()> {
 
 impl<'w, Q: QueryData, F: QueryFilter> QueryLens<'w, Q, F> {
     /// Create a [`Query`] from the underlying [`QueryState`].
-    pub fn query(&mut self) -> Query<'w, '_, Q, F> {
+    pub fn query(&mut self) -> Query<'_, '_, Q, F> {
+        Query {
+            world: self.world,
+            state: &self.state,
+            last_run: self.last_run,
+            this_run: self.this_run,
+        }
+    }
+}
+
+impl<'w, Q: ReadOnlyQueryData, F: QueryFilter> QueryLens<'w, Q, F> {
+    /// Create a [`Query`] from the underlying [`QueryState`].
+    /// This returns results with the actual "inner" world lifetime,
+    /// so it may only be used with read-only queries to prevent mutable aliasing.
+    pub fn query_inner(&self) -> Query<'w, '_, Q, F> {
         Query {
             world: self.world,
             state: &self.state,
@@ -2108,9 +2122,9 @@ impl<'w, Q: QueryData, F: QueryFilter> QueryLens<'w, Q, F> {
 }
 
 impl<'w, 's, Q: QueryData, F: QueryFilter> From<&'s mut QueryLens<'w, Q, F>>
-    for Query<'w, 's, Q, F>
+    for Query<'s, 's, Q, F>
 {
-    fn from(value: &'s mut QueryLens<'w, Q, F>) -> Query<'w, 's, Q, F> {
+    fn from(value: &'s mut QueryLens<'w, Q, F>) -> Query<'s, 's, Q, F> {
         value.query()
     }
 }