error[E0499]: cannot borrow `query` as mutable more than once at a time
  --> tests/ui/system_query_get_lifetime_safety.rs:8:14
   |
7  |     let a1 = query.get_mut(*e).unwrap();
   |              ----------------- first mutable borrow occurs here
8  |     let a2 = query.get_mut(*e).unwrap();
   |              ^^^^^^^^^^^^^^^^^ second mutable borrow occurs here
9  |     // this should fail to compile
10 |     println!("{} {}", a1.0, a2.0);
   |                       -- first borrow later used here
