error[E0499]: cannot borrow `foo[_]` as mutable more than once at a time
  --> $DIR/suggest-split-at-mut.rs:4:13
   |
LL |     let a = &mut foo[2];
   |             ----------- first mutable borrow occurs here
LL |     let b = &mut foo[3];
   |             ^^^^^^^^^^^ second mutable borrow occurs here
LL |     *a = 5;
   |     ------ first borrow later used here
   |
   = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
   = help: consider using `.swap(index_1, index_2)` to swap elements at the specified indices

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0499`.