error[E0499]: cannot borrow `arr[_]` as mutable more than once at a time
  --> $DIR/suggest-slice-swap.rs:5:33
   |
LL |     std::mem::swap(&mut arr[0], &mut arr[1]);
   |     -------------- -----------  ^^^^^^^^^^^ second mutable borrow occurs here
   |     |              |
   |     |              first mutable borrow occurs here
   |     first borrow later used by call
   |
help: use `.swap()` to swap elements at the specified indices instead
   |
LL |     arr.swap(1, 0);
   |     ~~~~~~~~~~~~~~

error: aborting due to 1 previous error

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