error[E0499]: cannot borrow `v` as mutable more than once at a time
  --> $DIR/one_line.rs:15:12
   |
15 |     v.push(v.pop().unwrap());
   |     -      ^               - first borrow ends here
   |     |      |
   |     |      second mutable borrow occurs here
   |     first mutable borrow occurs here

error: aborting due to previous error