error[E0499]: cannot borrow `v` as mutable more than once at a time
  --> $DIR/one_line.rs:3:12
   |
LL |     v.push(v.pop().unwrap());
   |     - ---- ^ second mutable borrow occurs here
   |     | |
   |     | first borrow later used by call
   |     first mutable borrow occurs here

error: aborting due to previous error

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