error[E0499]: cannot borrow `x` as mutable more than once at a time
  --> $DIR/borrowck-autoref-3261.rs:25:9
   |
LL |       (&mut x).with(
   |       --------
   |       |
   |  _____first mutable borrow occurs here
   | |
LL | |         |opt| { //~ ERROR cannot borrow `x` as mutable more than once at a time
   | |         ^^^^^ second mutable borrow occurs here
LL | |             match opt {
LL | |                 &Either::Right(ref f) => {
LL | |                     x = X(Either::Left((0, 0)));
   | |                     - second borrow occurs due to use of `x` in closure
...  |
LL | |             }
LL | |         })
   | |__________- borrow later used here

error: aborting due to previous error

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