error[E0499]: cannot borrow `x` as mutable more than once at a time
  --> $DIR/borrowck-autoref-3261.rs:15:9
   |
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 |                     x = X(Either::Left((0, 0)));
   |                     - borrow occurs due to use of `x` in closure
...
LL |         })
   |          - first borrow ends here

error: aborting due to previous error

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