error[E0500]: closure requires unique access to `x` but it is already borrowed
  --> $DIR/issue-27282-mutate-before-diverging-arm-1.rs:33:14
   |
LL |     match x {
   |           - borrow occurs here
...
LL |             (|| { *x = None; drop(force_fn_once); })();
   |              ^^    - second borrow occurs due to use of `x` in closure
   |              |
   |              closure construction occurs here
...
LL |         &mut Some(&a) if { // this binds to garbage if we've corrupted discriminant
   |         ------------- borrow later used here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0500`.