error[E0510]: cannot mutably borrow `x` in match guard
  --> $DIR/issue-27282-mutate-before-diverging-arm-2.rs:26:18
   |
LL |     match x {
   |           - value is immutable in match guard
...
LL |                 (|| { *x = None; drop(force_fn_once); })();
   |                  ^^   -- borrow occurs due to use of `x` in closure
   |                  |
   |                  cannot mutably borrow

error: aborting due to previous error

For more information about this error, try `rustc --explain E0510`.