error[E0521]: borrowed data escapes outside of function
  --> $DIR/region-invariant-static-error-reporting.rs:15:9
   |
LL | fn unify<'a>(x: Option<Invariant<'a>>, f: fn(Invariant<'a>)) {
   |              - `x` is a reference that is only valid in the function body
LL |     let bad = if x.is_some() {
LL |         x.unwrap()
   |         ^^^^^^^^^^ `x` escapes the function body here

error: aborting due to previous error