error[E0121]: the type placeholder `_` is not allowed within types on item signatures
  --> $DIR/issue-74086.rs:2:20
   |
LL |     static BUG: fn(_) -> u8 = |_| 8;
   |                    ^
   |                    |
   |                    not allowed in type signatures
   |                    help: use type parameters instead: `T`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0121`.