error[E0308]: mismatched types
  --> $DIR/unsafe-subtyping.rs:4:5
   |
LL | fn foo(x: Option<fn(i32)>) -> Option<unsafe fn(i32)> {
   |                               ---------------------- expected `Option<unsafe fn(i32)>` because of return type
LL |     x
   |     ^ expected unsafe fn, found safe fn
   |
   = note: expected enum `Option<unsafe fn(_)>`
              found enum `Option<fn(_)>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.