error[E0308]: mismatched types
  --> $DIR/unsafe-subtyping.rs:14:5
   |
LL | fn foo(x: Option<fn(i32)>) -> Option<unsafe fn(i32)> {
   |                               ---------------------- expected `std::option::Option<unsafe fn(i32)>` because of return type
LL |     x //~ ERROR mismatched types
   |     ^ expected unsafe fn, found normal fn
   |
   = note: expected type `std::option::Option<unsafe fn(i32)>`
              found type `std::option::Option<fn(i32)>`

error: aborting due to previous error

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