error[E0277]: expected a `std::ops::Fn<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:13:13
   |
LL |     let x = call_it(&square, 22);
   |             ^^^^^^^ expected an `Fn<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
   |
   = help: the trait `for<'r> std::ops::Fn<(&'r isize,)>` is not implemented for `unsafe fn(isize) -> isize {square}`
note: required by `call_it`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:8:1
   |
LL | fn call_it<F:Fn(&isize)->isize>(_: &F, _: isize) -> isize { 0 }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0277]: expected a `std::ops::FnMut<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:18:13
   |
LL |     let y = call_it_mut(&mut square, 22);
   |             ^^^^^^^^^^^ expected an `FnMut<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
   |
   = help: the trait `for<'r> std::ops::FnMut<(&'r isize,)>` is not implemented for `unsafe fn(isize) -> isize {square}`
note: required by `call_it_mut`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:9:1
   |
LL | fn call_it_mut<F:FnMut(&isize)->isize>(_: &mut F, _: isize) -> isize { 0 }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0277]: expected a `std::ops::FnOnce<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:23:13
   |
LL |     let z = call_it_once(square, 22);
   |             ^^^^^^^^^^^^ expected an `FnOnce<(&isize,)>` closure, found `unsafe fn(isize) -> isize {square}`
   |
   = help: the trait `for<'r> std::ops::FnOnce<(&'r isize,)>` is not implemented for `unsafe fn(isize) -> isize {square}`
note: required by `call_it_once`
  --> $DIR/unboxed-closures-wrong-arg-type-extern-fn.rs:10:1
   |
LL | fn call_it_once<F:FnOnce(&isize)->isize>(_: F, _: isize) -> isize { 0 }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0277`.