error[E0281]: type mismatch: `[closure@$DIR/unboxed-closures-vtable-mismatch.rs:22:23: 22:73]` implements the trait `std::ops::FnMut<(usize, isize)>`, but the trait `std::ops::FnMut<(isize, isize)>` is required
  --> $DIR/unboxed-closures-vtable-mismatch.rs:25:13
   |
22 |     let f = to_fn_mut(|x: usize, y: isize| -> isize { (x as isize) + y });
   |                       -------------------------------------------------- implements `std::ops::FnMut<(usize, isize)>`
...
25 |     let z = call_it(3, f);
   |             ^^^^^^^
   |             |
   |             requires `std::ops::FnMut<(isize, isize)>`
   |             expected isize, found usize
   |
   = note: required by `call_it`

error[E0281]: type mismatch: `[closure@$DIR/unboxed-closures-vtable-mismatch.rs:22:23: 22:73]` implements the trait `std::ops::FnOnce<(usize, isize)>`, but the trait `std::ops::FnOnce<(isize, isize)>` is required
  --> $DIR/unboxed-closures-vtable-mismatch.rs:25:13
   |
22 |     let f = to_fn_mut(|x: usize, y: isize| -> isize { (x as isize) + y });
   |                       -------------------------------------------------- implements `std::ops::FnOnce<(usize, isize)>`
...
25 |     let z = call_it(3, f);
   |             ^^^^^^^
   |             |
   |             requires `std::ops::FnOnce<(isize, isize)>`
   |             expected isize, found usize
   |
   = note: required by `call_it`

error: aborting due to previous error(s)