#![feature(type_alias_impl_trait)]
#![allow(dead_code)]

type Bug<T, U> = impl Fn(T) -> U + Copy;

#[define_opaque(Bug)]
const CONST_BUG: Bug<u8, ()> = unsafe { std::mem::transmute(|_: u8| ()) };
//~^ ERROR item does not constrain `Bug::{opaque#0}`
//~| ERROR: cannot transmute between types of different sizes, or dependently-sized types

#[define_opaque(Bug)]
fn make_bug<T, U: From<T>>() -> Bug<T, U> {
    |x| x.into()
}

fn main() {
    CONST_BUG(0);
}