#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use core::task::Poll;
fn main() {
    let res: Poll<Option<Result<u8, _>>> = Poll::Ready(Some("oops".parse()));
    let res = res.map_err(|_| 0_u8);
    assert_eq!(res, Poll::Ready(Some(Err(0))));
}