use std::future::Future;

pub trait Bound {}

pub struct Error;

impl Bound for Error {}

pub struct Wrap;

impl<T: Bound> From<T> for Wrap {
    fn from(input: T) -> Self {
        Wrap
    }
}

impl<T: Into<Wrap>> From<T> for Error {
    fn from(input: T) -> Self {
        Error
    }
}

fn fail() -> impl Future<Output = Result<(), Error>> {
    async move {
        let a: Result<(), Error> = Ok(());
        let a: () = a?;
        Ok(())
    }
}

fn fail() -> Result<(), Error> {
    let a: Result<(), Error> = Ok(());
    let a: () = a?;
    Ok(())
}