async fn a() {
}

fn a() -> impl Future {
    async move {}
}

async fn a()

fn a() -> impl Future

type Opaque<'a> =
    impl Future
    + Captures<'a>;

fn a<'a>(a: &'a ()) -> Opaque<'a> {
    async move {
    	let a = a;
    }
}

async move {}