#![feature(unboxed_closures)]

use std::future::Future;

fn foo<F, S>(_: F)
where
    F: for<'a> FnMut<(&'a mut S,)>,
    for<'a> <F as FnOnce<(&'a mut S,)>>::Output: Future<Output = ()>,
{}
async fn bar(x: &mut i32) {

}

fn main() {
    foo(bar);
}