//@ edition:2021 // FIXME(async_closures): This needs a better error message! #![feature(async_closure)] fn main() { fn needs_async_fn(_: impl async Fn()) {} let mut x = 1; needs_async_fn(async || { //~^ ERROR expected a closure that implements the `async Fn` trait, but this closure only implements `async FnMut` x += 1; }); }