error[E0525]: expected a closure that implements the `async Fn` trait, but this closure only implements `async FnMut`
  --> $DIR/wrong-fn-kind.rs:11:20
   |
LL |       needs_async_fn(async || {
   |       -------------- -^^^^^^^
   |       |              |
   |  _____|______________this closure implements `async FnMut`, not `async Fn`
   | |     |
   | |     required by a bound introduced by this call
LL | |
LL | |         x += 1;
   | |         - closure is `async FnMut` because it mutates the variable `x` here
LL | |     });
   | |_____- the requirement to implement `async Fn` derives from here
   |
note: required by a bound in `needs_async_fn`
  --> $DIR/wrong-fn-kind.rs:8:31
   |
LL |     fn needs_async_fn(_: impl async Fn()) {}
   |                               ^^^^^^^^^^ required by this bound in `needs_async_fn`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0525`.