error[E0525]: expected a closure that implements the `async Fn` trait, but this closure only implements `async FnOnce`
  --> $DIR/wrong-fn-kind.rs:17:20
   |
LL |       needs_async_fn(move || async move {
   |       -------------- -^^^^^^
   |       |              |
   |  _____|______________this closure implements `async FnOnce`, not `async Fn`
   | |     |
   | |     required by a bound introduced by this call
LL | |
LL | |         println!("{x}");
   | |                    - closure is `async FnOnce` because it moves the variable `x` out of its environment
LL | |     });
   | |_____- the requirement to implement `async Fn` derives from here
   |
note: required by a bound in `needs_async_fn`
  --> $DIR/wrong-fn-kind.rs:5:27
   |
LL | fn needs_async_fn(_: impl async Fn()) {}
   |                           ^^^^^^^^^^ required by this bound in `needs_async_fn`

error[E0596]: cannot borrow `x` as mutable, as it is a captured variable in a `Fn` closure
  --> $DIR/wrong-fn-kind.rs:9:20
   |
LL | fn needs_async_fn(_: impl async Fn()) {}
   |                      --------------- change this to accept `FnMut` instead of `Fn`
...
LL |     needs_async_fn(async || {
   |     -------------- ^^^^^^^^
   |     |              |
   |     |              cannot borrow as mutable
   |     |              in this closure
   |     expects `Fn` instead of `FnMut`
LL |
LL |         x += 1;
   |         - mutable borrow occurs due to use of `x` in closure

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0525, E0596.
For more information about an error, try `rustc --explain E0525`.