error: future cannot be sent between threads safely
  --> $DIR/unsend-future.rs:20:21
   |
LL |     require_handler(handler)
   |                     ^^^^^^^ future returned by `handler` is not `Send`
   |
   = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `*const i32`, which is required by `fn() -> impl Future<Output = ()> {handler}: Handler`
note: future is not `Send` as this value is used across an await
  --> $DIR/unsend-future.rs:15:14
   |
LL |     let a = &1 as *const i32;
   |         - has type `*const i32` which is not `Send`
LL |     async {}.await;
   |              ^^^^^ await occurs here, with `a` maybe used later
note: required by a bound in `require_handler`
  --> $DIR/unsend-future.rs:11:23
   |
LL | fn require_handler<H: Handler>(h: H) {}
   |                       ^^^^^^^ required by this bound in `require_handler`

error: aborting due to 1 previous error