error: future cannot be sent between threads safely
  --> $DIR/issue-67252-unnamed-future.rs:21:5
   |
LL |     spawn(async {
   |     ^^^^^ future created by async block is not `Send`
   |
   = help: within `[async block@$DIR/issue-67252-unnamed-future.rs:21:11: 25:6]`, the trait `Send` is not implemented for `*mut ()`
note: future is not `Send` as this value is used across an await
  --> $DIR/issue-67252-unnamed-future.rs:23:16
   |
LL |         let a = std::ptr::null_mut::<()>(); // `*mut ()` is not `Send`
   |             - has type `*mut ()` which is not `Send`
LL |         AFuture.await;
   |                ^^^^^^ await occurs here, with `a` maybe used later
note: required by a bound in `spawn`
  --> $DIR/issue-67252-unnamed-future.rs:9:13
   |
LL | fn spawn<T: Send>(_: T) {}
   |             ^^^^ required by this bound in `spawn`

error: aborting due to previous error