error: future cannot be sent between threads safely
  --> $DIR/issue-67252-unnamed-future.rs:18:5
   |
LL | fn spawn<T: Send>(_: T) {}
   |             ---- required by this bound in `spawn`
...
LL |     spawn(async {
   |     ^^^^^ future created by async block is not `Send`
   |
   = help: within `impl std::future::Future`, the trait `std::marker::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:20:9
   |
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
LL |     });
   |     - `_a` is later dropped here

error: aborting due to previous error