error[E0277]: `impl Future<Output = ()>` cannot be sent between threads safely
  --> $DIR/send-on-foreign-async-fn-in-trait.rs:9:16
   |
LL |     needs_send(T::test());
   |     ---------- ^^^^^^^^^ `impl Future<Output = ()>` cannot be sent between threads safely
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `Send` is not implemented for `impl Future<Output = ()>`
note: `<T as Foo>::test` is an `async fn` in trait, which does not automatically imply that its future is `Send`
  --> $DIR/auxiliary/foreign-async-fn.rs:4:5
   |
LL |     async fn test();
   |     ^^^^^^^^^^^^^^^^
note: required by a bound in `needs_send`
  --> $DIR/send-on-foreign-async-fn-in-trait.rs:8:27
   |
LL |     fn needs_send(_: impl Send) {}
   |                           ^^^^ required by this bound in `needs_send`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.