error[E0277]: the trait bound `fn() -> impl std::future::Future {foo}: std::future::Future` is not satisfied
  --> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:9:9
   |
LL | fn bar(f: impl Future<Output=()>) {}
   |    ---         ----------------- required by this bound in `bar`
...
LL |     bar(foo);
   |         ^^^
   |         |
   |         the trait `std::future::Future` is not implemented for `fn() -> impl std::future::Future {foo}`
   |         help: use parentheses to call the function: `foo()`

error: aborting due to previous error

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