error[E0277]: `()` is not a future
  --> $DIR/unnecessary-await.rs:9:10
   |
LL |     boo().await;
   |     -----^^^^^^ `()` is not a future
   |     |
   |     this call returns `()`
   |
   = help: the trait `Future` is not implemented for `()`
   = note: () must be a future or must implement `IntoFuture` to be awaited
   = note: required for `()` to implement `IntoFuture`
help: remove the `.await`
   |
LL -     boo().await;
LL +     boo();
   |
help: alternatively, consider making `fn boo` asynchronous
   |
LL | async fn boo() {}
   | +++++

error: aborting due to previous error

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