error: non-binding `let` on a future
  --> $DIR/let_underscore_future.rs:14:5
   |
LL |     let _ = some_async_fn();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`
   = note: `-D clippy::let-underscore-future` implied by `-D warnings`

error: non-binding `let` on a future
  --> $DIR/let_underscore_future.rs:15:5
   |
LL |     let _ = custom();
   |     ^^^^^^^^^^^^^^^^^
   |
   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`

error: non-binding `let` on a future
  --> $DIR/let_underscore_future.rs:19:5
   |
LL |     let _ = future;
   |     ^^^^^^^^^^^^^^^
   |
   = help: consider awaiting the future or dropping explicitly with `std::mem::drop`

error: aborting due to 3 previous errors