warning: method `into_future` is never used
  --> $DIR/issue-38033.rs:22:8
   |
LL | trait IntoFuture {
   |       ---------- method in this trait
...
LL |     fn into_future(self) -> Self::Future;
   |        ^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: 1 warning emitted