warning: the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/empty-ensures.rs:2:12
   |
LL | #![feature(contracts)]
   |            ^^^^^^^^^
   |
   = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
   = note: `#[warn(incomplete_features)]` on by default

error[E0277]: expected a `Fn(&_)` closure, found `()`
  --> $DIR/empty-ensures.rs:8:1
   |
LL | #[ensures()]
   | ^^^^^^^^^^^^
   | |
   | expected an `Fn(&_)` closure, found `()`
   | required by a bound introduced by this call
   |
   = help: the trait `for<'a> Fn(&'a _)` is not implemented for `()`
note: required by a bound in `build_check_ensures`
  --> $SRC_DIR/core/src/contracts.rs:LL:COL

error: aborting due to 1 previous error; 1 warning emitted

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