#[cfg_or_panic(..)]

Keep the function body under #[cfg(..)], or replace it with unimplemented!() under #[cfg(not(..))].

Example

use cfg_or_panic::cfg_or_panic;

#[cfg_or_panic(feature = "foo")]
fn foo() -> i32 {
    42
}

#[test]
#[cfg_attr(not(feature = "foo"), should_panic)]
fn test() {
    assert_eq!(foo(), 42);
}