How to suppress the warning for "drop_with_repr_extern" at a fine granularity?

I am currently experimenting with multi-threading code, and its performance is affected by whether two data members share the same cache line or not.

In order to avoid false-sharing, I need to specify the layout of the struct without the Rust compiler interfering, and thus I use repr(C). However, this same struct also implements Drop, and therefore the compiler warns about the "incompatibility" of repr(C) and Drop, which I care naught for.

However, attempting to silence this futile warning has proven beyond me.

Here is a reduced example:

#[repr(C)]
#[derive(Default, Debug)]
struct Simple<T> {
    item: T,
}

impl<T> Drop for Simple<T> {
    fn drop(&mut self) {}
}

fn main() {
    println!("{:?}", Simple::<u32>::default());
}

which emits #[warn(drop_with_repr_extern)].

I have tried specifying #[allow(drop_with_repr_extern)]:

• at struct
• at impl Drop
• at mod

and neither worked. Only the crate-level suppression worked, which is rather heavy-handed.

Which leads us to: is there a more granular way of suppressing this warning?

Note: remarks on a better way to ensure that two data members are spread over different cache lines are welcome; however they will not constitute answers on their own.