cfg_attr doesn't work in all contexts

[sfackler]

It's implemented as a syntax extension, so it only works when attached to an item. It should really be folded into the strip_cfg pass until syntax extensions are powerful enough to handle all the cases.

[huonw]

@sfackler is this fixed by #18634?

[sfackler]

Not entirely. It's still not going to handle attributes on patterns, fields, or variants AFAIKT.

[SergioBenitez]

This doesn't appear to be fixed when cfg_attr is used inside of a macro:

macro_rules! borked {
    () => {
        #[derive(Debug)] pub struct Good;
        #[cfg_attr(not(test), derive(Debug))] pub struct Bad;
    }
}

borked!();

fn main() {
    println!("{:?}", Good);
    println!("{:?}", Bad);
}

(via curmet @ IRC)

[kmcallister]

Thanks, I've opened #22250 about that issue.