First of all thanks for working on this feature. It might be really useful if done in the right way.
Unfortunately the advice currently given in the maintainer dashboard might not be applicable to in certain situations due to the way cargo publish works. I've filled Impossible to address warning in the Maintainer Dashboard (#179) 路 Issues 路 lib.rs / Lib.rs 馃敯 main project 路 GitLab for that and I'm mainly posting here for visibliy again. Given that there as no good solution for this problem yet, I'm quite sceptical of putting a warning on crates that does not satisfy these requirements, as there is as far as I'm aware just no alternative to this setup for proc-macro crates. Maybe it would be possible to actualy calculate the diff and somewhat judge what changed? (Athough I guess that's not possible as the git commit information itself is missing in this case, right?)