I mean, it's not too exciting: https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.4_.282017-11-01.29
> git-cinnabar ... 20
That seems to be an argument for removing git-cinnabar from core. I submitted it into core just to slim down my personal tap in the first place.
I honestly can't quite understand the rush...
> I don't think adding patches to a formula is any more desirable than vendoring a dependency. In fact less so, since vendoring would prevent recurrences of these issues in the future when mercurial does its next major release.
That argument can be used for any breaking API change (private or not), so I don't find it too convincing...
> also, explicitly disable inactive options to prevent opportunistic linkage
I think Mike hated this. And with `HOMEBREW_ENV_FILTERING` this may not be needed.
IMO the proper way to handle this is to wait for revdeps to catch up. There's already https://github.com/glandium/git-cinnabar/issues/141. If you start vendoring older versions whenever there are breaking API changes, homebrew/core will quickly become an unmaintainable mess. IMO vendoring should be used very carefully as a last resort.