Code review comment for ppa-dev-tools:add_rdepends_argument

First of all, thank you very much for implementing this feature. It is indeed one of the most useful parts of bileto, and I'd love to be able to use it from inside my Emacs instead of having to open a browser ;-).

Without entering the merit of the implementation itself, I'd like to discuss the approach you've taken to grab a copy of the archive's metadata needed for the rdep processing. I don't mind having to run rsync manually if needed, but I'm wondering if there are better, even simpler options out there.

For example, I know that Ubuntu Wire maintains http://qa.ubuntuwire.org/rdepends/ , which is itself used by the "reverse-depends" tool. The service is good, but unfortunately only outputs the *binary* packages, so there's some massaging needed in order to obtain the source packages (which is what we ultimately need for the autopkgtest URLs).

Another option I've used in the past (and implemented here: https://git.launchpad.net/~ubuntu-server/+git/ubuntu-helpers/tree/sergiodj/list-revdep-autopkgtest-links.sh) is to rely on chdist to pull the archive data for you. In my case, I also relied on chdist's "bin2src" script to do the conversion for me, but it seems like this is something you already have covered in your script. This chdist invocation could even be done inside a TemporaryDirectory so that you guarantee that no metadata will be left behind after the program's execution (although it might be interesting if the user could choose to keep the data for future invocations; anyway, implementation details).

The main point here is that I believe this metadata fetching could be further automated, which would be even more awesome. WDYT?