This needs access to the specfiles for all dependencies. The general, yum-based solution would be to download the srpms and extract specfile from there. This might be a lot to download.... Probably, some kind of shortcut would be possible for Fedora/bugzilla e. g., by git cloning just the top dir from the pkgs.fedoraproject.org.

Anyway, a pain. OTOH, it's not really easier manually, so this check is often forgotten.

EDIT: wrong again. The binary RPM:s actually contains the spec, so we can check this without access to the sources. Suddenly, this looks quite viable. [http://www.linuxquestions.org/questions/programming-9/how-to-extract-spec-file-from-rpm-file-426847/]

EDIT: The downside of this is the requirement to download all deps as RPM:s. It will take some disk space, but we don't care about disk space anyway, do we? And if done in parallel with the build, it shouldn't normally add any time.

EDIT: Reasonable trade-off: try repoquery first, with fallback to yum-downloader + local probes if package isn't found.

Fixed in c21b6ae841d37ed4