update-webkitgtk-libs has never worked in Fedora 22. The problem is that a package we do NOT build with jhbuild depends on a package that we do build with jhbuild (see bug #143537), which doesn't work in general because the jhbuild package may not contain functions that the system package depends on (the jhbuild version will almost always be older). This discourages use of the jhbuild environment, since it doesn't work. We should have a clear line between system dependencies and jhbuild dependencies, where no system dependency depends on a jhbuild dependency.
So far this has been an issue in a few cases. Perhaps we could just rework the policy to be that when there is an issue, we add a dependency in a special place in the file or to a special moduleset that is automatically installed.
That would be less robust, but much better than the status quo (a good compromise solution). In that case we would add pango (since jhbuild is unusable for me without it) but not libcroco (since it's not causing any practical problems for it to live in install-dependencies right now).
We agreed to only add these dependencies to jhbuild as problems arise, at least for now. Hopefully there are few issues in practice.
> the jhbuild version will almost always be older I was surprised by it, but indeed the moduleset points to rather old software versions (eg. cairo 1.12.8 vs the current stable 1.14.2). I guess that updating the dependencies to more up-to-date releases would solve the conflicts that Michael faces wrt. system libraries, but I don't know about how that would impact test results and what kind of burden would put on maintainers that would need to keep the moduleset fresh and potentially update the tests accordingly.