I am not sure how to check the lensfun version, but you can update the lensfun database using the following command:
Please note that you must have the lensfun-tools package installed in order for the above command to work. lensfun-tools can be installed with this command:
$ sudo dnf install lensfun-tools
So, what works for me is:
yaourt -S lensfun-git -> uninstalls lensfun (non-git in the process).
sudo ln -s liblensfun.so.2 liblensfun.so.1
I do get a connection refused error when runnin lensfun-update-data, but seeing that the updates and infrequent, and that my lenses are all in Adobe's profiles, I'm happy with this.
For Adobe profiles, you need DB version 2. The differences are small, however: Besides the Adobe profiles, the <real-focal-length> tag became an attribute of <distortion>.
Darktable won’t care which DB version you use, In particular, Adobe profiles will work with any Darktable version, as along is it supports the API of current Lensfun.