I just had a quick glance at the OBS build-logs for darktable 3.0.2 on Ubuntu 18.04 and 20.04 and noticed that the builds seem to fail while trying to apply a patch to src/iop/basicadj.c.
I speculate that this is the fix for the bug in the Basic Adjustments module that snuck into the 3.0.1 release and that @darix included in the RPM and DEB packages for that version.
[ 497s] dpkg-source -b BUILD
[ 498s] dpkg-source: info: using source format '3.0 (quilt)'
[ 498s] dpkg-source: info: building darktable using existing ./darktable_3.0.2.orig.tar.gz
[ 499s] patching file src/iop/basicadj.c
[ 499s] Hunk #1 FAILED at 90.
[ 499s] 1 out of 1 hunk FAILED
[ 499s] dpkg-source: info: the patch has fuzz which is not allowed, or is malformed
[ 499s] dpkg-source: info: if patch '8bceae80bd8459f4ec5929df75d6ec0471c3d26c.patch' is correctly applied by quilt, use 'quilt refresh' to update it
[ 499s] dpkg-source: error: LC_ALL=C patch -t -F 0 -N -p1 -u -V never -E -b -B .pc/8bceae80bd8459f4ec5929df75d6ec0471c3d26c.patch/ --reject-file=- < BUILD.orig.jIGtAP/debian/patches/8bceae80bd8459f4ec5929df75d6ec0471c3d26c.patch subprocess returned exit status 1
[ 499s] dpkg-buildpackage: error: dpkg-source -b BUILD subprocess returned exit status 2
I don’t have any experience with using OBS or packaging RPMs or DEB, so I really have no idea how to resolve this, other than trying to exclude that patch from the build process (b/c the fix should be already in the source for 3.0.2 in any case).