After a fresh install of leap 15.0, I added all of the usual long list of Qt libraries and development headers, but was still unable to build at all.
Blocking point 1: no qhelpgenerator found.
It is actually there, but as qhelpgenerator-qt5, which cmake does not find. It seems too ugly to partly installing some qt4 bits just for that, so instead I opted for a somewhat less ugly workaround:
cd /etc/alternatives
ln -s /usr/bin/qhelpconverter-qt5 qhelpconverter
ln -s /usr/bin/qhelpgenerator-qt5 qhelpgenerator
cd /usr/bin
ln -s /etc/alternatives/qhelpconverter qhelpconverter
ln -s /etc/alternatives/qhelpgenerator qhelpgenerator
This isn’t 100% elegant, but works and partly documents through the filesytem what fiddling has been done.
Actually, cmake uses a file (Qt5-config.cmake) in your Qt5 package to find all related info.
If for some reasons this file is not the same accross all distribution, results may vary.
It is possible that OpenSUSE distribute qhelpgenerator as a separate package for example, and require a manual settings.
Using symbolic link as a neat trick to just not think about it anymore, but I would not recommend it as a valid solution as it requires root.
Of course, this should be fixed by OpenSSUS upstream.