The required clang format version 6.0 is no longer available on openSUSE/Leap
On https://github.com/Kitware/CMake/blob/master/Help/dev/source.rst#c-code-style it is mentioned that clang-format is required in version 6.0.
The problem, at least with openSUSE/Leap 15.4 (the currently maintained version) is that this version is no longer available. The oldest available version is clang7, while the highest version is 13 according to http://download.opensuse.org/update/leap/15.4/sle/x86_64/.
The fact that this version is entered on the page is one problem, the bigger one is that clang-format.bash does not accept any other version without and thus contributions cannot be formatted locally.