Attempting to install devel/kf6-extra-cmake-modules on a system where devel/kf5-extra-cmake-modules is already installed will result in the following error: ===> Registering installation for kf6-extra-cmake-modules-6.0.0 Installing kf6-extra-cmake-modules-6.0.0... pkg-static: kf6-extra-cmake-modules-6.0.0 conflicts with kf5-extra-cmake-modules-5.115.0_1 (installs files into the same place). Problematic file: /usr/local/share/ECM/cmake/ECMConfig.cmake *** Error code 1
This is an unfortunate interaction between upstream (you can use kf6-ecm also for kf5, since it is backwards-compatible) and our packaging (you can't express "depend on either ecm version, I don't care") and historical pressure to avoid version bumps. They're not co-installable and it's going to stay that way until KF5-ECM turns into a stub (after quarterly splits off, probably really soon).