x11-misc/lightdm-kde has an undeclared dependency on kde-apps/plasma-runtime:4. Attempting to use/run it without this dependency installed will result in a white screen and the following error printed to stdout: file:///usr/share/apps/lightdm-kde-greeter/themes/userbar/main.qml:20:1: module "org.kde.plasma.components" is not installed import org.kde.plasma.components 0.1 as PlasmaComponents ^ I ran into this when cleaning up old KDE4 packages from my Plasma 5 system.
Thanks, fixed in git. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=508dc891164c8948ac5f80228bf9f2b2f99f2ecc