upgrading from Kubuntu 16.04 to 18.04 removes lightdm-kde-greeter, but does not install sddm

[andrearuggirello]

Upgrading from Kubuntu 16.04 to 18.04 removes lightdm-kde-greeter, but does not install sddm.

The problem arised from the fact that lightdm-kde-greeter didn't survive in 18.04, which is probably fine per se. Hence, do-release-upgrade prompted me to remove, among other things, lightdm-kde-greeter. I wasn't bothered, thinking that probably the KDE greeter moved behind the scenes to some other package. But once rebooted, the system was in an unpleasant state, since lightdm had no valid greeter to show, and an endless Kubuntu logo splash screen followed - until I resolved to reboot after a few minutes. Booting in recovery mode and just running "apt install sddm" fixed the issue, but a novice user would have a hard time finding the solution - I'm not sure this is the best way to handle a graceful migration from lightdm to sddm for KDE users, hence I'm reporting this bug. Perhaps by making lightdm-kde-greeter a virtual package implemented by sddm or sddm-theme-breeze we could provide a smoother experience...