Broken KDE initialization with `guix home`

[Philip McGrath]

Hi,

I'm trying to start using `guix home` on a fairly fresh install of 
Kubuntu 22.04 with SDDM and the KDE Plasma Wayland session. I'm running 
in to some problems when the session starts up: I suspect some 
environment variables may not be getting set when they need to be, but 
the symptoms are confusing: does anyone know what might be going on?

When I log in from SDDM (again, to a Wayland session, not X11), I see a 
splash screen with a spinner for a while, then the screen goes black. 
I've found at this point I can use the Alt-Space shortcut to access 
KRunner, which lets me run `plasmashell --replace` (and evidently finds 
"/usr/bin/plasmashell").

That gets a desktop to appear, but there are more problems. The 
"Application Launcher" menu doesn't show any desktop entries: there are 
"Favorites" and "All Applications" submenus (no others), but they are 
empty. A few applications are supposed to be pinned to the "Icons-only 
Task Manager" component of the default panel: "System Settings", 
"Discover" (c.f. Gnome Software), the file manager, and the browser. All 
of them show a blank paper icon instead of the actual icon. For the 
first two, hovering shows a tooltip reading "systemsettings.desktop" or 
"org.kde.discover.desktop", respectively, and clicking produces an error 
notification from "Plasma Workspace" saying "Unknown application 
folder". For the later two, the tooltip is blank, and the error message 
says "preferred://filemanager" or "preferred://browser", respectively. 
(Presumably these ought to be handled via KIO.)

Using KRunner also doesn't recognize available desktop entries, e.g. 
typing "kon" shows an item "Get Konsole…", which tries to install 
Konsole but actually produces an error window with titled "Error — KIO 
Client" saying "appstream://org.kde.konsole.desktop". However, typing 
"konsole" does get KRunner to offer to run the command, which it finds 
successfully in "/usr/bin/konsole". Inside the Bash shell Konsole 
starts, the output of `env` looks like I would expect, unless I'm 
missing something: in particular, `echo $XDG_DATA_DIRS` shows an entry 
for "/usr/share" in the search path, where the desktop files are e.g. 
"/usr/share/applications/org.kde.konsole.desktop".

I've also tried switching to a different tty and logging in to a 
non-graphical session. It also has expected results from `env`.

-Philip