Manually making a .desktop is what xmonad and fluxbox do: http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/wm.scm#n244 http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/wm.scm#n359 Hence this approach. I could also work on moving this to a patch. Which is preferred?
-Alex
