I would like to create a devilspie (the one with Lisp-like syntax, however, a solution for devilspie2 would be just as good) rule that matches windows of the Spotify music streaming app. Specifically, I would like to set its _GTK_THEME_VARIANT property to dark so that the color of its title bar matches the rest of its theme.
Currently, I am using
(is (window_class) "Spotify") as condition, which seems to work fine if I start devilspie when Spotify already has its window open. However, if I start Spotify when devispie is already running, my rule does not match. It seems Spotify only sets its window_class after its window was already created, therefore the match fails on the creation event. The same thing happens if I use (application_name) instead of (window_class). I can match other windows upon their creation with (window_class) just fine.
Is there any way to make a rule that can match Spotify windows when the app starts up?