gtk4 theme stopped working altogether

[RiedleroD]

This started a month ago, but I only had time to debug it now. sorry!

When starting any gtk4 application (tested with door-knocker and easyeffects) with any Arc theme enabled, it will spew the following error twice:

Gtk-WARNING **: 13:18:22.265: Theme parser error: gtk.css:1:1-66: Failed to import: The resource at “/org/gnome/arc-theme/gtk-main-dark.css” does not exist

looking in gtk.css reveals the following statement: @import url("resource:///org/gnome/arc-theme/gtk-main-dark.css"); which seems to be correct. as I understand it, this resource should be loaded from gtk.gresource in the same folder. using gresource list on that file confirms that it indeed contains the requested file.

I have honestly zero idea why this stopped working or how to fix it. Mostly because I cannot find any documentation for this stuff. I assume the gresource file is supposed to be auto-loaded (somehow) but isn't because gtk4 changed how autoloading works (for some reason). pure speculation tho, again, no idea.

I will continue to try debugging this, but I doubt I can get to any meaningful conclusion.

Incorrect	Correct

[RiedleroD]

oh I just realized: it does not work if the theme is set via envvar (GTK_THEME=Arc, errors as reported above) but it does work correctly if GTK_THEME is unset or empty and the theme is set via gsettings. what the hell

this is especially surprising, as the tested applications are libadwaita-based and therefore shouldn't even attempt to load the theme without GTK_THEME forcing it