Document how gtk themes and propagatedUserEnvPkgs work

[nh2]

Issue description

One of the things that confuses me on NixOS desktop is that I can make gtk themes available to XFCE using:

environment.systemPackages = with pkgs; [
  gnome-themes-standard
];

This doesn't seem to be documented anywhere, and I also don't understand how it works.

Does propagatedUserEnvPkgs play a role here? That functionality, too, seems completely undocumented.

Both these things should be described in the nixpkgs or NixOS manual.

[worldofpeace]

Do you mean propagation of the theme engines?

• nixpkgs/pkgs/data/themes/yaru/default.nix

  Line 18 in 951176e

  propagatedUserEnvPkgs = [ gtk-engine-murrine ];

Because in this example gnome-themes-extra doesn't do any kind of propagation of user environment packages. Themes work because they get linked at /run/current-system/sw/share/themes and end up in XDG_DATA_DIRS. Expected behavior of gtk. Otherwise some program is wrapped with a gtk theme in the same manner.

And we do document this in the nixpkgs manual

• https://nixos.org/nixpkgs/manual/#sec-language-gnome

What's probably missing is stuff like this in the NixOS manual.
(i.e the intended consumer of the information in the nixpkgs manual is people packaging gtk things for nixpkgs)

[worldofpeace]

Having something like #71079 would make the theming story for NixOS make a little more declarative sense. Though there's an issue with it being system-wide.
My thoughts at #70276 (comment) for a better user story.

[stale]

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[nh2]

still important to me

[stale]

I marked this as stale due to inactivity. → More info

[TLATER]

Is there any reason nobody has touched this since #71079 was reverted? I've been using home-manager for this, but surely a system-wide option would make sense?

[jtojnar]

@TLATER Probably because no-one interested in this found time to do this yet.

If someone wants to resurrect #71079, it should probably be based on RFC 42-style settings and modules for different GTK versions should be decoupled, as they are completely separate things.