GDK_PIXBUF_MODULE_FILE should not be set in DE modules (KDE, Xfce)

[jaens]

Issue description

Having both enabled at once in NixOS results in the following error: error: The unique option 'environment.variables.GDK_PIXBUF_MODULE_FILE' is defined multiple times, in '/home/jaen/Repositories/nixpkgs/nixos/modules/services/x11/desktop-managers/plasma5.nix' and '/home/jaen/Repositories/nixpkgs/nixos/modules/services/x11/desktop-managers/xfce.nix'.

(on the nixos-unstable channel)

Steps to reproduce

  services.xserver.desktopManager.plasma5.enable = true;
  services.xserver.desktopManager.xfce.enable = true;

Technical details

 - system: `"x86_64-linux"`
 - host os: `Linux 4.14.5, NixOS, 18.03.git.8989149 (Impala)`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 1.11.16`
 - channels(root): `"nixos-18.03pre122666.afe9649210c"`
 - channels(jaen): `""`
 - nixpkgs: `/home/jaen/Repositories/nixpkgs`

[jaens]

Looks like the conflict was introduced in 209cbf9fc7e7d70d254abf457f154a934201f420 cc @yegortimoshenko

[lukateras]

Indeed.

[lukateras]

I'll make a superficial fix, but I'm really not sure how to really resolve this. This environment variable isn't really specific to KDE or Xfce. Would it perhaps be a good idea to wrap all Gtk apps to have GDK_PIXBUF_MODULE_FILE?

/cc @jtojnar (GNOME), @ttuegel (KDE)

[lukateras]

@jaens: conflict has been fixed in https://github.com/NixOS/nixpkgs/commit/0dd6bd214da0b3ec79400a2910a0ca0a580eccf8, so you can enable KDE and Xfce at the same time, but underlying problem is not resolved yet, so I'm leaving the issue open.

[jtojnar]

IMHO, these things should be done in the derivation (for an example, see nautilus), possibly in some more automated way.

[ttuegel]

IMHO, these things should be done in the derivation (for an example, see nautilus), possibly in some more automated way.

This is done by wrapGAppsHook. The problem is, KDE needs GTK applications to support SVG icons, which requires a different module file than the wrapper uses. It looks like Xfce needs the same thing.

The correct solution is for KDE and Xfce to make the setting in their respective startup scripts.

[lukateras]

As I understand, currently SVG icons in GTK apps are broken in most environments, the only reason it might not be entirely obvious is that most themes and apps also package raster icons. It's not Xfce's or KDE's fault in any way, and icons would be as broken in, say, just bare Xmonad.

In that case I don't see any solution better than depending on librsvg in all GTK apps.

[burjui]

This is still a problem. Is there any solution?

[ambrop72]

I have developed a solution in pull request https://github.com/NixOS/nixpkgs/pull/42562. The change is against master but applies cleanly to 18.03. With this I can successfully enable Xfce and Plasma at the same time, and run Thunar from a Plasma session.

[jtojnar]

Fixed in #42562