nixos/desktops: deduplicate removePackagesByName

GNOME, MATE and LxQt all use removePackagesByName. Let’s move it to a single
place, rename the attributes to meaningful name and add docs.

nixos/modules/services/x11/desktop-managers/gnome3.nix

@@ -5,14 +5,6 @@ with lib;
 let
   cfg = config.services.xserver.desktopManager.gnome3;
 
-  # Remove packages of ys from xs, based on their names
-  removePackagesByName = xs: ys:
-    let
-      pkgName = drv: (builtins.parseDrvName drv.name).name;
-      ysNames = map pkgName ys;
-    in
-      filter (x: !(builtins.elem (pkgName x) ysNames)) xs;
-
   # Prioritize nautilus by default when opening directories
   mimeAppsList = pkgs.writeTextFile {
     name = "gnome-mimeapps";
@@ -167,7 +159,7 @@ in {
                                                 "${pkgs.gnome3.glib-networking.out}/lib/gio/modules"
                                                 "${pkgs.gnome3.gvfs}/lib/gio/modules" ];
     environment.systemPackages = pkgs.gnome3.corePackages ++ cfg.sessionPath
-      ++ (removePackagesByName pkgs.gnome3.optionalPackages config.environment.gnome3.excludePackages) ++ [
+      ++ (pkgs.gnome3.removePackagesByName pkgs.gnome3.optionalPackages config.environment.gnome3.excludePackages) ++ [
       pkgs.xdg-user-dirs # Update user dirs as described in http://freedesktop.org/wiki/Software/xdg-user-dirs/
     ];
 

nixos/modules/services/x11/desktop-managers/lxqt.nix

@@ -3,15 +3,6 @@
 with lib;
 
 let
-
-  # Remove packages of ys from xs, based on their names
-  removePackagesByName = xs: ys:
-    let
-      pkgName = drv: (builtins.parseDrvName drv.name).name;
-      ysNames = map pkgName ys;
-    in
-      filter (x: !(builtins.elem (pkgName x) ysNames)) xs;
-
   xcfg = config.services.xserver;
   cfg = xcfg.desktopManager.lxqt;
 
@@ -60,7 +51,7 @@ in
     environment.systemPackages =
       pkgs.lxqt.preRequisitePackages ++
       pkgs.lxqt.corePackages ++
-      (removePackagesByName
+      (pkgs.gnome3.removePackagesByName
         pkgs.lxqt.optionalPackages
         config.environment.lxqt.excludePackages);
 

nixos/modules/services/x11/desktop-managers/mate.nix

@@ -4,14 +4,6 @@ with lib;
 
 let
 
-  # Remove packages of ys from xs, based on their names
-  removePackagesByName = xs: ys:
-    let
-      pkgName = drv: (builtins.parseDrvName drv.name).name;
-      ysNames = map pkgName ys;
-    in
-      filter (x: !(builtins.elem (pkgName x) ysNames)) xs;
-
   addToXDGDirs = p: ''
     if [ -d "${p}/share/gsettings-schemas/${p.name}" ]; then
       export XDG_DATA_DIRS=$XDG_DATA_DIRS''${XDG_DATA_DIRS:+:}${p}/share/gsettings-schemas/${p.name}
@@ -96,7 +88,7 @@ in
 
     environment.systemPackages =
       pkgs.mate.basePackages ++
-      (removePackagesByName
+      (pkgs.gnome3.removePackagesByName
         pkgs.mate.extraPackages
         config.environment.mate.excludePackages);