xdg: add modules for supporting various XDG specs

nixos/modules/config/xdg/autostart.nix

@@ -0,0 +1,22 @@
+{ config, lib, ... }:
+
+with lib;
+{
+  options = {
+    xdg.autostart.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install files to support the 
+        <link xlink:href="https://specifications.freedesktop.org/autostart-spec/autostart-spec-latest.html">XDG Autostart specification</link>.
+      '';
+    };
+  };
+
+  config = mkIf config.xdg.autostart.enable {
+    environment.pathsToLink = [ 
+      "/etc/xdg/autostart"
+    ];
+  };
+
+}

nixos/modules/config/xdg/icons.nix

@@ -0,0 +1,27 @@
+{ config, lib, ... }:
+
+with lib;
+{
+  options = {
+    xdg.icons.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install files to support the 
+        <link xlink:href="https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html">XDG Icon Theme specification</link>.
+      '';
+    };
+  };
+
+  config = mkIf config.xdg.icons.enable {
+    environment.pathsToLink = [ 
+      "/share/icons" 
+      "/share/pixmaps" 
+    ];
+    
+    environment.profileRelativeEnvVars = {
+      XCURSOR_PATH = [ "/share/icons" ];
+    };
+  };
+
+}

nixos/modules/config/xdg/menus.nix

@@ -0,0 +1,25 @@
+{ config, lib, ... }:
+
+with lib;
+{
+  options = {
+    xdg.menus.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install files to support the 
+        <link xlink:href="https://specifications.freedesktop.org/menu-spec/menu-spec-latest.html">XDG Desktop Menu specification</link>.
+      '';
+    };
+  };
+
+  config = mkIf config.xdg.menus.enable {
+    environment.pathsToLink = [ 
+      "/share/applications"
+      "/share/desktop-directories"
+      "/etc/xdg/menus"
+      "/etc/xdg/menus/applications-merged"
+    ];
+  };
+
+}

nixos/modules/config/xdg/mime.nix

@@ -0,0 +1,26 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+{
+  options = {
+    xdg.mime.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install files to support the 
+        <link xlink:href="https://specifications.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-latest.html">XDG Shared MIME-info specification</link> and the
+        <link xlink:href="https://specifications.freedesktop.org/mime-apps-spec/mime-apps-spec-latest.html">XDG MIME Applications specification</link>.
+      '';
+    };
+  };
+
+  config = mkIf config.xdg.mime.enable {
+    environment.pathsToLink = [ "/share/mime" ];
+
+    environment.systemPackages = [ 
+      # this package also installs some useful data, as well as its utilities 
+      pkgs.shared-mime-info 
+    ];
+  };
+
+}