nixos/plotinus: add module to enable plotinus

nixos/modules/programs/plotinus.nix

@@ -0,0 +1,36 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.programs.plotinus;
+in
+{
+  meta = {
+    maintainers = pkgs.plotinus.meta.maintainers;
+    doc = ./plotinus.xml;
+  };
+
+  ###### interface
+
+  options = {
+    programs.plotinus = {
+      enable = mkOption {
+        default = false;
+        description = ''
+          Whether to enable the Plotinus GTK+3 plugin.  Plotinus provides a
+          popup (triggered by Ctrl-Shift-P) to search the menus of a
+          compatible application.
+        '';
+        type = types.bool;
+      };
+    };
+  };
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+    environment.variables.XDG_DATA_DIRS = [ "${pkgs.plotinus}/share/gsettings-schemas/${pkgs.plotinus.name}" ];
+    environment.variables.GTK3_MODULES = [ "${pkgs.plotinus}/lib/libplotinus.so" ];
+  };
+}