hplip: ensure plugin version always up-to-date

pkgs/misc/drivers/hplip/default.nix

@@ -1,10 +1,11 @@
 { stdenv, fetchurl, automake, pkgconfig
 , cups, zlib, libjpeg, libusb1, pythonPackages, saneBackends, dbus
 , polkit, qtSupport ? true, qt4, pythonDBus, pyqt4, net_snmp
-, withPlugin ? false
+, withPlugin ? false, substituteAll
 }:
 
-stdenv.mkDerivation rec {
+let
+
   name = "hplip-3.14.10";
 
   src = fetchurl {
@@ -12,12 +13,23 @@ stdenv.mkDerivation rec {
     sha256 = "164mm30yb61psk5j4ziybxdd310y09fixgl09hmb59ny261wvcqi";
   };
 
+  hplip_state =
+    substituteAll
+      {
+        src = ./hplip.state;
+        # evaluated this way, version is always up-to-date
+        version = (builtins.parseDrvName name).version;
+      };
+
   plugin = fetchurl {
     url = "http://www.openprinting.org/download/printdriver/auxfiles/HP/plugins/${name}-plugin.run";
     sha256 = "10cvgy1h84fwh7xpw4x6cbkpisqbn3nbcqrgd9xz5fc6mn0b95dk";
   };
 
-  hplip_state = ./hplip.state;
+in
+
+stdenv.mkDerivation {
+  inherit name src;
 
   prePatch = ''
     # HPLIP hardcodes absolute paths everywhere. Nuke from orbit.

pkgs/misc/drivers/hplip/hplip.state

@@ -1,4 +1,4 @@
 [plugin]
 installed=1
 eula=1
-version=3.14.4
+version=@version@