anchor.diff:  , plugins ? []
   , pam, withPAM ? stdenv.isLinux
   , systemd, withSystemd ? stdenv.isLinux
  +, libcap, withCap ? stdenv.isLinux
   , python2, python3, ncurses
   , ruby, php, libmysqlclient
   }:
  
positive.code:                  (  lib.optional withPAM "pam"
                   ++ lib.optional withSystemd "systemd_logger"
                   );
  
    passthru = {
      inherit python2 python3;
  
negative.code:   buildInputs =  [ jansson pcre ]
                ++ lib.optional withPAM pam
                ++ lib.optional withSystemd systemd
                ++ lib.optional withCap libcap
                ++ lib.concatMap (x: x.inputs) needed
                ;
  
  