anchor.diff:  
     config = mkIf cfg.enable {
   
  -    environment.systemPackages = [ pkgs.dbus_daemon pkgs.dbus_tools ];
  +    environment.systemPackages = [ pkgs.dbus.daemon pkgs.dbus_tools ];
   
       environment.etc = singleton
         { source = configDir;
  
positive.code: 
      users.extraGroups.messagebus.gid = config.ids.gids.messagebus;
  
      # FIXME: these are copied verbatim from the dbus source tree.  We
      # should install and use the originals.
      systemd.units."dbus.socket".text =
        ''
          [Unit]
          Description=D-Bus System Message Bus Socket
  
          [Socket]
          ListenStream=/var/run/dbus/system_bus_socket
        '';
  
      systemd.units."dbus.service".text =
        ''
          [Unit]
          Description=D-Bus System Message Bus
          Requires=dbus.socket
  
          [Service]
          ExecStartPre=${pkgs.dbus_tools}/bin/dbus-uuidgen --ensure
          ExecStartPre=-${pkgs.coreutils}/bin/rm -f /var/run/dbus/pid
          ExecStart=${pkgs.dbus_daemon}/bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation
          ExecReload=${pkgs.dbus_tools}/bin/dbus-send --print-reply --system --type=method_call --dest=org.freedesktop.DBus / org.freedesktop.DBus.ReloadConfig
          OOMScoreAdjust=-900
        '';
  
      security.setuidOwners = singleton
        { program = "dbus-daemon-launch-helper";
  
negative.code:     buildCommand = ''
        ensureDir $out
  
        cp -v ${pkgs.dbus.daemon}/etc/dbus-1/system.conf $out/system.conf
  
        # !!! Hm, these `sed' calls are rather error-prone...
  
  