nixos/mediawiki: don't clear default installed extensions

  pkg = pkgs.stdenv.mkDerivation rec {

    pname = "mediawiki-full";

    version = src.version;

    inherit (src) version;

    src = cfg.package;

    installPhase = ''

      mkdir -p $out

      cp -r * $out/

      rm -rf $out/share/mediawiki/skins/*

      rm -rf $out/share/mediawiki/extensions/*

      # try removing directories before symlinking to allow overwriting any builtin extension or skin

      ${concatStringsSep "\n" (mapAttrsToList (k: v: ''

        rm -rf $out/share/mediawiki/skins/${k}

        ln -s ${v} $out/share/mediawiki/skins/${k}

      '') cfg.skins)}

      ${concatStringsSep "\n" (mapAttrsToList (k: v: ''

        rm -rf $out/share/mediawiki/extensions/${k}

        ln -s ${if v != null then v else "$src/share/mediawiki/extensions/${k}"} $out/share/mediawiki/extensions/${k}

      '') cfg.extensions)}

    '';

      ++ optional (cfg.webserver == "apache" && cfg.database.createLocally && cfg.database.type == "postgres") "postgresql.service";

    users.users.${user} = {

      group = group;

      inherit group;

      isSystemUser = true;

    };

    users.groups.${group} = {};