{}:
{
  # This adds header colors to the builds, but it rebuilds the whole
  # world from scratch, so only use it to debug!
  # add it as postHook in derivations
  immaePostHook = ''
    header() {
      echo -ne "\033[1;36m"
      echo -n "$1"
      echo -e "\033[0m"
    }

    echoCmd() {
      printf "\033[1;34m%s:\033[0m" "$1"
      shift
      printf ' %q' "$@"
      echo
    }
  '';

  phpFpmPreStart = { app, varDir, keyFiles, actions }: ''
    if [ ! -f "${varDir}/currentWebappDir" -o \
        ! -f "${varDir}/currentKey" -o \
        "${app}" != "$(cat ${varDir}/currentWebappDir 2>/dev/null)" ] \
        || ! sha512sum -c --status ${varDir}/currentKey; then
      pushd ${app} > /dev/null
      ${builtins.concatStringsSep "\n  " actions}
      popd > /dev/null
      echo -n "${app}" > ${varDir}/currentWebappDir
      sha512sum ${builtins.concatStringsSep " " keyFiles} > ${varDir}/currentKey
    fi
  '';
}