#compdef nice

local -a specs=( '*:: : _normal -p $service' )

# See if the 1st arg is such as -10 --10 or -+10
if [[ $words[2] = -(-|+|)[0-9]## ]]; then
  if (( $CURRENT == 2 )); then
    _message 'niceness increment' && return
  fi
  compset -n 2  # Ignore the 1st arg
else
  if _pick_variant gnu=GNU unix --version; then
    specs+=(
      '(-)'{-n+,--adjustment=}'[adjust niceness]:niceness increment'
      '(* -)--help[display help and exit]'
      '(* -)--version[output version information and exit]'
    )
  else
    specs+=( '-n+[specify increment of niceness]:niceness increment' )
  fi
fi

_arguments : $specs