# from https://wiki.archlinux.org/index.php/Zsh#On-demand_rehash

zshcache_time="$(date +%s%N)"

autoload -Uz add-zsh-hook

rehash_precmd() {
  if [[ -e /var/cache/zsh/pacman ]]; then
    local paccache_time="$(date -r /var/cache/zsh/pacman +%s%N)"
    if ((zshcache_time < paccache_time)); then
      rehash
      zshcache_time="$paccache_time"
    fi
  fi
}

add-zsh-hook -Uz precmd rehash_precmd