zsh/Completion/Builtins/_compdef

#compdef compdef

local state line expl list disp

_arguments -C -s \
  '(-d)-a[make function autoloadable]' \
  '(-d -p -P)-n[leave existing definitions intact]' \
  '(-a -n -p -P -k -K)-d[delete]:*:completed command:->ccom' \
  '(-n -d -P -k -K)-p[completion for command matching pattern]:completion function:->cfun:pattern' \
  '(-n -d -p -k -K)-P[as -p for commands without own completion]:completion function:->cfun:pattern' \
  '(-d -p -P -K)-k[define widget and key binding]:completion function:->cfun:style:->style:*:key' \
  '(-d -p -P -k)-K[define multiple widgets based on function]:*::: :->multi' \
  ':completion function:->cfun' \
  '*:commands: _command_names' && return 0

if [[ $state = multi ]]; then
  case $(( CURRENT % 3 )) in
  0) _message key
     return 1;;
  1) state=cfun;;
  2) state=style;;
  esac
fi

case $state in
  ccom)
    _wanted commands expl 'completed command' compadd - ${(k)_comps}
  ;;
  cfun)
    list=( ${^fpath:/.}/_(|*[^~])(N:t) )
    if zstyle -T ":completion:${curcontext}:functions" prefix-hidden; then
      disp=( ${list[@]#_} )
      _wanted functions expl 'completion function' \
          compadd -d disp - "$list[@]"
    else
      _wanted functions expl 'completion function' compadd - "$list[@]"
    fi
  ;;
  style)
    _wanted widgetstyle expl 'widget style' \
        compadd -M 'r:|-=* r:|=*' \
            complete-word delete-char-or-list expand-or-complete \
            expand-or-complete-prefix list-choices menu-complete \
            menu-expand-or-complete reverse-menu-complete
  ;;
esac