zsh/Completion/Builtins/_zle

#compdef zle

local expl ret=1 st
local -a opts compwids state

compwids=(accept-and-menu-complete
	  complete-word
	  delete-char-or-list
	  expand-or-complete
	  expand-or-complete-prefix
	  list-choices
	  menu-complete
	  menu-expand-or-complete
	  reverse-menu-complete)

opts=(-A -C -D -L -M -N -R -U -a -c -l \* :)

_arguments -s -S \
    "($opts)-A[define widget alias]:old widget:->widget :new widget:->widget" \
    "($opts)-C[define completion widget]:new widget name:->comp-widget :completion widget:->builtin-comp-widget :widget shell function:->function" \
    "($opts)-D[delete widget]:*:widget:->widget" \
    "(${opts#-l})-L+[with -l, list as commands]:*:-:->listing" \
    "(${opts#-[La]})-l+[list user-defined widgets]:*:-:->listing" \
    "(${opts#-l})-a+[with -l, list all widgets]:*:-:->listing" \
    "($opts)-M[display message]:message: " \
    "($opts)-N[define new widget]:widget name:->widget-or-function ::widget shell function:->function" \
    "(${opts#-c})-R+[redisplay]:*:-:->redisplay" \
    "(${opts#-R})-c+[with -R, clear listing]:*:-:->redisplay" \
    "($opts)-U[unget to input stack]:string: " \
    '(-)::widget name:->call'

[[ $state == listing ]] &&
  _arguments -s -S \
    "-l[list user-defined widgets]" \
    "(-a)-L[list as commands]" \
    "(-L)-a[list all widgets]" \
    '(-)*:widget name:->widget'

for st in $state; do
  case $st in
    (call)
      if ((CURRENT > 2)); then
	_arguments \
          '(-N)-n[numeric prefix]:number: ' \
	  '(-n)-N[reset numeric prefix]' \
	  ':widget::' '(-)*:widget arguments: ' && ret=0
	  # :widget:: is a placeholder so we needn't shift words
	continue
      fi
      ;&
    (widget*)
      _wanted widgets expl widget compadd -k widgets && ret=0
      [[ $st != *function ]] && continue
      ;&
    (function)
      _wanted functions expl 'widget shell function' \
	compadd -k functions && ret=0
      ;;
    (comp-widget)
      _wanted widgets expl 'completion widget' \
	compadd -k "widgets[(R)(*:|)(.|)(${(j(|))compwids})(|:*)]" && ret=0
      ;&
    (builtin-comp-widget)
      _wanted widgets expl 'builtin completion widget' \
	compadd -k "widgets[(I)(.|)(${(j(|))compwids})]" && ret=0
      ;;
    (redisplay)
      _arguments -s \
        "-R[redisplay]" \
	"(*)-c[clear listing]" \
	"(-)::status line: " "*:strings to list: " && ret=0
      ;;
    (*) ret=$?;;
  esac
done

return ret