% cat ~/.vim/ftdetect/zshcompletion.vim
function! DetectZSHCompletion()
	if getline(1) =~ '^#\(autoload\|compdef\).*'
		set filetype=zsh
		set tabstop=2
		set softtabstop=2
		set shiftwidth=2
		set expandtab
	endif
endfunction

augroup filetypdetect
	au BufRead,BufNewFile * call DetectZSHCompletion()
augroup END