find real path of a zsh completion function

[Filipe Silva <filipe.silva@xxxxxxxxx>]

Hi. I'm trying to write a custom completion function for golang's go
command line, since none that works is available.

First thing I notice is that zsh already ships with a `_go` completion
function (which does not complete the go command) which is installed to
/usr/share/zsh/functions or something. so I rename that file.

now if I write `$ which _go` there is still a _go file somewhere:

_go () {
# undefined
builtin autoload -XUz
}

where is this file coming from? I've already searched through all of my
$fpath dirs.

I've tried:

readlink -f _go
realpath _go
which _go

none of those give me the exact path of this dangling file.

thanks in advance for any help