bug#30223: 27.0.50; Arglist of advised but undefined functions missing

["Basil L. Contovounesios" <contovob@tcd.ie>]

Steps to reproduce:

1. emacs -Q
2. (advice-add 'some-funbound-sym :override #'ignore)
3. C-h f some-funbound-sym RET

This results in the *Help* buffer reporting:

--8<---------------cut here---------------start------------->8---
some-funbound-sym is .

[Missing arglist.  Please make a bug report.]

Not documented.

[back]
--8<---------------cut here---------------end--------------->8---

which I presume is at least partially due to

  (get 'some-funbound-sym 'function-documentation)
    => (advice--make-docstring 'some-funbound-sym)

I wouldn't expect advised-but-undefined functions to have meaningful
documentation, but IMO the suggestion to make a bug report is
misleading, given that many users are likely to advise as-of-yet
undefined functions in their user-init-file.

-- 
Basil

In GNU Emacs 27.0.50 (build 25, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2018-01-22 built on thunk
Repository revision: c42959cc206bcb52baffd45f892da1b767f0f8c1
Windowing system distributor 'The X.Org Foundation', version 11.0.11905000
System Description: Debian GNU/Linux testing (buster)