bug#59314: 29.0.50; EUDC and message-mode header completion

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Alexander Adolf <alexander.adolf@condition-alpha.com> writes:

> Hello Eric,
>
> Apologies for chiming late into this.
>
> Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>
>> On 11/16/22 14:18 PM, Thomas Fitzsimmons wrote:
>>> [...]
>>>> Address completion in message-mode has stopped working in master,
>>>> possibly as a result of 0e25a39e69acca0324c326ea8e46b1725594bff5. This
>>>> has been reported for several contact-management backends that expect to
>>>> have their completions available with <TAB>.
>>>>
>>>> `completion-at-point-functions' contains '(eudc-capf-complete
>>>> message-completion-function t) at this point -- `eudc-capf-complete'
>>>> returns no matches, and no other functions in the list are consulted.
>>> [...]
>>> (add-hook 'completion-at-point-functions #'message-completion-function nil t)
>>>
>>>> On gnus.general, someone using BBDB and corfu reported that this recipe
>>>> fixed the problem:
>>>>
>>>>   (setq eudc-server-hotlist '(("localhost" . bbdb)))
>>>>
>>>>   (add-hook 'message-mode-hook
>>>>             (lambda ()
>>>>               (setq-local completion-at-point-functions
>>>>                           (delq 'message-completion-function
>>>>                                 completion-at-point-functions))))
>>>>
>>>> Someone else *not* using corfu reported that that didn't work for them.
>>>> Dunno.
>
> That the behaviour changes depending on the CAPF front-end (corfu in
> this case) could be indicative of the completion styles [1] kicking in.
> I've seen cases where my completion function did return results, but
> nothing was shown in the CAPF UI because the completion styles'
> "filtering" wouldn't leave any alternatives to show. Not to suggest that
> this is what's actually happening, but it's one possibility.
>
> [1] https://www.gnu.org/software/emacs/manual/html_node/emacs/Completion-Styles.html
>
> Other than that, I would be interested in reproducing this at my end -
> if possible - to see whether there's any corner case I missed. I seems
> that the change of eudc-server-hotlist from `nil' to `(("localhost" .
> ecomplete) ("localhost" . mailabbrev))` triggered this behaviour for
> you. With that value, no database files for ecomplete or mailabbrev, and
> all Elisp settings for ecomplete and mailabbrev at their default values,
> `eudc-capf-complete` does return nil for me. What else should I be doing
> to reproduce the issue?

I think Thomas already fixed it! Shortly after I reported.

Thanks,
Eric