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

[Alexander Adolf]

Thomas Fitzsimmons <fitzsim@fitzsim.org> writes:

>> [...]
>> Looking at this now.
>
> Great, thank you.
> [...]

With the default value of `completion-styles`, which is

     '(basic partial-completion emacs22)

I get no completion. But when setting it to

     '(substring partial-completion)

as I mentioned, I get this after calling `completion-at-point:`
----------------------------------------------------------------------
To:  <emacs-ert-test-
Subject: 
From: Alexander Adolf <alexanderadolf@laptop.fritz.box>
--text follows this line--
----------------------------------------------------------------------
Which I guess is kind of the expected result, as it inserts the longest
common prefix of the two candidates' email addresses.

I get the same result with `message-tab` (or just pressing TAB), btw.

Actually, I think the leading "<" should not be there? After appending
either "3", or "4" further completion attempts (using either function)
do not provide any results. But when I remove the leading "<", and try
to complete again (with either "3" or "4" added), I get the correct
result (for instance "Emacs ERT4 <emacs-ert-test-4@bbdb.gnu.org>").

Thus, it seems there are two things to further look into :

- set `completion-styles` to '(substring partial-completion) during the
  test

- make sure the leading "<" is not inserted when there is a partial
  match


Looking forward to your thoughts,

  --alexander