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

[Thomas Fitzsimmons <fitzsim@fitzsim.org>]

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

> Thomas Fitzsimmons <fitzsim@fitzsim.org> writes:
>
>> [...]
>> If I remove this line from message.el:
>>
>> (add-hook 'completion-at-point-functions #'eudc-capf-complete -1 t)
>>
>> and rebuild Emacs, then my recipe works, via:
>>
>> message-tab -...-> message-expand-name -> eudc-expand-inline
>>
>> The EUDC multi-selector UI is invoked allowing me to choose between
>> emacs-ert-test-3 and emacs-ert-test-4, and the full name and email
>> address is inserted correctly.  This is with completion-styles left at
>> its default value.
>>
>> So that's one code path validated, phew.
>> [...]
>
> There are two ends to this, I think.
>
> For one, you are no longer adding `eudc-capf-complete` to
> `completion-at-point-functions` in message mode. This seems fine given
> that we are not there yet to make `eudc-capf-complete` the default thing
> to happen in 29.

To be clear, I wasn't going to push a patch to remove that, at least not
yet.  It's not making anything worse, so might as well leave it as-is.

> [...]

I'm trying to get message--name-table's EUDC support working.  I only
wanted to remove eudc-capf-complete from the debugging equation, because
message--name-table existed way before eudc-capf-complete was
introduced.

I want to understand why it doesn't work (why it results in the " <..."
expansion).  I haven't delved deep enough into the completion-at-point
to figure that out.  I was hoping with your experience writing
eudc-capf-complete that you'd know what was wrong with
message--name-table's EUDC support.

I don't think completion-styles should have any bearing on this.
message--name-table's EUDC support has to be made to work with the
default completion-styles setting.  Do you know how to do that?

Thanks,
Thomas