Re: completion discrepancy between default completion and helm/ivy completions

[Alan Schmitt <alan.schmitt@polytechnique.org>]

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On 2016-11-13 10:38, Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Is it correct to register as a completion something that returns a
>> string?
>
> I don't understand the question: register where?  return a string in
> which case?

Thank you for bearing with me, here are the details.

org-contacts adds completions hooks to message mode:

(when (and org-contacts-enable-completion
	   (boundp 'completion-at-point-functions))
  (add-hook 'message-mode-hook 'org-contacts-setup-completion-at-point))

which does

(defun org-contacts-setup-completion-at-point ()
  "Add `org-contacts-message-complete-function' as a new function
to complete the thing at point."
  (add-to-list 'completion-at-point-functions
	       'org-contacts-message-complete-function))

That function basically checks if this is a place where completion
should happen (To field, for instance), then calls all the
org-contacts-complete-functions until one succeeds. One such function is
org-contacts-complete-group that, in some case, returns a function
taking unused arguments and returning the completion as a string. To
summarize, is it okay for a function in completion-at-point-functions to
return such a function? The docstring seems to say it's OK (except the
function returned should not have any argument), but discouraged. I
guess I should try to return something of the form (start end collection
. props) instead, with collection being a singleton…

>> Because it is what org-contacts does, but although it works with
>> the default completion code, it breaks ivy or helm style completions.
>
> AFAIK those frameworks probably don't handle well completion tables
> which use completion-boundaries, so I'd lean towards saying it's a bug
> or a known limitation of those frameworks.  But I haven't looked at them
> in a long while, so maybe this isn't true any more.

Thank you for your help, I'm starting to understand what is going on.
I'll keep digging.

Best,

Alan

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