Re: Completion with (:exclusive 'no) is called twice, and doesn't pass over on sole completion.

[Stefan Monnier]

> The completion in Emacs 24 is called twice.  For example

> (defun foo-completion ()
>   (when (save-excursion (re-search-backward "\\<\\w*" (point-at-bol) t))
>     (let ((token (match-string-no-properties 0))
>         (beg (match-beginning 0))
>         (end (match-end 0)))
>       (message "%s:" token)
>       (when (= end (point))
>       (list beg end (list "aaaa" "aaaaaaa" "bbbb" "truncat") :exclusive 
> 'no)))))

> (add-to-list 'completion-at-point-functions 'foo-completion) 
> ;; it is now (foo-completion lisp-completion-at-point t)

> Place your point at the end of 'aaaa and you try to complete. I am
> getting 

> aaa:
> aaaa:

> in my message buffer.  Which means the completion is called twice.

Not sure why, but not terribly problematic either.

> I hope this is not an intended behavior, as it might seriously
> interfere with custom completion.  For example I might want to have
> a different behavior on the second consequent invocation of the
> completion (give a message, modify the candidates etc).

No, completion-at-point-functions should return completion data and
can't know what that data will be used for.  Could be for TAB
completion, for on-the-fly popup completion à la auto-complete, for
display of the *Completions* buffer, or to decide whether we're still in
the same completion field (so as to pop-down the *Completions* buffer
when we leave that field), ...

> Second problem is that if the completion is sole, the handling is not
> passed over.

That's expected: completion is only passed over if the text doesn't
match any candidate.


        Stefan