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

[Stefan Monnier]

>> Not sure why, but not terribly problematic either.
> Right, unless the completion retrieval is computationally intensive.

That could be a problem, but I haven't seen a circumstance where this is
the case yet.  This computation is only meant to decide which completion
table to use at a given buffer position.  The exact set of candidates
can be computed later.

> Please see my other message with a more serious related issue.
> It might give some clues.

I do not see your other message.  Is it on emacs-devel or a bug-report?

> In my case it's meaningful, as I retrieve completions from a
> process.

Then you should probably get your completions from the completion-table,
rather than from completion-at-point-functions.
IOW your completion-at-point-functions should return (without contacting
any process, other than maybe checking whether a process exists)
a completion table that's a function, e.g. built with
completion-table-dynamic, or using complete-with-action and it's *that*
function which contacts the process.

> Also I think, popup functions should use a different list (like
> completion-popup-functions).

That might be right (tho I hope it's not), but it doesn't eliminate the
fact that completion-at-point-functions might be called in
various circumstances.

> As users might want to use different sets of completions.

I expect completion-at-point-functions to be setup by major modes rather
than by users.

> Also popup completions *must* be considerably less computationally
> intensive, so it's probably a different set of functions anyhow.

The way I see it, completion-at-point-functions would instead include in
the `props' it returns, enough info to determine whether to use that
completion data for popup completion.

>>> 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.
> IMHO, this is far form an ideal default.  Take an example of two
> completions, one for symbols, another for functions.  Or, even the
> etags completion which is always the last, and might give many more
> candidates with the same prefix.

You might be right.  The current behavior of "fall over" for
non-exclusive completion data is not cast in stone and is known to
have limitations.


        Stefan