bug#41531: 27.0.91; Better handle asynchronous eldoc backends

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> You mean a single call could return first a function signature and
>> a while later a docstring?
> No, that's not what I mean.  Those should be two different members of
> eldoc-documentation-functions (plural).

Great.

>>> The callback strategy makes it easy because there are lambda lists of
>>> all shapes and sizes.
>> It's trivial to use a list to bring the number back down to 1, so it's
>> not much of a difference.
> Yes, I agree, but it's IMO easier to read (funcall cb :foo 42 :baz 23)
> than (set-value fut (list :foo 42 :baz 23)).

I find the difference largely irrelevant.  Much more important is
what kinds of :foo and bar are allowed and what they do.

> In fact, a much better name for eldoc-documentation-function (singular)
> is eldoc-documentation-strategy, not least because it relieves us from
> this silly singular/plural confusion.

Sounds very good.  Changing its name will make it possible to fix the
current backward-incompatibility (which we'd fix by re-introducing a(n
obsolete) eldoc-documentation-function).


        Stefan