bug#41531: 27.0.91; Better handle asynchronous eldoc backends

[Dmitry Gutov]

On 07.07.2020 16:38, Stefan Monnier wrote:
> As long as it's done before we cut the `emacs-28` branch, I can't see
> any reason why we couldn't change the new (and hence not yet released,
> except for the GNU ELPA package) API in a backward-incompatible way
> (just like the eldoc-async already does).

It's a good point, and if that was all that we'd need to agree on, I'd 
be fine to proceed.

But if we just wanted to get async into Eglot, that's what my simple 
patch did: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=41531#8, 
proposed months ago. With minimal backward compatibility issues.

The current discussion, and the current eldoc-async branch adds some 
more design decisions, as well as breaking changes.

And those decisions seem to be informed and made necessary by the lack 
of standard functions for combining async computations that eldoc 
clients could use.

As soon as we get futures/promises/aio into the core, that will cease to 
be the case. But I fear we wouldn't be able to roll back the related 
decisions so easily, however.