bug#30039: 26.0.90; [26.1] Making my code warning free is impossible with when-let

[Eli Zaretskii]

> From: Nicolas Petton <nicolas@petton.fr>
> Cc: 30039@debbugs.gnu.org, npostavs@users.sourceforge.net
> Date: Wed, 10 Jan 2018 17:24:43 +0100
> 
> >> That’s a question we need to answer. I think supporting 2 releases would
> >> already be good (i.e., 26.1 does not deprecate but 26.2 does).
> >
> > That's not how we deprecate stuff.  We never wait with deprecation,
> > only with the actual removal.
> 
> But in this case it leads to an issue with linting: when-let cannot be
> used in packages if we want to support both Emacs 25 and 26, since
> when-let has been deprecated and when-let* didn't exist in Emacs 25.

It's unfortunate that we got into this situation, but we cannot change
the past, can we?  And releasing another Emacs 25.x, even if we decide
to do that, will change nothing, because users of Emacs 25.3 and older
will still have the same problem.

And frankly, a few byte-compilation warnings are not such a
catastrophe, we have many dozens of them when we build Emacs.