bug#66554: [PATCH] Add the public API of Compat to the core

[Stefan Kangas <stefankangas@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> +** New package Compat
>> +The Compat package on GNU ELPA provides forwards-compatibility
>> +support, so that packages that still provide support for older
>
> I think this is known as "backward compatibility".

AFAIU, backwards-compatibility is about making code written for Emacs 28
work without changes on Emacs 29 (N -> N+1).

But forwards-compatibility is about making code written for Emacs 29
work without changes on Emacs 28 (N -> N-1).

Compat is doing the latter.

>> +versions of Emacs can still make use of newer definitions that can be
>> +reasonably re-implemented in Elisp.  Now a "pseudo" Compat package is
>> +part of Emacs, that doesn't provide any compatibility support, but
>> +only implements the public-facing API of Compat so that core packages
>> +can use Compat, while also preventing the installation of Compat on
>> +the most recent version of Emacs.
>
> Not sure this detailed description is useful.  Why not just say that
> Compat is now also available with Emacs?

Maybe this could be moved to the git commit message, and we could focus
in the documentation on what the consequences are for users and authors
of third-party packages (not authors of :core packages, who are
basically in the know already).