Re: Compiled code in Emacs-26 will fail in Emacs-25 if use pcase [was: Add new bytecode op `switch' for implementing branch tables.]

[Robert Weiner]

Hi Stefan:

I'm with you on your thoughts about removing the need for users to often have to deal with byte-code or native-code compilation differences when running different major versions of Emacs.  But it is now 2022 and the situation seems to be much worse than it was five years ago.  Say you use Emacs 27, 28 and 29, some with native compilation and some not.  But you want to keep the same set of packages in use across all these installations.  You can set your user package directory so you get different package installs per Emacs version but we don't have a way to synchronize the set so that any missing or removed ones are updated as you move from version to version.

I just wanted to start some conversation on this and get people thinking about how to make this easier on users of multiple Emacs versions.  It is also an issue for package developers who want to test their package compatibility across major versions.

On Thu, Feb 23, 2017 at 10:11 AM Stefan Monnier <monnier@iro.umontreal.ca> wrote:

> I have this in my emacs config for a while now.
> It works pretty well. It also allows you to use an older emacs version
> without have to mess up the compiled elpa dir of the current version. The
> only side-effect is that when switching major versions the package
> updates/installs will happen independently.
>
> (setq package-user-dir (format "%selpa_%s/"
>                                user-emacs-directory emacs-major-version))

If it works for you, that's great.  Personally I'd find it annoying to
have a different set of installed packages per Emacs version.

I hope Emacs can slowly move toward a model where Elisp is byte-compiled
automatically and kept in a version-specific place (call it a cache) so
users don't have to know about bytecode compatibility issues.


        Stefan