bug#73926: 29.4; *-autoloads.el generation not reproducible

[Eli Zaretskii]

> From: Xiyue Deng <manphiz@gmail.com>
> Date: Mon, 21 Oct 2024 01:00:14 -0700
> 
> I was trying to debug a reproducibility test failure on muse-el in
> Debian Salsa CI reprotest[1].  It looks like that the contents of the
> generated autoload file depends on the input sequence of files and
> directories, and it looks like the `loaddefs-generate' doesn't enforce
> such a sequence to be consistent.
> 
> I have provided a patch (attached) to sort the input directories and
> files in an attempt to fix this reproducibility issue.

Did you time the modified code wrt the original one, especially when
generating loaddefs for the entire Emacs tree?  If the performance hit
is significant, we'd probably want to make this behavior optional,
like the other measures in Emacs that are meant to produce more
reproducible builds.

Also, AFAIK on MS-Windows directory-files produces a sorted list by
default (just in the reverse order), so in that case calling 'sort' is
not needed in the first place.

I also wonder whether this will produce the same order on different
operating systems, what with the file-encoding being a factor.

> --- a/lisp/emacs-lisp/loaddefs-gen.el
> +++ b/lisp/emacs-lisp/loaddefs-gen.el
> @@ -596,9 +596,13 @@ instead of just updating them with the new/changed 
> autoloads."
>                       (concat "\\`[^=.].*" (regexp-opt tmp t) "\\'")))
>        (files (apply #'nconc
>                      (mapcar (lambda (d)
> -                              (directory-files (expand-file-name d)
> -                                                  t files-re))
> -                            (if (consp dir) dir (list dir)))))
> +                              (sort
> +                               (directory-files (expand-file-name d)
> +                                                t files-re)
> +                               'string<))

Isn't string< the default when 'sort' is called to sort strings?

Thanks.