bug#63757: 29.0.91 order of package paths changed: random old versions of packages in load-path

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> -        (while
> -            (if (and (cdr old-pkgs)
> -                     (version-list-< version
> -                                     (package-desc-version (cadr
> old-pkgs))))
> -                (setq old-pkgs (cdr old-pkgs))
> -              (push new-pkg-desc (cdr old-pkgs))
> -              nil)))
> +        (progn
> +          ;; Prefer newer packages
> +          (while
> +              (if (and (cdr old-pkgs)
> +                       (version-list-< version
> +                                       (package-desc-version (cadr
> old-pkgs))))
> +                  (setq old-pkgs (cdr old-pkgs))
> +                (push new-pkg-desc (cdr old-pkgs))
> +                nil))
> +          ;; Prefer VC packages
> +          (let* ((pkg-desc0 (cdr (assq name package-alist)))
> +                 (pkg-desc
> +                  (apply 'append
> +                         (cl-reduce
> +                          (lambda (p1 p2)
> +                            (if (package-vc-p p1)
> +                                (push p1 (cl-first p2))
> +                              (push p1 (cl-second p2)))
> +                            p2)
> +                          pkg-desc0
> +                          :initial-value (list nil nil)
> +                          :from-end t))))
> +            (setf pkg-desc0 pkg-desc)
> +            (setq new-pkg-desc (car pkg-desc)))))

Why 2 loops?  The first loop is a kind of insertion sort, so what we want is
simply to replace the

    (version-list-< version (package-desc-version (cadr old-pkgs)))

test with one which places the VC packages first (tho I'm not sure why
one would need that: presumably the version in the VC package will
already be higher).

[ BTW the speed of this code can be fairly important for people who don't use
  `package-quickstart`.  I don't know if the added cost of the
  additional loop would be significant, but it's another reason to merge
  the two loops, I think.  ]


        Stefan