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

[Philip Kaludercic <philipk@posteo.net>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> I'd need to see the actual patch, but right now I'm inclined to leave
>> this problem unsolved in Emacs 29.  It only happens for people who
>> don't uninstall older versions of packages they install, and that's
>> not the workflow we support in Emacs 29.  The offending code was with
>> us since Aug 2022, so replacing it with something at the last moment
>> needs a very good reason.
>
> Actually, here's the patch that I'd suggest.
> It reverts the code to its Jan 2021 state, which, in my book, makes it
> safe enough.
>
> The current sort predicate is quite severely broken, so "no sort" can't
> be worse (especially since the list is supposed to be sorted already).
> Also it re-instates the "prefer a builtin package" which was lost along
> the way.

Together with the sorting patch from above, it seems this would also
work for VC packages, since "foo" is always listed before "foo-...".

>         Stefan
>
>
> diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
> index 8f266186d5e..7d5946fbfa9 100644
> --- a/lisp/emacs-lisp/package.el
> +++ b/lisp/emacs-lisp/package.el
> @@ -924,22 +924,14 @@ package-activate-1
>  
>  (defun package--get-activatable-pkg (pkg-name)
>    ;; Is "activatable" a word?
> -  (let ((pkg-descs (sort (cdr (assq pkg-name package-alist))
> -                         (lambda (p1 p2)
> -                           (let ((v1 (package-desc-version p1))
> -                                 (v2 (package-desc-version p2)))
> -                             (or
> -                              ;; Prefer VC packages.
> -                              (package-vc-p p1)
> -                              (package-vc-p p2)
> -                              ;; Prefer builtin packages.
> -                              (package-disabled-p p1 v1)
> -                              (not (package-disabled-p p2 v2))))))))
> +  (let ((pkg-descs (cdr (assq pkg-name package-alist))))
>      ;; Check if PACKAGE is available in `package-alist'.
>      (while
>          (when pkg-descs
>            (let ((available-version (package-desc-version (car pkg-descs))))
> -            (package-disabled-p pkg-name available-version)))
> +            (or (package-disabled-p pkg-name available-version)
> +                ;; Prefer a builtin package.
> +                (package-built-in-p pkg-name available-version))))
>        (setq pkg-descs (cdr pkg-descs)))
>      (car pkg-descs)))

-- 
Philip Kaludercic