bug#65475: 29.1; package-selected-packages variable is not updated when the last package is deleted

[Philip Kaludercic <philipk@posteo.net>]

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

>> +    (let ((package-alist                 ;see bug#65475
>>             (let ((pkgs (assq name package-alist)))
> [...]
>> +             (set-default-toplevel-value 'package-alist package-alist)
> [...]
>
> Eww!!
>
> If we really can't find a better option, we need to add a bunch of
> comments explaining why we ended up with such a hack.

It seems that it is only necessary to bind `package-alist' during the
invocation of `package--used-elsewhere-p', so this is a more
conservative proposal:


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From a8959f1b245540a2d0d158621dedf244ac133849 Mon Sep 17 00:00:00 2001
From: Philip Kaludercic <philipk@posteo.net>
Date: Wed, 13 Sep 2023 11:58:22 +0200
Subject: [PATCH] ; Handle edge-case when deleting the last package

* lisp/emacs-lisp/package.el (package-delete): Rebind 'package-alist'
while calling 'package--used-elsewhere-p'.  (bug#65475)
---
 lisp/emacs-lisp/package.el | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 3a019905960..02691ff7aa5 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -2521,8 +2521,12 @@ package-delete
                                            nil t)))
        (list (cdr (assoc package-name package-table))
              current-prefix-arg nil))))
-  (let ((dir (package-desc-dir pkg-desc))
-        (name (package-desc-name pkg-desc))
+  (let* ((dir (package-desc-dir pkg-desc))
+         (name (package-desc-name pkg-desc))
+         (new-package-alist (let ((pkgs (assq name package-alist)))
+                              (if (null (remove pkg-desc (cdr pkgs)))
+                                  (remq pkgs package-alist)
+                                package-alist)))
         pkg-used-elsewhere-by)
     ;; If the user is trying to delete this package, they definitely
     ;; don't want it marked as selected, so we remove it from
@@ -2541,7 +2545,8 @@ package-delete
                   (package-desc-full-name pkg-desc)))
           ((and (null force)
                 (setq pkg-used-elsewhere-by
-                      (package--used-elsewhere-p pkg-desc)))
+                      (let ((package-alist new-package-alist))
+                        (package--used-elsewhere-p pkg-desc)))) ;See bug#65475
            ;; Don't delete packages used as dependency elsewhere.
            (error "Package `%s' is used by `%s' as dependency, not deleting"
                   (package-desc-full-name pkg-desc)
@@ -2562,10 +2567,7 @@ package-delete
                (when (file-exists-p file)
                  (delete-file file))))
            ;; Update package-alist.
-           (let ((pkgs (assq name package-alist)))
-             (delete pkg-desc pkgs)
-             (unless (cdr pkgs)
-               (setq package-alist (delq pkgs package-alist))))
+           (setq package-alist new-package-alist)
            (package--quickstart-maybe-refresh)
            (message "Package `%s' deleted."
                     (package-desc-full-name pkg-desc))))))
-- 
2.39.2