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

[Philip Kaludercic]

Stefan Kangas <stefankangas@gmail.com> writes:

> reopen 65475
> thanks
>
> Eshel Yaron <me@eshelyaron.com> writes:
>
>>>> FWIW, I get the same non-empty `package-selected-packages` with Emacs
>>>> master built from source.  Indeed it looks like this issue isn't fully
>>>> fixed yet.
>>>
>>> Even if 610105ee81bbf79f72d4efb46d0caddf8d654cf1 was applied?
>>
>> Of course.
>
> Thanks for testing.  I'm reopening the bug.

Following Eshel's diagnosis, it seems it should be possible to solve the
bug by dynamically binding package-alist without the deleted package and
then updating the top-level value if everything went right:

diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 3a019905960..ed7d666ebf4 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -2533,42 +2533,44 @@ package-delete
                ;; upgraded package.
                (package--newest-p pkg-desc))
       (package--save-selected-packages (remove name 
package-selected-packages)))
-    (cond ((not (string-prefix-p (file-name-as-directory
-                                  (expand-file-name package-user-dir))
-                                 (expand-file-name dir)))
-           ;; Don't delete "system" packages.
-           (error "Package `%s' is a system package, not deleting"
-                  (package-desc-full-name pkg-desc)))
-          ((and (null force)
-                (setq pkg-used-elsewhere-by
-                      (package--used-elsewhere-p pkg-desc)))
-           ;; 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)
-                  (package-desc-name pkg-used-elsewhere-by)))
-          (t
-           (add-hook 'post-command-hook #'package-menu--post-refresh)
-           (package--delete-directory dir)
-           ;; Remove NAME-VERSION.signed and NAME-readme.txt files.
-           ;;
-           ;; NAME-readme.txt files are no longer created, but they
-           ;; may be left around from an earlier install.
-           (dolist (suffix '(".signed" "readme.txt"))
-             (let* ((version (package-version-join (package-desc-version 
pkg-desc)))
-                    (file (concat (if (string= suffix ".signed")
-                                      dir
-                                    (substring dir 0 (- (length version))))
-                                  suffix)))
-               (when (file-exists-p file)
-                 (delete-file file))))
-           ;; Update package-alist.
+    (let ((package-alist                 ;see bug#65475
            (let ((pkgs (assq name package-alist)))
-             (delete pkg-desc pkgs)
-             (unless (cdr pkgs)
-               (setq package-alist (delq pkgs package-alist))))
-           (package--quickstart-maybe-refresh)
-           (message "Package `%s' deleted."
-                    (package-desc-full-name pkg-desc))))))
+             (if (null (remove pkg-desc (cdr pkgs)))
+                 (remq pkgs package-alist)
+               package-alist))))
+      (cond ((not (string-prefix-p (file-name-as-directory
+                                    (expand-file-name package-user-dir))
+                                   (expand-file-name dir)))
+             ;; Don't delete "system" packages.
+             (error "Package `%s' is a system package, not deleting"
+                    (package-desc-full-name pkg-desc)))
+            ((and (null force)
+                  (setq pkg-used-elsewhere-by
+                        (package--used-elsewhere-p pkg-desc)))
+             ;; 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)
+                    (package-desc-name pkg-used-elsewhere-by)))
+            (t
+             (add-hook 'post-command-hook #'package-menu--post-refresh)
+             (package--delete-directory dir)
+             ;; Remove NAME-VERSION.signed and NAME-readme.txt files.
+             ;;
+             ;; NAME-readme.txt files are no longer created, but they
+             ;; may be left around from an earlier install.
+             (dolist (suffix '(".signed" "readme.txt"))
+               (let* ((version (package-version-join (package-desc-version 
pkg-desc)))
+                      (file (concat (if (string= suffix ".signed")
+                                        dir
+                                      (substring dir 0 (- (length version))))
+                                    suffix)))
+                 (when (file-exists-p file)
+                   (delete-file file))))
+             ;; Update package-alist.
+             (set-default-toplevel-value 'package-alist package-alist)
+             (package--quickstart-maybe-refresh)
+             (message "Package `%s' deleted."
+                      (package-desc-full-name pkg-desc)))))))
 
 ;;;###autoload
 (defun package-reinstall (pkg)

An alternative solution might just be to manually add a check at the end
of package-delete to handle the proper removal of the last package.