bug#57503: 28.1.91; package-selected-packages should not be saved to custom-file

[Robert Pluim]

>>>>> On Mon, 05 Sep 2022 13:51:00 +0200, Robert Pluim <rpluim@gmail.com> said:

>>>>> On Mon, 05 Sep 2022 13:16:24 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:
    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >>> Iʼm not convinced thatʼs necessary. I just did the following:
    >>> 
    >>> 1. emacs-29+my patch, install some packages => no 
package-selected-packages
    >>> setting
    >>> 2. emacs-28, run `package-list-packagesʼ => package-selected-packages
    >>> is populated with packages set in step 1, and saved in .emacs

    Lars> Oh, I didn't know that it was automatically recreated.  Then what's 
the
    Lars> point of the variable?  According to the doc string:

Of course one use case that breaks is to do

emacs-29->emacs-28, *delete* some packages, and then go back to
emacs-29, which will pick up the old multi-session value.

I guess we could change emacs-29 to refresh the multi-session value
every time you run `list-packages'.

Robert
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