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

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

Philip Kaludercic <philipk@posteo.net> writes:

> 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.

>
> Can you edebug the function and see if it behaves the way it should
> (evaluating the setq expression)?
>

AFAICT, `package--save-selected-packages` works fine now.  The problem
is elsewhere.

Namely, when deleting the last package with `package-delete`, what
happens is that `package--save-selected-packages` gets called twice.
The first time, it's called by `package--save-selected-packages` with a
nil argument.  This works as expected and sets
`package-selected-packages` to nil.

But then, `package--save-selected-packages` is called again by
`package--used-elsewhere-p` through `package-desc-status` and
`package--user-selected-p`, this time with a non-nil value `(chess)`
that's taken from `package-alist`, which is not yet updated at this
point in `package-delete`.  So `package-selected-packages` gets reset to
a non-nil value.