bug#63587: 29.0.91; package-menu-mark-upgrades does not show available upgrades

[Philip Kaludercic <philipk@posteo.net>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Fri, 19 May 2023 08:30:46 +0200
>> From: Andreas Kurth <emacs@akurth.de>
>> 
>> after setting package-install-upgrade-built-in to a non-nil value, the
>> command "M-x package-menu-mark-upgrades" won’t show upgradeable non
>> built-in packages (magit, embark, ...) any more. Same for pressing "U"
>> in the package menu. Also, the command "M-x list-packages" won’t
>> announce upgradeable packages in the echo area.
>> 
>> Setting package-install-upgrade-built-in to nil will revert that
>> faulty behaviour.
>> 
>> I bisected the error to commit
>> ba2c76fa2bc3aabfda7d1d09cc5148f3f9d8e08e in emacs-29 branch.
>
> Philip, could you please look into this issue?

I've taken a look at the issue, and think this small change should fix
the issue:


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diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index 325c7b4e0a6..01826da273d 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -3751,8 +3751,8 @@ package-menu--find-upgrades
         (and avail-pkg
              (version-list-< (package-desc-priority-version pkg-desc)
                              (package-desc-priority-version avail-pkg))
-             (xor (not package-install-upgrade-built-in)
-                  (package--active-built-in-p pkg-desc))
+             (or (not (package--active-built-in-p pkg-desc))
+                 package-install-upgrade-built-in)
              (push (cons name avail-pkg) upgrades))))
     upgrades))
 

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And before I just propose a different change, I'd like to try and prove
that it fixes the above issue.  For a package with an update, let

p := is a built-in package
q := built-in packages should be upgradede

The previous implementation with xor (p ⊻ q) correctly decides to
upgrade or not-upgrade the package in three of the four possible cases

p q   upgrade? 
--------------
t f   f
t t   t
f t   f        <-- this was Andreas case
f f   t

But since non-built-in packages should always be upgraded, we need to
change the condition to only be false when we have a built-in package
but `package-install-upgrade-built-in' is non-nil:

      ¬ (¬ q ∧ p)
    = ¬¬ q ∨ ¬p
    = q ∨ ¬p

as we see, this should solve the issue:

p q   upgrade? (p ∨ ¬q)
--------------
t f   f
t t   t
f t   t
f f   t

Does this look OK?