bug#62720: 29.0.60; Not easy at all to upgrade :core packages like Eglot

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

> I would think it's too late in the game to break compatibility.
> Naming aside package-install has certain behaviour that for a certain
> set of inputs used to produce predictable things.
> Now, for the same inputs it does nothing on Emacs 29.

The only way I can think of to preserve compatibility is to change the
behavior so it doesn't pay attention to "is builtin or not" but to "used
to be builtin before Emacs-29".  This would make a bad semantics even
worse, so I'd rather we fix the semantics to something clean.

> I think it should do the same thing, not only because it's
> nicer for the unsuspecting user, but also because trying to
> protect this user from "unintentional" upgrade of certain "unstable"
> packages, as it seems to be the idea here, is a losing game
> anyway, just because dependencies.

You may be right: maybe the distinction between "install only" and
"install&upgrade" isn't worth the trouble.

I think to get closer to a useful "install only" behavior we'd want that
command to prompt the user before upgrading dependencies (tho probably
only for those in `package-selected-packages`).

BTW, for me the reluctance to upgrade when asked to install isn't due to
the risk that the package is "unstable".  I'm not completely sure what
is the reason, admittedly, but it's closer to viewing it as a silent
"change of distribution", or maybe it's because I like to know when
behavior may change and merely installing a package shouldn't change
Emacs's behavior.


        Stefan