[arch-general] How to detect when a package is removed from a group in pacman

[F B]

> > Hi,
> > recently bin86 was removed from base-devel group but
> the unique way I
> > know to see this change is manually reading the pkg
> changelog in the
> > arch site. The problem is simple, how to detect this
> change in
> > pacman? For example, after a gnome upgrade, if a new
> package is added
> > to gnome group I can do: pacman -S --needed gnome to
> install the
> > missing package. But if a package is removed? How can
> I remove this
> > package that doesn't belong to a group anymore? I hope
> you understand
> > the question. Why not add metapackages (as for kde)
> for base,
> > base-devel, gnome and gnome-extra that doesn't have
> this problem?
> > 
> > 
> >       
> 
> Even if it was removed from the group, it could still be
> needed on your
> system.
> 
> pacman -Qdt might be more useful than checking if package x
> is still
> in group y.
> 

Yeah, obviously, but it's not this case.
The point is that there isn't a way to detect packages that are removed from a group so you can easily remove it; or at least I don't know a method to do it.