RE: On obsoleting defcustoms

[Drew Adams]

> > If people are concerned about someone continuing to use
> > something that's obsolete, why not just have Customize give
> > a warning/message saying that the option is obsolete
> 
> That's what we do now.  See `M-x customize-group RET browse-url RET'

I don't see any such warnings/messages there, until you
open the full doc string of an option.  If every option
in the group is obsolete, and so is the group itself
(which should presumably follow), then one might expect
a notification at the top (i.e. customize-group) level.

> in Emacs 27 for a bad case of what that might look like.

What's bad about it?

If all of those options still "work", a user should be
able to make use of Customize to change their values.

And if they don't work then there should be no supporting
code, and they'd be unrecognized - raise an error if
referenced in any way.  Typically, deprecated/obsolete !=
unsupported.  Does Emacs take the point of view that all
of this is unsupported?  If so, remove its code, so using
raises an error.

> > That's assuming that Emacs takes the (unusual, IME) point of
> > view that, once declared obsolete, something should no longer
> > be usable.
> 
> It's still usable with the patch, just not advertised.

Not advertising is fine.  Telling users, including in the
Customize UI, that something is obsolete is also fine.
What's not fine, IMO, is to remove it from Customize.  If
something is removed from Customize then it's not the case
that it's still usable with Customize (or Customize is
still usable for it).