bug#68246: 30.0.50; Add non-TS mode as extra parent of TS modes

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 15 Jan 2024 04:10:16 +0200
> Cc: 68246@debbugs.gnu.org, casouri@gmail.com, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> >> However it is not easy to quantify confused users looking to understand
> >> the new meaning of things in dir-locals.el.  Or users wondering why they
> >> need to set Eglot variables in both 'c++-mode-hook' and
> >> 'c++-ts-mode-hook' when all they see is 'c++-mode' in
> >> 'eglot-server-programs'.
> > 
> > Those users will hopefully submit bug reports or otherwise complain on
> > the Emacs mailing lists, and then we will know.
> 
> I rather wouldn't rely on that.

Why not?  The decisions we made are not arbitrary.  Given the best
consensus (or lack thereof) we could arrive upon after careful
consideration of the issues, it is perfectly fine to expect feedback
to set us straight if we made a mistake.

> > The recommendation is to use base modes where it makes sense, and the
> > installed changes around derived-mode-add-parents don't in any way
> > preclude having a base mode and don't make it harder.  But I don't
> > think we should force everyone in this situation to invent a base mode
> > as the sole means for solving this.
> 
> It's not like we don't have an existing solution for this: if there are 
> two different modes to configure, change the settings for both modes, or 
> alter two hooks.

This doesn't solve the problem at hand, since the differences between
the modes are not limited to these simple aspects.

Less magical and more verbose, but being explicit can 
> be good.
> 
> >> 2. Explicitly associating some major modes with languages or file types.
> >>     This doesn't seem hard and other further uses like suggesting modes
> >>     or packages to a new user based on languages have been proposed.
> > 
> > This is IMO a heavier and more thorough change, especially since Emacs
> > doesn't have the notion of "language".  This discussion shows that its
> > advantages are not evident, and moreover we don't even have a clear
> > shared view what will that entail.
> 
> Here's a draft patch of how a "language" could work. It doesn't alter 
> every entry, but it is backward compatible.

Like I said: it is heavier, so we should only do that if the simpler
method don't work well enough.  So thanks, but let's try the existing
simpler solution first and see if we need something better.