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

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  casouri@gmail.com,  68246@debbugs.gnu.org
> Date: Sun, 07 Jan 2024 23:11:00 -0500
> 
> >    (set-language-for-mode 'foo-ts-mode 'foo)
> 
> Maybe we want to introduce this concept, indeed.
> 
> maybe we want to that notion of "language" from elsewhere, such as
> the one used in LSP?

Please don't call it "language".  That'd be confusing.  LSP is about
programming languages, so "language" is natural there.  But in Emacs,
a major mode is more general than that.  For example, it is not
unthinkable to consider mail-mode to be the extra-parent of
message-mode (or vice versa) -- but what is the "language" in that
case?

> Or maybe we want to take it from MIME types?
> I'm sure there are other options out there.
> 
> Problem is: they come with their own complexities and corner cases.
> After all, this is inevitable when you create a taxonomy.
> IOW, while we *may* want to add support for an explicit notion of "file
> type", it's a whole problem in itself and it will not solve all
> our problems either.

File types also have problems: Emacs modes are sometimes defined for
buffers that don't visit files.

> In the mean time, I think `derived-mode-add-parents` is worth a try.
> As mentioned in some message up-thread, I'm not 100% confident that it
> won't introduce serious breakage.  But I think we do need more
> experience and installing my patch is a good way to do that.

Yes, I think we should try it and see what we learn.