Several Major Modes. [Was: master 7362554: Widen around c-font-lock-fontify-region. This fixes bug #38049.]

[Alan Mackenzie <acm@muc.de>]

Hello, Dmitry.

On Thu, Nov 14, 2019 at 00:33:33 +0200, Dmitry Gutov wrote:

[ .... ]

> >> In mmm-mode context, however, we apply definite boundaries to the
> >> region chunks. Here's an example of some Noweb code:
> >> https://en.wikipedia.org/wiki/Noweb#Example_of_a_simple_noweb_program

> >> The inside of hello.c block would be narrowed to.

> > I think I've said this before, but I don't think narrowing is the right
> > tool for that task.  I don't think there is a suitable tool in Emacs at
> > the moment.

> *shrug* We do the best with what we have.

Why can we not formulate something better, an enhancement to the Emacs
core which would support several major modes properly?  I have made
proposals in this area before, but I think they were to grandiose to be
implementable.

What seems to be needed is a way of partioning a buffer into several
sub-buffers (which I have called "islands" in the past), and having a new
type of local variable, one valid in exactly one sub-buffer.  More or
less.

> >> Now, I have remembered that CC Mode calls widen from many places
> >> already, so it already is problematic for using in a context like
> >> that.

> > It does, yes.  Users also use widening and narrowing.

I believe these problems won't go away, and there will always be
conflicts between CC Mode (as it is) and mmm-mode (as it is).

> It's a different thing. Strategically undoing interactively applied 
> narrowing is not hard.

-- 
Alan Mackenzie (Nuremberg, Germany).