bug#56682: feature/improved-locked-narrowing 9dee6df39c: Reworked locked narrowing.

[Dmitry Gutov]

On 30/01/2023 21:02, Eli Zaretskii wrote:
> > Date: Mon, 30 Jan 2023 20:56:15 +0200
> > Cc:56682@debbugs.gnu.org,monnier@iro.umontreal.ca
> > From: Dmitry Gutov<dgutov@yandex.ru>
> >
> > On 30/01/2023 19:11, Eli Zaretskii wrote:
> > > > Date: Mon, 30 Jan 2023 15:03:54 +0000
> > > > From: Gregory Heytings<gregory@heytings.org>
> > > > cc:56682@debbugs.gnu.org,monnier@iro.umontreal.ca
> > > >
> > > > > What exactly will that remove? only what's on the feature branch, or
> > > > > also some stuff on the emacs-29 branch?
> > > > The "locked narrowing" feature, IOW, the portions of editfns.c in which it
> > > > is implemented, and its use around pre-command-hook, post-command-hook and
> > > > fontification-functions.
> > > >
> > > > > And what are your reasons for removing this?  It is hard to tell whether
> > > > > or not I agree without knowing to what I should agree 😉
> > > > The reason is that I'm now convinced that it is not a good solution to the
> > > > problem of ill-behaving modes in the presence of long lines.
> > > So we are removing all the stuff that prevented font-lock from slowing
> > > down redisplay when long lines are in the buffer?  IOW, something
> > > which we have for several months, and which so far brought up only one
> > > complaint?
> > More than one, FTR.
> >
> > I'm not 100% sure what Gregory's plan is, but note that a significant
> > part of the redisplay slowdowns wasn't caused by font-lock, and thus the
> > removal of locking will not regress those performance improvements.
> >
> > And for those (potential?) cases where font-lock is a real problem for
> > performance, we could stop it from widening using an existing knob.
> Yes, this is an old and known disagreement between us.  But this is my
> decision to make, not anyone else's.

With the previous change that Gregory had made (different limits for 
different features, i.e. font-lock uses much wider narrowing bounds 
which are also customizable) I don't have that much of a horse in that 
race anymore.

Just helping clear up some misconceptions, if any.

Also note that previously, I'd never have suggested that redisplay code 
changes the value of font-lock-dont-widen.