bug#18856: 24.4; *grep* output buffer not getting fontified when jit-lock-defer-time is used

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: deng@randomsample.de,  18856@debbugs.gnu.org
> Date: Wed, 29 Oct 2014 00:06:14 -0400
> 
> >> To only defer fontification when we know "for sure" that the user is
> >> waiting for further processing.
> > Sorry, you lost me.  When input is pending, what further processing is
> > the user waiting for?
> 
> The user is waiting for Emacs to process the input that he's already sent.

Using an idle timer does that, right?

> > I don't think this is too high a price.  First, as Alain established,
> > what takes 90% of the time is not redisplay, but fontifications, and
> > those are run only once.
> 
> This 90% is for CC-mode, where font-lock is particularly expensive.

Yes, that's right.

> > And second, the 2nd redisplay will only redraw the portions that were
> > fontified, not the entire window.  So this is not "twice", but more
> > like 1.2 times.
> 
> The 1st redisplay also only redrew the portion that was modified, which
> is pretty close in many cases to the portion that later gets fontified.

I was thinking about scrolling with C-v, in which case the first
redisplay redraws almost the entire window.