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

From: Stefan Monnier <[email-masked]>
Date: Wed, 29 Oct 2014 18:16:00 -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?

Huh?  No, the user is waiting because Emacs hasn't replied yet.
Idle timers are for when the user hasn't given any command, so Emacs is
waiting, rather than the user.

>> 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.

Same difference: the 1st redisplay redraws almost the whole window, and
the second as well because almost none of the text had been
fontified earlier.

You're right, that the amount of redraw is not always exactly the same,
but I think that in many/most cases the two are comparable.

        Stefan