Re: bug-reference-prog-mode slows down CC Mode's scrolling by ~7%

[Eli Zaretskii]

> Date: Wed, 1 Sep 2021 17:55:46 +0000
> Cc: emacs-devel@gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > (I thought that the code in jit-lock.el already handled this case by
> > computing a kind-of "maximum" out of all the return values of
> > jit-lock-functions, and treating a nil return value as expected, but
> > maybe my reading of the code was incorrect?)
> 
> I think it rather uses the "minimum", i.e. the region common to all the
> return values from the jit-lock-functions.  If one of these values is nil
> (as is the case here), that boils down to exactly the 500-byte chunk.

Then I think the easiest fix is to get bug-reference-prog-mode return
a suitable value, or wrap it in a function that would.  Every function
that puts itself on jit-lock-functions without actually fontifying
anything should return BOB..EOB as the region it fontified, right?