bug#44983: Truncate long lines of grep output

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: juri@linkov.net,  44983@debbugs.gnu.org,  dgutov@yandex.ru
> Date: Fri, 29 Apr 2022 14:41:49 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> I thought I remembered there was a way to say to font-lock "ignore this
> >> bit of the buffer", but I can't find it now.  Do I misremember?
> >
> > Make the text invisible?
> 
> The text is covered by a display property, which should be much the same
> thing. 

Not really, it isn't.  The effect on the glass is the same, but the
effect on the display code is different.

> > If that doesn't help either, I suggest to profile the code, because it
> > could be the slow display is due to something else.
> 
> Hm, yes...  even if I disable font-lock-mode, it's still slow.

Then I think a profile should tell something interesting.