bug#44983: Truncate long lines of grep output

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: dgutov@yandex.ru,  44983@debbugs.gnu.org,  juri@linkov.net
> Date: Sat, 30 Apr 2022 13:02:59 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > We are not.  The display engine will never call jit-lock on a region
> > that starts in invisible text.  But a region that starts in visible
> > text can end in invisible text, and font-lock doesn't pay attention to
> > invisibility spec, AFAIR, it just looks at the buffer text
> > disregarding everything else.
> 
> Yes, that's correct, I think.  But shouldn't it be smarter here?  That
> is, the display engine does know that all the text it inserted was
> invisible

No, it doesn't know that.  The display engine handles the 'fontified'
property first, and the invisible property only after that.  Even more
importantly, the display engine handles these properties only when it
gets to a character with that property, so it's enough that we have a
single character with no invisible property that needs to be
fontified, to have the display engine invoke jit-lock on a chunk of
text starting with that visible character.