bug#61514: 30.0.50; sadistically long xml line hangs emacs

[Eli Zaretskii]

> Cc: "Mark A. Hershberger" <mah@everybody.org>, 61514@debbugs.gnu.org
> Date: Wed, 15 Feb 2023 13:58:37 +0000
> From: Gregory Heytings <gregory@heytings.org>
> 
> 
> >
> > It sounds like the bug lies somewhere in the intersection of nXML and 
> > the new long line fontification handling in Emacs 29 (with narrowing, 
> > perhaps)?
> 
> Yes, it's an example in which the cure of narrowing around 
> fontification-functions could be considered worse than the disease.  In 
> this particular case however, the fontification routines already failed to 
> do their job in Emacs 28 (and 24, 25, 26 and 27): after opening this file, 
> errors are displayed in the echo area, and the buffer remains unfontified.

If fontification-functions failed regardless of the restriction, then
perhaps fixing them so that they don't fail will also solve the
greater problem?

Btw, how does the narrowing make the matters worse, exactly? what is
the mechanism of worsening the situation in this case?