bug#57245: 29.0.50; M-> in a large XML file (without long lines) is slow

[Eli Zaretskii]

> Date: Wed, 17 Aug 2022 15:14:07 +0300
> Cc: 57245@debbugs.gnu.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> >> Which seems to be exactly the behavior the "font-lock narrowing" was
> >> supposed to guard from?
> > 
> > No.  It wasn't supposed to fix modes that foolishly scan the buffer
> > from BOB to point.
> 
> You might want to choose words better.

I did.

> > It was supposed to fix modes which scan from the
> > beginning of line, and that is (a) only a problem when lines are very
> > long, and (b) much harder to solve in the mode itself, because
> > font-lock very frequently uses anchored regexps and otherwise likes to
> > start from BOL, and syntax processing also likes starting from BOL.
> 
> syntax-wholelines-max handles that problem.

Only for syntax-related stuff.  And we have yet to see whether it's a
good enough job: that feature is too young to be sure.