bug#45898: 27.1; wedged in redisplay again

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: gerd.moellmann@gmail.com,  larsi@gnus.org,  psainty@orcon.net.nz,
>   Emacs-hacker2018@jovi.net,  45898@debbugs.gnu.org
> Date: Thu, 30 Jun 2022 15:56:41 -0400
> 
> >> Unsuprisingly so: none of `C-n/C-p/C-v/...` involve font-lock or
> >> jit-lock either during their operation or during the
> >> subsequent redisplay phase in the current code: the one-line is all
> >> fontified once and for all when you open the file and after that
> >> font-lock is not involved any more (until you make an edit, that is).
> >
> > That's only true if max-redisplay-ticks is zero.
> 
> Why would that make a difference?

Because if it is not zero, we won't let the entire line to be
fontified, we will stop that before it gets to the end of the line.

> When I try `master` with this set to
> 100000, the file still shows up with font-locking, so apparently it's
> been fully font-locked despite `max-redisplay-ticks`

You see only a small portion of the file.

> and after that
> font-locking (and syntax-propertize) won't make any difference any more
> (until the buffer is edited) since they're already done.
> [ Of course font-locking (and syntax-propertize) still do have an
>   effect in that the text-properties they applied can impact the time it
>   takes for the redisplay to do its job; so by "won't make any difference"
>   I mean that 0-cycles will be spent running font-lock of
>   syntax-propertize code.  ]

Sorry, I cannot parse this at all.