bug#56682: Fix the long lines font locking related slowdowns

[Eli Zaretskii]

> Date: Fri, 22 Jul 2022 10:16:52 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: Eli Zaretskii <eliz@gnu.org>
> 
> 
> The first step of the font locking related improvements was easier than I 
> thought.
> 
> Two following commands:
> 
> 1. C-x C-f dictionary.json RET y
> 
> 2. C-e
> 
> on my laptop, with Emacs from master from a week ago, take respectively 
> 150 seconds and 40 seconds.  With the improvements on master, 1 is 
> instantaneous but 2 still takes about 5 seconds.  Now, with the changes in 
> the feature/long-lines-and-font-locking branch, both are instantaneous. 
> The price of that speedup is that some portions of the buffer will be 
> mis-highlighted, which is unavoidable.

Thanks.  This is indeed the immediate idea for that aspect, but I
wonder what would developers of some major modes which widen the
buffer say about this.  Some of them were very much against such
restrictions in the past.