bug#18778: noticeable slowdown for buffers with long lines, word-wrap, and brackets

[Eli Zaretskii]

> From: Ivan Shmakov <ivan@siamics.net>
> Date: Mon, 20 Oct 2014 19:17:28 +0000
> 
>       • create a buffer with long lines (see below for the example
>         I’ve used), and (setq word-wrap t line-move-visual nil) there;
> 
>       • now, enclose every line in [, ] brackets (as in: M-x
>         replace-regexp RET .* RET [\&] RET; parentheses or curly
>         braces also exhibit the issue.)
> 
>       For the resulting buffer, operations like (next-line) or even
>       (recenter) now result in a noticeable delay.
> 
>       The issue doesn’t appear when word-wrap is not used, or when
>       there’s no brackets in the buffer.  Neither the issue appears in
>       Emacs built 2014-10-09 from a then-recent Git clone.
> 
>       I’ve used the output of the following Shell command as a test.
> 
> $ head -n 8192 < /usr/share/dict/american-english | fmt -w 1024 

Is it an important use case?  If so, what is the real-life situation
here?