bug#72826: 30.0.90; icomplete-in-buffer becomes unusably slow in large Eshell

[Eli Zaretskii]

> From: Sean Whitton <spwhitton@spwhitton.name>
> Cc: 72826@debbugs.gnu.org,  juri@linkov.net,  joaotavora@gmail.com
> Date: Fri, 04 Oct 2024 08:20:01 +0800
> 
> > Does it help to disable auto-composition-mode?
> 
> It looks like that slightly improves the situation, but does not fix it.
> It's still extremely slow.
> 
> I think I have a fix, which I've attached.  I'll test it locally for a
> couple of days before installing it.

Can you explain why taking a substring of the buffer text is TRT in
this case and how it makes such a big difference without omitting text
whose width should be measured?  IOW, are you saying the current code
produces too large width? if so, how can the layout of completion
candidates be correct?