bug#44007: 26.3; Strange shell mode performance

[Eli Zaretskii]

> Cc: Eli Zaretskii <eliz@gnu.org>, Herman@debbugs.gnu.org,
>  44007@debbugs.gnu.org
> From: Herman, Géza <geza.herman@gmail.com>
> Date: Fri, 28 Jan 2022 23:33:47 +0100
> 
> Yes, it still happens on current master for me.
> 
> By default, "seq 100000" takes ~3 sec. Pressing enter immediately after 
> executing the seq can make seq to take ~0.4 sec. Or if press enter 
> during "seq" several times, time can easily increase to >20 sec (this 
> issue seems to be related to bidi-paragraph-direction. If I set it to 
> left-to-right, this doesn't happen anymore - I've no idea why it matters).

If setting bidi-paragraph-direction to left-to-right fixes the
slowdown, then this is expected and not a bug.  When
bidi-paragraph-direction is nil, Emacs needs to determine the
paragraph direction from the strong directional characters in the
preceding paragraph of text, but "seq 100000" produces a long
paragraph that has no strong directional characters at all (digits
have "weak" directionality).