bug#64395: [PATCH] * src/xdisp.c (display_string): Don't truncate mode line in terminal

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 64395@debbugs.gnu.org
> Date: Sat, 01 Jul 2023 15:00:48 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > From: qijian gong <gongqijian@gmail.com>
> > Date: Sat, 1 Jul 2023 19:25:26 +0800
> > Cc: 64395@debbugs.gnu.org
> > 
> > The picture I sent earlier is an animation. It shows the entire reproduction process and the result.
> 
> Sorry, I didn't realize that it included animation.
> 
> I think I see the issue now.

OK, I've now found a way of reproducing the problem on a system to
which I have access.

Your proposed change fixes the problem, but it fixes it incorrectly:
after applying the patch, I see a truncation glyph "$" at the end of
the mode line.  This should never happen on the mode line: we don't
show truncation glyphs there.  Compare the display after applying your
patch with the mode-line displayed after evaluating the below:

 (setq mode-line-format
       (concat (format-mode-line
                "- Ln %l, Col %c ")
               (make-string 100 ?-)))

As you see, the expected display of the mode line that is truncated is
simply not to see the truncated part, without any "$" truncation
glyph at the end of the mode line.

So a slightly different change is needed to properly fix this case.
I'm working on such a proper fix.