bug#43835: 28.0.50; auto-hscroll-mode/current-line + show-paren-mode + gnus-summary-mode = bug

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: 43835@debbugs.gnu.org
> Date: Wed, 07 Oct 2020 22:54:51 +0200
> 
> 0. emacs -Q
> 1. Evaluate the following sexp:
> 
> (let ((buf (get-buffer-create "*test*")))
>   (with-current-buffer buf
>     (setq auto-hscroll-mode 'current-line
>         truncate-lines t
>         bidi-paragraph-direction 'left-to-right)
>     (insert "Subject: Re: bug#39280: 27.0.60; wdired-get-filename ignores 
> first argument (this is a test)\n")
>     (goto-char (point-min)))
>   (show-paren-mode)
>   (switch-to-buffer buf))
> 
> 2. Now typing `C-e' shows the problem.

bidi-paragraph-direction is set to left-to-right in any descendant of
prog-mode, in particular in Emacs Lisp mode.  And yet I couldn't
reproduce this in a Lisp buffer, no matter what I tried.  So that
setting is not the only cause.

If you add a line of text before and after the Subject line you insert
in the recipe, does the problem go away?  It does here.  But then I
wonder whether this problem only happens in Gnus with the very first
or the very last line of the summary buffer.  If that's not so, I'm
probably missing something else.

> Do you still want the output of trace-redisplay?

No, I can do that myself now.

Thanks.