bug#57728: 29.0.50; Emacs writes wrong glyph at the bottom-right corner of text terminals

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: akib@disroot.org,  57728@debbugs.gnu.org
> Date: Sun, 11 Sep 2022 20:18:03 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Doesn't happen here, neither on MS-Windows nor on GNU/Linux to which I
> > SSH-login via PuTTY (which AFAIK emulates xterm).  I guess this really
> > is specific to some terminals.
> 
> My example was with gnome-terminal on the current Ubuntu, for what it's
> worth.

Someone with access to that terminal will have to debug this.

My guess is that something we do when we rewrite the lines while
scrolling the display erases those glyphs by side effect, but Emacs
doesn't know that.  Since all the lines have the continuation glyph,
it makes sense for Emacs to rewrite only the part of each line up to
and excluding the continuation glyphs, relying on them to remain on
the glass.