bug#50983: 28.0.50; [REGRESSION, BUG] Display bugs with uncommon characters

[Alan Third]

On Sun, Oct 03, 2021 at 01:04:36PM +0300, Eli Zaretskii wrote:
> > Date: Sun, 3 Oct 2021 10:54:01 +0100
> > From: Alan Third <alan@idiocy.org>
> > Cc: Rudi C <rudiwillalwaysloveyou@gmail.com>, 50983@debbugs.gnu.org
> > 
> > For the record I can't see these problems on GUI emacs
> > on the mac, but I do see them in the terminal using iTerm2.
> 
> Does iTerm2 have some support for bidirectional text?  If so, you need
> to disable it for Emacs -nw to display bidirectional text correctly.

I don't see any options (but there are a LOT of options).

> > It looks like sometimes the display is incorrect, and other times the
> > action actually changes the underlying buffer contents in an
> > unexpected way.
> 
> Any idea what could cause that?  Does it happen with plain-ASCII text
> as well?

Actually, I was wrong. If I follow the instructions for the first
example, by removing the character indicated by an underscore in
Rudi's first screenshot, it actually deletes the previous "o" in
"note", and displays the rest wrongly, as shown in his second
screenshot.

If I put the cursor over that underscore character and do
describe-char, it tells me it's an "o", so the problem exists even
before editing.

I don't see these problems in normal ascii text, or even normal UTF-8
text, even RTL. For example the Hebrew text in HELLO behaves exactly
as I'd expect.
-- 
Alan Third