Re: Unicode confusables considered harmful

[Eli Zaretskii]

> Date: Sat, 6 Nov 2021 12:56:29 +0100
> From: Vasilij Schneidermann <mail@vasilij.de>
> Cc: emacs-devel@gnu.org
> 
> > Disabling bidi in Emacs is asking for trouble because one cannot do
> > that and rely on the display engine to still work correctly in all
> > cases.  Bidirectional support is nowadays hardwired into the display
> > engine and cannot be disabled completely.
> 
> If it works correctly in all the cases not using RTL scripts, that's
> fine by me.

That's not something I can say.  It's unreliable because some parts of
the display engine assume that bidi reordering always happens.  I
didn't try to find in which cases the result is OK, and don't intend
investing any time in doing so.

> And I'm far from the only one thinking like that.

If there are volunteers interested in adding such a feature to Emacs,
let them send patches.  The Emacs development team decided long ago to
make the reordering an inherent feature that doesn't need to be turned
off, and the development in the display engine since then didn't
bother to keep 2 separate code paths, one each for every value of
bidi-display-reordering.  And that's what we have now.

> > Please try the new command highlight-confusing-reorderings (available
> > on master), it is supposed to be the way to detect suspicious
> > reorderings without falsely flagging any legitimate ones.  (I can
> > easily understand how mentioning it could drown in the sea of the
> > other messages in this thread; sorry about that.)
> 
> I'm specifically not talking about reordering characters, but
> confusables, that is, characters that look visually identical. See
> https://unicode.org/reports/tr39/#Confusable_Detection for further
> elaboration on the topic. Hence the change of the subject line.

That's supposed to be the subject of uni-confusables in ELPA, I think.
It has nothing to do with bidirectional reordering, AFAIU.  If
uni-confusables doesn't do its job well enough, please submit bug
reports.