bug#9571: 24.0.50; user option to turn off bidi, please

[Eli Zaretskii <eliz@gnu.org>]

> From: Štěpán Němec <stepnem@gmail.com>
> Cc: 9571@debbugs.gnu.org
> Date: Fri, 23 Sep 2011 15:01:32 +0200
> 
> > I happen to be a documentation freak, and tried to do my best in
> > documenting everything related to bidi.  If you can suggest specific
> > changes to the user manual or NEWS about this, please do.  Saying in
> > the manual that some feature "means trouble" is not something we use
> > to do, because users will say "if it's trouble, why don't you fix
> > it?".  We need to find a way of saying something useful that will help
> > users nonetheless.  Suggestions are welcome.
> 
> When you take one example Lars reported recently -- a buffer where the
> current bidi code wasn't able to diagnose the paragraph direction
> properly (or something) in a relatively untypical buffer (a lot of long
> lines without paragraph breaks). It made the buffer unusable. Now, how
> would a user diagnose or solve this issue? How would the current
> documentation help him in doing so?

Documentation cannot help with this, because it was a bug.  It
happened in a situation that I never envisioned, and that took several
months to bump into, since bidi-display-reordering was turned on.  The
bug was fixed since then.

I expect users who bump into such issues, and cannot find anything to
help them in the manual, to ask for help on help-gnu-emacs or on
emacs-devel.  Then they will be provided with workarounds if they are
available, or with patches if not.  IOW, treat that as we always do
with bugs.

I also expect such issues to be extremely rare and marginal by the end
of the pretest, provided that people report the problems.

> I think unless you're pretty sure such problems are not likely to occur
> again, you should at least say (in NEWS if not in the manual; I would
> probably check the NEWS first in such situation anyway) that such things
> can happen and how to work around it

I wouldn't know what to say in a way that will be useful.  Bugs that
are reported are being fixed fairly quickly, so describing them would
be an exercise in futility.  Bugs that were not yet reported are
unknown and cannot be described.  The assumption that every single
slowdown and every display-related bug in Emacs 24 are due to the
bidirectional display engine is profoundly false, at least lately, so
saying "as soon as you see any problem whatsoever, turn off bidi"
would be crying wolf for no good reason.

IOW, I feel that the issue is blown out of proportions for reason I
cannot understand.  By and large, THERE IS NO PROBLEM.  Fear of
problems, maybe.  But no real problems, at least not reported ones.