bug#17577: 24.3.91; Error during redisplay prevent quitting.

[Eli Zaretskii <eliz@gnu.org>]

> From: Thierry Volpiatto <thierry.volpiatto@gmail.com>
> Date: Sat, 24 May 2014 06:50:26 +0200
> 
> we have an issue in helm that prevent quitting with C-g and return a
> error:
> 
> Error during redisplay: (eval (helm-show-candidate-number [...]

Please look in the helm code to find this eval expression.  The
problem is likely there.  In a nutshell, some helm code seems to be
incompatible with pre-redisplay-function (probably something related
to region or some such, but that's just a guess at this time).

> With this version of emacs (24.3.91) it is usable because I let-bounded
> `pre-redisplay-function' to nil, but the message is still here, with
> Emacs-24.4.50, quitting is nearly impossible, and the message contain
> byte-code.
> With emacs-24.3 it is working normally.
> This is relatively recent.
> 
> This is happening when hitting C-g on a helm command that use an async
> process, but only on the helm-locate command.
> 
> Another strange thing is when hitting C-g on a long helm-grep process,
> C-g works normally but return "Emacs-lisp:" in the minibuffer when done.
> 
> To reproduce:(best from emacs-24.4.50)

See above: please investigate helm code some more, it shouldn't be
necessary for us to install helm to find the offending code.  You are
the helm maintainer, so you are in a much better position to find the
offending code there.

Once the code is found, please show it here, and we can take it from
there, perhaps asking you a few questions.

Thank you.