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bug#7722: 24.0.50; Finding this C++ header file drops emacs into a infin

From: Alan Mackenzie
Subject: bug#7722: 24.0.50; Finding this C++ header file drops emacs into a infinite loop
Date: Sun, 13 Feb 2011 12:20:44 +0000
User-agent: Mutt/1.5.9i

Hi, Yidong!

On Fri, Feb 11, 2011 at 08:25:06PM -0500, Chong Yidong wrote:
> Alan Mackenzie <address@hidden> writes:

> > It was indeed such a loop.  It was caused by a 500n jit-lock boundary
> > falling in the middle of a template construct, hence the "necessity" of
> > all the whitespace to reproduce the failure.

> > Here's a putative patch for the problem.  I've refactored the offending
> > function by replacing obscenely nested `if'-forms with a simple `cond'.
> > I've also removed some narrowing (to the 500n limit) which should help
> > jit-lock, hopefully without hurting too much elsewhere.

> > Tassilo, would you try out the patch, please, and let me know how it
> > goes.  Thanks!

> Thanks.  This patch doesn't apply cleanly to the emacs-23 branch.

That surprises me.  Would you like me to rework the patch so that it

> Do you think we could apply it to the trunk, and just use the
> workaround in the branch ....

To be honest, I haven't really looked at the workaround.  I suppose it
would be OK.  However, the patched version passed all the CC Mode
regression tests (which are about half indentation, half font-locking),
so I'm fairly confident about it.

> .... (some of these logic changes don't look obvious to me)?

One of the fixes was removing a `narrow-to-region' around the region
being fontified.  In a jit-lock 500-byte chunk, this had the effect of
cutting necessary context off the end.

The other change was basically to refactor, in which the infinite looping
disappeared in the wash.  Although I could get edebug going on this loop,
the source was just too complicated to be worthwhile trying to understand
in detail.  (Believe me, I tried.  :-)

Incidentally, I'm not getting mail from emacs-devel or bug-gnu-emacs at
the moment, and I've not got enough energy to do anything about it.  Do
you know anything specific which might be doing this to me?

Alan Mackenzie (Nuremberg, Germany).

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