bug#59038: loading this base64 file makes emacs -Q 28.2 peg a core infinitely

[Alan Mackenzie]

Hello, Gerd and Phil.

On Sun, Nov 06, 2022 at 06:20:17 +0100, Gerd Möllmann wrote:
> Phil Sainty <psainty@orcon.net.nz> writes:

> > On 2022-11-06 12:41, Gregory Heytings wrote:
> >> That file opens just fine in other modes

> > It also opens fine in c-mode, with global-font-lock-mode disabled.

> >> Note that this bug has nothing to do with long lines.

> > I imagine that the font-lock issue is related to the line being
> > in excess of 21,000 chars (but general redisplay obviously doesn't
> > have problems with lines this 'small').

> > Reduced to 10,208 chars that file opens instantly under emacs -Q
> > in c-mode with font-lock enabled; but at 10,209 chars it hangs
> > Emacs (I killed it after waiting 4 minutes).

> It could also be that this is not something with the position of size,
> but with what's there at or around that position.  Just an idea.

I've identified the place in the code where it's looping, namely in the
defun c-brace-stack-at.

Gerd's Lisp backtraces earlier on in the thread were extremely helpful,
as was Phil's identification of the minimum size of buffer needed to
trigger the infinite loop.

I don't yet know why that function is looping, or why it does so only
from a certain length of buffer, but I'm working on it.

-- 
Alan Mackenzie (Nuremberg, Germany).