bug#40661: Crash in regex search during redisplay

[Richard Copley <rcopley@gmail.com>]

On Sat, 18 Apr 2020 at 12:57, Eli Zaretskii <eliz@gnu.org> wrote:
> OK, thank you and Daniel for the feedback, and thanks to Richard for
> finding this bug in the first place.
>
> I installed a fix on the emacs-27 branch, it avoids the crashes in the
> recipe posted by Richard.  Please eyeball the fix, in case I made some
> stupid mistake (my environment is rather noisy today, so I trust
> myself even less than I usually do).

There are a couple of points about the patch that aren't clear to me.
I think you have probably thought them already. I hope you don't mind
me asking for clarification.

I have a little worry about the situation where the procedure of doing
a "decoding" entails a regexp buffer search. (I can't make out whether
or not "decoding" means executing arbitrary Lisp code.) Is it
possible, with your patch, that we might re-enable buffer shrinking
sooner than desirable? (This is reiterating a worry you yourself
mentioned earlier, "I'm not sure we
want to conflate these two purposes".)

In the comment, you mention relocation as well as shrinking. Does it
make sense to combine this new guard with the existing
freeze_buffer_relocation in some way?