bug#40661: Crash in regex search during redisplay

[Stefan Monnier]

>> > Obviously, we cannot allow GC to run while regex routines do their
>> > work, because they are passed C pointers to buffer text.  The question
>> > is, where to disable GC?  We could do it inside
>> > update_syntax_table_forward, but UPDATE_SYNTAX_TABLE_FORWARD is called
>> > from many places that evidently have no problems with GC.  So my
>> > suggestion would be to disable GC inside re_match_2_internal instead.
>> > Comments?
>> Looks fine to me.
> So you prefer disabling GC to setting the inhibit_shrinking flag?
> I tend to agree with Daniel here, FWIW.

No, what I meant was that I'm fine with doing it "inside
re_match_2_internal" instead of "inside update_syntax_table_forward".
But I prefer if the "it" is setting `inhibit_shrinking` instead of
inhibiting the GC altogether.

> That's a project for another pandemic ;-)  I want a simple enough
> solution for now that we could install on the release branch.

Oh, for `emacs-27` that's clearly out, indeed.  But for `master` it
should not be that hard.  I think we can reuse `pending_funcalls`
for that.


        Stefan