bug#40661: Crash in regex search during redisplay

[Daniel Colascione <dancol@dancol.org>]

On April 17, 2020 6:56:00 AM Eli Zaretskii <eliz@gnu.org> wrote:

>> Date: Fri, 17 Apr 2020 14:22:00 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: 40661@debbugs.gnu.org
>>
>> 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.
>
> Alternatively, we could set the buffer's inhibit_shrinking flag while
> in re_match_2_internal.  Although that flag was introduced for a
> different purpose: for when we have stuff inside the gap that we don't
> want to lose.  The name of the flag notwithstanding, I'm not sure we
> want to conflate these two purposes.  But maybe it's better than
> preventing the GC entirely.

I think I'd prefer this approach to inhibiting GC entirely. I can imagine 
code allocating enough garbage that we really want to get rid of it, and 
inhibiting shrinking is more conservative.