Eli Zaretskii <eliz@gnu.org> writes:

>> From: Michael Welsh Duggan <mwd@md5i.com>
>> Cc: Michael Welsh Duggan <mwd@cert.org>,  Eli Zaretskii <eliz@gnu.org>,
>>   "mwd@md5i.com" <mwd@md5i.com>,  "schwab@linux-m68k.org"
>>  <schwab@linux-m68k.org>,  "47244@debbugs.gnu.org" <47244@debbugs.gnu.org>
>> Date: Wed, 24 Mar 2021 22:19:35 -0400
>> 
>> > --- a/src/buffer.c
>> > +++ b/src/buffer.c
>> > @@ -2151,6 +2151,9 @@ set_buffer_internal_1 (register struct buffer *b)
>> >
>> >    BUFFER_CHECK_INDIRECTION (b);
>> >
>> > +  if (!BUFFER_LIVE_P (b))
>> > +    error ("Selecting deleted buffer");
>> > +
>> >    old_buf = current_buffer;
>> >    current_buffer = b;
>> >    last_known_column_point = -1;   /* Invalidate indentation cache.  */
>> 
>> Okay.  Building now and will run until...something happens?  Should I be
>> expecting an Emacs error from this?
>
> Yes.
>
>> Should I breakpoint the error() clause?
>
> Better put a breakpoint on this call to 'error' instead, because
> 'error' could be called for unrelated reasons, and it could be caught
> -- you don't want those cases.

I have now hit this breakpoint.  Backtrace included.  xbacktrace was
empty.  I'll leave the gdb session up for forensics.