bug#53058: etc/DEBUG could say more about --enable-check-lisp-object-type

[Eli Zaretskii <eliz@gnu.org>]

> From: Sean Whitton <spwhitton@spwhitton.name>
> Cc: 53058@debbugs.gnu.org
> Date: Thu, 06 Jan 2022 16:46:24 -0700
> 
> Hello,
> 
> On Thu 06 Jan 2022 at 10:11PM +02, Eli Zaretskii wrote:
> 
> >> From: Sean Whitton <spwhitton@spwhitton.name>
> >> Date: Thu, 06 Jan 2022 11:20:19 -0700
> >>
> >> > Comparisons with structures, like foo == Qnil, aren't guaranteed to
> >> > work in GDB.  --enable-check-lisp-object-type makes Lisp objects be
> >> > structures rather than simple scalar values.
> >>
> >> Thanks -- how about the attached?
> >
> > Thanks, but the text there is inaccurate: NILP should still work with
> > structures, only == comparison probably won't.
> >
> > I'm actually not sure we should describe such subtleties in etc/DEBUG.
> 
> Fair -- what do you think about just saying that certain gdb features
> might not work, so one thing that you can try is to drop the flag?  The
> claim that it doesn't affect debugging at all is what threw me off
> recently, so that's the thing I'd really like to improve, I guess.

But it really doesn't affect the debugging.  You just need to
understand what it does, and if we describe this in etc/DEBUG, we'd
need to describe gobs of other similar factoids about the various
build options.