bug#41520: 28.0.50; Crash in character.h due to assertion error

[Pip Cet <pipcet@gmail.com>]

On Mon, May 25, 2020 at 3:07 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Mon, 25 May 2020 14:30:55 +0000
> > Cc: stefan@marxist.se, 41520@debbugs.gnu.org
> >
> > I'm attaching a patch with a few more cases. I don't have a strong
> > preference for either FETCH_BYTE or FETCH_CHAR where both will do, but
> > we should be consistent.
>
> I'm okay with those additional changes, but let's install them on
> master, as they are a cleanup, not a bug.

Sure.

> > > That would require us to maintain both character and byte positions
> > > where we use these macros,
> >
> > For now, I'd like to introduce them in Emacs proper only where we have
> > pairs of variables anyway.
>
> Maybe a new macro that accepts a 'struct text_pos'?

Yes, a pos_t would look like a struct text_pos, at least in non-debug builds.

> But wouldn't it be strange to see a macro that accepts a struct, but
> only uses one member of that struct?

I don't think so. CHARPOS and BYTEPOS already exist, and that's
precisely what they do.

What is a little strange is that the ancient convention of not
returning struct types is still followed in much of Emacs.

> > > Moreover, I think we prefer having assertions in the debug
> > > builds rather then silent fixups (and in production eassume compiles
> > > into something that doesn't abort).
> >
> > I see no way to have assertions
>
> I mean we already have assertions: that's what eassume does in a debug
> build.

Yes, but we could do with some stricter checking, I think.