bug#44942: 28.0.50; Emacs should print a backtrace on uncaught errors in batch mode

[Eli Zaretskii]

On December 7, 2020 12:29:16 PM GMT+02:00, Philipp Stephani 
<p.stephani2@gmail.com> wrote:
> Am So., 6. Dez. 2020 um 18:00 Uhr schrieb Eli Zaretskii
> <eliz@gnu.org>:
> >
> > > From: Philipp Stephani <p.stephani2@gmail.com>
> > > Date: Sun, 6 Dec 2020 17:50:17 +0100
> > >
> > > Am So., 29. Nov. 2020 um 16:27 Uhr schrieb Philipp Stephani
> > > <p.stephani2@gmail.com>:
> > > >
> > > Pushed to master as commit 40e11743ca.
> >
> > This is an incompatible change.
> 
> Is it? In other words, do we guarantee that no stack trace is being
> printed if debug-on-error is nil? I'd say that parsing error messages
> is brittle anyway, and we're not obliged to provide stable output

The behavior did change.  Since Emacs doesn't have a formal spec  its long-time 
behavior is a de-facto standard we should strive hard not to break.  As Stefan 
just pointed out, this change already broke 2 tests  if we need any proof.

> >  Is there a way to get back previous
> > behavior?  If so, please mention that in NEWS; if not, let's please
> > provide a way to get back the old behavior.
> 
> I'd be OK adding a variable for this, but on the other hand I'm not
> really convinced that this is really a breaking change (see above).

Yes, we do need to be able to get back the old bdhavior.