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

[Philipp Stephani <p.stephani2@gmail.com>]

Am Mo., 7. Dez. 2020 um 11:42 Uhr schrieb Eli Zaretskii <eliz@gnu.org>:
>
> 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.

Fair enough, I've added a new boolean variable for this.