bug#51037: [PATCH] Make `print-level` & `print-length` customizable in ERT batch tests

[Michael]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Michael <sp1ff@runbox.com> writes:
>
> > The issue: stack traces are printed by the `backtrace`
> > package. backtrace.el was authored by Gemini (which is why I've
> > added him to this thread). backtrace.el doesn't directly work 
> > in
> > terms of `print-le{ngth,vel}`: it defines a custom variable
> > `backtrace-line-length` and then adjusts print-level &
> > print-length in let bindings in order to:
> >
> >  1. try to respect the desired line length
> >  2. not trigger bug 31919 (Lisp Debugger doesn't work when at
> >  stack limit)
>
> [...]
>
> > For myself, I was quite surprised to all learn this: I had to
> > spend a fair bit of time digging through the source to find out
> > what was happening to my settings for print-length &
> > print-level.
>
> Yeah, I didn't remember `backtrace-line-length' either.  Perhaps 
> it
> should be linked to from the doc strings of print-length and
> print-level... 

I was thinking to augment the docstring for
`backtrace-line-lenght' to note that print-level & print-length
will be overiden to honor it.

> > My personal incliniation is to remove the 
> > `backtrace-line-length`
> > variable entirely, and make the `debug` package responsible for
> > controlling print-level so as to avoid 31919. But that's me: is
> > there a compelling use-case for backtrace.el working in terms 
> > of
> > limiting line length rather than just using 
> > `print-le{ve,ength}`?
>
> Well...  if we're talking in an ert context, it could increase 
> both the
> backtrace-line-length and max-lisp-eval-depth variables when 
> gathering
> the backtrace, I think?

The problem is that I can't know a priori how big I have to set
them in order to honor print-level & print-length. I think I can
short-circuit this entirely by setting `backtrace-line-length' to
nil or zero before printing the backtrace from ert. eval-level
shouldn't enter into it I think; the concern was that if code
exceeded max-lisp-eval-depth, and the debugger was triggered,
*then* backtrace.el might have problems. Do you see a reason to
be concerned outside of that corner case?

--
Michael <sp1ff@runbox.com>