bug#32012: 27.0.50; jit-lock--run-functions broken

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 32012@debbugs.gnu.org
> From: Andreas Röhler <andreas.roehler@online.de>
> Date: Sat, 30 Jun 2018 13:19:40 +0200
> 
> >> Hmm, by looking at its signature
> >>
> >> (defun jit-lock-fontify-now (&optional start end)
> >>
> >> Why that shouldn't work?
> > 
> > That's not what the backtrace suggests.  It suggests that you invoked
> > jit-lock--run-functions via eval-last-sexp.
> 
> Right. But the arguments are optional.
> Wherefrom to expect it failing?

A function that has optional argument doesn't necessarily support
invocation without arguments in any arbitrary context.  It could
support that just in some specific cases.  You can clearly see in the
function that when Start and END are nil, the function sets them to
some values, but those values might not make sense in some arbitrary
invocation context.

Anyway, this discussion would have been much less theoretical if you
would to show what exactly did you do in ert tests that caused the
problem.