bug#33414: 27.0.50; inhibit-changing-match-data can be t in syntax-propertize functions, breaking backtrace and looking-at

[Pip Cet]

On Sat, Nov 17, 2018 at 1:47 PM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Sat, 17 Nov 2018 13:30:04 +0000
> >
> > This was a bit tricky to debug because (backtrace) doesn't work when
> > inhibit-changing-match-data is t.  (In emacs -Q, enter
> >
> > (let ((inhibit-changing-match-data t)) (backtrace))
> >
> > into the *scratch* buffer and evaluate with C-M-x.)
>
> This works on the release branch, so I think it's a regression that
> needs to be fixed.

If I'm testing correctly,

(let ((inhibit-changing-match-data t)) (debug))

fails on both branches, which is also bad; I think that means the
issue is present in some form on both branches.

Maybe `save-match-data' should save/restore
`inhibit-changing-match-data' along with the actual match data?