bug#30964: python-mode failing "overlapping strings" assertion lately

[Noam Postavsky]

dancol@dancol.org writes:

> Has something changed in master that might be breaking python-mode? We
> keep hitting a parsing assertion.
>
> The surrounding code in python.el claims that
>
>                        ;; The assertion can only fail if syntax table
>                        ;; text properties and the `syntax-ppss' cache
>                        ;; are somehow out of whack.  This has been
>                        ;; observed when using `syntax-ppss' during
>                        ;; narrowing.
>                        (cl-assert (> string-start last-string-end)
>                                   :show-args
>                                   "\
> Overlapping strings detected (start=%d, last-end=%d)")
>
> I can _sometimes_ repro with (while (not (eobp))
> (python-nav-forward-statement)), but I haven't found a reliable test case.

How recent is "lately"?  Could it be related to [1: 14b9558752]?

[1: 14b9558752]: 2017-12-12 23:03:00 -0500
  * src/syntax.c (find_defun_start): Use syntax-ppss
  
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=14b95587520959c5b54356547a0a69932a9bb480