Subject: python-mode failing "overlapping strings" assertion lately

From: [email-masked]
Date: Tue, 27 Mar 2018 11:09:38 -0700

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.