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

From: Philipp Stephani <[email-masked]>
Date: Sat, 2 Jun 2018 21:03:10 +0200

Noam Postavsky <[email-masked]> schrieb am Mi., 30. Mai 2018 um
02:29 Uhr:

> Clément Pit-Claudel <[email-masked]> writes:
>
> > Here's a reliable repro:
> >
> > def f():
> >     "
> >
> > def g():
> >     """That's a docstring"""
> >     return ''
>
> It can be reduced a bit:
>
>
> Debugger entered--Lisp error: (cl-assertion-failed ((> string-start
> last-string-end) "Overlapping strings detected" 13 13))
>   cl--assertion-failed((> string-start last-string-end) "Overlapping
> strings detected" (13 13) nil)
>   python-nav-end-of-statement()
>   python-info-end-of-statement-p()
>   python-info-end-of-block-p()
>   python-nav--forward-sexp(-1 nil nil)
>   python-nav-forward-sexp(-1 nil nil)
>   python-nav-backward-sexp()
>   python-info-docstring-p((0 nil nil t nil nil 0 nil 1 nil nil))
>   python-font-lock-syntactic-face-function((0 nil nil t nil nil 0 nil 1
> nil nil))
>   font-lock-fontify-syntactically-region(1 15 nil)
>   font-lock-default-fontify-region(1 15 nil)
>   font-lock-fontify-region(1 15)
>   font-lock-fontify-block(nil)
>   funcall-interactively(font-lock-fontify-block nil)
>   call-interactively(font-lock-fontify-block nil nil)
>   command-execute(font-lock-fontify-block)
>
> I think the problem is that the assertion is off by 1, it currently
> asserts that there is at least one space between strings (because the
> end position goes *after* the string, while the start position is part
> of the string).
>
> I see the assertion was added in [1: 4fbd330fae].  Phillip, does my
> proposed change make sense to you?

Maybe :-)
Off-by-one errors are always a bit subtle, so it might definitely be the
case that there is one. If so, the problem could be further reduced to
' '' '
or similar. Could you add a unit test using such input and make sure that
it breaks without your patch?

>   ('make -C test python-tests' still
> passes.)
>
> --- i/lisp/progmodes/python.el
> +++ w/lisp/progmodes/python.el
> @@ -1506,7 +1506,7 @@ python-nav-end-of-statement
>                         ;; are somehow out of whack.  This has been
>                         ;; observed when using `syntax-ppss' during
>                         ;; narrowing.
> -                       (cl-assert (> string-start last-string-end)
> +                       (cl-assert (>= string-start last-string-end)
>                                    :show-args
>                                    "Overlapping strings detected")
>                         (goto-char string-start)
>
> [1: 4fbd330fae]: 2017-03-23 23:05:19 +0100
>   Protect against an infloop in python-mode
>
> https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=4fbd330fae54a9c45d4a717127aa86d75e9938d5
>
>