bug#24905: 25.1.50; Lock-up in python-mode

[Daniel Colascione <dancol@dancol.org>]

Fixed in master and emacs-25.

On Tue, Nov 08 2016, Daniel Colascione wrote:
> On Tue, Nov 08 2016, Daniel Colascione wrote:
>> On Tue, Nov 08 2016, Philipp Stephani wrote:
>>> echo ' "' > /tmp/a.py
>>> emacs -Q /tmp/a.py
>>>
>>> Emacs locks up immediately.
>>> Given that this is so easy to trigger, it should block the 25.2
>>> release.
>>
>> Can repro. Thanks for coming up with a small testcase.
>
> FWIW, the Lisp traceback is this:
>
> "syntax-ppss" (0xffff2978)
> "python-info-line-ends-backslash-p" (0xffff2e80)
> "python-nav-beginning-of-statement" (0xffff3388)
> "python-info-beginning-of-statement-p" (0xffff3840)
> "python-info-beginning-of-block-p" (0xffff3d38)
> "python-nav--forward-sexp" (0xffff43d8)
> "python-nav-forward-sexp" (0xffff4918)
> "python-nav-backward-sexp" (0xffff4e20)
> "python-info-docstring-p" (0xffff5378)
> "python-font-lock-syntactic-face-function" (0xffff5850)
> "font-lock-fontify-syntactically-region" (0xffff5e00)
> "font-lock-default-fontify-region" (0xffff6380)
> "font-lock-fontify-region" (0xffff6858)
> 0x1c27368 PVEC_COMPILED
> "run-hook-wrapped" (0xffff6f30)
> "jit-lock--run-functions" (0xffff74b0)
> "jit-lock-fontify-now" (0xffff7b08)
> "jit-lock-function" (0xffff80b8)
> "redisplay_internal (C function)" (0x0)
>
> We're actually finishing GC, by the way: this isn't a problem with
> the alloc.c guts, fortunately.  We're just generating tons of
> garbage. I've seen infloops in python.el's syntactic analysis
> before. This one looks worse than usual because it happens in redisplay.
>
> (Maybe redisplay should impose time limits on lisp that it runs?)