bug#21629: 25.0.50; python.el freezes up around docstrings.

bug#21629: 25.0.50; python.el freezes up around docstrings.

[Jacob MacDonald]

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Begin from a fresh 'emacs -Q'. Create a Python file. Insert a long
docstring which contains a header line and then a long body which
includes a few line breaks and spaces in it. The docstring should look
something like this:

"""test header

lorem ipsum... more text more text more text
x10 lines
...
...
"""

Save the file and close emacs. Start a fresh 'emacs -Q'. Open dired in
the directory which contains the Python file you created. Navigate to
the file and try to open in from dired. Emacs will freeze indefinitely
and eat all the system resources it can. You can break the cycle by
pressing C-q many times, but the freeze happens again on every single
redisplay. If you wait awhile before cancelling the redisplay, you may
see that fontification has frozen somewhere in the middle of the docstring.


In GNU Emacs 25.0.50.2 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.7)
 of 2015-10-05
Repository revision: 25b4572073179c8d6dc980ce2df3db4d96cd692f
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
System Description: Ubuntu Wily Werewolf (development branch)

Configured using:
 'configure --prefix=/home/jaccarmac/local/emacs'

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY LIBXML2 FREETYPE XFT
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Python

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Error during redisplay: (jit-lock-function 201) signaled (quit)
Error during redisplay: (jit-lock-function 301) signaled (quit)
Error during redisplay: (jit-lock-function 1) signaled (quit)
Error during redisplay: (jit-lock-function 101) signaled (quit)
Error during redisplay: (jit-lock-function 201) signaled (quit)
Error during redisplay: (jit-lock-function 301) signaled (quit)
QuitError during redisplay: (jit-lock-function 1) signaled (quit)
Error during redisplay: (jit-lock-function 101) signaled (quit)
Error during redisplay: (jit-lock-function 201) signaled (quit)
Error during redisplay: (jit-lock-function 301) signaled (quit)
Quit [2 times]

Load-path shadows:
None found.

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bug#21629: 25.0.50; python.el freezes up around docstrings.

[Eli Zaretskii]

> From: Jacob MacDonald <jaccarmac@gmail.com>
> Date: Tue, 06 Oct 2015 04:48:50 +0000
> 
> Begin from a fresh 'emacs -Q'. Create a Python file. Insert a long
> docstring which contains a header line and then a long body which
> includes a few line breaks and spaces in it. The docstring should look
> something like this:
> 
> """test header
> 
> lorem ipsum... more text more text more text
> x10 lines
> ...
> ...
> """
> 
> Save the file and close emacs. Start a fresh 'emacs -Q'. Open dired in
> the directory which contains the Python file you created. Navigate to
> the file and try to open in from dired. Emacs will freeze indefinitely
> and eat all the system resources it can. You can break the cycle by
> pressing C-q many times, but the freeze happens again on every single
> redisplay. If you wait awhile before cancelling the redisplay, you may
> see that fontification has frozen somewhere in the middle of the docstring.

It infloops in python-nav-end-of-statement.  The loop there ends up
one position before EOB, then jumps back to string-start, and so on
and so forth, ad nauseam.

I have no idea what causes this, but I hope Python-mode experts and
perhaps Stefan (due to syntax stuff) will be able to figure this out.

bug#21629: 25.0.50; python.el freezes up around docstrings.

[Andreas Röhler]

Am 06.10.2015 um 16:54 schrieb Eli Zaretskii:
>> From: Jacob MacDonald <jaccarmac@gmail.com>
>> Date: Tue, 06 Oct 2015 04:48:50 +0000
>>
>> Begin from a fresh 'emacs -Q'. Create a Python file. Insert a long
>> docstring which contains a header line and then a long body which
>> includes a few line breaks and spaces in it. The docstring should look
>> something like this:
>>
>> """test header
>>
>> lorem ipsum... more text more text more text
>> x10 lines
>> ...
>> ...
>> """
>>
>> Save the file and close emacs. Start a fresh 'emacs -Q'. Open dired in
>> the directory which contains the Python file you created. Navigate to
>> the file and try to open in from dired. Emacs will freeze indefinitely
>> and eat all the system resources it can. You can break the cycle by
>> pressing C-q many times, but the freeze happens again on every single
>> redisplay. If you wait awhile before cancelling the redisplay, you may
>> see that fontification has frozen somewhere in the middle of the docstring.
> It infloops in python-nav-end-of-statement.  The loop there ends up
> one position before EOB, then jumps back to string-start, and so on
> and so forth, ad nauseam.
>
> I have no idea what causes this, but I hope Python-mode experts and
> perhaps Stefan (due to syntax stuff) will be able to figure this out.
>
>
>
>

With a while-loop reading complex conditions IMO there is always an 
abstract danger.

python-mode.el uses a heuristic exit:

`py-max-specpdl-size' - default is `max-specpdl-size'

bug#21629: 25.0.50; python.el freezes up around docstrings.

[Luke Powers]

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fwiw, I went through the tree with bisect and found
3928ef2dd5b8febf3b1d9c1bfb22af3698d16bea
<https://github.com/emacs-mirror/emacs/commit/3928ef2dd5b8febf3b1d9c1bfb22af3698d16bea>
to be the first commit where the issue pops up.

On Thu, Oct 8, 2015 at 7:27 AM, Andreas Röhler <
andreas.roehler@easy-emacs.de> wrote:

>
> Am 06.10.2015 um 16:54 schrieb Eli Zaretskii:
>
>> From: Jacob MacDonald <jaccarmac@gmail.com>
>>> Date: Tue, 06 Oct 2015 04:48:50 +0000
>>>
>>> Begin from a fresh 'emacs -Q'. Create a Python file. Insert a long
>>> docstring which contains a header line and then a long body which
>>> includes a few line breaks and spaces in it. The docstring should look
>>> something like this:
>>>
>>> """test header
>>>
>>> lorem ipsum... more text more text more text
>>> x10 lines
>>> ...
>>> ...
>>> """
>>>
>>> Save the file and close emacs. Start a fresh 'emacs -Q'. Open dired in
>>> the directory which contains the Python file you created. Navigate to
>>> the file and try to open in from dired. Emacs will freeze indefinitely
>>> and eat all the system resources it can. You can break the cycle by
>>> pressing C-q many times, but the freeze happens again on every single
>>> redisplay. If you wait awhile before cancelling the redisplay, you may
>>> see that fontification has frozen somewhere in the middle of the
>>> docstring.
>>>
>> It infloops in python-nav-end-of-statement.  The loop there ends up
>> one position before EOB, then jumps back to string-start, and so on
>> and so forth, ad nauseam.
>>
>> I have no idea what causes this, but I hope Python-mode experts and
>> perhaps Stefan (due to syntax stuff) will be able to figure this out.
>>
>>
>>
>>
>>
> With a while-loop reading complex conditions IMO there is always an
> abstract danger.
>
> python-mode.el uses a heuristic exit:
>
> `py-max-specpdl-size' - default is `max-specpdl-size'
>
>
>
>

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