Fix #58

[younesaassila]

Fix #58 thanks to ChatGPT

Prompt

You are a Python expert. Your task is to detect the catastrophic backtracking error in a regex for a C formatter program.
If you cannot find the catastrophic backtracking error, it's okay to say so.
Here are our regex helpers:

# regex for a type
REGEX_TYPE = r"(?!return|goto)([a-z]+\s+)*[a-zA-Z_]\w*"
# regex for a c variable/function name
REGEX_NAME = r"\**[a-zA-Z_*()]\w*"
# regex for a name in a declaration context (with array and function ptr)
REGEX_DECL_NAME = r"\(?{name}(\[.*\])*(\)\(.*\))?".format(name=REGEX_NAME)

And here is the regex with the catastrophic backtracking error:

r"^(static\s+)?{type}\s+{name}\((.|\s)*?\);"

---

The regex you've provided indeed contains a potential catastrophic backtracking issue. The problematic part is the (.\|\s)*? section within the regex. This part can lead to catastrophic backtracking when trying to match certain inputs, especially if the input contains a long sequence of characters followed by a semicolon.

Here's why it's problematic:

• (.\|\s)*? attempts to match any character or whitespace zero or more times in a non-greedy manner. The problem is that when the regex engine encounters a character that doesn't match, it will backtrack and try different ways of matching characters and whitespace until it either succeeds or exhausts all possibilities. This can lead to an exponential number of possible paths that the engine explores, causing significant slowdown or even freezing on certain inputs.

To avoid this issue, you can use a more specific pattern to match the content within the parentheses in a safer way. Here's a modified version of the regex that should help avoid catastrophic backtracking:

r"^(static\s+)?{type}\s+{name}\([^)]*?\);"

In this modified regex, [^)]*? is used to match any sequence of characters except a closing parenthesis. This pattern ensures that the regex engine won't get stuck in catastrophic backtracking scenarios.

[younesaassila]

Do note that this only fixes the hanging. c_formatter_42 will still insert void in the comments when it sees something like bzero() (in the issue author input)

[cacharle]

Can you add a test with pytest-timeout?

@pytest.mark.timeout(60)
def test_foo():
    pass

[younesaassila]

@cacharle For the whole run_all procedure or just for line_break?

[cacharle]

Just for the example we know was infinite before your fix for now (so only line_break)

But I see you can set a global timeout in the setup.cfg file like so:

[pytest]
timeout = 20

https://pypi.org/project/pytest-timeout/

[younesaassila]

@cacharle Been trying to make it work for the last 30 minutes but it seems that pytest-timeout suffers from an issue with (at least) Python 3.10: pytest-dev/pytest-timeout#113
The timeout function just doesn't work as it is supposed to

[cacharle]

Works fine for me with python3.10

c_formatter_42 ❯ pytest tests/test_run.py -k foo
========================================================== test session starts ==========================================================
platform darwin -- Python 3.10.8, pytest-7.4.0, pluggy-1.3.0
rootdir: ~/git/c_formatter_42
configfile: setup.cfg
plugins: timeout-2.1.0, cov-4.1.0, clarity-1.0.1
collected 5 items / 4 deselected / 1 selected

tests/test_run.py F                                                                                                               [100%]

=============================================================== FAILURES ================================================================
_______________________________________________________________ test_foo ________________________________________________________________

    @pytest.mark.timeout(2)
    def test_foo():
>       time.sleep(10000)
E       Failed: Timeout >2.0s

tests/test_run.py:23: Failed

---------- coverage: platform darwin, python 3.10.8-final-0 ----------
Name                                                  Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------------------
c_formatter_42/__init__.py                                0      0   100%
c_formatter_42/__main__.py                               26     26     0%   15-63
c_formatter_42/data/__init__.py                           0      0   100%
c_formatter_42/formatters/__init__.py                     0      0   100%
c_formatter_42/formatters/align.py                       51     41    20%   32-96, 102, 107-109
c_formatter_42/formatters/clang_format.py                28     18    36%   31-45, 65-75
c_formatter_42/formatters/helper.py                      14      7    50%   27-34
c_formatter_42/formatters/hoist.py                       20     16    20%   45-80
c_formatter_42/formatters/line_breaker.py                49     42    14%   7-9, 13-36, 59-72, 76-77, 82-90
c_formatter_42/formatters/misc.py                         9      4    56%   17, 26, 34, 42
c_formatter_42/formatters/preprocessor_directive.py      23     21     9%   17-45
c_formatter_42/formatters/return_type_single_tab.py      12      9    25%   20-35
c_formatter_42/run.py                                    19     11    42%   29-39
-----------------------------------------------------------------------------------
TOTAL                                                   251    195    22%

======================================================== short test summary info ========================================================
FAILED tests/test_run.py::test_foo - Failed: Timeout >2.0s
==================================================== 1 failed, 4 deselected in 2.25s ====================================================

$ python --version
Python 3.10.8

$ pip list | grep time
pytest-timeout        2.1.0

with the following code:

import time


@pytest.mark.timeout(2)
def test_foo():
    time.sleep(10000)

[younesaassila]

@cacharle Alright well perhaps it's a Windows problem then. I'll push the test

[cacharle]

WSL 👀👀👀👀👀

[younesaassila]

WSL 👀👀👀👀👀

Yeah I use WSL for 42 projects, I'm just too lazy to setup all my Python env on there lol