Doesn't honor extend-exclude for nested file

[asarkar]

Describe the bug

Given the following configuration in pyproject.toml

[tool.black]
line-length = 120
extend-exclude = [
    '^(?:([^\/]+\/)+(?:test_.*\.py|.*_test\.py))$',
    '.github',
    '.mypy_cache',
    '.pytest_cache',
    'venv'
]

Black fails with the error:

Error: Invalid value for '--extend-exclude': Not a valid regular expression: unbalanced parenthesis at position 17

But this is a valid regex that's supposed to match any files starting or ending in test or files in a directory named test. For example, the following path matches the test directory:
myapp/folder/test/test_something.py

To Reproduce

I guess use the regex in a unit test that parses it?

Expected behavior

It should work. It would be even better if Black could use the extend-exclude list from flake8 or mypy, so that I don't have repeat it. The documentation only shows the max-line-length property.

Environment

• Black's version: 23.3.0
• OS: macOS Ventura 13.4.1, M1 chip
• Python version: (CPython) 3.11.3

[hauntsaninja]

The extend-exclude config is meant to be a str, not a list. The error message here could obviously be much better.

[asarkar]

@hauntsaninja Thanks, let me try that. Do you've any comment on the other thing I mentioned above?

It would be even better if Black could use the extend-exclude list from flake8 or mypy

[asarkar]

The extend-exclude config is meant to be a str

extend-exclude = """
/
^(?:(?:[^/]+/)+(?:test_.*\\.py|.*_test\\.py))$
| .github
/
"""

Nah, this doesn't work too. No error, but the file test_something.py gets formatted. Perhaps related to #3617?

[asarkar]

@hauntsaninja How does improving the error message fix the issue where the exclude doesn’t work at all?

[hauntsaninja]

You might want to be a little nicer to volunteers. Your regex is probably broken:

import re
exclude = """
/
^(?:(?:[^/]+/)+(?:test_.*\\.py|.*_test\\.py))$
| .github
/
"""
assert re.search(exclude, "something_test.py", flags=re.VERBOSE) is None
assert re.search(exclude, "/something_test.py", flags=re.VERBOSE) is None

Works fine for me:

λ cat pyproject.toml
[tool.black]
extend-exclude=".*_test.py"

λ cat something.py 
x = (
        'asdf'
        )

λ cat something_test.py 
x = (
        'asdf'
        )

λ black --check .
would reformat /Users/shantanu/dev/black/proj/something.py

Oh no! 💥 💔 💥
1 file would be reformatted.

[JelleZijlstra]

And on this one:

It would be even better if Black could use the extend-exclude list from flake8 or mypy

I don't think that's a good idea. People might exclude files from different tools for different reasons, and it is likely to be confusing if configuration for one tool magically affects another.