regression with path traversals in 21.5b2

[pLeBlanc93]

Describe the bug

Traceback (most recent call last):
  File "C:\python\conda\envs\clone\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "C:\python\conda\envs\clone\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\python\conda\envs\clone\Scripts\black.exe\__main__.py", line 7, in <module>
  File "C:\python\conda\envs\clone\lib\site-packages\black\__init__.py", line 1130, in patched_main
    main()
  File "C:\python\conda\envs\clone\lib\site-packages\click\core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "C:\python\conda\envs\clone\lib\site-packages\click\core.py", line 782, in main
    rv = self.invoke(ctx)
  File "C:\python\conda\envs\clone\lib\site-packages\click\core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\python\conda\envs\clone\lib\site-packages\click\core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "C:\python\conda\envs\clone\lib\site-packages\click\decorators.py", line 21, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "C:\python\conda\envs\clone\lib\site-packages\black\__init__.py", line 421, in main
    stdin_filename=stdin_filename,
  File "C:\python\conda\envs\clone\lib\site-packages\black\__init__.py", line 518, in get_sources
    gitignore,
  File "C:\python\conda\envs\clone\lib\site-packages\black\files.py", line 223, in gen_python_files
    gitignore + get_gitignore(child) if gitignore is not None else None,
TypeError: unsupported operand type(s) for +: 'PathSpec' and 'PathSpec'

It looks like this was introduced with b8450b9#diff-1a5882c84fe4b3f18199a3e021822c1ea4bdc3f86952ea450c4db15d9387c7c3L215

To Reproduce

1. Create a local folder black_test that has a file foo.py and an empty folder bar
2. black C:/temp/black_test

Expected behavior
This works with black 21.5b1

Environment (please complete the following information):

• Version: 21.5b2
• OS and Python version: Windows/Python 3.7.10 x64

Does this bug also happen on main?

Haven't tested main yet, but it's also present on 21.7b0

Additional context

[ichard26]

Hey thanks for the bug report! This isn't actually a bug with Black itself, the problem lies in pathspec. I'm not entirely sure how you managed to get a pathspec that isn't 0.8.1 or higher since version 21.4b1 (containing this commit: a0b4e60) bumped Black's minimum pathspec requirement:

black/setup.py

Lines 75 to 77 in 1728bb4

	"regex>=2020.1.8",
	"pathspec>=0.8.1, <1",
	"dataclasses>=0.6; python_version < '3.7'",

Why 0.8.1 specifically? It's the version that added addition support to PathSpec objects (see cpburnz/python-pathspec#43).

---

The reason why version 21.5b1 works is because nested .gitignore support didn't exist back then so addition support wasn't required. 21.5b2 was the first version with such support.

[pLeBlanc93]

Ahh, that explains it. Thanks for quick response!

I also do not understand why pip install "black==21.7b0" did not upgrade pathspec. But confirmed that manually upgrading pathspec makes this issue non-repro. How interesting...

[bashtage]

Recent black requires pathspec>=0.9.0 (as indicated in setup.py) which was also not automatically installed for me when installing black.