Black fails to find python files

Describe the bug Black, when run on a directory, fails to find python files contained in it.

To Reproduce Steps to reproduce the behavior: Directory structure:

tree src/cloudbuild 

src/cloudbuild
├── build
│   ├── build_args.py
│   ├── build_result.py
│   ├── build_tool.py
│   ├── config
│   │   ├── mypy_tool.ini
│   │   ├── pycodestyle_tool.ini
│   │   ├── pylint_tool.rc
│   │   ├── python_toolchain.yaml
│   │   └── test_coverage_tool.rc
│   ├── __init__.py
│   └── tool
│       ├── compile_tool.py
│       ├── docstr_coverage_tool.py
│       ├── __init__.py
│       ├── mypy_tool.py
│       ├── pycodestyle_tool.py
│       ├── pylint_tool.py
│       ├── python.py
│       ├── python_report_tool.py
│       └── unittest_tool.py
└── __init__.py

black src/cloudbuild/

All done! ✨ 🍰 ✨
1 file left unchanged.

black src/cloudbuild/build/tool/ 

No Python files are present to be formatted. Nothing to do 😴

black src/cloudbuild/build/tool/*

reformatted src/cloudbuild/build/tool/python.py
reformatted src/cloudbuild/build/tool/pycodestyle_tool.py
reformatted src/cloudbuild/build/tool/unittest_tool.py
reformatted src/cloudbuild/build/tool/mypy_tool.py
reformatted src/cloudbuild/build/tool/python_report_tool.py
reformatted src/cloudbuild/build/tool/pylint_tool.py
All done! ✨ 🍰 ✨

Expected behavior Running Black on a directory runs it on all python files within that directory and subdirectories.

Environment (please complete the following information):

• Version: both black-19.10b0 and master
• OS and Python version: Arch Linux, Python 3.7.2

Does this bug also happen on master? To answer this, you have two options: Yes

Additional context Add any other context about the problem here.

[lordmauve]

I think this is still a bug: the exclude pattern should not match path components that were given on the command line.

The example given above was

black src/cloudbuild/build/tool/ 

No Python files are present to be formatted. Nothing to do 😴

So the user has told it to act on a specifically specified directory. It has then evaluated that directory against the default --exclude patterns and concluded it has nothing to do.

IMHO when given a directory as a CLI argument, black should consider the paths of items in the directory relative to the directory given when applying the --exclude pattern.

[knatten]

Would you be willing to re-consider your default exclude patterns? We have several subfolders called build in our source code, and it caught me by surprise that these were excluded when I tried to format my source tree.