- when a trailing comma is specified in any bracket pair, that signals to Black
that this bracket pair needs to be always exploded, e.g. presented as "one
item per line";
- this causes some changes to previously formatted code that erroneously left
trailing commas embedded into single-line expressions;
- internally, Black needs to be able to identify trailing commas that it put
itself compared to pre-existing trailing commas. We do this by using/abusing
lib2to3's `was_checked` attribute. It's True for internally generated
trailing commas and False for pre-existing ones (in fact, for all
pre-existing leaves and nodes).
Fixes#1288
- Move black.py to src/black/__init__.py
- Have setuptools_scm make src/_black_version.py and exclude from git
- Move blackd.py to src/blackd/__init__.py
- Move blib2to3/ to src/
- Update `setup.py`
- Update unittests to pass
- Mostly path fixing + resolving
- Update CI
- pre-commit config
- appveyor + travis
Tested on my mac with python 3.7.5 via:
```
python3 -m venv /tmp/tb3
/tmp/tb3/bin/pip install --upgrade setuptools pip coverage pre-commit
/tmp/tb2/bin/pip install ~/repos/black/
cd ~/repos/black/
/tmp/tb2/bin/coverage run tests/test_black.py
/tmp/tb3/bin/pre-commit run -a
/tmp/tb3/bin/black --help
/tmp/tb3/bin/black ~/repos/ptr/ptr.py
```
