143 lines
4.9 KiB
Markdown
143 lines
4.9 KiB
Markdown
# The basics
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An overview on contributing to the _Black_ project.
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## Technicalities
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Development on the latest version of Python is preferred. You can use any operating
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system.
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Install development dependencies inside a virtual environment of your choice, for
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example:
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```console
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$ python3 -m venv .venv
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$ source .venv/bin/activate # activation for linux and mac
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$ .venv\Scripts\activate # activation for windows
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(.venv)$ pip install -r test_requirements.txt
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(.venv)$ pip install -e .[d]
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(.venv)$ pre-commit install
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```
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Before submitting pull requests, run lints and tests with the following commands from
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the root of the black repo:
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```console
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# Linting
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(.venv)$ pre-commit run -a
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# Unit tests
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(.venv)$ tox -e py
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# Optional Fuzz testing
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(.venv)$ tox -e fuzz
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# Format Black itself
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(.venv)$ tox -e run_self
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```
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### Development
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Further examples of invoking the tests
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```console
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# Run all of the above mentioned, in parallel
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(.venv)$ tox --parallel=auto
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# Run tests on a specific python version
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(.venv)$ tox -e py39
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# pass arguments to pytest
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(.venv)$ tox -e py -- --no-cov
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# print full tree diff, see documentation below
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(.venv)$ tox -e py -- --print-full-tree
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# disable diff printing, see documentation below
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(.venv)$ tox -e py -- --print-tree-diff=False
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```
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### Testing
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All aspects of the _Black_ style should be tested. Normally, tests should be created as
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files in the `tests/data/cases` directory. These files consist of up to three parts:
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- A line that starts with `# flags: ` followed by a set of command-line options. For
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example, if the line is `# flags: --preview --skip-magic-trailing-comma`, the test
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case will be run with preview mode on and the magic trailing comma off. The options
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accepted are mostly a subset of those of _Black_ itself, except for the
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`--minimum-version=` flag, which should be used when testing a grammar feature that
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works only in newer versions of Python. This flag ensures that we don't try to
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validate the AST on older versions and tests that we autodetect the Python version
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correctly when the feature is used. For the exact flags accepted, see the function
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`get_flags_parser` in `tests/util.py`. If this line is omitted, the default options
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are used.
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- A block of Python code used as input for the formatter.
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- The line `# output`, followed by the output of _Black_ when run on the previous block.
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If this is omitted, the test asserts that _Black_ will leave the input code unchanged.
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_Black_ has two pytest command-line options affecting test files in `tests/data/` that
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are split into an input part, and an output part, separated by a line with`# output`.
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These can be passed to `pytest` through `tox`, or directly into pytest if not using
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`tox`.
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#### `--print-full-tree`
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Upon a failing test, print the full concrete syntax tree (CST) as it is after processing
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the input ("actual"), and the tree that's yielded after parsing the output ("expected").
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Note that a test can fail with different output with the same CST. This used to be the
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default, but now defaults to `False`.
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#### `--print-tree-diff`
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Upon a failing test, print the diff of the trees as described above. This is the
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default. To turn it off pass `--print-tree-diff=False`.
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### News / Changelog Requirement
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`Black` has CI that will check for an entry corresponding to your PR in `CHANGES.md`. If
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you feel this PR does not require a changelog entry please state that in a comment and a
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maintainer can add a `skip news` label to make the CI pass. Otherwise, please ensure you
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have a line in the following format:
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```md
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- `Black` is now more awesome (#X)
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```
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Note that X should be your PR number, not issue number! To workout X, please use
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[Next PR Number](https://ichard26.github.io/next-pr-number/?owner=psf&name=black). This
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is not perfect but saves a lot of release overhead as now the releaser does not need to
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go back and workout what to add to the `CHANGES.md` for each release.
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### Style Changes
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If a change would affect the advertised code style, please modify the documentation (The
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_Black_ code style) to reflect that change. Patches that fix unintended bugs in
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formatting don't need to be mentioned separately though. If the change is implemented
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with the `--preview` flag, please include the change in the future style document
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instead and write the changelog entry under a dedicated "Preview changes" heading.
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### Docs Testing
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If you make changes to docs, you can test they still build locally too.
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```console
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(.venv)$ pip install -r docs/requirements.txt
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(.venv)$ pip install -e .[d]
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(.venv)$ sphinx-build -a -b html -W docs/ docs/_build/
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```
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## Hygiene
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If you're fixing a bug, add a test. Run it first to confirm it fails, then fix the bug,
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run it again to confirm it's really fixed.
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If adding a new feature, add a test. In fact, always add a test. But wait, before adding
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any large feature, first open an issue for us to discuss the idea first.
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## Finally
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Thanks again for your interest in improving the project! You're taking action when most
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people decide to sit and watch.
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