Nox

Claudio Jolowicz, Diego Ramirez, and Tom Fleet have become maintainers of Nox. We'd like to thank the following folks who contributed to this release:

- brettcannon
- cjolowicz
- dhermes
- DiddiLeija
- FollowTheProcess
- franekmagiera
- henryiii
- jugmac00
- maciej-lech
- nawatts
- Tolker-KU

New features:
- Add `mamba` backend (444, 448, 546, 551)
- Add `session.debug` to show debug-level messages (489)
- Add cookbook page to the documentation (483)
- Add support for the `FORCE_COLOR` environment variable (524, 548)
- Allow using `session.chdir()` as a context manager (543)
- Deprecate use of `session.install()` without a valid backend (537)

Improvements:
- Test against Python 3.10 (495, 502, 506)
- Add support for the `channel` option when using the `conda` backend (522)
- Show more specific error message when the `--keywords` expression contains a syntax error (493)
- Include reference to `session.notify()` in tutorial page (500)
- Document how `session.run()` fails and how to handle failures (533)
- Allow the list of sessions to be empty (523)

Bugfixes:
- Fix broken temporary directory when using `session.chdir()` (555, 556)
- Set the `CONDA_PREFIX` environment variable (538)
- Fix `bin` directory for the `conda` backend on Windows (535)

Internal changes:
- Replace deprecated `load_module` with `exec_module` (498)
- Include tests with source distributions (552)
- Add missing copyright notices (509)
- Use the new ReadTheDocs configurations (527)
- Bump the Python version used by ReadTheDocs to 3.8 (496)
- Improve the Sphinx config file (499)
- Update all linter versions (528)
- Add pre-commit and new checks (530, 539)
- Check `MANIFEST.in` during CI (552)
- Remove redundant `LICENSE` from `MANIFEST.in` (505)
- Make `setuptools` use the standard library's `distutils` to work around `virtualenv` bug. (547, 549)
- Use `shlex.join()` when logging a command (490)
- Use `shutil.rmtree()` over shelling out to `rm -rf` in noxfile (519)
- Fix missing Python 3.9 CI session (529)
- Unpin docs session and add `--error-on-missing-interpreter` to CI (532)
- Enable color output from Nox, pytest, and pre-commit during CI (542)
- Only run `conda_tests` session by default if user has conda installed (521)
- Update dependencies in `requirements-conda-test.txt` (536)

New features:
- Add `session.warn` to output warnings (482)
- Add a shared session cache directory (476)
- Add `session.invoked_from` (472)

Improvements:
- Conda logs now respect `nox.options.verbose` (466)
- Add `session.notify` example to docs (467)
- Add friendlier message if no `noxfile.py` is found (463)
- Show the `noxfile.py` docstring when using `nox -l` (459)
- Mention more projects that use Nox in the docs (460)

Internal changes:
- Move configs into pyproject.toml or setup.cfg (flake8) (484)
- Decouple `test_session_completer` from project level noxfile (480)
- Run Flynt to convert str.format to f-strings (464)
- Add python 3.10.0-rc2 to GitHub Actions (475, 479)
- Simplify CI build (461)
- Use PEP 517 build system, remove `setup.py`, use `setup.cfg` (456, 457, 458)
- Upgrade to mypy 0.902 (455)

Special thanks to our contributors:
- henryiii
- cjolowicz
- FollowTheProcess
- franekmagiera
- DiddiLeija

- Fix crash on Python 2 when reusing environments. (450)
- Hide staleness check behind a feature flag. (451)
- Group command-line options in `--help` message by function. (442)
- Avoid polluting tests with a .nox directory. (445)

- Add option `--no-install` to skip install commands in reused environments. (432)
- Add option `--force-python` as shorthand for `--python` and `--extra-python`. (427)
- Do not reuse environments if the interpreter or the environment type has changed. (418, 425, 428)
- Allow common variations in session names with parameters, such as double quotes instead of single quotes. Session names are considered equal if they produce the same Python AST. (417, 434)
- Preserve the order of parameters in session names. (401)
- Allow `nox.parametrize` to select the session Python. (413)
- Allow passing `posargs` when scheduling another session via `session.notify`. (397)
- Prevent sessions from modifying each other's posargs. (439)
- Add `nox.needs_version` to specify Nox version requirements. (388)
- Add `session.name` to get the session name. (386)
- Gracefully shutdown child processes. (393)
- Decode command output using the system locale if UTF-8 decoding fails. (380)
- Fix creation of Conda environments when `venv_params` is used. (420)
- Various improvements to Nox's type annotations. (376, 377, 378)
- Remove outdated notes on Windows compatibility from the documentation. (382)
- Increase Nox's test coverage on Windows. (300)
- Avoid mypy searching for configuration files in other directories. (402)
- Replace AppVeyor and Travis CI by GitHub Actions. (389, 390, 403)
- Allow colorlog <7.0.0. (431)
- Drop contexter from test requirements. (426)
- Upgrade linters to the latest version. (438)

- Fix `NoxColoredFormatter.format` (374)
- Use conda remove to clean up existing conda environments (373)
- Support users specifying an undeclared parametrization of python via `--extra-python` (361)
- Support double-digit minor version in `python` keyword (367)
- Add `py.typed` to `manifest.in` (360)
- Update Nox to latest supported python versions. (362)
- Decouple merging of `--python` with `nox.options` from `--sessions` and `--keywords` (359)
- Do not merge command-line options in place (357)

- `conda_install` and `install` args are now automatically double-quoted when needed. (312)
- Offline mode is now auto-detected by default by `conda_install`. This allows users to continue executing Nox sessions on already installed environments. (314)
- Fix the default paths for Conda on Windows where the `python.exe` found was not the correct one. (310)
- Add the `--add-timestamp` option (323)
- Add `Session.run_always()`. (331)