Decide on moving to pyproject.toml for build and tool configuration

[John-Sharples]

Context

PEP-517 and PEP-518 recommend a new standardised way to specify build requirements and dependencies, giving the option to remove existing setup.py files. While having a setup.py is still perfectly fine, pip now only supports it as legacy, preferring the use of pyproject.toml file.

As an added bonus, most tools (e.g. pytest, coverage) can also use pyproject.toml for configuration. Project metadata can also be stored in pyproject.toml. This gives a single place for build info, metadata, and all tool configuration.

METplus already has a pyproject.toml , However, it has the bare minimum content and could be expanded further.

Decision

Should METplus and the Analysis Tools should move to using pyproject.toml?

Pros:

• Keeps repos up to date with recommended build practices
• Prepare for possible future deprecation of setup.py
• May be able to remove existing requirements.txt and setup.py files
• simplify management of python tools, preventing proliferation of config files like .coveragerc and pytest.ini
• An incremental approach can be taken, e.g. move build info first, and tool configuration is a later merge.

Cons:

• This is a "nice to have" since setup.py is going to be fine for the foreseeable future. Would need to be prioritised against other project work.
• Docs will have to be carefully reviewed for each repo to ensure install information is up to date. Assuming everything is recommending pip there my be few changes.
• very old versions of pip (I think prior to v19) will fail to install without setup.py, noting that this is older than any version likely to be used for METplus Analysis Tools

Links for more info

https://packaging.python.org/en/latest/guides/writing-pyproject-toml/
https://packaging.python.org/en/latest/discussions/setup-py-deprecated/
https://docs.pytest.org/en/6.2.x/customize.html?highlight=pyproject%20toml#pyproject-toml
https://coverage.readthedocs.io/en/latest/config.html