Eventually deprecate setup.cfg, setup.py and move to pyproject.toml

[cdboer]

Is your feature request related to a problem? Please describe.
I'm always frustrated when preparing a new release, as i have to edit the project metadata in three different files.
For example, for minor version bumps or patches i have to edit:

• the gitlab2prov.__version__ module attribute contained in gitlab2prov/__init__.py
• the version number contained in the CITATION.cff
• the version number contained in the setup.cfg

Considering the DRY principle, this seems far from ideal.

I would like to reduce the number of files that hold the same information. Ideally i'd only want to edit a single file when preparing a release. Considering the tooling behind CITATION.cff doesn't allow to source metadata dynamically, a single file won't be achievable, though we can reduce the amount of files with duplicate information.

Describe the solution you'd like
In PEP 621 the python community chose to store project metadata in the pyproject.toml file. Our current build backend setuptools supports PEP 621 and is able to source the build metadata from it.

Proposal

• abandon/remove setup.py and setup.cfg
• store all project metadata in pyproject.toml, CITATION.cff
• let gitlab2prov.__version__ be the single ground truth for the package version number (Not achievable yet, CITATION.cff has to be edited aswell)

pyproject.toml supports dynamic metadata such as reading the version number from a module attribute, which allows us to read the package version from gitlab2prov.__version__. gitlab2prov.__version__ has to hold the version number, since the cli option --version has to correctly display the current version number and we can't read the version number from metadata files outside of the package scope.

This would leave us with two files that we have to edit for each release:

• CITATION.cff, since it does not allow us to source metadata dynamically
• gitlab2prov/__init__.py, to edit the module attribute gitlab2prov.__version__

One file less than before and hopefully the future allows us to reduce the amount of duplicated metadata even further, see citation-file-format/citation-file-format#374 (comment).

Additional context

• PEP 621
• Setuptools guide on PEP 621 compliance
• Python packaging user guide
• Single-sourcing the package-version

[cdboer]

We will have to change the current publishing workflow to reflect the removal of setup.py. See here for a publishing workflow using only pip.

[cdboer]

We also have to require setuptools 61.0.0 or higher. As it is the first version with PEP 621 support.

[cdboer]

Instead of installing requirements/dev-requirements using

pip install -r requirements.txt
pip install -r requirementst-dev.txt

users could install requirments using

pip install .
pip install .[dev]