WIP: Set license and license-files key in project metadata to follow PEP639

[weiji14]

Description of proposed changes

Specify exact variant of license using SPDX format (BSD-3-Clause) in the pyproject.toml file, remove license classifier.

References:

• https://peps.python.org/pep-0639
• https://discuss.python.org/t/pep-639-round-3-improving-license-clarity-with-better-package-metadata/53020/128 (PyPI added support for PEP639 in mid-Nov 2024)
• Apply PEP 639 pytest-dev/pytest#13014

Fixes #

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[seisman]

The changes look good to me, but I'm unsure if we need to wait for upstream changes in setuptools (e.g., pypa/setuptools#3596).

[weiji14]

Hmm, you're right that license-key doesn't work. I ran make package on commit cddb3ee and got an error like this:

python -m build
* Creating isolated environment: venv+pip...
* Installing packages in isolated environment:
  - setuptools>=64
  - setuptools_scm[toml]>=6.2
* Getting build dependencies for sdist...
configuration error: `project.license` must be valid exactly by one definition (2 matches found):

    - keys:
        'file': {type: string}
      required: ['file']
    - keys:
        'text': {type: string}
      required: ['text']

DESCRIPTION:
    `Project license <https://peps.python.org/pep-0621/#license>`_.

GIVEN VALUE:
    "BSD-3-Clause"

OFFENDING RULE: 'oneOf'

DEFINITION:
    {
        "oneOf": [
            {
                "properties": {
                    "file": {
                        "type": "string",
                        "$$description": [
                            "Relative path to the file (UTF-8) which contains the license for the",
                            "project."
                        ]
                    }
                },
                "required": [
                    "file"
                ]
            },
            {
                "properties": {
                    "text": {
                        "type": "string",
                        "$$description": [
                            "The license of the project whose meaning is that of the",
                            "`License field from the core metadata",
                            "<https://packaging.python.org/specifications/core-metadata/#license>`_."
                        ]
                    }
                },
                "required": [
                    "text"
                ]
            }
        ]
    }
Traceback (most recent call last):
  File "/home/user/mambaforge/envs/pygmt/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 389, in <module>
    main()
  File "/home/user/mambaforge/envs/pygmt/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 373, in main
    json_out["return_val"] = hook(**hook_input["kwargs"])
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/mambaforge/envs/pygmt/lib/python3.12/site-packages/pyproject_hooks/_in_process/_in_process.py", line 317, in get_requires_for_build_sdist
    return hook(config_settings)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/build_meta.py", line 337, in get_requires_for_build_sdist
    return self._get_build_requires(config_settings, requirements=[])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/build_meta.py", line 304, in _get_build_requires
    self.run_setup()
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/build_meta.py", line 320, in run_setup
    exec(code, locals())
  File "<string>", line 1, in <module>
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/__init__.py", line 117, in setup
    return distutils.core.setup(**attrs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/_distutils/core.py", line 157, in setup
    dist.parse_config_files()
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/dist.py", line 648, in parse_config_files
    pyprojecttoml.apply_configuration(self, filename, ignore_option_errors)
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/config/pyprojecttoml.py", line 72, in apply_configuration
    config = read_configuration(filepath, True, ignore_option_errors, dist)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/config/pyprojecttoml.py", line 140, in read_configuration
    validate(subset, filepath)
  File "/tmp/build-env-97hptb3y/lib/python3.12/site-packages/setuptools/config/pyprojecttoml.py", line 61, in validate
    raise ValueError(f"{error}\n{summary}") from None
ValueError: invalid pyproject.toml config: `project.license`.
configuration error: `project.license` must be valid exactly by one definition (2 matches found):

    - keys:
        'file': {type: string}
      required: ['file']
    - keys:
        'text': {type: string}
      required: ['text']


ERROR Backend subprocess exited when trying to invoke get_requires_for_build_sdist
make: *** [Makefile:29: package] Error 1

I changed it to just license = {text = "BSD-3-Clause"} following https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html#configuring-setuptools-using-pyproject-toml-files, and it seemed to work now, though unsure if this conforms to PEP639? We should monitor the Test PyPI build after merging this PR to see if it works on CI too.

[seisman]

https://peps.python.org/pep-0639/#deprecate-license-key-table-subkeys

If I understand it correctly, this syntax will be deprecated.

[weiji14]

Ah ok, I'll revert the change then and mark this PR as draft until setuptools supports PEP639 properly.