Make sure setuptools is compatible with PEP 639

[DimitriPapadopoulos]

Instead rely on project.license in pyproject.toml.

Let's see if this fixes this CI error:

         /home/runner/work/xarray/xarray/asv_bench/.asv/env/155223cc45b660fb8d622bace3e087eb/lib/python3.11/site-packages/setuptools_scm/_integration/setuptools.py:92: UserWarning: version of None already set
           warnings.warn(f"version of {dist_name} already set")
         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:
             "Apache-2.0"
   
         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"
                         ]
                     }
                 ]
             }

• Closes #xxxx
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

[DocOtak]

I think this error is saying that the thing in project.license needs to be an object, either:

{"text": "Apache-2.0"}

or

{"file": "LICENSE"}

which is a link to the file itself

[benbovy]

xref: #10355 (comment)

more context: https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files

[DimitriPapadopoulos]

Right, requiring text = or file = means an old version of setuptools is being used. We need pypa/setuptools@fb161a2, which means seutptools ≥ 77.

However, if I understand you correctly, this is not compatible with Numpy 2.2:

xarray/asv_bench/asv.conf.json

Line 63 in 22bd964

"numpy": ["2.2"],

We'll probably have to partially revert #10300 and fall back to pre-PEP639 format. Wait, no, according to #10355 there's more to that.

I guess the real question is why I saw this issue surface recently in CI tests?

[benbovy]

I guess the real question is why I saw this issue surface recently in CI tests?

The error you mention above is from the asv benchmarks (only running CI after adding the corresponding label), for which Xarray is installed with --no-build-isolation. I tried to remove that flag in #10355 so a recent version of setutools can be picked without conflicting with numpy, but for some reason it didn't work.