Thanks for pointing me to this, I am new to using pyproject.toml (which is where it looks like much of this metadata comes from).

I'm reading this page (https://packaging.python.org/en/latest/specifications/declaring-project-metadata/) for guidance, and it seems that many of these fields should be defined, based on content in pyproject.toml. I'm reluctant to add undocumented fields, given that uploading to pypi is essentially a you-only-get-one-shot-to-upload-your-version-so-get-it-right-on-the-first-try interface.

I see that there are some classifiers that need to be added, which I have done and committed to the master branch. But if there are additional fields that you can provide in a tested PR, they would be welcome.

According to what I see in the pyproject.toml it should work. In our own project we forgo the [project]-section completely and specify everything in the [tools.poetry] section which produces the desired JSON. I see two possible reasons here:

1. We are missing something obvious
2. Something is off with the release procedure for pypi (Something configured wrong? Missed steps? Innocent Typo?)

I'm reluctant to add undocumented fields, given that uploading to pypi is essentially a you-only-get-one-shot-to-upload-your-version-so-get-it-right-on-the-first-try interface.

Maybe test.pypi.org can help?

It's not perfect (for example, you also can't delete releases), but at least a wrong release does not pollute the (main) pypi index. I sometimes use it to test-deploy RCs exactly when I have concerns about metadata etc.

I don't think pyparsing is doing anything wrong.

If you look at the metadata for Flit's own releases (e.g. https://pypi.org/pypi/flit/3.10.1/json), they look much the same.

Part of the issue seems to be that setting license metadata was poorly-specified until Metadata 2.4, which deprecates both the License :: classifiers and the License metadata field in favor of two new fields, License-Expression and License-File.

The newly-deprecated License field explicitly deferred to the classifiers; from the spec:

Text indicating the license covering the distribution where the license is not a selection from the “License” Trove classifiers.

It appears that, in metadata 2.3 (the version Flit generates) and lower, the license is supposed to be taken from the License :: classifier when present. (pyparsing includes a License :: OSI Approved :: MIT License classifier).

Flit doesn't yet support Metadata 2.4 (probably soon), when it does it will be able to add License-File to the wheel metadata, or (if it's specified in the pyproject.toml — though TBH I'm still not sure how) an SPDX License-Expression.

(Edit: In the absence of Metadata 2.4 License-File, turns out the only thing license = {file = "LICENSE"} does in a pyproject.toml is cause the file to be copied into the .dist-info directory for the wheel.)