tests: use toml for tox

[henryiii]

I am trying the (fairly) new native TOML support for tox here. I've not used it before, and got some help from the Tox discord (thanks to @gaborbernat!). Currently, you pretty much have to have 4.22+ to use it; tox-dev/tox#3402 would allow a workaround for (somewhat) older tox's.

Thoughts?

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📚 Documentation preview 📚: https://dependency-groups--17.org.readthedocs.build/en/17/

[henryiii]

Oh, by the way, either seems to work, was testing. The config will show the full section name, tool.tox.env.mypy.

[sirosen]

I want to get a chance to play with this before approving/merging, which realistically means a couple of weeks wait time as I'm not really available right now. I hope that's okay.
I don't think we'd need any special compatibility (like a stub .ini file) for older tox versions. They'd simply be unsupported by the project, and I think that's fine.

Having worked through the conversion, do you see major benefits to the new TOML syntax other than having everything embedded in the pyproject file? i.e. If this were a conversion to tox.toml, what would the benefits of the new format be?

I ask because I've seen the new TOML support in tox docs and have been wondering about why I should (or shouldn't) convert. It looks like it's easier from the maintainer side, but ini support isn't going away (at least not soon?), so I'm not clear on the user benefits.
It does look like there are some environment inheritance options, and I guess we could parse and lint or even generate content with tomlkit? But those seem a little niche, so I'm wondering if I've missed some key improvements.

[henryiii]

No rush at all, or even expectation that it is merged, I mostly wanted to learn the new TOML configuration.

I'm personally fond of fewer top-level files, since they push the readme down on the page and make the repo appear more complex. It's also rather similar to uv and hatch, which can be configured in pyproject.toml too. But tox is a pretty good candidate for a top level file, so tox.toml is fine too, I think it's still a small improvement.

The main features so far are:

• TOML is better than not-really-a-format .cfg/ini, things like lists are actually part of the language. Also, this is the last bit of ini/cfg left.
• Less terse. A bit longer, but easier for a newcomer to read (I think), less magic.
• Can be validated - I'm working on setting up a Schema for validate-pyproject and check-jsonschema (feat: adding a json schema command tox-dev/tox#3446)

(Personally, I'm still a fan of nox, and only use tox on a few projects - mostly ones that also have a tox maintainer too. ;) )