Add discussion about zoneinfo package to wasm-constraints.md

[hoodmane]

📚 Documentation

By default, zoneinfo is missing all the timezones. It's necessary to install the tzdata package to get them. I think we should:

1. mention this in wasm-constraints docs
2. add tzdata package recipe (I thought we already had one but it doesn't seem so)
3. maybe make tzinfo warn instructing the user to install tzdata if it's used without installing tzdata

[joemarshall]

yes to this. Needed for pyarrow also, so I don't mind doing it while I'm on that. It's a pure python package, so the recipe should be trivial.

[joemarshall]

I've put in a PR for this. If you build with zoneinfo in the package list, it at least means that importing zoneinfo will give the pyodide 'can't import package tzdata' message I think, as zoneinfo tries to load tzdata. It would be possible to include tzdata in the main pyodide distribution, but it is a 300kb wheel, so I'm guessing that's too much extra?

[hoodmane]

Yeah I don't think we want to add 300kb. People can install tzdata if they need it. Ideally we ought to put a custom warning if they import zoneinfo without loading tzdata though.

[joemarshall]

Yeah I don't think we want to add 300kb. People can install tzdata if they need it. Ideally we ought to put a custom warning if they import zoneinfo without loading tzdata though.

Yeah, I added a patch to give a warning when you lookup a timezone with zoneinfo and it fails. That way it doesn't error if you don't need to see the error (e.g. you're including some package that imports zoneinfo but don't use any time zone related functionality yourself), and also it doesn't error if you're in node.js with access to /usr/local/zoneinfo )