Add type checker

[Kludex]

This PR adds type checker to tox.

PyRight Vs MyPy

There's a lot of discussion around about which one to use. I don't think it matters much which one to choose. There are points where Python itself is not specific, and then the type checkers have freedom to choose the behavior they want... Example:

• mypy: On strict mode, you need to add -> None on the return statement.
• pyright: infers that is None, so you don't need to add -> None.

PyRight is easier for VSCode users, me included... 👀

About the ecosystem... I think most of them use mypy, but Pydantic for example, uses PyRight.

If you look at the projects I maintain (starlette, uvicorn), I use mypy on them, but I have to say that is a bit more practical to have the type checker match my IDE.

Anyway... I hope this is not an issue, and we can start with this setup.

[Kludex]

cc @emdneto (asked about this on PM) and @lzchen (since you been happy with the type hints PRs 👀 👍)

[xrmx]

I don't have any preference but I think you missed that we are using mypy in opentelemetry-python

[Kludex]

I was checking opentelemetry-python, and it seems that pyright is also present there?

https://github.com/open-telemetry/opentelemetry-python/blob/17782492f5cec2e093fcd02e983d7f5e638b7cca/tox.ini#L349-L358

A bit more into it... Seems like if pyright looks at the pyproject, the type checker is disabled... 🤔

https://github.com/open-telemetry/opentelemetry-python/blob/17782492f5cec2e093fcd02e983d7f5e638b7cca/pyproject.toml#L5-L12

[Kludex]

I took some time trying to set up mypy to see how that would look like, and it just took too much of my time, and I was not able to make it work properly...

I'm happy to close this if people are strong on mypy, but I'm not willing to spend more time trying it.

[Kludex]

I think the mypy setup on opentelemetry-python is not taking in consideration all local packages.

It would be great if people could share opinions on this, I want to continue adding type hints, but without regressions.

[emdneto]

Thanks. Discussed this at SIG (01/09) and agreed to move forward with pyright in contrib and include some packages to be typechecked. After that, also adopt pyright in core as well.

nit: can we include the packages you've added type hints?

[Kludex]

Not yet, cause I've mainly added type hints on public APIs. I need to add more stuff to them that I was not very strict.

[aabmass]

Very exciting, thank you!