🐛 Fix support for UnionType with Python 3.11

[jonaslb]

Fixes #533, which already had good details and a proposal for a solution, based on using get_args and get_origin from the typing module instead of the __args__ and __origin__ attributes. So I went and did that.

We also needed to actually handle the UnionType in addition to the Union from before.

Now there was a bit of a headache in terms of writing this in a backwards compatible way. What I've done is place the compatibility code into _compat_utils.py. But let me know if you'd prefer to keep it in main.py.

I also added a single test, just an adapted copy of another one with the x | None syntax. It is conditioned on Python >= 3.10, so it shouldn't fail on older Pythons.

[github-actions]

📝 Docs preview for commit 1f9dd82 at: https://63ddbef8955c2d354bae0bbd--typertiangolo.netlify.app

[jonaslb]

It looks like mypy behaves differently in the different tests across versions. 3.6, 3.10 and 3.11 are ok, but 3.7, 3.8 and 3.9 are not. That seems confusing. I can maybe look at it another day again, otherwise if someone can see why it happens let me know.

[github-actions]

📝 Docs preview for commit 84ad04c at: https://63e1682403f85605237e7c38--typertiangolo.netlify.app

[jonaslb]

Failures are down to mypy version I think, it works fine here with latest. I see some errors in other places though (unrelated to my changes).

Also realized there is already another PR for this issue (just references other issue numbers, so I hadn't seen it): #522

Regardless, hope to see either PR merged. Ping @tiangolo

[austin-silk]

@tiangolo - can we merge this please?

[jonaslb]

Rebased on master and now all is green 👍

Still happy to make adaptations or answer questions.

[jonaslb]

@svlandeg I gather that #676 is the preferred solution to the UnionType situation? Should I just close this? Will we ever get anything on the topic merged - ie. what's blocking?

[svlandeg]

Hi @jonaslb, we've been going through the backlog of PRs to label them and connect related ones. We've already reviewed, adapted and merged a bunch for last week's releases 0.9.1 through 0.11.0. Open-source maintenance costs time and effort as I hope you can appreciate ;-) Thanks for your contributions (and patience) so far, we'll definitely get to this! It's fine to keep this one open in the meantime.

[jonaslb]

Open-source maintenance costs time and effort as I hope you can appreciate ;-)

Of course, and it's great to see that time is now being spent on typer also from the maintainer side ;-) I'm looking forward to engaging about details here if this PR turns out to be the preferred one out of the many submitted on the topic.

[svlandeg]

I confirmed that this behaviour works in 3.10 but broke in 3.11, and the unit test introduced in this PR captures the bug nicely.

I updated this PR so that the changes would be more minimal, using the variables from _typing that were introduced precisely for this type of usage.

This PR now closely resembles #676, though this one captures a few additional cases where __args__ and __origin__ are called directly in the main code. I think it's a good idea to rewrite all of these cases.

As such, I recommend to merge this PR and close #676 (and #739), but I'll leave the final decision with Tiangolo.