Run tests against python 3.10

[maffoo]

Test against all the versions.

[maffoo]

Looks like we will need to update the grpc library version to support 3.10.

[MichaelBroughton]

Looks like the least intrusive upgrade here is grpcio-tools~=1.36.0 in protos.txt. This would take the bundled protoc to 3.14 from 3.13.0. Would this interfere with any of the cirq-google gapic or proto stuff @maffoo , @verult , @wcourtney ?

[verult]

I'm not aware of any problems with device and program protos. If we can go further and move to 3.15, that'd be even better - optional fields are only supported in >=3.15 and I'd like to make the gate_duration field optional if time allows before Cirq 1.0. But this is by no means a strong requirement.

[maffoo]

@MichaelBroughton, I don't think bumping the grpcio-tools version will be a problem for cirq-google; we will have to regenerate the proto files, but that's easy, and the gapic code now uses the proto library instead of google.protobuf so it doesn't care about the protoc version.

@verult, in proto3 all fields are optional by default, so I don't think we need to do anything special to treat gate_duration as optional. Do you have any more information about the change in 3.15 that you're interested in?

[verult]

The feature I'm looking for is to be able to distinguish between an unset field and a field which is set to the default value of the type. For gate_duration, it's to be able to tell whether a gate has 0 duration vs no duration information. But this isn't a strong requirement because gate_duration is mostly informational.

See: https://stackoverflow.com/questions/42622015/how-to-define-an-optional-field-in-protobuf-3

[maffoo]

Hm, we need to update mypy to get it to install on mac/windows with 3.10, but updating mypy update is not trivial. I'm inclined to disable 3.10 tests for windows and mac for now and do that as a follow-up.

[MichaelBroughton]

Why is updating mypy not trivial ?

[maffoo]

When I tried updating mypy to ~0.800 I saw O(20) new type errors; when I updated to the latest 0.961 it was more like O(50) errors. It might be that these are easy to fix, I didn't dive too deep. But in any even it felt like that might be better as a separate PR.

[maffoo]

mypy updated in #5767 so that we can now run 3.10 tests on windows and mac. @MichaelBroughton, PTAL.

[pavoljuhas]

LGTM.

[viathor]

me wants this

(making new cirq virtualenv and grpcio-tools fails to build, hoping this is the fix)

[CirqBot]

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