Handles type checks for Type[Protocol]

[williamlw999-fb]

I noticed that typeguard wasn't able to correctly type check passed in classes when the type hint was a Type[Protocol]. You would receive an error like: TypeError: Protocols with non-method members don't support issubclass(). Using isinstance() in these situations would be able to correctly type check the passed in class. I also added a warning when a Protocol wasn't annotated with runtime_checkable to make it more explicit when typeguard was unable to perform type checking.

Tests:
Added a data protocol to improve coverage
Added a test for checking Type[Protocol]

[deathowl]

Hey @agronholm , could you take a look at this PR? As this would be needed in testslide facebook/TestSlide#333.

[agronholm]

The 2.x series (current master) has been frozen for new features; you should rebase this against the 3.0 branch.

[agronholm]

I've merged the 3.0 branch to master now to prevent any further confusion.

[coveralls]

Coverage increased (+0.04%) to 88.642% when pulling bd2982b on williamlw999-fb:fix_type_protocol into a298d6c on agronholm:master.

[williamlw999-fb]

@agronholm Thanks for helping out with the 3.0 rebase! I've updated my PR and made sure all signals are green. Let me know if there's anything else you'd like me to address for this PR

[agronholm]

Looks good at a glance; I will do a more thorough review later.

[agronholm]

This PR confuses me. You seem to be dropping type checking support for static protocols. Why?

[williamlw999-fb]

Static protocols were never supported by Typeguard. See line 501 of _checkers.py: if getattr(origin_type, "_is_runtime_protocol", False):.

StaticProtocol is defined without @runtime_checkable, so it does not pass that if statement in check_protocol(). This means typeguard doesn't type check StaticProtocol and always returns None. (See python docs on the runtime_checkable decorator https://docs.python.org/3/library/typing.html#typing.runtime_checkable). I've added a warning to make sure that users are aware when their protocol is not being type checked, and I updated the test to check for that warning.

The main fix in the PR is the addition of check_protocol in the check_class function to handle cases where you have a type hint like Type[Protocol].

[williamlw999-fb]

To be more specific, I've made sure that the the type checker can detect not only that the instanceFoo() is a RuntimeProtocol, but also that the class Foo is a Type[RuntimeProtocol].

There were no changes made to the how Typeguard handles StaticProtocol aside from warning the user that Python (and subsequently Typeguard) can't check protocols not decorated with @runtime_checkable at runtime.

[williamlw999-fb]

Does this help clarify the PR?

[agronholm]

Looks good, just one tiny nit.

[agronholm]

Thanks!

[williamlw999-fb]

Thanks for updating the lint and accepting the PR!