Changed typing_extensions.pyi to declare its own private version of Protocol

[erictraut]

Changed typing_extensions.pyi to declare its own private version of Protocol rather than re-exporting the symbol imported from typing. This allows pyright to warn users about runtime exceptions when they attempt to use typing.Protocol on versions of Python prior to 3.7.

[erictraut]

This is related to issue #7130

[AlexWaygood]

Should the changes #7037 made to runtime_checkable also be reverted?

[erictraut]

Pyright doesn't currently have a version check for runtime_checkable, so that change wouldn't have any effect. I don't mind adding it for consistency if you'd prefer.

[AlexWaygood]

Pyright doesn't currently have a version check for runtime_checkable, so that change wouldn't have any effect. I don't mind adding it for consistency if you'd prefer.

I'm easy either way if it doesn't break pyright :) I vote for leaving it as it is in that case — it keeps code duplication to a minimum

[JelleZijlstra]

Actually I'd prefer we change it too, so that any type checker that does want to error for use of runtime_checkable on 3.6 can do so.

[erictraut]

@JelleZijlstra, I've reverted the recent change for runtime_checkable as you suggested.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉