Mikhail Golubev 190a55438e [python] Special-case typing.Generic while calculating a class MRO ...

typing.Generic is a magical class that can be specified in any position
in the list of base classes, not affecting the MRO consistency. It's done by
the custom __mro_entries__ implementation in typing._BaseGenericAlias (Python < 3.12),
which skips this Generic entry if there are other generic classes following
it on the list of superclasses. Namely, it's possible to do the following:

```
class Base(Generic[T]):
    pass

class MyClass(Generic[T], Base[T]):
    pass
```

which would cause a TypeError for regular classes. Since it broke our implementation
of the C3 algorithm in PyClassImpl.getMROAncestorTypes, we now special-case it by
always moving typing.Generic to the very end of the base class list while constructing
MRO.

See https://github.com/python/cpython/blob/3.11/Lib/typing.py#L1298 for a pure-Python
version of typing._BaseGenericAlias.__mro_entries__ and a relevant discussion in
https://github.com/python/cpython/issues/106102.

GitOrigin-RevId: e7d765193d532ab8457133e8fb5ad06840d89225

2024-10-02 14:29:04 +00:00

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