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## Summary It doesn't seem to be necessary for our generics implementation to carry the `GenericContext` in the `ClassBase` variants. Removing it simplifies the code, fixes many TODOs about `Generic` or `Protocol` appearing multiple times in MROs when each should only appear at most once, and allows us to more accurately detect runtime errors that occur due to `Generic` or `Protocol` appearing multiple times in a class's bases. In order to remove the `GenericContext` from the `ClassBase` variant, it turns out to be necessary to emulate `typing._GenericAlias.__mro_entries__`, or we end up with a large number of false-positive `inconsistent-mro` errors. This PR therefore also does that. Lastly, this PR fixes the inferred MROs of PEP-695 generic classes, which implicitly inherit from `Generic` even if they have no explicit bases. ## Test Plan mdtests
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Class definitions in stubs
Cyclical class definition
[environment]
python-version = "3.12"
In type stubs, classes can reference themselves in their base class definitions. For example, in
typeshed, we have class str(Sequence[str]): ....
class Foo[T]: ...
class Bar(Foo[Bar]): ...
reveal_type(Bar) # revealed: <class 'Bar'>
reveal_type(Bar.__mro__) # revealed: tuple[<class 'Bar'>, <class 'Foo[Bar]'>, typing.Generic, <class 'object'>]
Access to attributes declared in stubs
Unlike regular Python modules, stub files often omit the right-hand side in declarations, including
in class scope. However, from the perspective of the type checker, we have to treat them as bindings
too. That is, symbol: type is the same as symbol: type = ....
One implication of this is that we'll always treat symbols in class scope as safe to be accessed from the class object itself. We'll never infer a "pure instance attribute" from a stub.
b.pyi:
from typing import ClassVar
class C:
class_or_instance_var: int
from typing import ClassVar, Literal
from b import C
# No error here, since we treat `class_or_instance_var` as bound on the class.
reveal_type(C.class_or_instance_var) # revealed: int