626f716de6
## Summary I mirrored some of the idioms that @AlexWaygood used in the MRO work. Closes https://github.com/astral-sh/ruff/issues/14096. --------- Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
4.2 KiB
Default
class M(type): ...
reveal_type(M.__class__) # revealed: Literal[type]
object
reveal_type(object.__class__) # revealed: Literal[type]
type
reveal_type(type.__class__) # revealed: Literal[type]
Basic
class A(type): ...
class B(metaclass=A): ...
reveal_type(B.__class__) # revealed: Literal[A]
Invalid metaclass
If a class is a subclass of a class with a custom metaclass, then the subclass will also have that metaclass.
class M: ...
class A(metaclass=M): ...
# TODO: emit a diagnostic for the invalid metaclass
reveal_type(A.__class__) # revealed: Literal[M]
Linear inheritance
If a class is a subclass of a class with a custom metaclass, then the subclass will also have that metaclass.
class M(type): ...
class A(metaclass=M): ...
class B(A): ...
reveal_type(B.__class__) # revealed: Literal[M]
Conflict (1)
The metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases. ("Strict subclass" is a synonym for "proper subclass"; a non-strict subclass can be a subclass or the class itself.)
class M1(type): ...
class M2(type): ...
class A(metaclass=M1): ...
class B(metaclass=M2): ...
# error: [conflicting-metaclass] "The metaclass of a derived class (`C`) must be a subclass of the metaclasses of all its bases, but `M1` and `M2` have no subclass relationship"
class C(A, B): ...
reveal_type(C.__class__) # revealed: Unknown
Conflict (2)
The metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases. ("Strict subclass" is a synonym for "proper subclass"; a non-strict subclass can be a subclass or the class itself.)
class M1(type): ...
class M2(type): ...
class A(metaclass=M1): ...
# error: [conflicting-metaclass] "The metaclass of a derived class (`B`) must be a subclass of the metaclasses of all its bases, but `M2` and `M1` have no subclass relationship"
class B(A, metaclass=M2): ...
reveal_type(B.__class__) # revealed: Unknown
Common metaclass
A class has two explicit bases, both of which have the same metaclass.
class M(type): ...
class A(metaclass=M): ...
class B(metaclass=M): ...
class C(A, B): ...
reveal_type(C.__class__) # revealed: Literal[M]
Metaclass metaclass
A class has an explicit base with a custom metaclass. That metaclass itself has a custom metaclass.
class M1(type): ...
class M2(type, metaclass=M1): ...
class M3(M2): ...
class A(metaclass=M3): ...
class B(A): ...
reveal_type(A.__class__) # revealed: Literal[M3]
Diamond inheritance
class M(type): ...
class M1(M): ...
class M2(M): ...
class M12(M1, M2): ...
class A(metaclass=M1): ...
class B(metaclass=M2): ...
class C(metaclass=M12): ...
# error: [conflicting-metaclass] "The metaclass of a derived class (`D`) must be a subclass of the metaclasses of all its bases, but `M1` and `M2` have no subclass relationship"
class D(A, B, C): ...
reveal_type(D.__class__) # revealed: Unknown
Unknown
from nonexistent_module import UnknownClass # error: [unresolved-import]
class C(UnknownClass): ...
reveal_type(C.__class__) # revealed: Literal[type]
class M(type): ...
class A(metaclass=M): ...
class B(A, UnknownClass): ...
# TODO: This should resolve to `type[M] | Unknown` instead
reveal_type(B.__class__) # revealed: Literal[M]
Duplicate
class M(type): ...
class A(metaclass=M): ...
class B(A, A): ... # error: [duplicate-base] "Duplicate base class `A`"
reveal_type(B.__class__) # revealed: Literal[M]
Non-class
When a class has an explicit metaclass that is not a class, the value should be returned as is.
class A(metaclass=1): ...
reveal_type(A.__class__) # revealed: Literal[1]
Cyclic
Retrieving the metaclass of a cyclically defined class should not cause an infinite loop.
class A(B): ... # error: [cyclic-class-def]
class B(C): ... # error: [cyclic-class-def]
class C(A): ... # error: [cyclic-class-def]
reveal_type(A.__class__) # revealed: Unknown
PEP 695 generic
class M(type): ...
class A[T: str](metaclass=M): ...
reveal_type(A.__class__) # revealed: Literal[M]