Fix accessing unannotated implicit class methods (#7739)

Fixes #7735

The fix is quite straightforward, this was not triggered before because all common cases go troigh other code paths.

Author: ilevkivskyi

mypy/checkmember.py

@@ -736,7 +736,14 @@ def analyze_class_attribute_access(itype: Instance,
             mx.not_ready_callback(name, mx.context)
             return AnyType(TypeOfAny.from_error)
     else:
-        return function_type(cast(FuncBase, node.node), mx.builtin_type('builtins.function'))
+        assert isinstance(node.node, FuncBase)
+        typ = function_type(node.node, mx.builtin_type('builtins.function'))
+        # Note: if we are accessing class method on class object, the cls argument is bound.
+        # Annotated and/or explicit class methods go through other code paths above, for
+        # unannotated implicit class methods we do this here.
+        if node.node.is_class:
+            typ = bind_self(typ, is_classmethod=True)
+        return typ
 
 
 def add_class_tvars(t: ProperType, itype: Instance, isuper: Optional[Instance],

test-data/unit/check-classes.test

@@ -6387,6 +6387,42 @@ class MidBase(Base): pass
 [file init_subclass/__init__.py]
 [builtins fixtures/object_with_init_subclass.pyi]
 
+[case testInitSubclassUnannotated]
+class A:
+    def __init_subclass__(cls, *args, **kwargs):
+        super().__init_subclass__(*args, **kwargs)
+
+class B(A):
+    pass
+
+reveal_type(A.__init_subclass__)  # N: Revealed type is 'def (*args: Any, **kwargs: Any) -> Any'
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassUnannotatedMulti]
+from typing import ClassVar, List, Type
+
+class A:
+    registered_classes: ClassVar[List[Type[A]]] = []
+    def __init_subclass__(cls, *args, register=True, **kwargs):
+        if register:
+            cls.registered_classes.append(cls)
+        super().__init_subclass__(*args, **kwargs)
+
+class B(A): ...
+class C(A, register=False): ...
+class D(C): ...
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testClassMethodUnannotated]
+class C:
+    def __new__(cls): ...
+    @classmethod
+    def meth(cls): ...
+
+reveal_type(C.meth)  # N: Revealed type is 'def () -> Any'
+reveal_type(C.__new__)  # N: Revealed type is 'def (cls: Type[__main__.C]) -> Any'
+[builtins fixtures/classmethod.pyi]
+
 [case testOverrideGenericSelfClassMethod]
 from typing import Generic, TypeVar, Type, List
 

test-data/unit/fixtures/object_with_init_subclass.pyi

@@ -1,4 +1,4 @@
-from typing import Sequence, Iterator, TypeVar, Mapping, Iterable, Optional, Union, overload, Tuple, Generic
+from typing import Sequence, Iterator, TypeVar, Mapping, Iterable, Optional, Union, overload, Tuple, Generic, List
 
 class object:
     def __init__(self) -> None: ...
@@ -34,6 +34,15 @@ class tuple(Generic[T]): pass
 class function: pass
 class ellipsis: pass
 
+# copy-pasted from list.pyi
+class list(Sequence[T]):
+    def __iter__(self) -> Iterator[T]: pass
+    def __mul__(self, x: int) -> list[T]: pass
+    def __setitem__(self, x: int, v: T) -> None: pass
+    def __getitem__(self, x: int) -> T: pass
+    def __add__(self, x: List[T]) -> T: pass
+    def __contains__(self, item: object) -> bool: pass
+
 # copy-pasted from dict.pyi
 class dict(Mapping[KT, VT]):
     @overload