remove catchall return, add test case about the Any inheritance

Author: mkurnikov

mypy/checker.py

@@ -1628,25 +1628,6 @@ def check_compatibility(self, name: str, base1: TypeInfo,
             return
         first = base1[name]
         second = base2[name]
-        if isinstance(first.node, TypeInfo) and isinstance(second.node, TypeInfo):
-            # Checking compatibility of two nested classes with the same name is disabled.
-            # It creates a lot of false positives in frameworks like Django, DRF and others,
-            # where nested classes is used to define custom properties for the outer class, like
-            #     class MyModel:
-            #         class Meta:
-            #             abstract = True
-            #
-            # This is technically unsafe, it create false-negatives in cases like
-            # class Mixin1:
-            #     class Meta:
-            #         def get() -> int: pass
-            # class Mixin2:
-            #     class Meta:
-            #         def get() -> str: pass
-            # class A(Mixin2, Mixin1):
-            #     pass
-            # var: Mixin1 = A(); var.Meta.get()  # return type will be "str"
-            return
         first_type = self.determine_type_of_class_member(first)
         second_type = self.determine_type_of_class_member(second)
 

test-data/unit/check-multiple-inheritance.test

@@ -241,7 +241,7 @@ def dec(f: Callable[..., T]) -> Callable[..., T]:
 main:3: error: Cannot determine type of 'f' in base class 'B'
 main:3: error: Cannot determine type of 'f' in base class 'C'
 
-[case testMultipleInheritanceNestedClassesWithSameNameAllowed]
+[case testMultipleInheritanceOfNestedClassesWithSameNameButNotSubclassesOfOneAnother]
 class Mixin1:
     class Meta:
         pass
@@ -251,6 +251,7 @@ class Mixin2:
 class A(Mixin1, Mixin2):
     pass
 [out]
+main:7: error: Definition of "Meta" in base class "Mixin1" is incompatible with definition in base class "Mixin2"
 
 [case testMultipleInheritanceFailIfNestedClassAndAttrHaveSameName]
 class Mixin1:
@@ -338,3 +339,28 @@ class Base2:
 class Combo(Base2, Base1): ...
 [out]
 main:9: error: Definition of "NestedVar" in base class "Base2" is incompatible with definition in base class "Base1"
+
+[case testDoNotFailIfBothNestedClassesInheritFromAny]
+from typing import Any
+class Mixin1:
+    class Meta(Any):
+        pass
+class Mixin2:
+    class Meta(Any):
+        pass
+class A(Mixin1, Mixin2):
+    pass
+[out]
+
+[case testDoNotFailIfOneOfNestedClassesIsOuterInheritedFromAny]
+from typing import Any
+class Outer(Any):
+    pass
+class Mixin1:
+    Meta = Outer
+class Mixin2:
+    class Meta(Any):
+        pass
+class A(Mixin1, Mixin2):
+    pass
+[out]