Bind self to the current class when checking multiple inheritance compat

Author: sterliakov

mypy/checker.py

@@ -2232,7 +2232,7 @@ def bind_and_map_method(
                 is_class_method = sym.node.is_class
 
             mapped_typ = cast(FunctionLike, map_type_from_supertype(typ, sub_info, super_info))
-            active_self_type = self.scope.active_self_type()
+            active_self_type = fill_typevars(sub_info)
             if isinstance(mapped_typ, Overloaded) and active_self_type:
                 # If we have an overload, filter to overloads that match the self type.
                 # This avoids false positives for concrete subclasses of generic classes,

test-data/unit/check-generic-subtyping.test

@@ -1220,3 +1220,23 @@ class D4(A[U], B[U]): pass
 class D5(A[U], B[T]): pass  # E: Definition of "fn" in base class "A" is incompatible with definition in base class "B" \
                             # E: Definition of "x" in base class "A" is incompatible with definition in base class "B"
 [builtins fixtures/tuple.pyi]
+
+[case testSelfInMultipleInheritance]
+from typing_extensions import Self
+
+class A:
+    foo: int
+    def method(self: Self, other: Self) -> None:
+        self.foo
+        other.foo
+
+class B:
+    bar: str
+    def method(self: Self, other: Self) -> None:
+        self.bar
+        other.bar
+
+class C(A, B):  # OK: both methods take Self
+    pass
+
+[builtins fixtures/tuple.pyi]