add test for generic instantiation

Author: elazarg

test-data/unit/check-selftype.test

@@ -449,6 +449,35 @@ reveal_type(X1.ft())  # E: Revealed type is 'Type[__main__.X]'
 
 [builtins fixtures/property.pyi]
 
+[case testSelfTypeProperSupertypeAttributeGeneric]
+from typing import Callable, TypeVar, Generic
+Q = TypeVar('Q', covariant=True)
+class K(Generic[Q]):
+    q: Q
+T = TypeVar('T')
+class A(K[Q]):
+    @property
+    def g(self: K[object]) -> int: return 0
+    @property
+    def gt(self: K[T]) -> T: return self.q
+    f: Callable[[object], int]
+    ft: Callable[[T], T]
+
+class B(A[Q]):
+    pass
+a: A[int]
+b: B[str]
+reveal_type(a.g)  # E: Revealed type is 'builtins.int'
+--reveal_type(a.gt)  # E: Revealed type is 'builtins.int'
+reveal_type(a.f())  # E: Revealed type is 'builtins.int'
+--reveal_type(a.ft())  # E: Revealed type is '__main__.A*[builtins.int]'
+reveal_type(b.g)  # E: Revealed type is 'builtins.int'
+--reveal_type(b.gt)  # E: Revealed type is '__main__.B*[builtins.str]'
+reveal_type(b.f())  # E: Revealed type is 'builtins.int'
+--reveal_type(b.ft())  # E: Revealed type is '__main__.B*[builtins.str]'
+
+[builtins fixtures/property.pyi]
+
 [case testSelfTypeNotSelfType]
 # Friendlier error messages for common mistakes. See #2950
 class A: