If a generic class is subscripted, infer that class itself

Closes pylint-dev/pylint#3131
Closes pylint-dev/pylint#3505

ChangeLog

@@ -2,6 +2,11 @@
 astroid's ChangeLog
 ===================
 
+* If a generic class is subscripted, infer that class itself
+
+  Closes PyCQA/pylint#3131
+  Closes PyCQA/pylint#3505
+
 What's New in astroid 2.4.0?
 ============================
 Release Date: 2020-04-27

astroid/inference.py

@@ -368,6 +368,10 @@ def infer_subscript(self, context=None):
         if value is util.Uninferable:
             yield util.Uninferable
             return None
+        if isinstance(value, nodes.ClassDef):
+            if value.is_subtype_of("typing.Generic"):
+                yield value
+                return None
         for index in self.slice.infer(context):
             if index is util.Uninferable:
                 yield util.Uninferable

tests/unittest_inference.py

@@ -374,6 +374,30 @@ class A(B):  #@
         self.assertIs(a2_ancestors[0], b)
         self.assertIs(a2_ancestors[1], a1)
 
+    @pytest.mark.skipif(sys.version_info < (3, 5), reason="Needs 'typing' module")
+    def test_ancestors_generic(self):
+        code = """
+            from typing import Generic, TypeVar
+
+            T = TypeVar('T')
+
+            class A(Generic[T]):  #@
+                pass
+
+            class B(A[T]):  #@
+                pass
+
+            class C(B[int]):  #@
+                pass
+        """
+        a, b, c = extract_node(code, __name__)
+        ancestors = list(c.ancestors())
+        self.assertEqual(len(ancestors), 4)
+        self.assertIs(ancestors[0], b)
+        self.assertIs(ancestors[1], a)
+        self.assertEqual(ancestors[2].name, "Generic")
+        self.assertEqual(ancestors[3].name, "object")
+
     def test_f_arg_f(self):
         code = """
             def f(f=1):