Restore setting a Call as a base for classes using `six.with_metaclass` (#2049) (#2067)

Harden support for using enums as metaclasses.

Fixes the crash in PyCQA/pylint#5935 by adopting the check
for not-none bases as in ClassDef._inferred_bases without recausing
the false positive reported in PyCQA/pylint#7506, which requires
correct bases.

(cherry picked from commit b5ebf994a1c6039fa8ca4706889e007700cdf41a)

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

2 files changed, 16 insertions, 3 deletions

diff --git a/tests/brain/test_six.py b/tests/brain/test_six.py
index 1ff184d3..c9dac562 100644
--- a/tests/brain/test_six.py
+++ b/tests/brain/test_six.py
@@ -110,8 +110,7 @@ class SixBrainTest(unittest.TestCase):
         inferred = next(ast_node.infer())
         self.assertIsInstance(inferred, nodes.ClassDef)
         self.assertEqual(inferred.name, "B")
-        self.assertIsInstance(inferred.bases[0], nodes.Name)
-        self.assertEqual(inferred.bases[0].name, "C")
+        self.assertIsInstance(inferred.bases[0], nodes.Call)
         ancestors = tuple(inferred.ancestors())
         self.assertIsInstance(ancestors[0], nodes.ClassDef)
         self.assertEqual(ancestors[0].name, "C")
@@ -131,7 +130,7 @@ class SixBrainTest(unittest.TestCase):
             bar = 1
         """
         klass = astroid.extract_node(code)
-        assert list(klass.ancestors())[-1].name == "Enum"
+        assert next(klass.ancestors()).name == "Enum"
 
     def test_six_with_metaclass_with_additional_transform(self) -> None:
         def transform_class(cls: Any) -> ClassDef:
diff --git a/tests/test_scoped_nodes.py b/tests/test_scoped_nodes.py
index a69983c6..2722c56f 100644
--- a/tests/test_scoped_nodes.py
+++ b/tests/test_scoped_nodes.py
@@ -1403,6 +1403,20 @@ class ClassNodeTest(ModuleLoader, unittest.TestCase):
         self.assertEqual(["object"], [base.name for base in klass.ancestors()])
         self.assertEqual("type", klass.metaclass().name)
 
+    @unittest.skipUnless(HAS_SIX, "These tests require the six library")
+    def test_metaclass_generator_hack_enum_base(self):
+        """Regression test for https://github.com/PyCQA/pylint/issues/5935"""
+        klass = builder.extract_node(
+            """
+            import six
+            from enum import Enum, EnumMeta
+
+            class PetEnumPy2Metaclass(six.with_metaclass(EnumMeta, Enum)): #@
+                DOG = "dog"
+        """
+        )
+        self.assertEqual(list(klass.local_attr_ancestors("DOG")), [])
+
     def test_add_metaclass(self) -> None:
         klass = builder.extract_node(
             """