Fix inference of Enum.__members__ property for subclasses

Ref pylint-dev/pylint#2626. Ref pylint-dev/pylint#3535. Ref pylint-dev/pylint#4358.
This updates the namedtuple/enum brain to add a dictionary for
__members__

astroid/brain/brain_namedtuple_enum.py

@@ -315,6 +315,7 @@ def infer_enum_class(node):
         if node.root().name == "enum":
             # Skip if the class is directly from enum module.
             break
+        dunder_members = {}
         for local, values in node.locals.items():
             if any(not isinstance(value, nodes.AssignName) for value in values):
                 continue
@@ -372,7 +373,16 @@ def name(self):
                 for method in node.mymethods():
                     fake.locals[method.name] = [method]
                 new_targets.append(fake.instantiate_class())
+                dunder_members[local] = fake
             node.locals[local] = new_targets
+        members = nodes.Dict(parent=node)
+        members.postinit(
+            [
+                (nodes.Const(k, parent=members), nodes.Name(v.name, parent=members))
+                for k, v in dunder_members.items()
+            ]
+        )
+        node.locals["__members__"] = [members]
         break
     return node
 

tests/unittest_scoped_nodes.py

@@ -2054,6 +2054,22 @@ class Derived(Parent):
     assert isinstance(inferred, objects.Property)
 
 
+def test_issue940_enums_as_a_real_world_usecase():
+    node = builder.extract_node(
+        """
+    from enum import Enum
+    class Sounds(Enum):
+        bee = "buzz"
+        cat = "meow"
+    Sounds.__members__
+    """
+    )
+    inferred_result = next(node.infer())
+    assert isinstance(inferred_result, nodes.Dict)
+    actual = [k.value for k, _ in inferred_result.items]
+    assert sorted(actual) == ["bee", "cat"]
+
+
 def test_metaclass_cannot_infer_call_yields_an_instance():
     node = builder.extract_node(
         """