Support inference of Enum subclasses.

ChangeLog

@@ -9,6 +9,13 @@ Release date: TBA
 * Import from ``astroid.node_classes`` and ``astroid.scoped_nodes`` has been deprecated in favor of
   ``astroid.nodes``. Only the imports from ``astroid.nodes`` will work in astroid 3.0.0.
 
+* Add support for arbitrary Enum subclass hierachies
+
+  Closes PyCQA/pylint#533
+  Closes PyCQA/pylint#2224
+  Closes PyCQA/pylint#2626
+
+
 What's New in astroid 2.6.7?
 ============================
 Release date: TBA

astroid/brain/brain_namedtuple_enum.py

@@ -28,12 +28,14 @@
 import keyword
 from textwrap import dedent
 
+import astroid
 from astroid import arguments, inference_tip, nodes, util
 from astroid.builder import AstroidBuilder, extract_node
 from astroid.exceptions import (
     AstroidTypeError,
     AstroidValueError,
     InferenceError,
+    MroError,
     UseInferenceDefault,
 )
 from astroid.manager import AstroidManager
@@ -354,9 +356,7 @@ def __mul__(self, other):
 
 def infer_enum_class(node):
     """Specific inference for enums."""
-    for basename in node.basenames:
-        # TODO: doesn't handle subclasses yet. This implementation
-        # is a hack to support enums.
+    for basename in (b for cls in node.mro() for b in cls.basenames):
         if basename not in ENUM_BASE_NAMES:
             continue
         if node.root().name == "enum":
@@ -417,9 +417,9 @@ def name(self):
                     # should result in some nice symbolic execution
                     classdef += INT_FLAG_ADDITION_METHODS.format(name=target.name)
 
-                fake = AstroidBuilder(AstroidManager()).string_build(classdef)[
-                    target.name
-                ]
+                fake = AstroidBuilder(
+                    AstroidManager(), apply_transforms=False
+                ).string_build(classdef)[target.name]
                 fake.parent = target.parent
                 for method in node.mymethods():
                     fake.locals[method.name] = [method]
@@ -544,18 +544,49 @@ def infer_typing_namedtuple(node, context=None):
     return infer_named_tuple(node, context)
 
 
+def _is_enum_subclass(cls: astroid.ClassDef) -> bool:
+    """Return whether cls is a subclass of an Enum.
+
+    Warning: For efficiency purposes, this function immediately returns False if enum hasn't
+    been imported in the module of the ClassDef. This means it fails to detect an Enum
+    subclass that is imported from a new module and subclassed, e.g.
+
+        # a.py
+        import enum
+
+        class A(enum.Enum):
+            pass
+
+        # b.py
+        from a import A
+
+        class B(A):  # is_enum_subclass returns False
+            attr = 1
+    """
+    mod_locals = cls.root().locals
+    if "enum" not in mod_locals and all(
+        base not in mod_locals for base in ENUM_BASE_NAMES
+    ):
+        return False
+
+    try:
+        return any(
+            klass.name in ENUM_BASE_NAMES
+            and getattr(klass.root(), "name", None) == "enum"
+            for klass in cls.mro()
+        )
+    except MroError:
+        return False
+
+
 AstroidManager().register_transform(
     nodes.Call, inference_tip(infer_named_tuple), _looks_like_namedtuple
 )
 AstroidManager().register_transform(
     nodes.Call, inference_tip(infer_enum), _looks_like_enum
 )
 AstroidManager().register_transform(
-    nodes.ClassDef,
-    infer_enum_class,
-    predicate=lambda cls: any(
-        basename for basename in cls.basenames if basename in ENUM_BASE_NAMES
-    ),
+    nodes.ClassDef, infer_enum_class, predicate=_is_enum_subclass
 )
 AstroidManager().register_transform(
     nodes.ClassDef, inference_tip(infer_typing_namedtuple_class), _has_namedtuple_base

astroid/nodes/scoped_nodes.py

@@ -63,7 +63,7 @@
 from astroid.interpreter.dunder_lookup import lookup
 from astroid.interpreter.objectmodel import ClassModel, FunctionModel, ModuleModel
 from astroid.manager import AstroidManager
-from astroid.nodes import node_classes
+from astroid.nodes import Const, node_classes
 
 ITER_METHODS = ("__iter__", "__getitem__")
 EXCEPTION_BASE_CLASSES = frozenset({"Exception", "BaseException"})
@@ -2962,7 +2962,12 @@ def _inferred_bases(self, context=None):
 
         for stmt in self.bases:
             try:
-                baseobj = next(stmt.infer(context=context.clone()))
+                # Find the first non-None inferred base value
+                baseobj = next(
+                    b
+                    for b in stmt.infer(context=context.clone())
+                    if not (isinstance(b, Const) and b.value is None)
+                )
             except (InferenceError, StopIteration):
                 continue
             if isinstance(baseobj, bases.Instance):

tests/unittest_brain.py

@@ -791,6 +791,24 @@ def __init__(self, name, enum_list):
         test = next(enumeration.igetattr("test"))
         self.assertEqual(test.value, 42)
 
+    def test_user_enum_false_positive(self):
+        # Test that a user-defined class named Enum is not considered a builtin enum.
+        ast_node = astroid.extract_node(
+            """
+        class Enum:
+            pass
+
+        class Color(Enum):
+            red = 1
+
+        Color.red #@
+        """
+        )
+        inferred = ast_node.inferred()
+        self.assertEqual(len(inferred), 1)
+        self.assertIsInstance(inferred[0], astroid.Const)
+        self.assertEqual(inferred[0].value, 1)
+
     def test_ignores_with_nodes_from_body_of_enum(self):
         code = """
         import enum
@@ -1051,6 +1069,65 @@ def func(self):
         assert isinstance(inferred, bases.Instance)
         assert inferred.pytype() == ".TrickyEnum.value"
 
+    def test_enum_subclass_member_name(self):
+        ast_node = astroid.extract_node(
+            """
+        from enum import Enum
+
+        class EnumSubclass(Enum):
+            pass
+
+        class Color(EnumSubclass):
+            red = 1
+
+        Color.red.name #@
+        """
+        )
+        inferred = ast_node.inferred()
+        self.assertEqual(len(inferred), 1)
+        self.assertIsInstance(inferred[0], astroid.Const)
+        self.assertEqual(inferred[0].value, "red")
+
+    def test_enum_subclass_member_value(self):
+        ast_node = astroid.extract_node(
+            """
+        from enum import Enum
+
+        class EnumSubclass(Enum):
+            pass
+
+        class Color(EnumSubclass):
+            red = 1
+
+        Color.red.value #@
+        """
+        )
+        inferred = ast_node.inferred()
+        self.assertEqual(len(inferred), 1)
+        self.assertIsInstance(inferred[0], astroid.Const)
+        self.assertEqual(inferred[0].value, 1)
+
+    def test_enum_subclass_member_method(self):
+        # See Pylint issue #2626
+        ast_node = astroid.extract_node(
+            """
+        from enum import Enum
+
+        class EnumSubclass(Enum):
+            def hello_pylint(self) -> str:
+                return self.name
+
+        class Color(EnumSubclass):
+            red = 1
+
+        Color.red.hello_pylint()  #@
+        """
+        )
+        inferred = ast_node.inferred()
+        self.assertEqual(len(inferred), 1)
+        self.assertIsInstance(inferred[0], astroid.Const)
+        self.assertEqual(inferred[0].value, "red")
+
 
 @unittest.skipUnless(HAS_DATEUTIL, "This test requires the dateutil library.")
 class DateutilBrainTest(unittest.TestCase):