gh-102549: [Enum] fail enum creation when data type raises in __init__ (GH-103149)

(cherry picked from commit 2a4d8c0a9e)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>

Lib/enum.py

@@ -250,23 +250,20 @@ class _proto_member:
             args = (args, )     # wrap it one more time
         if not enum_class._use_args_:
             enum_member = enum_class._new_member_(enum_class)
-            if not hasattr(enum_member, '_value_'):
+        else:
+            enum_member = enum_class._new_member_(enum_class, *args)
+        if not hasattr(enum_member, '_value_'):
+            if enum_class._member_type_ is object:
+                enum_member._value_ = value
+            else:
                 try:
                     enum_member._value_ = enum_class._member_type_(*args)
                 except Exception as exc:
-                    enum_member._value_ = value
-        else:
-            enum_member = enum_class._new_member_(enum_class, *args)
-            if not hasattr(enum_member, '_value_'):
-                if enum_class._member_type_ is object:
-                    enum_member._value_ = value
-                else:
-                    try:
-                        enum_member._value_ = enum_class._member_type_(*args)
-                    except Exception as exc:
-                        raise TypeError(
-                                '_value_ not set in __new__, unable to create it'
-                                ) from None
+                    new_exc = TypeError(
+                            '_value_ not set in __new__, unable to create it'
+                            )
+                    new_exc.__cause__ = exc
+                    raise new_exc
         value = enum_member._value_
         enum_member._name_ = member_name
         enum_member.__objclass__ = enum_class

Lib/test/test_enum.py

@@ -2787,6 +2787,26 @@ class TestSpecial(unittest.TestCase):
         self.assertEqual(FlagFromChar.a, 158456325028528675187087900672)
         self.assertEqual(FlagFromChar.a|1, 158456325028528675187087900673)
 
+    def test_init_exception(self):
+        class Base:
+            def __init__(self, x):
+                raise ValueError("I don't like", x)
+        with self.assertRaises(TypeError):
+            class MyEnum(Base, enum.Enum):
+                A = 'a'
+                def __init__(self, y):
+                    self.y = y
+        with self.assertRaises(ValueError):
+            class MyEnum(Base, enum.Enum):
+                A = 'a'
+                def __init__(self, y):
+                    self.y = y
+                def __new__(cls, value):
+                    member = Base.__new__(cls)
+                    member._value_ = Base(value)
+                    return member
+
+
 class TestOrder(unittest.TestCase):
     "test usage of the `_order_` attribute"
 

Misc/NEWS.d/next/Library/2023-03-27-19-21-51.gh-issue-102549.NQ6Nlv.rst

@@ -0,0 +1 @@
+Don't ignore exceptions in member type creation.