Fix @deprecated on classes with only __new__ (#193)

Author: JelleZijlstra

CHANGELOG.md

@@ -1,8 +1,10 @@
 # Unreleased
 
-- Fix regression in version 4.6.1 where comparing a generic class against a 
+- Fix use of `@deprecated` on classes with `__new__` but no `__init__`.
+  Patch by Jelle Zijlstra.
+- Fix regression in version 4.6.1 where comparing a generic class against a
   runtime-checkable protocol using `isinstance()` would cause `AttributeError`
-  to be raised if using Python 3.7
+  to be raised if using Python 3.7.
 
 # Release 4.6.1 (May 23, 2023)
 

src/test_typing_extensions.py

@@ -357,6 +357,7 @@ class A:
             with self.assertRaises(TypeError):
                 A(42)
 
+    def test_class_with_init(self):
         @deprecated("HasInit will go away soon")
         class HasInit:
             def __init__(self, x):
@@ -366,6 +367,7 @@ def __init__(self, x):
             instance = HasInit(42)
         self.assertEqual(instance.x, 42)
 
+    def test_class_with_new(self):
         has_new_called = False
 
         @deprecated("HasNew will go away soon")
@@ -382,6 +384,8 @@ def __init__(self, x) -> None:
             instance = HasNew(42)
         self.assertEqual(instance.x, 42)
         self.assertTrue(has_new_called)
+
+    def test_class_with_inherited_new(self):
         new_base_called = False
 
         class NewBase:
@@ -402,6 +406,23 @@ class HasInheritedNew(NewBase):
         self.assertEqual(instance.x, 42)
         self.assertTrue(new_base_called)
 
+    def test_class_with_new_but_no_init(self):
+        new_called = False
+
+        @deprecated("HasNewNoInit will go away soon")
+        class HasNewNoInit:
+            def __new__(cls, x):
+                nonlocal new_called
+                new_called = True
+                obj = super().__new__(cls)
+                obj.x = x
+                return obj
+
+        with self.assertWarnsRegex(DeprecationWarning, "HasNewNoInit will go away soon"):
+            instance = HasNewNoInit(42)
+        self.assertEqual(instance.x, 42)
+        self.assertTrue(new_called)
+
     def test_function(self):
         @deprecated("b will go away soon")
         def b():

src/typing_extensions.py

@@ -2497,11 +2497,11 @@ def decorator(__arg: _T) -> _T:
                 @functools.wraps(original_new)
                 def __new__(cls, *args, **kwargs):
                     warnings.warn(__msg, category=category, stacklevel=stacklevel + 1)
-                    # Mirrors a similar check in object.__new__.
-                    if not has_init and (args or kwargs):
-                        raise TypeError(f"{cls.__name__}() takes no arguments")
                     if original_new is not object.__new__:
                         return original_new(cls, *args, **kwargs)
+                    # Mirrors a similar check in object.__new__.
+                    elif not has_init and (args or kwargs):
+                        raise TypeError(f"{cls.__name__}() takes no arguments")
                     else:
                         return original_new(cls)