Backport recent change to NamedTuple classes regarding __set_name__ (#303)

Author: AlexWaygood

CHANGELOG.md

@@ -9,6 +9,10 @@
   argument to the `msg` parameter. Patch by Alex Waygood.
 - Exclude `__match_args__` from `Protocol` members,
   this is a backport of https://github.com/python/cpython/pull/110683
+- When creating a `typing_extensions.NamedTuple` class, ensure `__set_name__`
+  is called on all objects that define `__set_name__` and exist in the values
+  of the `NamedTuple` class's class dictionary. Patch by Alex Waygood,
+  backporting https://github.com/python/cpython/pull/111876.
 
 # Release 4.8.0 (September 17, 2023)
 

src/test_typing_extensions.py

@@ -56,6 +56,11 @@
 # versions, but not all
 HAS_FORWARD_MODULE = "module" in inspect.signature(typing._type_check).parameters
 
+skip_if_early_py313_alpha = skipIf(
+    sys.version_info[:4] == (3, 13, 0, 'alpha') and sys.version_info.serial < 3,
+    "Bugfixes will be released in 3.13.0a3"
+)
+
 ANN_MODULE_SOURCE = '''\
 from typing import Optional
 from functools import wraps
@@ -5548,6 +5553,136 @@ class GenericNamedTuple(NamedTuple, Generic[T]):
 
         self.assertEqual(CallNamedTuple.__orig_bases__, (NamedTuple,))
 
+    @skip_if_early_py313_alpha
+    def test_setname_called_on_values_in_class_dictionary(self):
+        class Vanilla:
+            def __set_name__(self, owner, name):
+                self.name = name
+
+        class Foo(NamedTuple):
+            attr = Vanilla()
+
+        foo = Foo()
+        self.assertEqual(len(foo), 0)
+        self.assertNotIn('attr', Foo._fields)
+        self.assertIsInstance(foo.attr, Vanilla)
+        self.assertEqual(foo.attr.name, "attr")
+
+        class Bar(NamedTuple):
+            attr: Vanilla = Vanilla()
+
+        bar = Bar()
+        self.assertEqual(len(bar), 1)
+        self.assertIn('attr', Bar._fields)
+        self.assertIsInstance(bar.attr, Vanilla)
+        self.assertEqual(bar.attr.name, "attr")
+
+    @skipIf(
+        TYPING_3_12_0,
+        "__set_name__ behaviour changed on py312+ to use BaseException.add_note()"
+    )
+    def test_setname_raises_the_same_as_on_other_classes_py311_minus(self):
+        class CustomException(BaseException): pass
+
+        class Annoying:
+            def __set_name__(self, owner, name):
+                raise CustomException
+
+        annoying = Annoying()
+
+        with self.assertRaises(RuntimeError) as cm:
+            class NormalClass:
+                attr = annoying
+        normal_exception = cm.exception
+
+        with self.assertRaises(RuntimeError) as cm:
+            class NamedTupleClass(NamedTuple):
+                attr = annoying
+        namedtuple_exception = cm.exception
+
+        expected_note = (
+            "Error calling __set_name__ on 'Annoying' instance "
+            "'attr' in 'NamedTupleClass'"
+        )
+
+        self.assertIs(type(namedtuple_exception), RuntimeError)
+        self.assertIs(type(namedtuple_exception), type(normal_exception))
+        self.assertEqual(len(namedtuple_exception.args), len(normal_exception.args))
+        self.assertEqual(
+            namedtuple_exception.args[0],
+            normal_exception.args[0].replace("NormalClass", "NamedTupleClass")
+        )
+
+        self.assertIs(type(namedtuple_exception.__cause__), CustomException)
+        self.assertIs(
+            type(namedtuple_exception.__cause__), type(normal_exception.__cause__)
+        )
+        self.assertEqual(
+            namedtuple_exception.__cause__.args, normal_exception.__cause__.args
+        )
+
+    @skipUnless(
+        TYPING_3_12_0,
+        "__set_name__ behaviour changed on py312+ to use BaseException.add_note()"
+    )
+    @skip_if_early_py313_alpha
+    def test_setname_raises_the_same_as_on_other_classes_py312_plus(self):
+        class CustomException(BaseException): pass
+
+        class Annoying:
+            def __set_name__(self, owner, name):
+                raise CustomException
+
+        annoying = Annoying()
+
+        with self.assertRaises(CustomException) as cm:
+            class NormalClass:
+                attr = annoying
+        normal_exception = cm.exception
+
+        with self.assertRaises(CustomException) as cm:
+            class NamedTupleClass(NamedTuple):
+                attr = annoying
+        namedtuple_exception = cm.exception
+
+        expected_note = (
+            "Error calling __set_name__ on 'Annoying' instance "
+            "'attr' in 'NamedTupleClass'"
+        )
+
+        self.assertIs(type(namedtuple_exception), CustomException)
+        self.assertIs(type(namedtuple_exception), type(normal_exception))
+        self.assertEqual(namedtuple_exception.args, normal_exception.args)
+
+        self.assertEqual(len(namedtuple_exception.__notes__), 1)
+        self.assertEqual(
+            len(namedtuple_exception.__notes__), len(normal_exception.__notes__)
+        )
+
+        self.assertEqual(namedtuple_exception.__notes__[0], expected_note)
+        self.assertEqual(
+            namedtuple_exception.__notes__[0],
+            normal_exception.__notes__[0].replace("NormalClass", "NamedTupleClass")
+        )
+
+    @skip_if_early_py313_alpha
+    def test_strange_errors_when_accessing_set_name_itself(self):
+        class CustomException(Exception): pass
+
+        class Meta(type):
+            def __getattribute__(self, attr):
+                if attr == "__set_name__":
+                    raise CustomException
+                return object.__getattribute__(self, attr)
+
+        class VeryAnnoying(metaclass=Meta): pass
+
+        very_annoying = VeryAnnoying()
+
+        with self.assertRaises(CustomException):
+            class Foo(NamedTuple):
+                attr = very_annoying
+
 
 class TypeVarTests(BaseTestCase):
     def test_basic_plain(self):

src/typing_extensions.py

@@ -2467,11 +2467,35 @@ def __new__(cls, typename, bases, ns):
                     class_getitem = typing.Generic.__class_getitem__.__func__
                     nm_tpl.__class_getitem__ = classmethod(class_getitem)
             # update from user namespace without overriding special namedtuple attributes
-            for key in ns:
+            for key, val in ns.items():
                 if key in _prohibited_namedtuple_fields:
                     raise AttributeError("Cannot overwrite NamedTuple attribute " + key)
-                elif key not in _special_namedtuple_fields and key not in nm_tpl._fields:
-                    setattr(nm_tpl, key, ns[key])
+                elif key not in _special_namedtuple_fields:
+                    if key not in nm_tpl._fields:
+                        setattr(nm_tpl, key, ns[key])
+                    try:
+                        set_name = type(val).__set_name__
+                    except AttributeError:
+                        pass
+                    else:
+                        try:
+                            set_name(val, nm_tpl, key)
+                        except BaseException as e:
+                            msg = (
+                                f"Error calling __set_name__ on {type(val).__name__!r} "
+                                f"instance {key!r} in {typename!r}"
+                            )
+                            # BaseException.add_note() existed on py311,
+                            # but the __set_name__ machinery didn't start
+                            # using add_note() until py312.
+                            # Making sure exceptions are raised in the same way
+                            # as in "normal" classes seems most important here.
+                            if sys.version_info >= (3, 12):
+                                e.add_note(msg)
+                                raise
+                            else:
+                                raise RuntimeError(msg) from e
+
             if typing.Generic in bases:
                 nm_tpl.__init_subclass__()
             return nm_tpl