Make TypeAliasType __module__ writable (#744)

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f35c482..77b27dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Unreleased
 
+- Make `typing_extensions.TypeAliasType`'s `__module__` attribute writable.
+  Backport of CPython PR
+  [#149172](https://github.com/python/cpython/pull/149172).
 - Fix setting of `__required_keys__` and `__optional_keys__` when inheriting
   keys with the same name.
 - Fix incorrect behaviour on Python 3.9 and Python 3.10 that meant that

src/test_typing_extensions.py

diff --git a/src/test_typing_extensions.py b/src/test_typing_extensions.py
index c702532..c3aede8 100644
--- a/src/test_typing_extensions.py
+++ b/src/test_typing_extensions.py
@@ -7114,7 +7114,7 @@
                 'AsyncGenerator', 'ContextManager', 'AsyncContextManager',
                 'ParamSpec', 'TypeVar', 'TypeVarTuple', 'get_type_hints',
             }
-        if sys.version_info < (3, 14):
+        if sys.version_info < (3, 15):
             exclude |= {
                 'TypeAliasType'
             }
@@ -8286,11 +8286,12 @@
             "attribute '__parameters__' of 'typing.TypeAliasType' objects is not writable",
         ):
             Simple.__parameters__ = (T,)
-        with self.assertRaisesRegex(
-            AttributeError,
-            "attribute '__module__' of 'typing.TypeAliasType' objects is not writable",
-        ):
-            Simple.__module__ = 42
+
+        # __module__ is the exception---it's assignable
+        module_sentinel = object()
+        Simple.__module__ = module_sentinel
+        self.assertIs(Simple.__module__, module_sentinel)
+
         with self.assertRaisesRegex(
             AttributeError,
             "'typing.TypeAliasType' object has no attribute 'some_attribute'",

src/typing_extensions.py

diff --git a/src/typing_extensions.py b/src/typing_extensions.py
index 05d4522..e370475 100644
--- a/src/typing_extensions.py
+++ b/src/typing_extensions.py
@@ -3677,14 +3677,14 @@
                 return typing.Union[other, self]
 
 
-# Breakpoint: https://github.com/python/cpython/pull/124795
-if sys.version_info >= (3, 14):
+# Breakpoint: https://github.com/python/cpython/pull/149172
+if sys.version_info >= (3, 15):
     TypeAliasType = typing.TypeAliasType
-# <=3.13
+# <=3.14
 else:
     # Breakpoint: https://github.com/python/cpython/pull/103764
     if sys.version_info >= (3, 12):
-        # 3.12-3.13
+        # 3.12-3.14
         def _is_unionable(obj):
             """Corresponds to is_unionable() in unionobject.c in CPython."""
             return obj is None or isinstance(obj, (
@@ -3797,7 +3797,7 @@
             self.__name__ = name
 
         def __setattr__(self, name: str, value: object, /) -> None:
-            if hasattr(self, "__name__"):
+            if hasattr(self, "__name__") and name != "__module__":
                 self._raise_attribute_error(name)
             super().__setattr__(name, value)
 
@@ -3808,7 +3808,7 @@
             # Match the Python 3.12 error messages exactly
             if name == "__name__":
                 raise AttributeError("readonly attribute")
-            elif name in {"__value__", "__type_params__", "__parameters__", "__module__"}:
+            elif name in {"__value__", "__type_params__", "__parameters__"}:
                 raise AttributeError(
                     f"attribute '{name}' of 'typing.TypeAliasType' objects "
                     "is not writable"