gh-158418: Fix zero-argument super() in ctypes.util.struct methods

@struct builds a new class and copies the decorated class's namespace
into it, so the __class__ cell of the copied methods still pointed at
the discarded class. Rebind that cell to the returned class, as
dataclasses does for slots=True.

Author: fedonman

Lib/ctypes/util.py

@@ -1,7 +1,7 @@
 import os
 import sys
 
-from dataclasses import dataclass
+from dataclasses import dataclass, _update_func_cell_for__class__
 
 lazy import functools
 lazy import inspect
@@ -478,6 +478,17 @@ class _Struct(endian_class):
         _fields_ = fields
         _anonymous_ = anonymous
 
+    for member in vars(_Struct).values():
+        if not isinstance(member, type) and hasattr(member, '__wrapped__'):
+            member = inspect.unwrap(member)
+        if isinstance(member, property):
+            functions = (member.fget, member.fset, member.fdel)
+        else:
+            functions = (member,)
+        for func in functions:
+            if inspect.isfunction(func):
+                _update_func_cell_for__class__(func, decorated_class, _Struct)
+
     return _Struct
 
 

Lib/test/test_ctypes/test_structures.py

@@ -955,6 +955,37 @@ class Foo:
 
         self.assertEqual(Foo.__name__, "Foo")
 
+    @subTests("endian", ["native", "little", "big"])
+    def test_struct_util_class_cell(self, endian):
+        @struct_util(endian=endian)
+        class Foo:
+            x: c_int
+
+            def __init__(self, x=0):
+                super().__init__(x)
+
+        self.assertEqual(Foo(1).x, 1)
+
+        @struct_util(endian=endian)
+        class Foo:
+            x: c_int
+
+            @classmethod
+            def create(cls):
+                return super().__new__(cls)
+
+        self.assertIsInstance(Foo.create(), Foo)
+
+        @struct_util(endian=endian)
+        class Foo:
+            x: c_int
+
+            @property
+            def cls(self):
+                return __class__
+
+        self.assertIs(Foo().cls, Foo)
+
     def test_string_annotations(self):
         from test.test_ctypes import struct_str_ann
         Point = struct_str_ann.Point