1 files changed, 80 insertions, 0 deletions
diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index cdf4a91..ab23206 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -576,6 +576,86 @@ class StructureTestCase(unittest.TestCase):
             self.assertEqual(f2, [0x4567, 0x0123, 0xcdef, 0x89ab,
                                   0x3210, 0x7654, 0xba98, 0xfedc])
 
+    def test_union_by_value(self):
+        # See bpo-16575
+
+        # These should mirror the structures in Modules/_ctypes/_ctypes_test.c
+
+        class Nested1(Structure):
+            _fields_ = [
+                ('an_int', c_int),
+                ('another_int', c_int),
+            ]
+
+        class Test4(Union):
+            _fields_ = [
+                ('a_long', c_long),
+                ('a_struct', Nested1),
+            ]
+
+        class Nested2(Structure):
+            _fields_ = [
+                ('an_int', c_int),
+                ('a_union', Test4),
+            ]
+
+        class Test5(Structure):
+            _fields_ = [
+                ('an_int', c_int),
+                ('nested', Nested2),
+                ('another_int', c_int),
+            ]
+
+        test4 = Test4()
+        dll = CDLL(_ctypes_test.__file__)
+        with self.assertRaises(TypeError) as ctx:
+            func = dll._testfunc_union_by_value1
+            func.restype = c_long
+            func.argtypes = (Test4,)
+            result = func(test4)
+        self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
+                         'a union by value, which is unsupported.')
+        test5 = Test5()
+        with self.assertRaises(TypeError) as ctx:
+            func = dll._testfunc_union_by_value2
+            func.restype = c_long
+            func.argtypes = (Test5,)
+            result = func(test5)
+        self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
+                         'a union by value, which is unsupported.')
+
+        # passing by reference should be OK
+        test4.a_long = 12345;
+        func = dll._testfunc_union_by_reference1
+        func.restype = c_long
+        func.argtypes = (POINTER(Test4),)
+        result = func(byref(test4))
+        self.assertEqual(result, 12345)
+        self.assertEqual(test4.a_long, 0)
+        self.assertEqual(test4.a_struct.an_int, 0)
+        self.assertEqual(test4.a_struct.another_int, 0)
+        test4.a_struct.an_int = 0x12340000
+        test4.a_struct.another_int = 0x5678
+        func = dll._testfunc_union_by_reference2
+        func.restype = c_long
+        func.argtypes = (POINTER(Test4),)
+        result = func(byref(test4))
+        self.assertEqual(result, 0x12345678)
+        self.assertEqual(test4.a_long, 0)
+        self.assertEqual(test4.a_struct.an_int, 0)
+        self.assertEqual(test4.a_struct.another_int, 0)
+        test5.an_int = 0x12000000
+        test5.nested.an_int = 0x345600
+        test5.another_int = 0x78
+        func = dll._testfunc_union_by_reference3
+        func.restype = c_long
+        func.argtypes = (POINTER(Test5),)
+        result = func(byref(test5))
+        self.assertEqual(result, 0x12345678)
+        self.assertEqual(test5.an_int, 0)
+        self.assertEqual(test5.nested.an_int, 0)
+        self.assertEqual(test5.another_int, 0)
+
 class PointerMemberTestCase(unittest.TestCase):
 
     def test(self):