bpo-30353: Fix pass by value for structs on 64-bit Cygwin/MinGW (GH-1559)

2 files changed, 26 insertions, 0 deletions

diff --git a/Lib/ctypes/test/test_as_parameter.py b/Lib/ctypes/test/test_as_parameter.py
index 2a3484b..a264057 100644
--- a/Lib/ctypes/test/test_as_parameter.py
+++ b/Lib/ctypes/test/test_as_parameter.py
@@ -169,6 +169,10 @@ class BasicWrapTestCase(unittest.TestCase):
         s2h = dll.ret_2h_func(self.wrap(inp))
         self.assertEqual((s2h.x, s2h.y), (99*2, 88*3))
 
+        # Test also that the original struct was unmodified (i.e. was passed by
+        # value)
+        self.assertEqual((inp.x, inp.y), (99, 88))
+
     def test_struct_return_8H(self):
         class S8I(Structure):
             _fields_ = [("a", c_int),
diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index 2e778fb..d90c711 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -417,6 +417,28 @@ class StructureTestCase(unittest.TestCase):
         self.assertEqual(s.second, 0xcafebabe)
         self.assertEqual(s.third, 0x0bad1dea)
 
+    def test_pass_by_value_in_register(self):
+        class X(Structure):
+            _fields_ = [
+                ('first', c_uint),
+                ('second', c_uint)
+            ]
+
+        s = X()
+        s.first = 0xdeadbeef
+        s.second = 0xcafebabe
+        dll = CDLL(_ctypes_test.__file__)
+        func = dll._testfunc_reg_struct_update_value
+        func.argtypes = (X,)
+        func.restype = None
+        func(s)
+        self.assertEqual(s.first, 0xdeadbeef)
+        self.assertEqual(s.second, 0xcafebabe)
+        got = X.in_dll(dll, "last_tfrsuv_arg")
+        self.assertEqual(s.first, got.first)
+        self.assertEqual(s.second, got.second)
+
+
 class PointerMemberTestCase(unittest.TestCase):
 
     def test(self):