bpo-37140 ctypes change made clang fail to build

Lib/ctypes/test/test_structures.py

@@ -4,6 +4,7 @@
 from struct import calcsize
 import _ctypes_test
 import test.support
+import sys
 
 class SubclassesTest(unittest.TestCase):
     def test_subclass(self):
@@ -438,6 +439,38 @@ class X(Structure):
         self.assertEqual(s.first, got.first)
         self.assertEqual(s.second, got.second)
 
+    # bpo-37140: ctypes change made clang fail to build
+    def test_pass_by_value_string_buffer(self):
+        dll = CDLL(_ctypes_test.__file__)
+        dll.my_strdup.restype = POINTER(c_char)
+        dll.my_free.restype = None
+
+        # This should mirror the structure in Modules/_ctypes/_ctypes_test.c
+        class X(Structure):
+            _fields_ = [
+                ('first', c_ulong),
+                ('second', c_ulong),
+                ('third', POINTER(c_char)),
+            ]
+            def __del__(self):
+                # Windows throws 'Windows fatal exception: access violation'
+                # on second call to __del__
+                # causing this test to fail
+                dll.my_free(self.third)
+
+        hello = b"Hello"
+        s = X()
+        s.first = 0xdeadbeef
+        s.second = 0xcafebabe
+        s.third = dll.my_strdup(hello)
+        func = dll._testfunc_large_struct_update_value_string_buffer
+        func.argtypes = (X,)
+        func.restype = None
+        func(s)
+        self.assertEqual(s.first, 0xdeadbeef)
+        self.assertEqual(s.second, 0xcafebabe)
+        # string is already freed by pass-by-value copy of struct 's'
+        #self.assertEqual(s.third[0], b'J')
 
 class PointerMemberTestCase(unittest.TestCase):
 

Modules/_ctypes/_ctypes.c

@@ -431,7 +431,7 @@ StructUnionType_paramfunc(CDataObject *self)
     parg->pffi_type = &stgdict->ffi_type_pointer;
     parg->value.p = copied_self->b_ptr;
     parg->size = copied_self->b_size;
-    parg->obj = (PyObject *)copied_self;
+    parg->obj = PyTuple_Pack(2, self, copied_self);
     return parg;
 }
 

Modules/_ctypes/_ctypes_test.c

@@ -57,6 +57,26 @@ _testfunc_large_struct_update_value(Test in)
     ((volatile Test *)&in)->third = 0x0badf00d;
 }
 
+typedef struct {
+    unsigned long first;
+    unsigned long second;
+    char *third;
+} TestStringBuffer;
+
+/*
+ * See issue 37140. Update a structure passed by value
+ * that contains a pointer to a string and a destructor;
+ * the pointer to the string should not be double-freed.
+ */
+
+EXPORT(void)
+_testfunc_large_struct_update_value_string_buffer(TestStringBuffer in)
+{
+    ((volatile TestStringBuffer *)&in)->first = 0x0badf00d;
+    ((volatile TestStringBuffer *)&in)->second = 0x0badf00d;
+    ((volatile TestStringBuffer *)&in)->third[0] = 'J';
+}
+
 typedef struct {
     unsigned int first;
     unsigned int second;