Backport rev 51819 from Thomas Heller

Anonymous structure fields that have a bit-width specified did not work,
and they gave a strange error message from PyArg_ParseTuple:
   function takes exactly 2 arguments (3 given).

Lib/ctypes/test/test_bitfields.py

@@ -215,5 +215,14 @@ class BitFieldTest(unittest.TestCase):
                         ("b", c_ubyte, 4)]
         self.failUnlessEqual(sizeof(X), sizeof(c_byte))
 
+    def test_anon_bitfields(self):
+        # anonymous bit-fields gave a strange error message
+        class X(Structure):
+            _fields_ = [("a", c_byte, 4),
+                        ("b", c_ubyte, 4)]
+        class Y(Structure):
+            _anonymous_ = ["_"]
+            _fields_ = [("_", X)]
+
 if __name__ == "__main__":
     unittest.main()

Modules/_ctypes/stgdict.c

@@ -177,11 +177,11 @@ MakeFields(PyObject *type, CFieldObject *descr,
 
 	for (i = 0; i < PySequence_Fast_GET_SIZE(fieldlist); ++i) {
 		PyObject *pair = PySequence_Fast_GET_ITEM(fieldlist, i); /* borrowed */
-		PyObject *fname, *ftype;
+		PyObject *fname, *ftype, *bits;
 		CFieldObject *fdescr;
 		CFieldObject *new_descr;
 		/* Convert to PyArg_UnpackTuple... */
-		if (!PyArg_ParseTuple(pair, "OO", &fname, &ftype)) {
+		if (!PyArg_ParseTuple(pair, "OO|O", &fname, &ftype, &bits)) {
 			Py_DECREF(fieldlist);
 			return -1;
 		}