SWIG_AsWCharPtrAndSize improper operation if cptr NULL

SF bug #1327

This doesn't have any noticeable effect with the usage of
SWIG_AsWCharPtrAndSize as shipped by SWIG, but could be a problem if a
user is using this function with cptr equal to zero and psize is non-zero
 - the length would be incorrectly set due to the call to PyUnicode_GetSize
failing.

Examples/test-suite/li_std_wstring.i

@@ -38,6 +38,14 @@ wchar_t* test_cvalue(wchar_t* x) {
 }
   
 
+wchar_t* test_wchar_overload() {
+   return 0;
+}
+
+wchar_t* test_wchar_overload(wchar_t *x) {
+   return x;
+}
+
 std::wstring test_value(std::wstring x) {
    return x;
 }

Examples/test-suite/python/li_std_wstring_runme.py

@@ -13,6 +13,12 @@ if li_std_wstring.test_ccvalue(x) != x:
 if li_std_wstring.test_cvalue(x) != x:
   raise RuntimeError("bad string mapping")
 
+if li_std_wstring.test_wchar_overload(x) != x:
+  raise RuntimeError("bad string mapping")
+
+if li_std_wstring.test_wchar_overload("not unicode") != "not unicode":
+  raise RuntimeError("bad string mapping")
+
 if li_std_wstring.test_value(x) != x:
   print x, li_std_wstring.test_value(x)
   raise RuntimeError("bad string mapping")

Lib/python/pywstrings.swg

@@ -18,9 +18,7 @@ SWIG_AsWCharPtrAndSize(PyObject *obj, wchar_t **cptr, size_t *psize, int *alloc)
   int isunicode = PyUnicode_Check(obj);
 %#if PY_VERSION_HEX < 0x03000000
   if (!isunicode && PyString_Check(obj)) {
-    if (cptr) {
+    obj = tmp = PyUnicode_FromObject(obj);
-      obj = tmp = PyUnicode_FromObject(obj);
-    }
     isunicode = 1;
   }
 %#endif