Correct a crash when two successive unicode allocations fail with a MemoryError:

the freelist contained half-initialized objects with freed pointers.

The comment
/* XXX UNREF/NEWREF interface should be more symmetrical */
was copied from tupleobject.c, and appears in some other places.
I sign the petition.

Lib/test/test_unicode.py

@@ -1113,6 +1113,20 @@ def __format__(self, format_spec):
         #  will fail
         self.assertRaises(UnicodeEncodeError, "foo{0}".format, u'\u1000bar')
 
+    def test_raiseMemError(self):
+        # Ensure that the freelist contains a consistent object, even
+        # when a string allocation fails with a MemoryError.
+        # This used to crash the interpreter,
+        # or leak references when the number was smaller.
+        try:
+            u"a" * (sys.maxint // 2 - 100)
+        except MemoryError:
+            pass
+        try:
+            u"a" * (sys.maxint // 2 - 100)
+        except MemoryError:
+            pass
+
 def test_main():
     test_support.run_unittest(__name__)
 

Objects/unicodeobject.c

@@ -315,7 +315,7 @@ PyUnicodeObject *_PyUnicode_New(Py_ssize_t length)
 	    if ((unicode->length < length) &&
                 unicode_resize(unicode, length) < 0) {
 		PyObject_DEL(unicode->str);
-		goto onError;
+		unicode->str = NULL;
 	    }
 	}
         else {
@@ -352,6 +352,8 @@ PyUnicodeObject *_PyUnicode_New(Py_ssize_t length)
     return unicode;
 
  onError:
+    /* XXX UNREF/NEWREF interface should be more symmetrical */
+    _Py_DEC_REFTOTAL;
     _Py_ForgetReference((PyObject *)unicode);
     PyObject_Del(unicode);
     return NULL;