Also emit a warning if the class decorated by @NoPickle directly impl…

…ements one of the methods we override.

CHANGES.rst

@@ -11,7 +11,9 @@
   subclasses of ``Persistent``, depending on the MRO,
   but that's always been the case for regular objects). A
   ``Persistent`` subclass being decorated with ``@NoPickle`` doesn't
-  make much sense, so a ``RuntimeWarning`` is issued.
+  make much sense, so a ``RuntimeWarning`` is issued. A warning is
+  also issued if the class directly implements one of the pickle
+  protocol methods.
 
 - Updating objects that use ``createFieldProperties`` or otherwise
   have ``FieldProperty`` objects in their type is at least 10% faster

src/nti/externalization/persistence.py

@@ -18,6 +18,7 @@
     from itertools import izip
 except ImportError: # pragma: no cover
     izip = zip
+import warnings
 
 import persistent
 from persistent.list import PersistentList
@@ -277,14 +278,16 @@ class CanPickle(Persistent, Root):
     def __reduce_ex__(self, protocol=0):
         raise TypeError(msg)
 
-
-    cls.__reduce_ex__ = __reduce_ex__
-    cls.__reduce__ = __reduce_ex__
-    cls.__getstate__ = __reduce_ex__
+    for meth in '__reduce_ex__', '__reduce__', '__getstate__':
+        if vars(cls).get(meth) is not None:
+            warnings.warn(RuntimeWarning("Using @NoPickle an a class that implements " + meth),
+                          stacklevel=2)
+        setattr(cls, meth, __reduce_ex__)
 
     if issubclass(cls, persistent.Persistent):
-        import warnings
         warnings.warn(RuntimeWarning("Using @NoPickle an a Persistent subclass"),
                       stacklevel=2)
 
+
+
     return cls

src/nti/externalization/tests/test_persistence.py

@@ -286,13 +286,37 @@ def test_persistent_mixin2(self):
     def test_persistent_mixin3(self):
         self._all_persists_fail(GlobalNoPicklePersistentMixin3)
 
-    def test_persistent_emits_warning(self):
+    def _check_emits_warning(self, kind):
         with warnings.catch_warnings(record=True) as w:
-            class P(Persistent):
-                pass
-            NoPickle(P)
+            NoPickle(kind)
 
         assert_that(w, has_length(1))
         assert_that(w[0].message, is_(RuntimeWarning))
         self.assertIn("Using @NoPickle",
                       str(w[0].message))
+
+    def test_persistent_emits_warning(self):
+        class P(Persistent):
+            pass
+        self._check_emits_warning(P)
+
+    def test_getstate_emits_warning(self):
+        class P(object):
+            def __getstate__(self):
+                "Does nothing"
+
+        self._check_emits_warning(P)
+
+    def test_reduce_emits_warning(self):
+        class P(object):
+            def __reduce__(self):
+                "Does nothing"
+
+        self._check_emits_warning(P)
+
+    def test_reduce_ex_emits_warning(self):
+        class P(object):
+            def __reduce_ex__(self):
+                "Does nothing"
+
+        self._check_emits_warning(P)