add message back to Function and emit warning

fixes #64

CHANGES.txt

@@ -13,8 +13,11 @@ Bug Fixes
   reverted.  When you supply ``None`` as the ``default`` argument to a String,
   the rendered serialize() value will again be ``'None'``.  Sorry.
 
-- Normalize ``message`` argument to ``colander.Function`` -> ``msg`` (matches
-  other APIs.
+- Normalize ``colander.Function`` argument ``message`` to be ``msg``. This now
+  matches other APIs within Colander. The ``message`` argument is now
+  deprecated and a warning will be emitted.
+  https://github.com/Pylons/colander/issues/31
+  https://github.com/Pylons/colander/issues/64
 
 - ``iso8601.py``:  Convert ``ValueError`` (raised by ``datetime``) into
   ``ParseErrorr`` in ``parse_date``, so that the validation machinery

colander/__init__.py

@@ -230,8 +230,18 @@ class Function(object):
     The default value for the ``msg`` when not provided via the
     constructor is ``Invalid value``.
     """
-    def __init__(self, function, msg=_('Invalid value')):
+    def __init__(self, function, msg=None, message=None):
         self.function = function
+        # Handle bw compat
+        if msg is None and message is None:
+            msg = _('Invalid value')
+        elif message is not None:
+            warnings.warn(
+                'The "message" argument has been deprecated, use "msg" '
+                'instead.',
+                DeprecationWarning
+                )
+            msg = message
         self.msg = msg
 
     def __call__(self, node, value):

colander/tests/test_colander.py

@@ -243,6 +243,27 @@ class TestFunction(unittest.TestCase):
         e = invalid_exc(validator, None, None)
         self.assertEqual(e.msg, 'fail')
 
+    def test_deprecated_message(self):
+        validator = self._makeOne(lambda x: False, message='depr')
+        e = invalid_exc(validator, None, None)
+        self.assertEqual(e.msg.interpolate(), 'depr')
+
+    def test_deprecated_message_warning(self):
+        import warnings
+        orig_warn = warnings.warn
+        log = []
+        def warn(message, category=None, stacklevel=1):
+            log.append((message, category, stacklevel))
+        try:
+            # Monkey patching warn since catch_warnings context manager
+            # is not working when running the full suite
+            warnings.warn = warn
+            validator = self._makeOne(lambda x: False, message='depr')
+            invalid_exc(validator, None, None)
+            self.assertEqual(len(log), 1)
+        finally:
+            warnings.warn = orig_warn
+
     def test_error_message_adds_mapping_to_configured_message(self):
         validator = self._makeOne(lambda x: False, msg='fail ${val}')
         e = invalid_exc(validator, None, None)