Add a custom error message argument for missing schema nodes

missing_msg lets the developer specify a custom message in place of the
default "Required" if the node is missing.

CHANGES.txt

@@ -53,6 +53,9 @@ Features
 - The ``typ`` of a ``SchemaNode`` can optionally be pased in as a keyword
   argument. See https://github.com/Pylons/colander/issues/90
 
+- Add a ``missing_msg`` argument to ``SchemaNode`` that specifies the error
+  message to be used when the node is required and missing
+
 1.0a5 (2013-05-31)
 ------------------
 

colander/__init__.py

@@ -1743,6 +1743,9 @@ class _SchemaNode(object):
       :attr:`colander.drop`, the node is dropped from the schema if it isn't
       set during serialization/deserialization.
 
+    - ``missing_msg``: Optional error message to be used if the value is
+      required and missing.
+
     - ``preparer``: Optional preparer for this node.  It should be
       an object that implements the
       :class:`colander.interfaces.Preparer` interface.
@@ -1787,6 +1790,7 @@ class _SchemaNode(object):
     validator = None
     default = null
     missing = required
+    missing_msg = _('Required')
     name = ''
     raw_title = _marker
     title = ''
@@ -1928,9 +1932,9 @@ class _SchemaNode(object):
         if appstruct is null:
             appstruct = self.missing
             if appstruct is required:
-                raise Invalid(self, _('Required'))
+                raise Invalid(self, self.missing_msg)
             if isinstance(appstruct, deferred): # unbound schema with deferreds
-                raise Invalid(self, _('Required'))
+                raise Invalid(self, self.missing_msg)
             # We never deserialize or validate the missing value
             return appstruct
 

colander/tests/test_colander.py

@@ -2438,6 +2438,13 @@ class TestSchemaNode(unittest.TestCase):
         node.missing = 'abc'
         self.assertEqual(node.deserialize(null), 'abc')
 
+    def test_deserialize_value_is_null_with_missing_msg(self):
+        from colander import null
+        typ = DummyType()
+        node = self._makeOne(typ, missing_msg='Missing')
+        e = invalid_exc(node.deserialize, null)
+        self.assertEqual(e.msg, 'Missing')
+
     def test_deserialize_noargs_uses_default(self):
         typ = DummyType()
         node = self._makeOne(typ)