Fix: propagate exceptions from slow_validate

traits/ctraits.c

@@ -3915,11 +3915,12 @@ validate_trait_complex ( trait_object * trait, has_traits_object * obj,
             case 8:  /* Perform 'slow' validate check: */
                 result = PyObject_CallMethod( PyTuple_GET_ITEM( type_info, 1 ),
                                   "slow_validate", "(OOO)", obj, name, value );
-                if ( result != NULL )
-                    return result;
 
-                PyErr_Clear();
-                break;
+                if (result == NULL && PyErr_ExceptionMatches(TraitError)) {
+                    PyErr_Clear();
+                    break;
+                }
+                return result;
 
             case 9:  /* Tuple item check: */
                 result = validate_trait_tuple_check(

traits/tests/test_regression.py

@@ -12,9 +12,10 @@
     Property,
     on_trait_change,
 )
+from traits.testing.optional_dependencies import numpy, requires_numpy
 from traits.trait_errors import TraitError
+from traits.trait_handlers import TraitType
 from traits.trait_types import Bool, DelegatesTo, Either, Instance, Int, List
-from traits.testing.optional_dependencies import numpy, requires_numpy
 
 if numpy is not None:
     from traits.trait_numeric import Array
@@ -108,6 +109,20 @@ def set_changed(self):
         self.changed = True
 
 
+class RaisingValidator(TraitType):
+    """ Trait type whose ``validate`` method raises an inappropriate exception.
+
+    Used for testing propagation of that exception.
+    """
+    info_text = "bogus"
+
+    #: The default value for the trait:
+    default_value = None
+
+    def validate(self, object, name, value):
+        raise ZeroDivisionError("Just testing")
+
+
 class TestRegression(unittest.TestCase):
     def test_default_value_for_no_cache(self):
         """ Make sure that CTrait.default_value_for() does not cache the
@@ -258,3 +273,16 @@ class StrictDummy(HasStrictTraits):
         a = StrictDummy()
         with self.assertRaises(TraitError):
             setattr(a, u"forbidden", 53)
+
+    def test_validate_exception_propagates(self):
+        class A(HasTraits):
+            foo = RaisingValidator()
+
+            bar = Either(None, RaisingValidator())
+
+        a = A()
+        with self.assertRaises(ZeroDivisionError):
+            a.foo = "foo"
+
+        with self.assertRaises(ZeroDivisionError):
+            a.bar = "foo"