Set the field and value of ValidationError raised by checking constra…

…ints. Fixes #66

CHANGES.rst

@@ -5,7 +5,10 @@
 4.6.2 (unreleased)
 ==================
 
-- Nothing changed yet.
+- Fix checking a field's constraint to set the ``field`` and ``value``
+  properties if the constraint raises a ``ValidationError``. See
+  `issue 66
+  <https://github.com/zopefoundation/zope.schema/issues/66>`_.
 
 
 4.6.1 (2018-09-10)

src/zope/schema/_bootstrapfields.py

@@ -331,7 +331,15 @@ def _validate(self, value):
         if self._type is not None and not isinstance(value, self._type):
             raise WrongType(value, self._type, self.__name__).with_field_and_value(self, value)
 
-        if not self.constraint(value):
+        try:
+            constraint = self.constraint(value)
+        except ValidationError as e:
+            if e.field is None:
+                e.field = self
+            if e.value is None:
+                e.value = value
+            raise
+        if not constraint:
             raise ConstraintNotSatisfied(value, self.__name__).with_field_and_value(self, value)
 
     def get(self, object):

src/zope/schema/tests/test__bootstrapfields.py

@@ -527,6 +527,30 @@ def _fail(value):
         field._type = int
         field.validate(1)  # doesn't raise
 
+    def test_validate_constraint_raises_custom_exception(self):
+        from zope.schema._bootstrapinterfaces import ValidationError
+
+        def _fail(value):
+            raise ValidationError
+        field = self._makeOne(constraint=_fail)
+        with self.assertRaises(ValidationError) as exc:
+            field.validate(1)
+
+        self.assertIs(exc.exception.field, field)
+        self.assertEqual(exc.exception.value, 1)
+
+    def test_validate_constraint_raises_custom_exception_no_overwrite(self):
+        from zope.schema._bootstrapinterfaces import ValidationError
+
+        def _fail(value):
+            raise ValidationError(value).with_field_and_value(self, self)
+        field = self._makeOne(constraint=_fail)
+        with self.assertRaises(ValidationError) as exc:
+            field.validate(1)
+
+        self.assertIs(exc.exception.field, self)
+        self.assertIs(exc.exception.value, self)
+
     def test_get_miss(self):
         field = self._makeOne(__name__='nonesuch')
         inst = DummyInst()