Fix the error properties for propertyNames.

Note that propertyNames is another example (like #119)
of something that needs an additional way to say it
has errored on a *key* within the instance.

So, that's still missing, but path is not the right
thing, same as in the earlier instances.

It's also becoming somewhat clear that compound
validators should possibly grow a way to become lazy...

Author: Julian

jsonschema/_validators.py

@@ -26,7 +26,6 @@ def propertyNames(validator, propertyNames, instance, schema):
         for error in validator.descend(
             instance=property,
             schema=propertyNames,
-            path=property,  # FIXME: path?
         ):
             yield error
 

jsonschema/tests/test_validators.py

@@ -881,6 +881,20 @@ def test_additionalItems_with_items(self):
         self.assertEqual(e1.validator, "type")
         self.assertEqual(e2.validator, "minimum")
 
+    def test_propertyNames(self):
+        instance = {"foo": 12}
+        schema = {"propertyNames": {"not": {"const": "foo"}}}
+
+        validator = validators.Draft7Validator(schema)
+        error, = validator.iter_errors(instance)
+
+        self.assertEqual(error.validator, "not")
+        self.assertEqual(
+            error.message,
+            "%r is not allowed for %r" % ({"const": "foo"}, "foo"),
+        )
+        self.assertEqual(error.path, deque([]))
+
 
 class MetaSchemaTestsMixin(object):
     # TODO: These all belong upstream