Revert "Remove failure version number"

This will likely cause a major version bump,
let's not do that right now, because well its not
really worth such a bump for just this change.

This reverts commit c560e71d91.

Change-Id: I3aafa02da91bc39456c705e9f05ec2de625f7e6c

taskflow/tests/unit/test_failure.py

@@ -152,6 +152,14 @@ class FailureObjectTestCase(test.TestCase):
         }
         self.assertRaises(exceptions.InvalidFormat,
                           failure.Failure.validate, f)
+        f = {
+            'exception_str': 'blah',
+            'traceback_str': 'blah',
+            'exc_type_names': ['Exception'],
+            'version': -1,
+        }
+        self.assertRaises(exceptions.InvalidFormat,
+                          failure.Failure.validate, f)
 
     def test_valid_from_dict_to_dict(self):
         f = _captured_failure('Woot!')

taskflow/types/failure.py

@@ -121,6 +121,7 @@ class Failure(mixins.StrMixin):
     backport at https://pypi.python.org/pypi/traceback2/ to (hopefully)
     simplify the methods and contents of this object...
     """
+    DICT_VERSION = 1
 
     BASE_EXCEPTIONS = ('BaseException', 'Exception')
     """
@@ -136,6 +137,10 @@ class Failure(mixins.StrMixin):
             "cause": {
                 "type": "object",
                 'properties': {
+                    'version': {
+                        "type": "integer",
+                        "minimum": 0,
+                    },
                     'exception_str': {
                         "type": "string",
                     },
@@ -462,6 +467,10 @@ class Failure(mixins.StrMixin):
     def from_dict(cls, data):
         """Converts this from a dictionary to a object."""
         data = dict(data)
+        version = data.pop('version', None)
+        if version != cls.DICT_VERSION:
+            raise ValueError('Invalid dict version of failure object: %r'
+                             % version)
         causes = data.get('causes')
         if causes is not None:
             data['causes'] = tuple(cls.from_dict(d) for d in causes)
@@ -473,6 +482,7 @@ class Failure(mixins.StrMixin):
             'exception_str': self.exception_str,
             'traceback_str': self.traceback_str,
             'exc_type_names': list(self),
+            'version': self.DICT_VERSION,
             'causes': [f.to_dict() for f in self.causes],
         }