--- a/hgext3rd/evolve/__init__.py	Fri Jan 19 16:44:00 2018 +0530
+++ b/hgext3rd/evolve/__init__.py	Fri Jan 19 17:29:48 2018 +0530
@@ -947,16 +947,6 @@
     _deprecatealias('gup', 'next')
     _deprecatealias('gdown', 'previous')
 
-class MultipleSuccessorsError(RuntimeError):
-    """Exception raised by _singlesuccessor when multiple successor sets exists
-
-    The object contains the list of successorssets in its 'successorssets'
-    attribute to call to easily recover.
-    """
-
-    def __init__(self, successorssets):
-        self.successorssets = successorssets
-
 def _singlesuccessor(repo, p):
     """returns p (as rev) if not obsolete or its unique latest successors
 
@@ -975,7 +965,7 @@
         obs = obs.parents()[0]
         newer = compat.successorssets(repo, obs.node())
     if len(newer) > 1 or len(newer[0]) > 1:
-        raise MultipleSuccessorsError(newer)
+        raise utility.MultipleSuccessorsError(newer)
 
     return repo[newer[0][0]].rev()
 
@@ -996,7 +986,7 @@
         for p in repo[r].parents():
             try:
                 succ = _singlesuccessor(repo, p)
-            except MultipleSuccessorsError as exc:
+            except utility.MultipleSuccessorsError as exc:
                 dependencies[r] = exc.successorssets
                 continue
             if succ in revs:
@@ -1164,7 +1154,7 @@
         # no args and parent is obsolete, update to successors
         try:
             ctx = repo[_singlesuccessor(repo, repo['.'])]
-        except MultipleSuccessorsError as exc:
+        except utility.MultipleSuccessorsError as exc:
             repo.ui.write_err('parent is obsolete with multiple successors:\n')
             for ln in exc.successorssets:
                 for n in ln:

--- a/hgext3rd/evolve/utility.py	Fri Jan 19 16:44:00 2018 +0530
+++ b/hgext3rd/evolve/utility.py	Fri Jan 19 17:29:48 2018 +0530
@@ -66,3 +66,13 @@
     if maxrevs is not None and maxrevs < len(repo.unfiltered()):
         return False
     return True
+
+class MultipleSuccessorsError(RuntimeError):
+    """Exception raised by _singlesuccessor when multiple successor sets exists
+
+    The object contains the list of successorssets in its 'successorssets'
+    attribute to call to easily recover.
+    """
+
+    def __init__(self, successorssets):
+        self.successorssets = successorssets