--- a/hgext3rd/evolve/obscache.py	Wed May 10 11:52:11 2017 +0200
+++ b/hgext3rd/evolve/obscache.py	Thu May 11 16:05:50 2017 +0200
@@ -109,22 +109,13 @@
     # In pratice the cache is only updated after each transaction within a
     # lock. So we should be fine. We could enforce this with a new repository
     # requirement (or fix the race, that is not too hard).
-    invalid = (False, 0, 0)
-    if key is None:
-        return invalid
 
-    ### Is the cache valid ?
+    status = _checkkey(repo, key)
+    if status is None:
+        return (False, 0, 0)
+
     keytiprev, keytipnode, keyobslength, keyobssize, keyobskey = key
-    # check for changelog strip
-    cl = repo.changelog
-    tiprev = len(cl) - 1
-    if (tiprev < keytiprev
-            or cl.node(keytiprev) != keytipnode):
-        return invalid
-    # check for obsstore strip
-    obssize, obskey = repo.obsstore.cachekey(index=keyobssize)
-    if obskey != keyobskey:
-        return invalid
+    tiprev, obssize, __ = status
 
     ### cache is valid, is there anything to update
 
@@ -140,6 +131,24 @@
 
     return True, startrev, startidx
 
+def _checkkey(repo, key):
+    """internal function"""
+    if key is None:
+        return None
+
+    ### Is the cache valid ?
+    keytiprev, keytipnode, keyobslength, keyobssize, keyobskey = key
+    # check for changelog strip
+    cl = repo.changelog
+    tiprev = len(cl) - 1
+    if (tiprev < keytiprev
+            or cl.node(keytiprev) != keytipnode):
+        return None
+    # check for obsstore strip
+    obssize, obskey = repo.obsstore.cachekey(index=keyobssize)
+    if obskey != keyobskey:
+        return None
+    return tiprev, obssize, obskey
 
 # XXX copied as is from Mercurial 4.2 and added the "offset" parameters
 @util.nogc