diff -r 1464183343b3 -r f8db458651c8 mercurial/revlog.py
--- a/mercurial/revlog.py	Wed Aug 15 15:20:44 2018 +0200
+++ b/mercurial/revlog.py	Fri Jul 20 13:32:17 2018 +0200
@@ -2095,6 +2095,16 @@
         else:
             return rev - 1
 
+    def issnapshot(self, rev):
+        """tells whether rev is a snapshot
+        """
+        if rev == nullrev:
+            return True
+        deltap = self.deltaparent(rev)
+        if deltap == nullrev:
+            return True
+        return False
+
     def revdiff(self, rev1, rev2):
         """return or calculate a delta between two revisions