diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2732,7 +2732,18 @@ class _descgeneratorset(_generatorset):
         self._cache[x] = False
         return False
 
-class spanset(_orderedsetmixin):
+def spanset(repo, start=None, end=None):
+    """factory function to dispatch between fullreposet and actual spanset
+
+    Feel free to update all spanset call sites and kill this function at some
+    point.
+    """
+    if start is None and end is None:
+        return fullreposet(repo)
+    return _spanset(repo, start, end)
+
+
+class _spanset(_orderedsetmixin):
     """Duck type for baseset class which represents a range of revisions and
     can work lazily and without having all the range in memory
 
@@ -2851,7 +2862,7 @@ class spanset(_orderedsetmixin):
     def filter(self, l):
         return orderedlazyset(self, l, ascending=self.isascending())
 
-class fullreposet(spanset):
+class fullreposet(_spanset):
     """a set containing all revisions in the repo
 
     This class exists to host special optimisation.