mercurial/upgrade.py

--- a/mercurial/upgrade.py	Mon Jul 16 17:10:52 2018 -0700
+++ b/mercurial/upgrade.py	Thu Jun 21 18:05:55 2018 +0200
@@ -61,7 +61,9 @@
     the dropped requirement must appear in the returned set for the upgrade
     to be allowed.
     """
-    return set()
+    return {
+        localrepo.SPARSEREVLOG_REQUIREMENT,
+    }
 
 def supporteddestrequirements(repo):
     """Obtain requirements that upgrade supports in the destination.
@@ -77,6 +79,7 @@
         'generaldelta',
         'revlogv1',
         'store',
+        localrepo.SPARSEREVLOG_REQUIREMENT,
     }
 
 def allowednewrequirements(repo):
@@ -93,6 +96,7 @@
         'dotencode',
         'fncache',
         'generaldelta',
+        localrepo.SPARSEREVLOG_REQUIREMENT,
     }
 
 def preservedrequirements(repo):