mercurial/revlog.py

--- a/mercurial/revlog.py	Wed Jan 30 18:15:38 2019 +0100
+++ b/mercurial/revlog.py	Thu Jan 24 18:22:47 2019 -0500
@@ -497,6 +497,9 @@
         else:
             raise error.RevlogError(_('unknown version (%d) in revlog %s') %
                                     (fmt, self.indexfile))
+        # sparse-revlog can't be on without general-delta (issue6056)
+        if not self._generaldelta:
+            self._sparserevlog = False
 
         self._storedeltachains = True