diff -r 99c5922b1641 -r 100f0ddb029b mercurial/configitems.py
--- a/mercurial/configitems.py	Sun Oct 08 21:36:26 2017 +0200
+++ b/mercurial/configitems.py	Sun Oct 08 21:41:22 2017 +0200
@@ -116,6 +116,9 @@
 coreconfigitem('devel', 'bundle2.debug',
     default=False,
 )
+coreconfigitem('devel', 'cache-vfs',
+    default=None,
+)
 coreconfigitem('devel', 'check-locks',
     default=False,
 )