diff -r 84c6b9384d6a -r 85a2db47ad50 mercurial/configitems.py
--- a/mercurial/configitems.py	Tue Oct 17 21:15:31 2017 +0200
+++ b/mercurial/configitems.py	Mon Oct 16 17:41:27 2017 +0200
@@ -249,6 +249,9 @@
 coreconfigitem('devel', 'user.obsmarker',
     default=None,
 )
+coreconfigitem('devel', 'warn-config-unknown',
+    default=None,
+)
 coreconfigitem('diff', 'nodates',
     default=False,
 )