diff -r 5d29c55414b3 -r cb7140e230c8 mercurial/configitems.py
--- a/mercurial/configitems.py	Wed Jun 28 14:53:54 2017 -0700
+++ b/mercurial/configitems.py	Wed Jun 28 13:19:40 2017 +0200
@@ -56,6 +56,9 @@
 
 coreconfigitem = getitemregister(coreitems)
 
+coreconfigitem('devel', 'all-warnings',
+    default=False,
+)
 coreconfigitem('patch', 'fuzz',
     default=2,
 )