diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -56,6 +56,9 @@ def getitemregister(configtable):
 
 coreconfigitem = getitemregister(coreitems)
 
+coreconfigitem('devel', 'all-warnings',
+    default=False,
+)
 coreconfigitem('patch', 'fuzz',
     default=2,
 )