diff -r 28a65fd4b359 -r 2529e2ae9f4c mercurial/configitems.py
--- a/mercurial/configitems.py	Sat Jun 17 12:15:28 2017 +0200
+++ b/mercurial/configitems.py	Sat Jun 17 12:33:59 2017 +0200
@@ -33,3 +33,9 @@
         msg = "duplicated config item registration for '%s.%s'"
         raise error.ProgrammingError(msg % (item.section, item.name))
     section[item.name] = item
+
+# Registering actual config items
+
+coreconfigitem('ui', 'quiet',
+    default=False,
+)