diff -r 324b4b10351e -r 25b2868206e2 mercurial/configitems.py
--- a/mercurial/configitems.py	Tue Oct 02 17:34:34 2018 -0700
+++ b/mercurial/configitems.py	Fri Sep 07 11:16:06 2018 -0400
@@ -377,6 +377,9 @@
 coreconfigitem('devel', 'warn-config-unknown',
     default=None,
 )
+coreconfigitem('devel', 'debug.copies',
+    default=False,
+)
 coreconfigitem('devel', 'debug.extensions',
     default=False,
 )