diff -r 9f95f0bb343b -r 649f3b0495c8 mercurial/configitems.py
--- a/mercurial/configitems.py	Fri Jun 30 03:31:35 2017 +0200
+++ b/mercurial/configitems.py	Wed Jun 28 13:31:51 2017 +0200
@@ -89,6 +89,9 @@
 coreconfigitem('devel', 'disableloaddefaultcerts',
     default=False,
 )
+coreconfigitem('devel', 'legacy.exchange',
+    default=list,
+)
 coreconfigitem('devel', 'servercafile',
     default='',
 )