diff -r 4591c9791a82 -r e06719b7544d mercurial/configitems.py
--- a/mercurial/configitems.py	Wed Dec 12 22:45:02 2018 +0900
+++ b/mercurial/configitems.py	Thu Dec 13 14:44:54 2018 -0500
@@ -1307,6 +1307,9 @@
 coreconfigitem('web', 'cache',
     default=True,
 )
+coreconfigitem('web', 'comparisoncontext',
+    default=5,
+)
 coreconfigitem('web', 'contact',
     default=None,
 )