diff -r 8782076874f5 -r 6cd8d8203204 mercurial/ui.py
--- a/mercurial/ui.py	Sat Oct 14 15:43:06 2017 -0400
+++ b/mercurial/ui.py	Fri Oct 13 15:58:54 2017 -0400
@@ -53,6 +53,8 @@
 [commands]
 # Make `hg status` emit cwd-relative paths by default.
 status.relative = yes
+# Refuse to perform an `hg update` that would cause a file content merge
+update.check = noconflict
 
 [diff]
 git = 1