diff -r 5d00e6061ba2 -r 56469d475341 mercurial/commands.py
--- a/mercurial/commands.py	Sun Aug 26 15:52:34 2018 -0400
+++ b/mercurial/commands.py	Sun Aug 26 16:42:28 2018 -0400
@@ -4559,8 +4559,13 @@
     all, mark, unmark, show, nostatus, remerge = \
         [opts.get(o) for o in flaglist]
 
-    if len(list(filter(None, [show, mark, unmark, remerge]))) > 1:
-        raise error.Abort(_("too many options specified"))
+    actioncount = len(list(filter(None, [show, mark, unmark, remerge])))
+    if actioncount > 1:
+        raise error.Abort(_("too many actions specified"))
+    elif (actioncount == 0
+          and ui.config('commands', 'resolve.explicit-re-merge')):
+        hint = _('use --mark, --unmark, --list or --re-merge')
+        raise error.Abort(_('no action specified'), hint=hint)
     if pats and all:
         raise error.Abort(_("can't specify --all and patterns"))
     if not (all or pats or show or mark or unmark):