--- a/mercurial/merge.py	Sat Aug 17 18:28:55 2019 +0900
+++ b/mercurial/merge.py	Wed Aug 21 13:14:39 2019 -0700
@@ -2025,7 +2025,8 @@
                 raise error.Abort(_("outstanding uncommitted merge"))
             ms = mergestate.read(repo)
             if list(ms.unresolved()):
-                raise error.Abort(_("outstanding merge conflicts"))
+                raise error.Abort(_("outstanding merge conflicts"),
+                                  hint=_("use 'hg resolve' to resolve"))
         if branchmerge:
             if pas == [p2]:
                 raise error.Abort(_("merging with a working directory ancestor"