diff -r db11f8f39caf -r 00402df57db7 mercurial/hg.py
--- a/mercurial/hg.py	Mon Sep 28 16:54:35 2020 +0200
+++ b/mercurial/hg.py	Mon Sep 28 08:07:09 2020 -0700
@@ -1049,6 +1049,10 @@
     When overwrite is set, changes are clobbered, merged else
 
     returns stats (see pydoc mercurial.merge.applyupdates)"""
+    repo.ui.deprecwarn(
+        b'prefer merge.update() or merge.clean_update() over hg.updaterepo()',
+        b'5.7',
+    )
     return mergemod._update(
         repo,
         node,