--- a/mercurial/scmutil.py	Thu Sep 03 11:07:47 2020 -0400
+++ b/mercurial/scmutil.py	Tue Sep 01 18:08:24 2020 +0530
@@ -1492,6 +1492,11 @@
     return requirements, None
 
 
+def istreemanifest(repo):
+    """ returns whether the repository is using treemanifest or not """
+    return requirementsmod.TREEMANIFEST_REQUIREMENT in repo.requirements
+
+
 def writereporequirements(repo, requirements=None):
     """ writes requirements for the repo to .hg/requires """
     if requirements: