--- a/hgext3rd/topic/revset.py	Tue Apr 07 15:39:23 2020 +0200
+++ b/hgext3rd/topic/revset.py	Mon Apr 20 00:05:05 2020 +0800
@@ -164,7 +164,10 @@
 
     def topicrel(repo, subset, x, *args):
         subset &= topicset(repo, subset, x)
-        return revset.generationsrel(repo, subset, x, *args)
+        # not using revset.generationssubrel directly because it was renamed
+        # hg <= 5.3 (8859de3e83dc)
+        generationssubrel = revset.subscriptrelations[b'generations']
+        return generationssubrel(repo, subset, x, *args)
 
     revset.subscriptrelations[b'topic'] = topicrel
     revset.subscriptrelations[b't'] = topicrel