--- a/mercurial/obsolete.py	Wed Jul 19 13:17:49 2017 -0700
+++ b/mercurial/obsolete.py	Wed Apr 03 11:21:27 2019 -0700
@@ -743,7 +743,7 @@
                 pruned = [m for m in succsmarkers.get(current, ()) if not m[1]]
                 direct.update(pruned)
             direct -= seenmarkers
-            pendingnodes = set([m[0] for m in direct])
+            pendingnodes = {m[0] for m in direct}
             seenmarkers |= direct
             pendingnodes -= seennodes
             seennodes |= pendingnodes