diff -r ff72bd52d56a -r 9d2b2df2c2ba mercurial/fancyopts.py
--- a/mercurial/fancyopts.py	Fri Mar 06 10:52:44 2020 +0100
+++ b/mercurial/fancyopts.py	Fri Mar 06 13:27:41 2020 -0500
@@ -314,7 +314,7 @@
     argmap = {}
     defmap = {}
     negations = {}
-    alllong = set(o[1] for o in options)
+    alllong = {o[1] for o in options}
 
     for option in options:
         if len(option) == 5: