diff -r 517a2c1cb788 -r 2174f54aab18 mercurial/upgrade_utils/engine.py
--- a/mercurial/upgrade_utils/engine.py	Sun Aug 01 10:57:21 2021 -0400
+++ b/mercurial/upgrade_utils/engine.py	Mon Aug 02 08:05:13 2021 -0400
@@ -201,7 +201,7 @@
 
     # Perform a pass to collect metadata. This validates we can open all
     # source files and allows a unified progress bar to be displayed.
-    for rl_type, unencoded, encoded, size in alldatafiles:
+    for rl_type, unencoded, size in alldatafiles:
         if not rl_type & store.FILEFLAGS_REVLOG_MAIN:
             continue