diff -r ecf6d7aa874b -r 0428978bca22 mercurial/commit.py
--- a/mercurial/commit.py	Tue Oct 06 19:11:34 2020 +0530
+++ b/mercurial/commit.py	Sat Oct 10 12:43:04 2020 +0530
@@ -155,7 +155,7 @@
     copy_sd = repo.filecopiesmode == b'changeset-sidedata'
     if copy_sd and len(ctx.parents()) > 1:
         if ms.active():
-            for fname in sorted(ms._stateextras.keys()):
+            for fname in sorted(ms.allextras().keys()):
                 might_removed = ms.extras(fname).get(b'merge-removal-candidate')
                 if might_removed == b'yes':
                     if fname in ctx: