diff --git a/mercurial/commit.py b/mercurial/commit.py
--- a/mercurial/commit.py
+++ b/mercurial/commit.py
@@ -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:
diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -2107,7 +2107,7 @@
     fm_files.end()
 
     fm_extras = fm.nested(b'extras')
-    for f, d in sorted(pycompat.iteritems(ms._stateextras)):
+    for f, d in sorted(pycompat.iteritems(ms.allextras())):
         if f in ms:
             # If file is in mergestate, we have already processed it's extras
             continue
diff --git a/mercurial/mergestate.py b/mercurial/mergestate.py
--- a/mercurial/mergestate.py
+++ b/mercurial/mergestate.py
@@ -306,7 +306,12 @@
             ):
                 yield f
 
+    def allextras(self):
+        """ return all extras information stored with the mergestate """
+        return self._stateextras
+
     def extras(self, filename):
+        """ return extras stored with the mergestate for the given filename """
         return self._stateextras[filename]
 
     def _resolve(self, preresolve, dfile, wctx):