diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -558,27 +558,7 @@ class changelog(revlog.revlog):
         sortedfiles = sorted(files.touched)
         sidedata = None
         if self._copiesstorage == b'changeset-sidedata':
-            sidedata = {}
-            p1copies = files.copied_from_p1
-            if p1copies:
-                p1copies = metadata.encodecopies(sortedfiles, p1copies)
-                sidedata[sidedatamod.SD_P1COPIES] = p1copies
-            p2copies = files.copied_from_p2
-            if p2copies:
-                p2copies = metadata.encodecopies(sortedfiles, p2copies)
-                sidedata[sidedatamod.SD_P2COPIES] = p2copies
-            filesadded = files.added
-            if filesadded:
-                filesadded = metadata.encodefileindices(sortedfiles, filesadded)
-                sidedata[sidedatamod.SD_FILESADDED] = filesadded
-            filesremoved = files.removed
-            if filesremoved:
-                filesremoved = metadata.encodefileindices(
-                    sortedfiles, filesremoved
-                )
-                sidedata[sidedatamod.SD_FILESREMOVED] = filesremoved
-            if not sidedata:
-                sidedata = None
+            sidedata = metadata.encode_copies_sidedata(files)
 
         if extra:
             extra = encodeextra(extra)
diff --git a/mercurial/metadata.py b/mercurial/metadata.py
--- a/mercurial/metadata.py
+++ b/mercurial/metadata.py
@@ -254,6 +254,30 @@ def decodefileindices(files, data):
         return None
 
 
+def encode_copies_sidedata(files):
+    sortedfiles = sorted(files.touched)
+    sidedata = {}
+    p1copies = files.copied_from_p1
+    if p1copies:
+        p1copies = encodecopies(sortedfiles, p1copies)
+        sidedata[sidedatamod.SD_P1COPIES] = p1copies
+    p2copies = files.copied_from_p2
+    if p2copies:
+        p2copies = encodecopies(sortedfiles, p2copies)
+        sidedata[sidedatamod.SD_P2COPIES] = p2copies
+    filesadded = files.added
+    if filesadded:
+        filesadded = encodefileindices(sortedfiles, filesadded)
+        sidedata[sidedatamod.SD_FILESADDED] = filesadded
+    filesremoved = files.removed
+    if filesremoved:
+        filesremoved = encodefileindices(sortedfiles, filesremoved)
+        sidedata[sidedatamod.SD_FILESREMOVED] = filesremoved
+    if not sidedata:
+        sidedata = None
+    return sidedata
+
+
 def _getsidedata(srcrepo, rev):
     ctx = srcrepo[rev]
     filescopies = computechangesetcopies(ctx)