diff -r 93f4e183b3f5 -r f8330a3fc39f mercurial/revlogutils/deltas.py
--- a/mercurial/revlogutils/deltas.py	Sun Jun 20 23:05:58 2021 +0200
+++ b/mercurial/revlogutils/deltas.py	Mon Jun 07 11:59:27 2021 +0200
@@ -1070,7 +1070,7 @@
         context.
         """
         if target_rev is None:
-            curr = len(self.revlog)
+            target_rev = len(self.revlog)
 
         if not revinfo.textlen:
             return self._fullsnapshotinfo(fh, revinfo, target_rev)