--- a/mercurial/revlogutils/constants.py	Mon Apr 05 12:20:52 2021 +0200
+++ b/mercurial/revlogutils/constants.py	Mon Apr 05 12:21:01 2021 +0200
@@ -44,6 +44,19 @@
 # 20 bytes: nodeid
 INDEX_ENTRY_V0 = struct.Struct(b">4l20s20s20s")
 
+## index v1
+#  6 bytes: offset
+#  2 bytes: flags
+#  4 bytes: compressed length
+#  4 bytes: uncompressed length
+#  4 bytes: base rev
+#  4 bytes: link rev
+#  4 bytes: parent 1 rev
+#  4 bytes: parent 2 rev
+# 32 bytes: nodeid
+INDEX_ENTRY_V1 = struct.Struct(b">Qiiiiii20s12x")
+assert INDEX_ENTRY_V1.size == 32 * 2
+
 # revlog index flags
 
 # For historical reasons, revlog's internal flags were exposed via the