diff -r 21025a4107d4 -r 294afb982a88 mercurial/error.py
--- a/mercurial/error.py	Mon Sep 09 14:03:12 2019 +0200
+++ b/mercurial/error.py	Wed Sep 04 00:59:15 2019 +0200
@@ -44,6 +44,13 @@
 class RevlogError(StorageError):
     __bytes__ = _tobytes
 
+class SidedataHashError(RevlogError):
+
+    def __init__(self, key, expected, got):
+        self.sidedatakey = key
+        self.expecteddigest = expected
+        self.actualdigest = got
+
 class FilteredIndexError(IndexError):
     __bytes__ = _tobytes