--- a/mercurial/revlog.py Mon May 03 12:18:48 2021 +0200
+++ b/mercurial/revlog.py Mon May 03 12:18:58 2021 +0200
@@ -3082,6 +3082,18 @@
# Nothing to generate or remove
return
+ # changelog implement some "delayed" writing mechanism that assume that
+ # all index data is writen in append mode and is therefor incompatible
+ # with the seeked write done in this method. The use of such "delayed"
+ # writing will soon be removed for revlog version that support side
+ # data, so for now, we only keep this simple assert to highlight the
+ # situation.
+ delayed = getattr(self, '_delayed', False)
+ diverted = getattr(self, '_divert', False)
+ if delayed and not diverted:
+ msg = "cannot rewrite_sidedata of a delayed revlog"
+ raise error.ProgrammingError(msg)
+
new_entries = []
# append the new sidedata
with self._datafp(b'a+') as fp: