--- a/mercurial/copies.py Wed Jan 27 22:10:57 2021 -0800
+++ b/mercurial/copies.py Thu Jan 28 00:14:15 2021 -0800
@@ -1229,8 +1229,11 @@
new_copies = pathcopies(base, ctx)
parent = wctx.p1()
_filter(parent, wctx, new_copies)
- # extra filtering to drop copy information for files that existed before
- # the graft (otherwise we would create merge filelog for non-merge commit
+ # Extra filtering to drop copy information for files that existed before
+ # the graft. This is to handle the case of grafting a rename onto a commit
+ # that already has the rename. Otherwise the presence of copy information
+ # would result in the creation of an empty commit where we would prefer to
+ # not create one.
for dest, __ in list(new_copies.items()):
if dest in parent:
del new_copies[dest]