rebase --preserve-merges: keep all merge commits including empty ones
Since 90e1818f9a (git-rebase: add keep_empty flag, 2012-04-20) 'git rebase --preserve-merges' fails to preserve empty merge commits unless --keep-empty is also specified. Merge commits should be preserved in order to preserve the structure of the rebased graph, even if the merge commit does not introduce changes to the parent.
Teach rebase not to drop merge commits only because they are empty.
A special case which is not handled by this change is for a merge commit whose parents are now the same commit because all the previous different parents have been dropped as a result of this rebase or some previous operation.
Signed-off-by: Phil Hord <firstname.lastname@example.org> Acked-by: Neil Horman <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>