rebase -r: do not (re-)generate root commits with `--root` *and* `--onto`

When rebasing a complete commit history onto a given commit, it is
pretty obvious that the root commits should be rebased on top of said
given commit.

To test this, let's kill two birds with one stone and add a test case to
t3427-rebase-subtree.sh that not only demonstrates that this works, but
also that `git rebase -r` works with merge strategies now.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/sequencer.h b/sequencer.h
index 0c494b83d4..d506081d3c 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -142,6 +142,12 @@ int sequencer_remove_state(struct replay_opts *opts);
  */
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
 #define TODO_LIST_APPEND_TODO_HELP (1U << 5)
+/*
+ * When generating a script that rebases merges with `--root` *and* with
+ * `--onto`, we do not want to re-generate the root commits.
+ */
+#define TODO_LIST_ROOT_WITH_ONTO (1U << 6)
+
 
 int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 			  const char **argv, unsigned flags);