rebase -i: support --root without --onto

Allow --root to be specified to rebase -i without --onto, making it
possible to edit and re-order all commits right back to the root(s).

If there is a conflict to be resolved when applying the first change,
the user will expect a sane index and working tree to get sensible
behaviour from git-diff and friends, so create a sentinel commit with an
empty tree to rebase onto. Automatically squash the sentinel with any
commits rebased directly onto it, so they end up as root commits in
their own right and retain their authorship and commit message.

Implicitly use rebase -i for non-interactive rebase of --root without
an --onto argument now that rebase -i can correctly do this.

Signed-off-by: Chris Webb <chris@arachsys.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 26 insertions, 6 deletions

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 0c19b7c753..fcb5f618da 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -417,6 +417,29 @@ record_in_rewritten() {
 	esac
 }
 
+do_pick () {
+	if test "$(git rev-parse HEAD)" = "$squash_onto"
+	then
+		# Set the correct commit message and author info on the
+		# sentinel root before cherry-picking the original changes
+		# without committing (-n).  Finally, update the sentinel again
+		# to include these changes.  If the cherry-pick results in a
+		# conflict, this means our behaviour is similar to a standard
+		# failed cherry-pick during rebase, with a dirty index to
+		# resolve before manually running git commit --amend then git
+		# rebase --continue.
+		git commit --allow-empty --allow-empty-message --amend \
+			   --no-post-rewrite -n -q -C $1 &&
+			pick_one -n $1 &&
+			git commit --allow-empty --allow-empty-message \
+				   --amend --no-post-rewrite -n -q -C $1 ||
+			die_with_patch $1 "Could not apply $1... $2"
+	else
+		pick_one $1 ||
+			die_with_patch $1 "Could not apply $1... $2"
+	fi
+}
+
 do_next () {
 	rm -f "$msg" "$author_script" "$amend" || exit
 	read -r command sha1 rest < "$todo"
@@ -428,16 +451,14 @@ do_next () {
 		comment_for_reflog pick
 
 		mark_action_done
-		pick_one $sha1 ||
-			die_with_patch $sha1 "Could not apply $sha1... $rest"
+		do_pick $sha1 "$rest"
 		record_in_rewritten $sha1
 		;;
 	reword|r)
 		comment_for_reflog reword
 
 		mark_action_done
-		pick_one $sha1 ||
-			die_with_patch $sha1 "Could not apply $sha1... $rest"
+		do_pick $sha1 "$rest"
 		git commit --amend --no-post-rewrite || {
 			warn "Could not amend commit after successfully picking $sha1... $rest"
 			warn "This is most likely due to an empty commit message, or the pre-commit hook"
@@ -451,8 +472,7 @@ do_next () {
 		comment_for_reflog edit
 
 		mark_action_done
-		pick_one $sha1 ||
-			die_with_patch $sha1 "Could not apply $sha1... $rest"
+		do_pick $sha1 "$rest"
 		warn "Stopped at $sha1... $rest"
 		exit_with_patch $sha1 0
 		;;