[PATCH] rebase -i: handle fixup of root commit correctly

[Chris Webb <chris@arachsys.com>]

There is a bug with git rebase -i --root when a fixup or squash line is
applied to the new root. We attempt to amend the commit onto which they
apply with git reset --soft HEAD^ followed by a normal commit. Unlike a
real commit --amend, this sequence will fail against a root commit as it
has no parent.

Fix rebase -i to use commit --amend for fixup and squash instead, and
add a test for the case of a fixup of the root commit.

Signed-off-by: Chris Webb <chris@arachsys.com>
---

Sorry, I should have spotted this issue when I did the original root-rebase
series. I've checked that this patch doesn't break any of the existing
tests, as well as satisfying the newly introduced check for the root-fixup
case.

 git-rebase--interactive.sh    | 25 +++++++++++++------------
 t/t3404-rebase-interactive.sh |  8 ++++++++
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index bef7bc0..0d2056f 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -493,25 +493,28 @@ do_next () {
 		author_script_content=$(get_author_ident_from_commit HEAD)
 		echo "$author_script_content" > "$author_script"
 		eval "$author_script_content"
-		output git reset --soft HEAD^
-		pick_one -n $sha1 || die_failed_squash $sha1 "$rest"
+		if ! pick_one -n $sha1
+		then
+			git rev-parse --verify HEAD >"$amend"
+			die_failed_squash $sha1 "$rest"
+		fi
 		case "$(peek_next_command)" in
 		squash|s|fixup|f)
 			# This is an intermediate commit; its message will only be
 			# used in case of trouble.  So use the long version:
-			do_with_author output git commit --no-verify -F "$squash_msg" ||
+			do_with_author output git commit --amend --no-verify -F "$squash_msg" ||
 				die_failed_squash $sha1 "$rest"
 			;;
 		*)
 			# This is the final command of this squash/fixup group
 			if test -f "$fixup_msg"
 			then
-				do_with_author git commit --no-verify -F "$fixup_msg" ||
+				do_with_author git commit --amend --no-verify -F "$fixup_msg" ||
 					die_failed_squash $sha1 "$rest"
 			else
 				cp "$squash_msg" "$GIT_DIR"/SQUASH_MSG || exit
 				rm -f "$GIT_DIR"/MERGE_MSG
-				do_with_author git commit --no-verify -e ||
+				do_with_author git commit --amend --no-verify -F "$GIT_DIR"/SQUASH_MSG -e ||
 					die_failed_squash $sha1 "$rest"
 			fi
 			rm -f "$squash_msg" "$fixup_msg"
@@ -748,7 +751,6 @@ In both case, once you're done, continue with:
 		fi
 		. "$author_script" ||
 			die "Error trying to find the author identity to amend commit"
-		current_head=
 		if test -f "$amend"
 		then
 			current_head=$(git rev-parse --verify HEAD)
@@ -756,13 +758,12 @@ In both case, once you're done, continue with:
 			die "\
 You have uncommitted changes in your working tree. Please, commit them
 first and then run 'git rebase --continue' again."
-			git reset --soft HEAD^ ||
-			die "Cannot rewind the HEAD"
+			do_with_author git commit --amend --no-verify -F "$msg" -e ||
+				die "Could not commit staged changes."
+		else
+			do_with_author git commit --no-verify -F "$msg" -e ||
+				die "Could not commit staged changes."
 		fi
-		do_with_author git commit --no-verify -F "$msg" -e || {
-			test -n "$current_head" && git reset --soft $current_head
-			die "Could not commit staged changes."
-		}
 	fi
 
 	record_in_rewritten "$(cat "$state_dir"/stopped-sha)"
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 8078db6..3f75d32 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -903,4 +903,12 @@ test_expect_success 'rebase -i --root temporary sentinel commit' '
 	git rebase --abort
 '
 
+test_expect_success 'rebase -i --root fixup root commit' '
+	git checkout B &&
+	FAKE_LINES="1 fixup 2" git rebase -i --root &&
+	test A = $(git cat-file commit HEAD | sed -ne \$p) &&
+	test B = $(git show HEAD:file1) &&
+	test 0 = $(git cat-file commit HEAD | grep -c ^parent\ )
+'
+
 test_done
-- 
1.7.11.2.251.g6a928a6