rebase -i: fix interrupted squashing

When a squashing merge failed, the first commit would not be replaced,
due to "git reset --soft" being called with an unmerged index.

Noticed by Uwe Kleine-König.

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

git-rebase--interactive.sh

@@ -260,8 +260,8 @@ do_next () {
 		esac
 
 		failed=f
-		pick_one -n $sha1 || failed=t
 		output git reset --soft HEAD^
+		pick_one -n $sha1 || failed=t
 		author_script=$(get_author_ident_from_commit $sha1)
 		echo "$author_script" > "$DOTEST"/author-script
 		case $failed in

t/t3404-rebase-interactive.sh

@@ -221,4 +221,34 @@ test_expect_success 'multi-squash only fires up editor once' '
 	test 1 = $(git show | grep ONCE | wc -l)
 '
 
+test_expect_success 'squash works as expected' '
+	for n in one two three four
+	do
+		echo $n >> file$n &&
+		git add file$n &&
+		git commit -m $n
+	done &&
+	one=$(git rev-parse HEAD~3) &&
+	FAKE_LINES="1 squash 3 2" git rebase -i HEAD~3 &&
+	test $one = $(git rev-parse HEAD~2)
+'
+
+test_expect_success 'interrupted squash works as expected' '
+	for n in one two three four
+	do
+		echo $n >> conflict &&
+		git add conflict &&
+		git commit -m $n
+	done &&
+	one=$(git rev-parse HEAD~3) &&
+	! FAKE_LINES="1 squash 3 2" git rebase -i HEAD~3 &&
+	(echo one; echo two; echo four) > conflict &&
+	git add conflict &&
+	! git rebase --continue &&
+	echo resolved > conflict &&
+	git add conflict &&
+	git rebase --continue &&
+	test $one = $(git rev-parse HEAD~2)
+'
+
 test_done