rebase --root: print usage on too many args

Just like

  git rebase --onto newbase upstream branch error

displays the usage message, so should clearly

  git rebase --onto newbase --root branch error

, but it doesn't. Instead, it ignores both "branch" and "error" and
rebases the current HEAD. This is because we try to match the number
of remainging arguments "$#", which fails to match "1" argument and
matches the "*" that really should have been a "0".

Make sure we display usage information when too many arguments are
given. Also fail-fast in case of similar bugs in the future by
matching on exactly 0 arguments and failing on unknown numbers.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -400,6 +400,7 @@ else
 	test -z "$onto" && die "You must specify --onto when using --root"
 	unset upstream_name
 	unset upstream
+	test $# -gt 1 && usage
 	upstream_arg=--root
 fi
 
@@ -450,7 +451,7 @@ case "$#" in
 		die "fatal: no such branch: $1"
 	fi
 	;;
-*)
+0)
 	# Do not need to switch branches, we are already on it.
 	if branch_name=`git symbolic-ref -q HEAD`
 	then
@@ -462,6 +463,9 @@ case "$#" in
 	fi
 	orig_head=$(git rev-parse --verify "${branch_name}^0") || exit
 	;;
+*)
+	die "BUG: unexpected number of arguments left to parse"
+	;;
 esac
 
 require_clean_work_tree "rebase" "Please commit or stash them."

t/t3412-rebase-root.sh

@@ -23,9 +23,15 @@ test_expect_success 'prepare repository' '
 '
 
 test_expect_success 'rebase --root expects --onto' '
+	git checkout -B fail other &&
 	test_must_fail git rebase --root
 '
 
+test_expect_success 'rebase --root fails with too many args' '
+	git checkout -B fail other &&
+	test_must_fail git rebase --onto master --root fail fail
+'
+
 test_expect_success 'setup pre-rebase hook' '
 	mkdir -p .git/hooks &&
 	cat >.git/hooks/pre-rebase <<EOF &&
@@ -42,7 +48,7 @@ cat > expect <<EOF
 EOF
 
 test_expect_success 'rebase --root --onto <newbase>' '
-	git checkout -b work &&
+	git checkout -b work other &&
 	git rebase --root --onto master &&
 	git log --pretty=tformat:"%s" > rebased &&
 	test_cmp expect rebased