t5520: test --rebase failure on unborn branch with index

Commit 19a7fcb (allow pull --rebase on branch yet to be born,
2009-08-11) special cases git-pull on an unborn branch in a different
code path such that git-pull --rebase is still valid even though there
is no HEAD yet.

This code path still ensures that there is no index in order not to lose
any staged changes. Implement a test to ensure that this check is
triggered.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5520-pull.sh

@@ -412,6 +412,21 @@ test_expect_success 'pull --rebase works on branch yet to be born' '
 	test_cmp expect actual
 '
 
+test_expect_success 'pull --rebase fails on unborn branch with staged changes' '
+	test_when_finished "rm -rf empty_repo2" &&
+	git init empty_repo2 &&
+	(
+		cd empty_repo2 &&
+		echo staged-file >staged-file &&
+		git add staged-file &&
+		test "$(git ls-files)" = staged-file &&
+		test_must_fail git pull --rebase .. master 2>err &&
+		test "$(git ls-files)" = staged-file &&
+		test "$(git show :staged-file)" = staged-file &&
+		test_i18ngrep "unborn branch with changes added to the index" err
+	)
+'
+
 test_expect_success 'setup for detecting upstreamed changes' '
 	mkdir src &&
 	(cd src &&