sparse-checkout: upgrade repository to version 1 when enabling extension

The 'extensions' configuration variable gets special meaning in the new
repository version, so when enabling the extension we should upgrade the
repository to version 1.

Signed-off-by: Xin Li <delphij@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -249,6 +249,8 @@ static int set_config(enum sparse_checkout_mode mode)
 {
 	const char *config_path;
 
+	if (upgrade_repository_format(1) < 0)
+		die(_("unable to upgrade repository format to enable worktreeConfig"));
 	if (git_config_set_gently("extensions.worktreeConfig", "true")) {
 		error(_("failed to set extensions.worktreeConfig setting"));
 		return 1;

t/t2404-worktree-config.sh

@@ -23,8 +23,10 @@ test_expect_success 'config --worktree without extension' '
 '
 
 test_expect_success 'enable worktreeConfig extension' '
+	git config core.repositoryformatversion 1 &&
 	git config extensions.worktreeConfig true &&
-	test_cmp_config true extensions.worktreeConfig
+	test_cmp_config true extensions.worktreeConfig &&
+	test_cmp_config 1 core.repositoryformatversion
 '
 
 test_expect_success 'config is shared as before' '