transport: die if server options are unsupported

Server options were added in commit 5e3548e ("fetch: send server
options when using protocol v2", 2018-04-24), supported only for
protocol version 2. But if the user specifies server options, and the
protocol version being used doesn't support them, the server options are
silently ignored.

Teach any transport users to die instead in this situation, just like
how "push" dies if push options are provided when the server doesn't
support them.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5702-protocol-v2.sh

@@ -182,6 +182,13 @@ test_expect_success 'server-options are sent when using ls-remote' '
 	grep "server-option=world" log
 '
 
+test_expect_success 'warn if using server-option with ls-remote with legacy protocol' '
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 git -c protocol.version=0 \
+		ls-remote -o hello -o world "file://$(pwd)/file_parent" master 2>err &&
+
+	test_i18ngrep "see protocol.version in" err &&
+	test_i18ngrep "server options require protocol version 2 or later" err
+'
 
 test_expect_success 'clone with file:// using protocol v2' '
 	test_when_finished "rm -f log" &&
@@ -251,6 +258,18 @@ test_expect_success 'server-options are sent when fetching' '
 	grep "server-option=world" log
 '
 
+test_expect_success 'warn if using server-option with fetch with legacy protocol' '
+	test_when_finished "rm -rf temp_child" &&
+
+	git init temp_child &&
+
+	test_must_fail env GIT_TEST_PROTOCOL_VERSION=0 git -C temp_child -c protocol.version=0 \
+		fetch -o hello -o world "file://$(pwd)/file_parent" master 2>err &&
+
+	test_i18ngrep "see protocol.version in" err &&
+	test_i18ngrep "server options require protocol version 2 or later" err
+'
+
 test_expect_success 'upload-pack respects config using protocol v2' '
 	git init server &&
 	write_script server/.git/hook <<-\EOF &&

transport.c

@@ -252,6 +252,14 @@ static int connect_setup(struct transport *transport, int for_push)
 	return 0;
 }
 
+static void die_if_server_options(struct transport *transport)
+{
+	if (!transport->server_options || !transport->server_options->nr)
+		return;
+	advise(_("see protocol.version in 'git help config' for more details"));
+	die(_("server options require protocol version 2 or later"));
+}
+
 /*
  * Obtains the protocol version from the transport and writes it to
  * transport->data->version, first connecting if not already connected.
@@ -286,6 +294,7 @@ static struct ref *handshake(struct transport *transport, int for_push,
 		break;
 	case protocol_v1:
 	case protocol_v0:
+		die_if_server_options(transport);
 		get_remote_heads(&reader, &refs,
 				 for_push ? REF_NORMAL : 0,
 				 &data->extra_have,
@@ -363,6 +372,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 		break;
 	case protocol_v1:
 	case protocol_v0:
+		die_if_server_options(transport);
 		refs = fetch_pack(&args, data->fd, data->conn,
 				  refs_tmp ? refs_tmp : transport->remote_refs,
 				  dest, to_fetch, nr_heads, &data->shallow,