Add `-t get_marks` and use more i3-like marks

In i3 every mark is unique and one mark cannot be used in more than one
window, sway behavior has been amended to match this.
`swaymsg -t get_marks` will now return an array of all marks used in sway.

See #98

sway/commands/mark.c

@@ -5,6 +5,15 @@
 #include "list.h"
 #include "stringop.h"
 
+static void find_marks_callback(swayc_t *container, void *_mark) {
+	char *mark = (char *)_mark;
+
+	int index;
+	if (container->marks && ((index = list_seq_find(container->marks, (int (*)(const void *, const void *))strcmp, mark)) != -1)) {
+		list_del(container->marks, index);
+	}
+}
+
 struct cmd_results *cmd_mark(int argc, char **argv) {
 	struct cmd_results *error = NULL;
 	if (config->reading) return cmd_results_new(CMD_FAILURE, "mark", "Can't be used in config file.");
@@ -30,6 +39,10 @@ struct cmd_results *cmd_mark(int argc, char **argv) {
 
 	if (argc) {
 		char *mark = join_args(argv, argc);
+
+		// Remove all existing marks of this type
+		container_map(&root_container, find_marks_callback, mark);
+
 		if (view->marks) {
 			if (add) {
 				int index;

sway/ipc-server.c

@@ -63,6 +63,7 @@ void ipc_client_handle_command(struct ipc_client *client);
 bool ipc_send_reply(struct ipc_client *client, const char *payload, uint32_t payload_length);
 void ipc_get_workspaces_callback(swayc_t *workspace, void *data);
 void ipc_get_outputs_callback(swayc_t *container, void *data);
+static void ipc_get_marks_callback(swayc_t *container, void *data);
 
 void ipc_init(void) {
 	ipc_socket = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
@@ -464,6 +465,19 @@ void ipc_client_handle_command(struct ipc_client *client) {
 		goto exit_cleanup;
 	}
 
+	case IPC_GET_MARKS:
+	{
+		if (!(client->security_policy & IPC_FEATURE_GET_MARKS)) {
+			goto exit_denied;
+		}
+		json_object *marks = json_object_new_array();
+		container_map(&root_container, ipc_get_marks_callback, marks);
+		const char *json_string = json_object_to_json_string(marks);
+		ipc_send_reply(client, json_string, (uint32_t) strlen(json_string));
+		json_object_put(marks);
+		goto exit_cleanup;
+	}
+
 	case IPC_GET_VERSION:
 	{
 		json_object *version = ipc_json_get_version();
@@ -617,6 +631,16 @@ void ipc_get_outputs_callback(swayc_t *container, void *data) {
 	}
 }
 
+static void ipc_get_marks_callback(swayc_t *container, void *data) {
+	json_object *object = (json_object *)data;
+	if (container->marks) {
+		for (int i = 0; i < container->marks->length; ++i) {
+			char *mark = (char *)container->marks->items[i];
+			json_object_array_add(object, json_object_new_string(mark));
+		}
+	}
+}
+
 void ipc_send_event(const char *json_string, enum ipc_command_type event) {
 	static struct {
 		enum ipc_command_type event;