Introduce create_output command (for developer use)

Should help with testing hotplugging.

include/sway/commands.h

@@ -103,6 +103,7 @@ sway_cmd cmd_client_urgent;
 sway_cmd cmd_client_placeholder;
 sway_cmd cmd_client_background;
 sway_cmd cmd_commands;
+sway_cmd cmd_create_output;
 sway_cmd cmd_debuglog;
 sway_cmd cmd_default_border;
 sway_cmd cmd_default_floating_border;

sway/commands.c

@@ -143,6 +143,7 @@ static struct cmd_handler config_handlers[] = {
 /* Runtime-only commands. Keep alphabetized */
 static struct cmd_handler command_handlers[] = {
 	{ "border", cmd_border },
+	{ "create_output", cmd_create_output },
 	{ "exit", cmd_exit },
 	{ "floating", cmd_floating },
 	{ "fullscreen", cmd_fullscreen },

sway/commands/create_output.c

@@ -0,0 +1,39 @@
+#include <wlr/backend/multi.h>
+#include <wlr/backend/wayland.h>
+#include <wlr/backend/x11.h>
+#include "sway/commands.h"
+#include "sway/server.h"
+#include "log.h"
+
+static void create_output(struct wlr_backend *backend, void *data) {
+	bool *done = data;
+	if (*done) {
+		return;
+	}
+
+	if (wlr_backend_is_wl(backend)) {
+		wlr_wl_output_create(backend);
+		*done = true;
+	} else if (wlr_backend_is_x11(backend)) {
+		wlr_x11_output_create(backend);
+		*done = true;
+	}
+}
+
+/**
+ * This command is intended for developer use only.
+ */
+struct cmd_results *cmd_create_output(int argc, char **argv) {
+	sway_assert(wlr_backend_is_multi(server.backend),
+			"Expected a multi backend");
+
+	bool done = false;
+	wlr_multi_for_each_backend(server.backend, create_output, &done);
+
+	if (!done) {
+		return cmd_results_new(CMD_INVALID, "create_output",
+				"Can only create outputs for Wayland or X11 backends");
+	}
+
+	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
+}

sway/meson.build

@@ -35,6 +35,7 @@ sway_sources = files(
 	'commands/bind.c',
 	'commands/border.c',
 	'commands/client.c',
+	'commands/create_output.c',
 	'commands/default_border.c',
 	'commands/default_floating_border.c',
 	'commands/default_orientation.c',