Allow swaybg to be disabled

Same as #2791 but for swaybg.

Fixes #2790

sway/commands/swaybg_command.c

@@ -9,12 +9,17 @@ struct cmd_results *cmd_swaybg_command(int argc, char **argv) {
 		return error;
 	}
 
-	if (config->swaybg_command) {
 	free(config->swaybg_command);
-	}
-	config->swaybg_command = join_args(argv, argc);
+	config->swaybg_command = NULL;
+
+	char *new_command = join_args(argv, argc);
+	if (strcmp(new_command, "-") != 0) {
+		config->swaybg_command = new_command;
 		wlr_log(WLR_DEBUG, "Using custom swaybg command: %s",
 				config->swaybg_command);
+	} else {
+		free(new_command);
+	}
 
 	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
 }

sway/config.c

@@ -136,6 +136,7 @@ void free_config(struct sway_config *config) {
 	free(config->floating_scroll_left_cmd);
 	free(config->floating_scroll_right_cmd);
 	free(config->font);
+	free(config->swaybg_command);
 	free((char *)config->current_config_path);
 	free((char *)config->current_config);
 	free(config);
@@ -240,6 +241,8 @@ static void config_defaults(struct sway_config *config) {
 
 	if (!(config->active_bar_modifiers = create_list())) goto cleanup;
 
+	if (!(config->swaybg_command = strdup("swaybg"))) goto cleanup;
+
 	if (!(config->config_chain = create_list())) goto cleanup;
 	config->current_config_path = NULL;
 	config->current_config = NULL;

sway/config/output.c

@@ -229,17 +229,16 @@ void apply_output_config(struct output_config *oc, struct sway_output *output) {
 		}
 	}
 
-	if (oc && oc->background) {
 	if (output->bg_pid != 0) {
 		terminate_swaybg(output->bg_pid);
 	}
-
+	if (oc && oc->background && config->swaybg_command) {
 		wlr_log(WLR_DEBUG, "Setting background for output %d to %s",
 				output_i, oc->background);
 
 		size_t len = snprintf(NULL, 0, "%s %d \"%s\" %s %s",
-				config->swaybg_command ? config->swaybg_command : "swaybg",
-				output_i, oc->background, oc->background_option,
+				config->swaybg_command, output_i, oc->background,
+				oc->background_option,
 				oc->background_fallback ? oc->background_fallback : "");
 		char *command = malloc(len + 1);
 		if (!command) {
@@ -247,8 +246,8 @@ void apply_output_config(struct output_config *oc, struct sway_output *output) {
 			return;
 		}
 		snprintf(command, len + 1, "%s %d \"%s\" %s %s",
-				config->swaybg_command ? config->swaybg_command : "swaybg",
-				output_i, oc->background, oc->background_option,
+				config->swaybg_command, output_i, oc->background,
+				oc->background_option,
 				oc->background_fallback ? oc->background_fallback : "");
 		wlr_log(WLR_DEBUG, "-> %s", command);
 
@@ -260,6 +259,7 @@ void apply_output_config(struct output_config *oc, struct sway_output *output) {
 			free(command);
 		}
 	}
+
 	if (oc) {
 		switch (oc->dpms_state) {
 		case DPMS_ON:
@@ -353,4 +353,3 @@ void create_default_output_configs(void) {
 		list_add(config->output_configs, oc);
 	}
 }
-

sway/sway.5.scd

@@ -71,6 +71,9 @@ The following commands may only be used in the configuration file.
 	Executes custom background _command_. Default is _swaybg_. Refer to
 	*output* below for more information.
 
+	It can be disabled by setting the command to a single dash:
+	_swaybg\_command -_
+
 *swaynag\_command* <command>
 	Executes custom command for _swaynag_. Default is _swaynag_. Additional
 	arguments may be appended to the end. This should only be used to either