Implement 'smart_gaps' feature from i3-gaps

include/config.h

@@ -181,6 +181,7 @@ struct sway_config {
 	bool seamless_mouse;
 
 	bool edge_gaps;
+	bool smart_gaps;
 	int gaps_inner;
 	int gaps_outer;
 };

sway/commands.c

@@ -68,6 +68,7 @@ static sway_cmd cmd_reload;
 static sway_cmd cmd_resize;
 static sway_cmd cmd_scratchpad;
 static sway_cmd cmd_set;
+static sway_cmd cmd_smart_gaps;
 static sway_cmd cmd_split;
 static sway_cmd cmd_splith;
 static sway_cmd cmd_splitt;
@@ -1480,6 +1481,23 @@ static struct cmd_results *cmd_gaps(int argc, char **argv) {
 	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
 }
 
+static struct cmd_results *cmd_smart_gaps(int argc, char **argv) {
+	struct cmd_results *error = NULL;
+	if ((error = checkarg(argc, "smart_gaps", EXPECTED_EQUAL_TO, 1))) {
+		return error;
+	}
+
+	if (strcasecmp(argv[0], "on") == 0) {
+		config->smart_gaps = true;
+	} else if (strcasecmp(argv[0], "off") == 0) {
+		config->smart_gaps = false;
+	} else {
+		return cmd_results_new(CMD_INVALID, "smart_gaps", "Expected 'smart_gaps <on|off>'");
+	}
+
+	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
+}
+
 static struct cmd_results *cmd_kill(int argc, char **argv) {
 	if (config->reading) return cmd_results_new(CMD_FAILURE, "kill", "Can't be used in config file.");
 	if (!config->active) return cmd_results_new(CMD_FAILURE, "kill", "Can only be used when sway is running.");
@@ -2048,6 +2066,7 @@ static struct cmd_handler handlers[] = {
 	{ "scratchpad", cmd_scratchpad },
 	{ "seamless_mouse", cmd_seamless_mouse },
 	{ "set", cmd_set },
+	{ "smart_gaps", cmd_smart_gaps },
 	{ "split", cmd_split },
 	{ "splith", cmd_splith },
 	{ "splitt", cmd_splitt },

sway/config.c

@@ -170,6 +170,7 @@ static void config_defaults(struct sway_config *config) {
 	config->reading = false;
 
 	config->edge_gaps = true;
+	config->smart_gaps = false;
 	config->gaps_inner = 0;
 	config->gaps_outer = 0;
 

sway/container.c

@@ -675,7 +675,7 @@ int swayc_gap(swayc_t *container) {
 		return container->gaps >= 0 ? container->gaps : config->gaps_inner;
 	} else if (container->type == C_WORKSPACE) {
 		int base = container->gaps >= 0 ? container->gaps : config->gaps_outer;
-		if (config->edge_gaps) {
+		if (config->edge_gaps && !(config->smart_gaps && container->children->length == 1)) {
 			// the inner gap is created via a margin around each window which
 			// is half the gap size, so the workspace also needs half a gap
 			// size to make the outermost gap the same size (excluding the

sway/layout.c

@@ -406,7 +406,7 @@ void update_geometry(swayc_t *container) {
 		if (op->focused == ws) {
 			wlc_view_bring_to_front(container->handle);
 		}
-	} else if (!config->edge_gaps && gap > 0) {
+	} else if ((!config->edge_gaps && gap > 0) || (config->smart_gaps && ws->children->length == 1)) {
 		// Remove gap against the workspace edges. Because a pixel is not
 		// divisable, depending on gap size and the number of siblings our view
 		// might be at the workspace edge without being exactly so (thus test

sway/sway.5.txt

@@ -154,6 +154,10 @@ or triggered at runtime.
 	workspace (or current workspace), and _current_ changes gaps for the current
 	view or workspace.
 
+**smart_gaps** <on|off>::
+	If smart_gaps are _on_ then gaps will only be enabled if a workspace has more
+	than one child container.
+
 **mode** <mode_name>::
 	Switches to the given mode_name. the default mode is simply _default_. To
 	create a new mode in config append _{_ to this command, the following lines