introduce hide_edge_borders lone_tab

Behaves same as _both_ in i3wm with regards to tabbed/stacked containers. If
there is only one tabbed/stacked container child, title bar is hidden.

Related issues and merge requests: swaywm#3031, swaywm#3002, swaywm#2912, swaywm#2987.

include/sway/config.h

@@ -302,6 +302,7 @@ enum edge_border_types {
 	E_BOTH,		/**< hide vertical and horizontal edge borders */
 	E_SMART, /**< hide both if precisely one window is present in workspace */
 	E_SMART_NO_GAPS, /**< hide both if one window and gaps to edge is zero */
+	E_LONE_TAB, /**< E_BOTH, that also applies to tabbed/stacked 1-child cons */
 };
 
 enum sway_popup_during_fullscreen {

sway/commands/hide_edge_borders.c

@@ -21,9 +21,11 @@ struct cmd_results *cmd_hide_edge_borders(int argc, char **argv) {
 		config->hide_edge_borders = E_SMART;
 	} else if (strcmp(argv[0], "smart_no_gaps") == 0) {
 		config->hide_edge_borders = E_SMART_NO_GAPS;
+	} else if (strcmp(argv[0], "lone_tab") == 0) {
+		config->hide_edge_borders = E_LONE_TAB;
 	} else {
 		return cmd_results_new(CMD_INVALID, "Expected 'hide_edge_borders "
-				"<none|vertical|horizontal|both|smart|smart_no_gaps>'");
+				"<none|vertical|horizontal|both|smart|smart_no_gaps|lone_tab>'");
 	}
 	config->saved_edge_borders = config->hide_edge_borders;
 

sway/desktop/render.c

@@ -841,6 +841,15 @@ static void render_containers_stacked(struct sway_output *output,
 
 static void render_containers(struct sway_output *output,
 		pixman_region32_t *damage, struct parent_data *parent) {
+	if (config->hide_edge_borders == E_LONE_TAB
+				&& parent->children->length == 1) {
+		struct sway_container *child = parent->children->items[0];
+		if (child->view) {
+			render_containers_linear(output,damage, parent);
+			return;
+		}
+	}
+
 	switch (parent->layout) {
 	case L_NONE:
 	case L_HORIZ:

sway/sway.5.scd

@@ -493,8 +493,9 @@ The default colors are:
 	This affects new workspaces only, and is used when the workspace doesn't
 	have its own gaps settings (see: workspace <ws> gaps ...).
 
-*hide_edge_borders* none|vertical|horizontal|both|smart|smart_no_gaps
-	Hides window borders adjacent to the screen edges. Default is _none_.
+*hide_edge_borders* none|vertical|horizontal|both|smart|smart_no_gaps|lone_tab
+	Hides window borders adjacent to the screen edges. Default is _none_. The
+	_lone_tab_ option is same as _both_ in i3 with regards to tabbed containers.
 
 *input* <input_device> <input-subcommands...>
 	For details on input subcommands, see *sway-input*(5).

sway/tree/view.c

@@ -246,14 +246,18 @@ void view_autoconfigure(struct sway_view *view) {
 	// In a tabbed or stacked container, the container's y is the top of the
 	// title area. We have to offset the surface y by the height of the title,
 	// bar, and disable any top border because we'll always have the title bar.
-	enum sway_container_layout layout = container_parent_layout(con);
-	if (layout == L_TABBED && !container_is_floating(con)) {
-		y_offset = container_titlebar_height();
-		con->border_top = false;
-	} else if (layout == L_STACKED && !container_is_floating(con)) {
-		list_t *siblings = container_get_siblings(con);
-		y_offset = container_titlebar_height() * siblings->length;
-		con->border_top = false;
+	list_t *siblings = container_get_siblings(con);
+	bool show_titlebar = config->hide_edge_borders != E_LONE_TAB ||
+		(config->hide_edge_borders == E_LONE_TAB && siblings->length > 1);
+	if (show_titlebar && !container_is_floating(con)) {
+		enum sway_container_layout layout = container_parent_layout(con);
+		if (layout == L_TABBED) {
+			y_offset = container_titlebar_height();
+			con->border_top = false;
+		} else if (layout == L_STACKED) {
+			y_offset = container_titlebar_height() * siblings->length;
+			con->border_top = false;
+		}
 	}
 
 	double x, y, width, height;