input: implement cycling through keyboard layout list

sway/commands/input/xkb_switch_layout.c

@@ -1,4 +1,5 @@
 #define _POSIX_C_SOURCE 200809L
+#include <assert.h>
 #include "sway/config.h"
 #include "sway/commands.h"
 #include "sway/input/input-manager.h"
@@ -13,6 +14,26 @@ static void switch_layout(struct wlr_keyboard *kbd, xkb_layout_index_t idx) {
 		kbd->modifiers.latched, kbd->modifiers.locked, idx);
 }
 
+static xkb_layout_index_t get_current_layout_index(struct wlr_keyboard *kbd) {
+	xkb_layout_index_t num_layouts = xkb_keymap_num_layouts(kbd->keymap);
+	assert(num_layouts > 0);
+
+	xkb_layout_index_t layout_idx;
+	for (layout_idx = 0; layout_idx < num_layouts; layout_idx++) {
+		if (xkb_state_layout_index_is_active(kbd->xkb_state,
+				layout_idx, XKB_STATE_LAYOUT_EFFECTIVE)) {
+			break;
+		}
+	}
+	return layout_idx;
+}
+
+static void switch_layout_relative(struct wlr_keyboard *kbd, int dir) {
+	xkb_layout_index_t num_layouts = xkb_keymap_num_layouts(kbd->keymap);
+	xkb_layout_index_t idx = get_current_layout_index(kbd);
+	switch_layout(kbd, (idx + num_layouts + dir) % num_layouts);
+}
+
 struct cmd_results *input_cmd_xkb_switch_layout(int argc, char **argv) {
 	struct cmd_results *error = NULL;
 	if ((error = checkarg(argc, "xkb_switch_layout", EXPECTED_EQUAL_TO, 1))) {
@@ -28,11 +49,21 @@ struct cmd_results *input_cmd_xkb_switch_layout(int argc, char **argv) {
 	}
 
 	const char *layout_str = argv[0];
+	int relative, layout;
 
-	char *end;
-	int layout = strtol(layout_str, &end, 10);
-	if (layout_str[0] == '\0' || end[0] != '\0' || layout < 0) {
-		return cmd_results_new(CMD_FAILURE, "Invalid layout index.");
+	if (strcmp(layout_str, "next") == 0) {
+		relative = 1;
+	} else if (strcmp(layout_str, "prev") == 0) {
+		relative = -1;
+	} else {
+		char *end;
+		layout = strtol(layout_str, &end, 10);
+		if (layout_str[0] == '\0' || end[0] != '\0') {
+			return cmd_results_new(CMD_FAILURE, "Invalid argument.");
+		} else if (layout < 0) {
+			return cmd_results_new(CMD_FAILURE, "Invalid layout index.");
+		}
+		relative = 0;
 	}
 
 	struct sway_input_device *dev;
@@ -45,7 +76,11 @@ struct cmd_results *input_cmd_xkb_switch_layout(int argc, char **argv) {
 		if (dev->wlr_device->type != WLR_INPUT_DEVICE_KEYBOARD) {
 			continue;
 		}
-		switch_layout(dev->wlr_device->keyboard, layout);
+		if (relative) {
+			switch_layout_relative(dev->wlr_device->keyboard, relative);
+		} else {
+			switch_layout(dev->wlr_device->keyboard, layout);
+		}
 	}
 
 	return cmd_results_new(CMD_SUCCESS, NULL);

sway/sway-input.5.scd

@@ -66,10 +66,14 @@ For more information on these xkb configuration options, see
 *input* <identifier> xkb_rules <rules>
 	Sets files of rules to be used for keyboard mapping composition.
 
-*input* <identifier> xkb_switch_layout <index>
-	Changes the active keyboard layout index. This can be used when multiple
-	layouts are configured with *xkb_layout*. A list of layouts you can switch
-	between can be obtained with *swaymsg -t get_inputs*.
+*input* <identifier> xkb_switch_layout <index>|next|prev
+	Changes the active keyboard layout to <index> counting from zero or to
+	next or previous layout on the list. If there is no next or previous
+	layout, this command hops to the other end of the list.
+
+	This can be used when multiple layouts are configured with *xkb_layout*.
+	A list of layouts you can switch between can be obtained with
+	*swaymsg -t get_inputs*.
 
 *input* <identifier> xkb_variant <variant>
 	Sets the variant of the keyboard like _dvorak_ or _colemak_.