ipc-json,swaysavetree: round-trip placeholder swallows

ipc_json_describe_container emits the original swallows JSON for
unfilled placeholders. New sway-save-tree binary dumps a
workspace tiling tree as append_layout-compatible JSON,
synthesising swallows from app_id / class / instance.

include/sway/tree/container.h

@@ -9,6 +9,7 @@
 
 struct sway_view;
 struct sway_seat;
+struct json_object;
 
 enum sway_container_layout {
 	L_NONE,
@@ -146,6 +147,7 @@ struct sway_container {
 	// i3-shaped array so IPC can echo it verbatim for round-trip.
 	bool is_placeholder;
 	list_t *swallows; // struct criteria *
+	struct json_object *swallows_json;
 
 	struct {
 		struct wl_signal destroy;

meson.build

@@ -195,6 +195,7 @@ subdir('protocols')
 subdir('common')
 subdir('sway')
 subdir('swaymsg')
+subdir('swaysavetree')
 
 if get_option('swaybar') or get_option('swaynag')
 	subdir('client')

sway/ipc-json.c

@@ -776,6 +776,11 @@ static void ipc_json_describe_container(struct sway_container *c, json_object *o
 	if (c->view) {
 		ipc_json_describe_view(c, object);
 	}
+
+	if (c->is_placeholder && c->swallows_json) {
+		json_object_object_add(object, "swallows",
+				json_object_get(c->swallows_json));
+	}
 }
 
 struct focus_inactive_data {

sway/tree/container.c

@@ -7,6 +7,7 @@
 #include <wlr/types/wlr_linux_dmabuf_v1.h>
 #include <wlr/types/wlr_output_layout.h>
 #include <wlr/types/wlr_subcompositor.h>
+#include <json.h>
 #include "sway/config.h"
 #include "sway/criteria.h"
 #include "sway/desktop/transaction.h"
@@ -471,6 +472,9 @@ void container_destroy(struct sway_container *con) {
 		}
 		list_free(con->swallows);
 	}
+	if (con->swallows_json) {
+		json_object_put(con->swallows_json);
+	}
 
 	if (con->view && con->view->container == con) {
 		con->view->container = NULL;

sway/tree/load_layout.c

@@ -363,6 +363,8 @@ static struct sway_container *build_node(struct json_object *obj,
 		}
 		c->is_placeholder = true;
 		c->swallows = sw;
+		// Retained so IPC can echo it verbatim for round-trip.
+		c->swallows_json = json_object_get(swallows_v);
 	} else {
 		// Leaf without swallows is an empty split with no children. i3 does
 		// not produce these; treat as an error to avoid silently leaving

sway/tree/view.c

@@ -16,6 +16,7 @@
 #if WLR_HAS_XWAYLAND
 #include <wlr/xwayland.h>
 #endif
+#include <json.h>
 #include "list.h"
 #include "log.h"
 #include "sway/criteria.h"
@@ -823,6 +824,10 @@ static void promote_placeholder(struct sway_container *placeholder,
 		list_free(placeholder->swallows);
 		placeholder->swallows = NULL;
 	}
+	if (placeholder->swallows_json) {
+		json_object_put(placeholder->swallows_json);
+		placeholder->swallows_json = NULL;
+	}
 	placeholder->is_placeholder = false;
 
 	if (placeholder->pending.children) {

swaysavetree/main.c

@@ -0,0 +1,292 @@
+// sway-save-tree: dump a workspace's tiling tree as JSON for `swaymsg
+// append_layout`. Counterpart to i3-save-tree(1).
+
+#include <getopt.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <sys/time.h>
+#include <json.h>
+#include "ipc-client.h"
+#include "ipc.h"
+#include "log.h"
+
+static void usage(void) {
+	fprintf(stderr,
+		"Usage: sway-save-tree --workspace <name|number>\n"
+		"\n"
+		"Dump the tiling tree of the named workspace as JSON suitable for\n"
+		"`swaymsg append_layout`. Output is sent to stdout.\n"
+		"\n"
+		"Floating windows are skipped in this release.\n");
+}
+
+// Anchored, metachar-escaped copy so swallows match the value literally.
+static char *anchored_regex(const char *s) {
+	if (!s) {
+		return NULL;
+	}
+	size_t n = strlen(s);
+	char *out = malloc(n * 2 + 3);
+	if (!out) {
+		return NULL;
+	}
+	size_t pos = 0;
+	out[pos++] = '^';
+	for (size_t i = 0; i < n; i++) {
+		char c = s[i];
+		if (strchr(".\\+*?()[]{}|^$", c)) {
+			out[pos++] = '\\';
+		}
+		out[pos++] = c;
+	}
+	out[pos++] = '$';
+	out[pos] = '\0';
+	return out;
+}
+
+// Returns NULL if the view has nothing identifiable; caller drops the leaf.
+static struct json_object *synth_swallows(struct json_object *view_obj) {
+	struct json_object *app_id = NULL, *wp = NULL;
+	const char *class = NULL, *instance = NULL;
+
+	json_object_object_get_ex(view_obj, "app_id", &app_id);
+
+	if (json_object_object_get_ex(view_obj, "window_properties", &wp)) {
+		struct json_object *cls, *inst;
+		if (json_object_object_get_ex(wp, "class", &cls)) {
+			class = json_object_get_string(cls);
+		}
+		if (json_object_object_get_ex(wp, "instance", &inst)) {
+			instance = json_object_get_string(inst);
+		}
+	}
+
+	struct json_object *entry = json_object_new_object();
+	bool added = false;
+
+	if (app_id && json_object_get_type(app_id) == json_type_string) {
+		const char *s = json_object_get_string(app_id);
+		if (s && *s) {
+			char *re = anchored_regex(s);
+			if (re) {
+				json_object_object_add(entry, "app_id",
+						json_object_new_string(re));
+				free(re);
+				added = true;
+			}
+		}
+	}
+	if (class) {
+		char *re = anchored_regex(class);
+		if (re) {
+			json_object_object_add(entry, "class",
+					json_object_new_string(re));
+			free(re);
+			added = true;
+		}
+	}
+	if (instance) {
+		char *re = anchored_regex(instance);
+		if (re) {
+			json_object_object_add(entry, "instance",
+					json_object_new_string(re));
+			free(re);
+			added = true;
+		}
+	}
+
+	if (!added) {
+		json_object_put(entry);
+		return NULL;
+	}
+
+	struct json_object *arr = json_object_new_array();
+	json_object_array_add(arr, entry);
+	return arr;
+}
+
+static void copy_key(struct json_object *src, struct json_object *dst,
+		const char *key) {
+	struct json_object *v;
+	if (json_object_object_get_ex(src, key, &v)) {
+		json_object_object_add(dst, key, json_object_get(v));
+	}
+}
+
+static struct json_object *build_layout_node(struct json_object *src) {
+	struct json_object *out = json_object_new_object();
+
+	copy_key(src, out, "layout");
+	copy_key(src, out, "name");
+	copy_key(src, out, "border");
+	copy_key(src, out, "current_border_width");
+	copy_key(src, out, "percent");
+	copy_key(src, out, "marks");
+
+	// Unfilled placeholders carry their original swallows; pass it through.
+	struct json_object *swallows;
+	if (json_object_object_get_ex(src, "swallows", &swallows) &&
+			json_object_is_type(swallows, json_type_array) &&
+			json_object_array_length(swallows) > 0) {
+		json_object_object_add(out, "swallows", json_object_get(swallows));
+		return out;
+	}
+
+	struct json_object *nodes;
+	bool has_nodes = json_object_object_get_ex(src, "nodes", &nodes) &&
+			json_object_is_type(nodes, json_type_array) &&
+			json_object_array_length(nodes) > 0;
+
+	if (has_nodes) {
+		struct json_object *out_nodes = json_object_new_array();
+		size_t n = json_object_array_length(nodes);
+		for (size_t i = 0; i < n; i++) {
+			struct json_object *child = json_object_array_get_idx(nodes, i);
+			struct json_object *built = build_layout_node(child);
+			if (built) {
+				json_object_array_add(out_nodes, built);
+			}
+		}
+		if (json_object_array_length(out_nodes) == 0) {
+			json_object_put(out_nodes);
+			json_object_put(out);
+			return NULL;
+		}
+		json_object_object_add(out, "nodes", out_nodes);
+		return out;
+	}
+
+	struct json_object *synth = synth_swallows(src);
+	if (!synth) {
+		json_object_put(out);
+		return NULL;
+	}
+	json_object_object_add(out, "swallows", synth);
+	return out;
+}
+
+// Recursive search of the tree for the requested workspace.
+static struct json_object *find_workspace(struct json_object *node,
+		const char *name) {
+	struct json_object *type;
+	if (json_object_object_get_ex(node, "type", &type) &&
+			json_object_get_type(type) == json_type_string &&
+			strcmp(json_object_get_string(type), "workspace") == 0) {
+		struct json_object *ws_name;
+		if (json_object_object_get_ex(node, "name", &ws_name) &&
+				strcmp(json_object_get_string(ws_name), name) == 0) {
+			return node;
+		}
+	}
+	struct json_object *nodes;
+	if (json_object_object_get_ex(node, "nodes", &nodes) &&
+			json_object_is_type(nodes, json_type_array)) {
+		size_t n = json_object_array_length(nodes);
+		for (size_t i = 0; i < n; i++) {
+			struct json_object *child = json_object_array_get_idx(nodes, i);
+			struct json_object *match = find_workspace(child, name);
+			if (match) {
+				return match;
+			}
+		}
+	}
+	return NULL;
+}
+
+int main(int argc, char **argv) {
+	const char *workspace = NULL;
+	static const struct option long_opts[] = {
+		{"workspace", required_argument, NULL, 'w'},
+		{"help",      no_argument,       NULL, 'h'},
+		{0,           0,                 0,    0  },
+	};
+	int opt;
+	while ((opt = getopt_long(argc, argv, "w:h", long_opts, NULL)) != -1) {
+		switch (opt) {
+		case 'w':
+			workspace = optarg;
+			break;
+		case 'h':
+		default:
+			usage();
+			return opt == 'h' ? 0 : 1;
+		}
+	}
+	if (!workspace) {
+		usage();
+		return 1;
+	}
+
+	char *socket_path = get_socketpath();
+	if (!socket_path) {
+		fprintf(stderr, "sway-save-tree: cannot find sway IPC socket\n");
+		return 1;
+	}
+	int fd = ipc_open_socket(socket_path);
+	free(socket_path);
+	struct timeval timeout = {.tv_sec = 3, .tv_usec = 0};
+	ipc_set_recv_timeout(fd, timeout);
+	uint32_t len = 0;
+	char *resp = ipc_single_command(fd, IPC_GET_TREE, "", &len);
+	if (!resp) {
+		fprintf(stderr, "sway-save-tree: GET_TREE IPC failed\n");
+		return 1;
+	}
+
+	struct json_tokener *tok = json_tokener_new();
+	struct json_object *root = json_tokener_parse_ex(tok, resp, len);
+	json_tokener_free(tok);
+	free(resp);
+	if (!root) {
+		fprintf(stderr, "sway-save-tree: failed to parse GET_TREE response\n");
+		return 1;
+	}
+
+	struct json_object *ws = find_workspace(root, workspace);
+	if (!ws) {
+		fprintf(stderr, "sway-save-tree: workspace '%s' not found\n",
+				workspace);
+		json_object_put(root);
+		return 1;
+	}
+
+	struct json_object *floating;
+	if (json_object_object_get_ex(ws, "floating_nodes", &floating) &&
+			json_object_is_type(floating, json_type_array) &&
+			json_object_array_length(floating) > 0) {
+		fprintf(stderr, "sway-save-tree: ignoring %zu floating window(s) on "
+				"workspace '%s' (tiling-only in this release)\n",
+				json_object_array_length(floating), workspace);
+	}
+
+	struct json_object *nodes;
+	if (!json_object_object_get_ex(ws, "nodes", &nodes) ||
+			!json_object_is_type(nodes, json_type_array) ||
+			json_object_array_length(nodes) == 0) {
+		fprintf(stderr, "sway-save-tree: workspace '%s' has no tiling "
+				"children\n", workspace);
+		json_object_put(root);
+		return 1;
+	}
+
+	struct json_object *out = json_object_new_array();
+	size_t n = json_object_array_length(nodes);
+	for (size_t i = 0; i < n; i++) {
+		struct json_object *child = json_object_array_get_idx(nodes, i);
+		struct json_object *built = build_layout_node(child);
+		if (built) {
+			json_object_array_add(out, built);
+		}
+	}
+
+	const char *str = json_object_to_json_string_ext(out,
+			JSON_C_TO_STRING_PRETTY);
+	puts(str);
+
+	json_object_put(out);
+	json_object_put(root);
+	return 0;
+}

swaysavetree/meson.build

@@ -0,0 +1,8 @@
+executable(
+	'sway-save-tree',
+	'main.c',
+	include_directories: [sway_inc],
+	dependencies: [jsonc],
+	link_with: [lib_sway_common],
+	install: true
+)