exec: export matched container id if present

Provides matched container id to each command execution via
handler_context. If there is no matched node, the handler_context has
the focused node. The idea is that this can simplify scripting.

Relates to PR 6160 at i3

Author: RobertMueller2

sway/commands/exec_always.c

@@ -28,13 +28,22 @@ struct cmd_results *cmd_exec_validate(int argc, char **argv) {
 struct cmd_results *cmd_exec_process(int argc, char **argv) {
 	struct cmd_results *error = NULL;
 	char *cmd = NULL;
+	bool matched_container_id = false;
 	bool no_startup_id = false;
-	if (strcmp(argv[0], "--no-startup-id") == 0) {
-		no_startup_id = true;
-		--argc; ++argv;
-		if ((error = checkarg(argc, argv[-1], EXPECTED_AT_LEAST, 1))) {
-			return error;
+	int argv_counter=-1;
+	while (argc > 0 && has_prefix(*argv, "--")) {
+		if (strcmp(argv[0], "--matched-container-id") == 0) {
+			matched_container_id = true;
+		} else if (strcmp(argv[0], "--no-startup-id") == 0) {
+			no_startup_id = true;
+		} else {
+			return cmd_results_new(CMD_INVALID, "Unrecognized argument '%s'", *argv);
 		}
+		--argc; ++argv; argv_counter--;
+	}
+
+	if ((error = checkarg(argc, argv[argv_counter], EXPECTED_AT_LEAST, 1))) {
+		return error;
 	}
 
 	if (argc == 1 && (argv[0][0] == '\'' || argv[0][0] == '"')) {
@@ -61,6 +70,26 @@ struct cmd_results *cmd_exec_process(int argc, char **argv) {
 			}
 		}
 
+		if (matched_container_id && config->handler_context.node != NULL) {
+			size_t con_id = config->handler_context.node->id;
+			int con_id_len = snprintf(NULL, 0, "%zu", con_id);
+			if (con_id_len < 0) {
+				sway_log(SWAY_ERROR, "Unable to determine buffer length for SWAY_EXEC_CON_ID");
+				goto no_con_id_export;
+			}
+			// accommodate \0
+			con_id_len++;
+			char* con_id_str = malloc(con_id_len);
+			if (!con_id_str) {
+				sway_log(SWAY_ERROR, "Unable to allocate buffer for SWAY_EXEC_CON_ID");
+				goto no_con_id_export;
+			}
+			snprintf(con_id_str, con_id_len, "%zu", con_id);
+			setenv("SWAY_EXEC_CON_ID", con_id_str, 1);
+			free(con_id_str);
+		}
+no_con_id_export:
+
 		execlp("sh", "sh", "-c", cmd, (void*)NULL);
 		sway_log_errno(SWAY_ERROR, "execve failed");
 		_exit(0); // Close child process

sway/sway.5.scd

@@ -697,10 +697,13 @@ The default colors are:
 	windows that are spawned in floating mode, not windows that become floating
 	afterwards.
 
-*exec* <shell command>
-	Executes _shell command_ with sh.
+*exec* [--matched-container-id] [--no-startup-id] <shell command>
+	Executes _shell command_ with sh. The _--matched-container-id_ option
+	exports matched container if following a criteria match or the focused
+	node otherwise in SWAY_EXEC_CON_ID. The _--no_startup_id_ option prevents
+	exporting of DESKTOP_STARTUP_ID.
 
-*exec_always* <shell command>
+*exec_always* [--matched-container-id] [--no-startup-id] <shell command>
 	Like *exec*, but the shell command will be executed _again_ after *reload*.
 
 *floating_maximum_size* <width> x <height>