Use an enum for client exit reasons, from George Nachman.

client.c

@@ -35,7 +35,16 @@
 
 struct imsgbuf	client_ibuf;
 struct event	client_event;
-const char     *client_exitmsg;
+enum {
+	CLIENT_EXIT_NONE,
+	CLIENT_EXIT_DETACHED,
+	CLIENT_EXIT_DETACHED_HUP,
+	CLIENT_EXIT_LOST_TTY,
+	CLIENT_EXIT_TERMINATED,
+	CLIENT_EXIT_LOST_SERVER,
+	CLIENT_EXIT_EXITED,
+	CLIENT_EXIT_SERVER_EXITED,
+} client_exitreason = CLIENT_EXIT_NONE;
 int		client_exitval;
 enum msgtype	client_exittype;
 int		client_attached;
@@ -121,6 +130,31 @@ failed:
 	return (-1);
 }
 
+/* Get exit string from reason number. */
+const char *
+client_exit_message(void)
+{
+	switch (client_exitreason) {
+	case CLIENT_EXIT_NONE:
+		break;
+	case CLIENT_EXIT_DETACHED:
+		return ("detached");
+	case CLIENT_EXIT_DETACHED_HUP:
+		return ("detached and SIGHUP");
+	case CLIENT_EXIT_LOST_TTY:
+		return ("lost tty");
+	case CLIENT_EXIT_TERMINATED:
+		return ("terminated");
+	case CLIENT_EXIT_LOST_SERVER:
+		return ("lost server");
+	case CLIENT_EXIT_EXITED:
+		return ("exited");
+	case CLIENT_EXIT_SERVER_EXITED:
+		return ("server exited");
+	}
+	return ("unknown reason");
+}
+
 /* Client main loop. */
 int
 client_main(int argc, char **argv, int flags)
@@ -170,7 +204,8 @@ client_main(int argc, char **argv, int flags)
 	 * if the socket path matches $TMUX, this is probably the same server.
 	 */
 	if (shell_cmd == NULL && environ_path != NULL &&
-	    cmdflags & CMD_CANTNEST && strcmp(socket_path, environ_path) == 0) {
+	    (cmdflags & CMD_CANTNEST) &&
+	    strcmp(socket_path, environ_path) == 0) {
 		log_warnx("sessions should be nested with care. "
 		    "unset $TMUX to force.");
 		return (1);
@@ -223,8 +258,8 @@ client_main(int argc, char **argv, int flags)
 
 	/* Print the exit message, if any, and exit. */
 	if (client_attached) {
-		if (client_exitmsg != NULL && !login_shell)
+		if (client_exitreason != CLIENT_EXIT_NONE && !login_shell)
-			printf("[%s]\n", client_exitmsg);
+			printf("[%s]\n", client_exit_message());
 
 		ppid = getppid();
 		if (client_exittype == MSG_DETACHKILL && ppid > 1)
@@ -323,12 +358,12 @@ client_signal(int sig, unused short events, unused void *data)
 	} else {
 		switch (sig) {
 		case SIGHUP:
-			client_exitmsg = "lost tty";
+			client_exitreason = CLIENT_EXIT_LOST_TTY;
 			client_exitval = 1;
 			client_write_server(MSG_EXITING, NULL, 0);
 			break;
 		case SIGTERM:
-			client_exitmsg = "terminated";
+			client_exitreason = CLIENT_EXIT_TERMINATED;
 			client_exitval = 1;
 			client_write_server(MSG_EXITING, NULL, 0);
 			break;
@@ -380,7 +415,7 @@ client_callback(unused int fd, short events, void *data)
 	return;
 
 lost_server:
-	client_exitmsg = "lost server";
+	client_exitreason = CLIENT_EXIT_LOST_SERVER;
 	client_exitval = 1;
 	event_loopexit(NULL);
 }
@@ -477,9 +512,9 @@ client_dispatch_attached(void)
 
 			client_exittype = imsg.hdr.type;
 			if (imsg.hdr.type == MSG_DETACHKILL)
-				client_exitmsg = "detached and SIGHUP";
+				client_exitreason = CLIENT_EXIT_DETACHED_HUP;
 			else
-				client_exitmsg = "detached";
+				client_exitreason = CLIENT_EXIT_DETACHED;
 			client_write_server(MSG_EXITING, NULL, 0);
 			break;
 		case MSG_EXIT:
@@ -488,7 +523,7 @@ client_dispatch_attached(void)
 				fatalx("bad MSG_EXIT size");
 
 			client_write_server(MSG_EXITING, NULL, 0);
-			client_exitmsg = "exited";
+			client_exitreason = CLIENT_EXIT_EXITED;
 			break;
 		case MSG_EXITED:
 			if (datalen != 0)
@@ -501,7 +536,7 @@ client_dispatch_attached(void)
 				fatalx("bad MSG_SHUTDOWN size");
 
 			client_write_server(MSG_EXITING, NULL, 0);
-			client_exitmsg = "server exited";
+			client_exitreason = CLIENT_EXIT_SERVER_EXITED;
 			client_exitval = 1;
 			break;
 		case MSG_SUSPEND: