Rename session idx to session id throughout and add $ prefix to targets to use

it, extended from a diff from George Nachman.

client.c

@@ -270,7 +270,7 @@ client_main(int argc, char **argv, int flags)
 	if (msg == MSG_COMMAND) {
 		/* Fill in command line arguments. */
 		cmddata.pid = environ_pid;
-		cmddata.idx = environ_idx;
+		cmddata.session_id = environ_session_id;
 
 		/* Prepare command for server. */
 		cmddata.argc = argc;

cmd-server-info.c

@@ -102,7 +102,7 @@ cmd_server_info_exec(unused struct cmd *self, struct cmd_q *cmdq)
 		*strchr(tim, '\n') = '\0';
 
 		cmdq_print(cmdq, "%2u: %s: %u windows (created %s) [%ux%u] "
-		    "[flags=0x%x]", s->idx, s->name,
+		    "[flags=0x%x]", s->id, s->name,
 		    winlink_count(&s->windows), tim, s->sx, s->sy, s->flags);
 		RB_FOREACH(wl, winlinks, &s->windows) {
 			w = wl->window;

cmd.c

@@ -122,6 +122,7 @@ struct session	*cmd_choose_session(int);
 struct client	*cmd_choose_client(struct clients *);
 struct client	*cmd_lookup_client(const char *);
 struct session	*cmd_lookup_session(const char *, int *);
+struct session	*cmd_lookup_session_id(const char *);
 struct winlink	*cmd_lookup_window(struct session *, const char *, int *);
 int		 cmd_lookup_index(struct session *, const char *, int *);
 struct window_pane *cmd_lookup_paneid(const char *);
@@ -357,8 +358,8 @@ cmd_current_session(struct cmd_q *cmdq, int prefer_unattached)
 	}
 
 	/* Use the session from the TMUX environment variable. */
-	if (data != NULL && data->pid == getpid() && data->idx != -1) {
-		s = session_find_by_index(data->idx);
+	if (data != NULL && data->pid == getpid() && data->session_id != -1) {
+		s = session_find_by_id(data->session_id);
 		if (s != NULL)
 			return (s);
 	}
@@ -550,6 +551,21 @@ cmd_lookup_client(const char *name)
 	return (NULL);
 }
 
+/* Find the target session or report an error and return NULL. */
+struct session *
+cmd_lookup_session_id(const char *arg)
+{
+	char	*endptr;
+	long	 id;
+
+	if (arg[0] != '$')
+		return (NULL);
+	id = strtol(arg + 1, &endptr, 10);
+	if (arg[1] != '\0' && *endptr == '\0')
+		return (session_find_by_id(id));
+	return (NULL);
+}
+
 /* Lookup a session by name. If no session is found, NULL is returned. */
 struct session *
 cmd_lookup_session(const char *name, int *ambiguous)
@@ -558,6 +574,10 @@ cmd_lookup_session(const char *name, int *ambiguous)
 
 	*ambiguous = 0;
 
+	/* Look for $id first. */
+	if ((s = cmd_lookup_session_id(name)) != NULL)
+		return (s);
+
 	/*
 	 * Look for matches. First look for exact matches - session names must
 	 * be unique so an exact match can't be ambigious and can just be

control-notify.c

@@ -154,7 +154,7 @@ control_notify_attached_session_changed(struct client *c)
 		return;
 	s = c->session;
 
-	control_write(c, "%%session-changed %d %s", s->idx, s->name);
+	control_write(c, "%%session-changed %d %s", s->id, s->name);
 }
 
 void

format.c

@@ -280,6 +280,7 @@ format_session(struct format_tree *ft, struct session *s)
 	format_add(ft, "session_windows", "%u", winlink_count(&s->windows));
 	format_add(ft, "session_width", "%u", s->sx);
 	format_add(ft, "session_height", "%u", s->sy);
+	format_add(ft, "session_id", "%u", s->id);
 
 	sg = session_group_find(s);
 	format_add(ft, "session_grouped", "%d", sg != NULL);

server-fn.c

@@ -39,7 +39,7 @@ server_fill_environ(struct session *s, struct environ *env)
 		term = options_get_string(&s->options, "default-terminal");
 		environ_set(env, "TERM", term);
 
-		idx = s->idx;
+		idx = s->id;
 	} else
 		idx = -1;
 	pid = getpid();

session.c

@@ -29,7 +29,7 @@
 /* Global session list. */
 struct sessions	sessions;
 struct sessions dead_sessions;
-u_int		next_session;
+u_int		next_session_id;
 struct session_groups session_groups;
 
 struct winlink *session_next_alert(struct winlink *);
@@ -69,14 +69,14 @@ session_find(const char *name)
 	return (RB_FIND(sessions, &sessions, &s));
 }
 
-/* Find session by index. */
+/* Find session by id. */
 struct session *
-session_find_by_index(u_int idx)
+session_find_by_id(u_int id)
 {
 	struct session	*s;
 
 	RB_FOREACH(s, sessions, &sessions) {
-		if (s->idx == idx)
+		if (s->id == id)
 			return (s);
 	}
 	return (NULL);
@@ -120,13 +120,13 @@ session_create(const char *name, const char *cmd, const char *cwd,
 
 	if (name != NULL) {
 		s->name = xstrdup(name);
-		s->idx = next_session++;
+		s->id = next_session_id++;
 	} else {
 		s->name = NULL;
 		do {
-			s->idx = next_session++;
+			s->id = next_session_id++;
 			free (s->name);
-			xasprintf(&s->name, "%u", s->idx);
+			xasprintf(&s->name, "%u", s->id);
 		} while (RB_FIND(sessions, &sessions, s) != NULL);
 	}
 	RB_INSERT(sessions, &sessions, s);

tmux.1

@@ -369,9 +369,9 @@ Clients may be listed with the
 command.
 .Pp
 .Ar target-session
-is either the name of a session (as listed by the
+is the session id prefixed with a $, the name of a session (as listed by the
 .Ic list-sessions
-command) or the name of a client with the same syntax as
+command), or the name of a client with the same syntax as
 .Ar target-client ,
 in which case the session attached to the client is used.
 When looking for the session name,
@@ -3085,6 +3085,7 @@ The following variables are available, where appropriate:
 .It Li "session_group" Ta "Number of session group"
 .It Li "session_grouped" Ta "1 if session in a group"
 .It Li "session_height" Ta "Height of session"
+.It Li "session_id" Ta "Unique session ID"
 .It Li "session_name" Ta "Name of session"
 .It Li "session_width" Ta "Width of session"
 .It Li "session_windows" Ta "Number of windows in session"

tmux.c

@@ -48,7 +48,7 @@ char		 socket_path[MAXPATHLEN];
 int		 login_shell;
 char		*environ_path;
 pid_t		 environ_pid = -1;
-int		 environ_idx = -1;
+int		 environ_session_id = -1;
 
 __dead void	 usage(void);
 void	 	 parseenvironment(void);
@@ -147,16 +147,16 @@ parseenvironment(void)
 {
 	char	*env, path[256];
 	long	 pid;
-	int	 idx;
+	int	 id;
 
 	if ((env = getenv("TMUX")) == NULL)
 		return;
 
-	if (sscanf(env, "%255[^,],%ld,%d", path, &pid, &idx) != 3)
+	if (sscanf(env, "%255[^,],%ld,%d", path, &pid, &id) != 3)
 		return;
 	environ_path = xstrdup(path);
 	environ_pid = pid;
-	environ_idx = idx;
+	environ_session_id = id;
 }
 
 char *

tmux.h

@@ -462,8 +462,8 @@ enum msgtype {
  * Don't forget to bump PROTOCOL_VERSION if any of these change!
  */
 struct msg_command_data {
-	pid_t		pid;	/* PID from $TMUX or -1 */
-	int		idx;	/* index from $TMUX or -1 */
+	pid_t		pid;		/* from $TMUX or -1 */
+	int		session_id;	/* from $TMUX or -1 */
 
 	int		argc;
 	char		argv[COMMAND_LENGTH];
@@ -1086,7 +1086,7 @@ struct session_group {
 TAILQ_HEAD(session_groups, session_group);
 
 struct session {
-	u_int		 idx;
+	u_int		 id;
 
 	char		*name;
 	char		*cwd;
@@ -1513,7 +1513,7 @@ extern char	 socket_path[MAXPATHLEN];
 extern int	 login_shell;
 extern char	*environ_path;
 extern pid_t	 environ_pid;
-extern int	 environ_idx;
+extern int	 environ_session_id;
 void		 logfile(const char *);
 const char	*getshell(void);
 int		 checkshell(const char *);
@@ -2287,7 +2287,7 @@ int	session_cmp(struct session *, struct session *);
 RB_PROTOTYPE(sessions, session, entry, session_cmp);
 int		 session_alive(struct session *);
 struct session	*session_find(const char *);
-struct session	*session_find_by_index(u_int);
+struct session	*session_find_by_id(u_int);
 struct session	*session_create(const char *, const char *, const char *,
 		     struct environ *, struct termios *, int, u_int, u_int,
 		     char **);

window-choose.c

@@ -859,7 +859,7 @@ window_choose_add_session(struct window_pane *wp, struct client *c,
 	struct window_choose_data	*wcd;
 
 	wcd = window_choose_data_create(TREE_SESSION, c, c->session);
-	wcd->idx = s->idx;
+	wcd->idx = s->id;
 
 	wcd->tree_session = s;
 	wcd->tree_session->references++;