Use pointer rather than index for the client's last session.

cmd-new-session.c

@@ -122,7 +122,7 @@ int
 cmd_new_session_exec(struct cmd *self, struct cmd_ctx *ctx)
 {
 	struct cmd_new_session_data	*data = self->data;
-	struct session			*s, *groupwith;
+	struct session			*s, *old_s, *groupwith;
 	struct window			*w;
 	struct window_pane		*wp;
 	struct environ			 env;
@@ -279,17 +279,16 @@ cmd_new_session_exec(struct cmd *self, struct cmd_ctx *ctx)
 	if (!detached) {
 		if (ctx->cmdclient != NULL) {
 			server_write_client(ctx->cmdclient, MSG_READY, NULL, 0);
-			if (ctx->cmdclient->session != NULL) {
+
-				session_index(ctx->cmdclient->session,
+			old_s = ctx->cmdclient->session;
-				    &ctx->cmdclient->last_session);
+			if (old_s != NULL)
-			}
+				ctx->cmdclient->last_session = old_s;
 			ctx->cmdclient->session = s;
 			server_redraw_client(ctx->cmdclient);
 		} else {
-			if (ctx->curclient->session != NULL) {
+			old_s = ctx->curclient->session;
-				session_index(ctx->curclient->session,
+			if (old_s != NULL)
-				    &ctx->curclient->last_session);
+				ctx->curclient->last_session = old_s;
-			}
 			ctx->curclient->session = s;
 			server_redraw_client(ctx->curclient);
 		}

cmd-switch-client.c

@@ -159,9 +159,8 @@ cmd_switch_client_exec(struct cmd *self, struct cmd_ctx *ctx)
 			return (-1);
 		}
 	} else if (data->flag_last) {
-		if (c->last_session != UINT_MAX &&
+		if (c->last_session != NULL && session_alive(c->last_session))
-		    c->last_session < ARRAY_LENGTH(&sessions))
+			s = c->last_session;
-			s = ARRAY_ITEM(&sessions, c->last_session);
 		if (s == NULL) {
 			ctx->error(ctx, "can't find last session");
 			return (-1);
@@ -172,7 +171,7 @@ cmd_switch_client_exec(struct cmd *self, struct cmd_ctx *ctx)
 		return (-1);
 
 	if (c->session != NULL)
-		session_index(c->session, &c->last_session);
+		c->last_session = c->session;
 	c->session = s;
 
 	recalculate_sizes();

server-client.c

@@ -78,7 +78,7 @@ server_client_create(int fd)
 	c->title = NULL;
 
 	c->session = NULL;
-	c->last_session = UINT_MAX;
+	c->last_session = NULL;
 	c->tty.sx = 80;
 	c->tty.sy = 24;
 

server-fn.c

@@ -399,7 +399,7 @@ server_destroy_session(struct session *s)
 			c->session = NULL;
 			c->flags |= CLIENT_EXIT;
 		} else {
-			c->last_session = UINT_MAX;
+			c->last_session = NULL;
 			c->session = s_new;
 			server_redraw_client(c);
 		}

tmux.h

@@ -1155,7 +1155,7 @@ struct client {
 	struct mode_key_data prompt_mdata;
 
 	struct session	*session;
-	u_int            last_session;
+	struct session	*last_session;
 
 	int		 references;
 };