Check whether there are multiple active connections in cider-rotate-default-connection

Author: bbatsov

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 * [cider-nrepl#438](https://github.com/clojure-emacs/cider-nrepl/pull/438): Improve startup time by deferring loading CIDER's middleware until the first usage.
 * [#2078](https://github.com/clojure-emacs/cider/pull/2078): Improve startup time by bundling together sync requests during startup.
+* `cider-rotate-default-connection` will warn if you use it with only a single active connection.
 
 ### Bugs Fixed
 

cider-client.el

@@ -1150,11 +1150,13 @@ default connection."
   "Rotate and display the default nREPL connection."
   (interactive)
   (cider-ensure-connected)
-  (setq cider-connections
-        (append (cdr cider-connections)
-                (list (car cider-connections))))
-  (message "Default nREPL connection: %s"
-           (cider--connection-info (car cider-connections))))
+  (if (= (length (cider-connections)) 1)
+      (user-error "There's just a single active nREPL connection")
+    (setq cider-connections
+          (append (cdr cider-connections)
+                  (list (car cider-connections))))
+    (message "Default nREPL connection: %s"
+           (cider--connection-info (car cider-connections)))))
 
 (defun cider-replicate-connection (&optional conn)
   "Establish a new connection based on an existing connection.