Here's what I used, but it's not working

(defun cider-force-connect ()
  (interactive)
  (let ((repl (cider-current-repl nil nil)))
    (when repl
      (cider-quit repl))
    (cider-connect (plist-put '(:host "localhost" :cljs-repl-type shadow)
                              :port (cl-second (cl-first (cider-locate-running-nrepl-ports)))))))

(defun cider-force-eval-buffer ()
  (interactive)
  (let ((repl (cider-current-repl nil nil)))
    (when (not repl)
      (cider-force-connect))
    (cider-eval-buffer)))

First and second bullet point should be orthogonal. A connection is supposed to be reasonably long-lived You most likely don't want to setup/teardown a bunch of stuff every time you want to eval a buffer I do respect the intent to keep things minimalistic, but I'd heartily recommend to understand how this stuff is supposed to work, and make some minimal adaptations to your intended workflow, accordingly

I think that's I tried to do. My cider-force-eval-buffer has

(when (not repl)
      (cider-force-connect))

I tried to understand how port detection is supposed to work, but it's fairly complex. It seems to be using "ps u | grep java | grep -v leiningen | grep nrepl.cmdline" as a heuristic, which often fails I couldn't figure out how or when .nrepl-port is used (is this documented somewhere?)

But it also resets the conn, for some reason

(when repl
      (cider-quit repl))

These are two different functions. cider-force-connect is only called when no pre-existing repl exists

The current internal incantation is:

(format "ps u | grep -E 'java|%s' | grep -E 'nrepl.cmdline|%s' | grep -v -E 'leiningen|grep'"
                                   bb-indicator
                                   bb-indicator)

Good idea. I'll try upgrading to latest CIDER

Having said that, the newer incantation also won't work, I think, because I'm not using nrepl.cmdline (I'm calling nrepl.server/start-server from the code). Perhaps .nrepl-port is an easier technique for my use case? It has the advantage of being project-relative (I see the code is using clojure-project-dir, which sounds right)

I'd like to figure out how .nrepl-port is written typcally – is that a lein thing, or does nrepl.cmdline do that?

Yes, we have helpers that read .nrepl-port There's defun nrepl-extract-port (dir) available > I'd like to figure out how .nrepl-port is written typcally – is that a lein thing, or does nrepl.cmdline do that? It's standard from https://github.com/nrepl/nrepl so most servers will just write it

Alright, will try that next

OK that worked. Here's what I came up with

(defun cider-force-connect ()
  (interactive)
  (let ((port (nth 1 (car (cider-locate-running-nrepl-ports (clojure-project-root-path))))))
    (if port
        (cider-nrepl-connect
         (thread-first
           nil
           (cider--update-project-dir)
           (plist-put :host "localhost")
           (plist-put :port port)
           (cider--check-existing-session)
           (plist-put :repl-init-function nil)
           (plist-put :session-name nil)
           (plist-put :repl-type 'clj)))
      (cider-connect))))

no idea if you're interested, but there's a (cider-connected-p) that should tell you if cider is connected or not - which might be better than port hunting? Or did that not work?

@U0P0TMEFJ I'm port-hunting to find the right process to connect to, not to see if CIDER is connected

... so you are - I missed that - apologies