How do I update Clojure dependencies when working with nrepl.el?

Question

As I understand it, when I do nrepl-jack-in a REPL is loaded along with all the dependencies defined in project.clj. If I then update project.clj to add a new dependency, do I need to kill the server and re-run nrepl-jack-in or is there way to update the dependencies in the current REPL?

Answer 1

Update: Maybe there is some hope, See https://github.com/cemerick/pomegranate

Previously:

The short answer is yes - you do have to restart the JVM process.

I am aware of no good way to update dependencies in a live repl. Leiningen (called by nrepl-jack-in) will manage dependencies and set up the classpath only upon restarting. Trying to do something dynamic and clever is horribly fragile.

The struck out text below is factually true but upon a moment's reflection seemed such bad advice I have marked it up as such...

If you have a local dependency (e.g. jar file) you might use the long-time deprecated function add-classpath at the repl. But you will be entering the dragon infested swamp of java classloaders.

Answer 2

Restarting the REPL seems to be the simplest way. This can be done with:

M-x cider-restart

That also appears to accomplish a lein deps. So the whole process of adding a new dependency simply involves adding the require to your project.clj and then invoking cider-restart.

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Another (very convenient) way is to use clj-refactor. Adding the artifact (C-c m a p or cljr-add-project-dependency) will prompt for the version you want, automatically put the new dependency into your project.clj file, and reload your session.

Answer 3

Before pomegranate existed, I wrote my own library to dynamically load dependencies.

https://github.com/bmillare/dj

After the release of lein2 and how it under the covers can use pomegrante, I rewrote dj to use this underneath. So, even if you don't use 'dj', it might be a useful as a reference to see what its doing.