Analysing re-frame subscriptions using Clj-Kondo

This is a simple project to demonstrate and give the boilerplate for how to analyse re-frame keywords in your codebase. This implementation prints out 4 types of warnings:

• A subscription is used but never registered
• A subscription is registered but never used
• An event is called but never registered
• An event is registered but never used

Keep in mind that this is performing a static analysis on the codebase, and any dynamic uses of subscribing and dispatching will not be caught.

(let [event-vec [:do-something!]]
  ;; Cannot extract the event keyword from the `event-vec` symbol
  (rf/dispatch event-vec)) 

There are two parts to this implementation:

• Some .clj-kondo/hooks to annotate keywords in the codebase when they are used by re-frame.
• A script.clj using the analysis output of Kondo to match and print the warnings.

Here's output when linting the bit of code in the src directory:

src/app/core.cljs:8 Call to unregistered subscription :app.core/undefined-sub
src/app/core.cljs:9 Dispatching unregistered event :app.core/undefined-event
src/app/db.cljs:8 Registering unused subscription :app.db/orphaned-sub
src/app/db.cljs:7 Registering unused event :app.db/orphaned-event

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Using this script

This project is not intended to be a library (yet?). It's informational, and intended to be copied and modified for your own use cases.

But to get this example working clone the repo, cd into the directory and then:

Using from JVM Clojure

💡Easy and quick

clj -M -m analyse-re-frame

This should run the -main function in scripts/analyse_re_frame.clj and print out the example output as seen above.

Using as Babashka script

👍 Recommended for you project

A small tweak needs to be done to lint from babashka. You need to call clj-kondo.main/run! from a pod. See: https://github.com/babashka/pod-registry/blob/master/examples/clj-kondo.clj

You need to make this changes to the script:

1. Require babashka pods

Remove the existing namespace declaration (along with the kondo require) and replace it with:

(ns analyse-re-frame
  (:require [babashka.pods :as pods]))

2. Require the Clj-Kondo pod

Add these lines at the top of the file after the NS declaration:

;; Replace the version with latest or whatever version you want to use.
(pods/load-pod 'clj-kondo/clj-kondo "2021.10.19") 
(require '[pod.borkdude.clj-kondo :as clj-kondo])

3. Run the script using Babashka!

bb --classpath "scripts" -f scripts/analyse_re_frame.clj -m analyse-re-frame/-main

And you should get similar results.

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Modifying this script

You might be using your own custom dispatch, subscribe, reg-xx functions that wrap re-frame. If you do so you need to make some changes. Annotating re-frame reg-xx functions is already supported in kondo, this repo contains hooks to annotate subscribe and dispatch calls. Both hooks work a bit differently so different changes are required:

Your own dispatch / subscribe calls

1. Add an entry to the hooks defined here following the same pattern. This will annotate the keyword used by the subscription. You can add as many variants as you like, as long as the shape (e.g:(subscribe [key & args])) stays the same. If it's not the same structure you will need to edit the hooks to annotate the keyword correctly.

You could get the same result with adding a :lint-as entry for these as well.

Your own reg-sub / reg-event

For your own reg-xx functions, two things need to be done:

1. Add a :lint-as entry in the Kondo config.
2. Add your custom symbol to the correct set in the filter functions here

This is needed because the annotation will have your own custom symbol (that's the behavior of the built-in re-frame hooks) and the script needs to know what kind of annotation it is.

Make this into a library / linter?

If you'd like to see this packaged in a library or custom linter of some sorts, feel free to show this interest in the form of a Github Issue or post in the #clj-kondo Slack channel.