Getting Timbre v 4.x logging working

core.clj

;; Taoensso.timbre has been a very good Clojure logging library, but v4.0 was a 
;; breaking change and it took me a while to get my head round it, although in 
;; fact it's very simple. If you're having trouble with it, try this, which is
;; very simple and works with Timbre 4.7.4

(ns ^{:doc "After upgrading Timbre from 3.x to 4.x, all my applications broke.
      I wrote this little test piece to understand what was going wrong. It works."
      :author "Simon Brooke"}
  chainsaw.core
  (:require
    [taoensso.timbre :as timbre]
    [taoensso.timbre.appenders.3rd-party.rotor :as rotor])
  (:gen-class))

(def log-config
  {:level :debug
   :appenders
   {:rotating (rotor/rotor-appender
                        {:path "chainsaw.log"
                         :max-size (* 512 1024)
                         :backlog 10})}})

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (timbre/merge-config! log-config)
  (timbre/info "Chainsaw starting up")
  (println "Hello, World!")
  (timbre/info "Chainsaw shutting down"))