Adding a "compilation phase" to Heroku's publishing process (a.k.a. slug compilation)

heroku_autobuild.clj

(use 'robert.hooke)
(require 'leiningen.deps)
(require 'lancet.core)
(import (java.io File)
        (java.net URL URLClassLoader)
        (java.lang.reflect Method))

;; based on code from leiningen.deps (version 1.6.1)
(defn- find-lib-jars [project]
  (.listFiles (File. (:library-path project))))

(defn ^{:internal true} find-jars
  [project]
  (filter #(.endsWith (.getName %) ".jar")
          (concat (find-lib-jars project)
                  (.listFiles (File. (:root project) "lib/dev")))))

(defn call [^String nm & args]
  (when-let [fun (ns-resolve *ns* (symbol nm))]
    (apply fun args)))

(defn add-to-cp [#^File jar]
  (let [#^URL url (.. jar toURI toURL)
        url-ldr-cls (. (URLClassLoader. (into-array URL [])) getClass)
        arr-cls (into-array Class [(. url getClass)])
        arr-obj (into-array Object [url])
        #^Method mthd (. url-ldr-cls getDeclaredMethod "addURL" arr-cls)]
    (doto mthd
      (.setAccessible true)
      (.invoke (ClassLoader/getSystemClassLoader) arr-obj))
    (println (format "Added %s to classpath" jar))))

(defn wrapper [method & args]
  (let [result (apply method args)
        jars (find-jars (first args))]
    (doseq [jar jars] (add-to-cp jar))
    (require 'leiningen.mvn)
    (call "leiningen.mvn/mvn" (first args) "package" "-DskipTests=true")
    result))

(add-hook #'leiningen.deps/deps wrapper)