Clojure hack to overwrite the JVM's System/getenv map for environment variables without touching the actual environment. Definitely not safe.

env.clj

(ns env
  "Clojure hack to overwrite the JVM's System/getenv map for environment variables without touching the actual environment. Definitely not safe."
  (:import (java.util Collections Map)))

(defn -unsafe-set-env [new-env]
  (try
    (let [clazz (Class/forName "java.lang.ProcessEnvironment")]
      (doseq [field ["theEnvironment" "theCaseInsensitiveEnvironment"]]
        (let [env-field (doto (.getDeclaredField clazz field) (.setAccessible true))]
          (.putAll ^Map (.get env-field nil) new-env))))
    (catch NoSuchFieldException e
      (let [env (System/getenv)]
        (doseq [clazz (.getDeclaredClasses Collections)]
          (when (= (.getName clazz) "java.util.Collections$UnmodifiableMap")
            (let [field (doto (.getDeclaredField clazz "m") (.setAccessible true))
                  obj (.get field env)]
              (.clear ^Map obj)
              (.putAll ^Map obj (into new-env env)))))))))

(defmacro with-unsafe-merge-env [new-env-vars & body]
  `(let [env# (into {} (System/getenv))
         _# (-unsafe-set-env (merge env# ~new-env-vars))
         ret# (do ~@body)]
     (-unsafe-set-env env#)
     ret#))