Clojure macro: with-span

telemetry.clj

(def ^:dynamic *spans* nil)

(defn assoc-span [span-id & args]
  (swap! *spans* #(for [span %]
                    (if (= (:id span) span-id)
                      (apply assoc span args)
                      span))))

(defmacro with-span [name details & body]
  `(if *spans*
     (let [start# (System/currentTimeMillis)
           parent# (first (remove :duration @*spans*))
           my-id# (random-uuid)
           _# (swap! *spans* conj (cond-> {:name ~name
                                           :id my-id#
                                           :start-ms start#
                                           :details ~details}
                                    parent# (assoc :parent-id (:id parent#))))
           res# (try
                  ~@body
                  (catch Exception e#
                    (assoc-span my-id#
                                :error? true
                                :duration (- (System/currentTimeMillis) start#))
                    (throw e#)))]
       (assoc-span my-id# :duration (- (System/currentTimeMillis) start#))
       res#)
     (do ~@body)))