fn_closures.clj

(ns foo
  (:import
   [clojure.lang Compiler Compiler$C]))

(defn get-closure-names* [form env]
  (let [ex      (with-bindings {Compiler/LOCAL_ENV env}
                  (Compiler/analyze Compiler$C/EXPRESSION form))
        closes  (.closes ex)]
    (->> closes
         (keys) ;; у них ключи и значения совпадают
         (map #(.-sym %)))))
    
(defmacro get-closure-names [form]
  `(quote ~(get-closure-names* form &env)))

(let [a 1
      b 2]
  (get-closure-names (fn [x] [a]))) ;;=> '(a)