gistfile1.txt

~/Projects/clojurescript (master*) $ rlwrap ./script/repl  
Clojure 1.4.0
(require '[cljs.compiler :as comp])
(require '[cljs.analyzer :as ana])

;; This trickery seems to be the minimum logic to prepare a top level namespace
(def repl-env
  (binding [ana/*cljs-ns* 'cljs.user]
    (-> (ana/empty-env)
        (ana/analyze '(ns some-ns))
        :env
        (assoc :ns (ana/get-namespace ana/*cljs-ns*)))))

(defn analyze [form]
  (binding [ana/*cljs-warn-on-undeclared* true]
    (ana/analyze repl-env form)))

(-> '(defprotocol P
       (f [_ x]))
  analyze
  keys)
nil
user=> nil
user=> user=> user=> #'user/repl-env
user=> user=> #'user/analyze
user=> user=> WARNING: Use of undeclared Var some-ns/f at line 16 
WARNING: Use of undeclared Var some-ns/f at line 16 
(:env :op :form :statements :ret :children)