*cljs-compiler-env* does not get set on setup error

[johnbendi]

When starting the cljs-repl of piggieback the *cljs-compiler-env* does not get set causing the repl to bootstrap cljs.core on every evaluation. There should be a provision for setup errors so that the env gets reset properly.

The actual error causing it in my case is reported here: https://groups.google.com/forum/#!topic/clojurescript/ewRpTfSOYq8

Thanks, John

[cemerick]

Looking at the groups thread, I only see mention of RangeErrors coming out of your JavaScript environment. Anything related to *cljs-compiler-env* would be a Clojure exception; do you have a stack trace of that somewhere?

[johnbendi]

Yes the error is related to my Javascript environment. But what I wanted you to take note of was that any such error which is happening on first call to cljs-repl will not abort after run-cljs-repl executes in the code below but goes ahead to set! *cljs-repl-env* and *ns* despite *cljs-compiler-env* not been set. Which will still make the cljs-repl prompt appear to users and cause the reloading of cljs.core on every evaluation adding 2-3 seconds because *cls-compiler-env* was not set on the first call. Unless the user is deeply knowledgeadble to know that this is not the intended behavior. So what I am saying is there should be a way to catch the first -evaluation error and prevent cls-repl from executing the rest of its body.

(defn cljs-repl
  "Starts a ClojureScript REPL over top an nREPL session.  Accepts
   all options usually accepted by e.g. cljs.repl/repl."
  [repl-env & {:as options}]
  ;; TODO I think we need a var to set! the compiler environment from the REPL
  ;; environment after each eval
  (try
    (let [repl-env (delegating-repl-env repl-env nil)]
      (set! ana/*cljs-ns* 'cljs.user)
      ;; this will implicitly set! *cljs-compiler-env*
      (run-cljs-repl (assoc ieval/*msg* ::first-cljs-repl true)
        (nrepl/code
          (+ 1)
          ;; (ns cljs.user
          ;;   (:require
          ;;    [clojure.browser.repl]
          ;;    [cljs.repl :refer-macros (source doc find-doc
          ;;                               apropos dir pst)]))
          )
        repl-env nil options)
      ;; (clojure.pprint/pprint (:options @*cljs-compiler-env*))
      (set! *cljs-repl-env* repl-env)
      (set! *cljs-repl-options* options)
      ;; interruptible-eval is in charge of emitting the final :ns response in this context
      (set! *original-clj-ns* *ns*)
      (set! *ns* (find-ns ana/*cljs-ns*))
      (println "To quit, type::" :cljs/quit))
    (catch Exception e
      (set! *cljs-repl-env* nil)
      (throw e))))

I hope the issue is clear enough. This took me days to observe as I was not familiar with the new changes made from 1.6.

[cemerick]

Okay, I see what you mean now. The fix for this would be to have cljs-repl check that *cljs-compiler-env* is non-nil before continuing on to set the rest of the dynamic environment that piggieback manages, and throw an error instead. Happy to take a PR for that if someone wants to add a check before I get around to it.

Of course, this won't fix the underlying problem (which does not require piggieback to reproduce, IIRC?).

[bbatsov]

Is this still an issue?