Debugger incorrectly steps through conditional forms

[vspinu]

Once #435 is in, try

#dbg
(defn tt [a]
  (let [b (+ a 1)]
    #?(:clj (do
              (loop [b b]
                (if (pos? b)
                  (recur (- b 1))
                  (println "clj"))))
       :cljs (println "cljs"))))

(tt 2)

The debugger within :clj form breaks almost immediately.

[bbatsov]

@FiV0 You might consider taking a stab at this one as well.

[FiV0]

@bbatsov Had seen it. You can assign it to me if you want.

[FiV0]

@bbatsov @vspinu For this one I need some pointers/help. Consider the following code

#dbg
#?(:cljs (+ 1 2) :clj (inc (inc 1)))

In the maybe-debug function

cider-nrepl/src/cider/nrepl/middleware/debug.clj

Lines 612 to 617 in f71b851

	(defn- maybe-debug
	"Return msg, prepared for debugging if code contains debugging macros."
	[{:keys [code ns] :as msg}]
	;; The best way of checking if there's a #break reader-macro in
	;; `code` is by reading it, in which case it toggles `has-debug?`.
	(let [has-debug? (atom false)

the code is still in string form, so something like "#dbg\n#?(....)". Once the evaluation gets to instrument-and-eval

cider-nrepl/src/cider/nrepl/middleware/debug.clj

Lines 594 to 597 in f71b851

	(defn instrument-and-eval [form]
	(let [form1 (ins/instrument-tagged-code form)]
	;; (ins/print-form form1 true false)
	(try

the code has been "read" as clojure data and the form is just (inc (inc 1)), so somewhere in between some reading seems to happen. I am assuming this happens in some lower handler in the nrepl. Is that correct? Essentially when reading such a form we need to do something like (read-string {:read-cond :preserve} "#dbg\n#?(....)") as otherwise the bookkeeping of where stuff is located fails.
Maybe it's this line?
https://github.com/nrepl/nrepl/blob/1cc9baae631703c184894559a2232275dc50dff6/src/clojure/nrepl/middleware/interruptible_eval.clj#L110-L111

[bbatsov]

Yeah, I think that's the line. nREPL basically just delegates to Clojure's own REPL, so it wouldn't have to reimplement its functionality.

[FiV0]

@bbatsov You think it would be ok to add an option to nrepl so that code is read with :preserve. We could then do a first read via nrepl, locate stuff corretly in cider-nrepl, do a second read also in cider-nrepl and then do stuff as usual. I don't see how to solve this one otherwise.

[bbatsov]

Probably that'd be fine. What exactly does :preserve do? If it doesn't affect the evaluation then we can safely enable it.