Fix broken instrumentation of forms with #? conditionals

[vspinu]

Any forms that contain reader conditionals cannot be instrumented:

(defn tt [a]
  (let [b (+ a 1)]
    #?(:clj (println "clj")
       :cljs (println "cljs"))))

The reason is that conditionals are disabled by default in clojure's readers.

[bbatsov]

I guess this should also have some test and a changelog entry on CIDER's side ideally.

[Malabarba]

Stepping through these forms probably won't work when they're slightly more complicated, but it's better than the current situation of not reading them at all.

[vspinu]

Indeed, debugger breaks on more complex inputs. Opening a separate #437 for that.

@bbatsov there is little point of testing whether debugger enters the form or not. More specific tests of #437 will do that automatically. I will add the log entry on the cider side for multiple fixes at once.

[bbatsov]

Shouldn't we check for them explicitly? Seems a bit arbitrary to check that something is 3+ characters.

[vspinu]

I am not completely sure what you mean but we do check for all of them explicitly with that fake reader above. All of them have >= 4 chars this is why 3 characters threshold. It's indeed arbitrary but avoids entering that code in simple cases when there is obviously no reader there. It could be 6 there just as fine :).

As mentioned in the comment, new line in REPL will throw and trigger that catch over there. When debugging I am placing a print there to see exactly what is going on, and those useless throws interfere with the experience. Does this clarify your question?

[bbatsov]

Well, I guess you can just write more explanations here and that would be enough. I just assume that if some code is confusing to me it will probably be confusing to someone else as well.