stderr output is not printed to repl

[whysoserious]

Try running this code in cider repl:

user> (try
        (throw (Exception. "dupa"))
        (catch Exception e (println "this works")
               (.printStackTrace e)))
this works
;; => nil

Use the template below when reporting bugs. Please, make sure that
you're running the latest stable CIDER and that the problem you're reporting
hasn't been reported (and potentially fixed) already.

Steps to reproduce the problem

Run this code in cider repl:

(try
  (throw (Exception. "dupa"))
  (catch Exception e 
    (println "this works")
    (.printStackTrace e)))

Expected behavior

this works
STACKTRACE SHOULD BE PRINTED HERE
;; => nil

Actual behavior

this works
;; => nil

Environment & Version information

CIDER version information

; CIDER 0.10.2 (Java 1.8.0_25, Clojure 1.7.0, nREPL 0.2.12)

but it's also confirmed to fail in 0.11-SNAPSHOT

Emacs version

GNU Emacs 24.4.1 (x86_64-apple-darwin13.4.0, NS apple-appkit-1265.21) of 2014-10-21 on builder10-9.porkrind.org

Operating system

MacOS 10.10.5

[bbatsov]

Excellent bug report! Thanks! :-)

[bbatsov]

So, it seems we forgot to handle stderr in our out middleware (https://github.com/clojure-emacs/cider-nrepl/blob/master/src/cider/nrepl/middleware/out.clj). Probably the stderr is ending up in the nrepl-server buffer.

[Malabarba]

Looking through that code now, I don't think I could have done a better job at making it specific to out. 😝

I wish I'd made it slightly more general.

[bbatsov]

You and me both. We definitely have to fix this before the release. If you don't have time I'll update it over the weekend (or at least I hope I'll have time for this).

[Malabarba]

I'll have a bit of time sunday night.

[bbatsov]

OK, I'm leaving this to you then. :-)

[Malabarba]

Actually, I just gave it a try over lunch and I don't know how to get it to work.

Redirecting #'*err* didn't have any effect for me.

Remember how we can redirect Clojure's *out* but not Java's stdout? I think this is the same problem, but with err.

[bbatsov]

Remember how we can redirect Clojure's out but not Java's stdout?

Actually I don't - aren't they the same thing? But I'm guessing even if this is true, it still makes sense to redirect *err* although it won't fix this particular problem.

[Malabarba]

Actually I don't - aren't they the same thing?

Apparently not. To change Java's out we have to call setSystemOut, there's a comment about it on the code.

But I'm guessing even if this is true, it still makes sense to redirect *err* although it won't fix this particular problem.

Yes, but I failed to do that. :-P
Maybe I was just testing it wrong, but I couldn't get *err* to print on the REPL. For instance, no matter what I did, the following code would always print on the server buffer:

(binding [*out* *err*]
  (println "PRINT ME"))

[bbatsov]

Just generify the existing code and we'll take it from there. Baby steps. :-)

[Malabarba]

See clojure-emacs/cider-nrepl#304

[bbatsov]

(binding out err)

P.S. This works fine for me.

[Malabarba]

Yes. Because that's inside an Eval session. The point of this middleware is to redirect prints that happen on the server out (outside any Eval session).