stderr not sent back to client

[tzzh]

When running bb --nrepl-server and the connecting to it with a nrpel client for examplelein repl :connect 1667, stderr is not visible in the client, for example the following doesn't print anything

user=> (binding [*out* *err*]
    #_=>   (println "Hello, STDERR!"))
nil

[borkdude]

Hey @tzzh, thanks for the issue. We have tests for normal output here:

https://github.com/babashka/babashka.nrepl/blob/master/test/babashka/nrepl/server_test.clj#L213-L230

It should not be too hard to support the same for :err probably.

[tzzh]

Hey, so I realised when running this code that sci/err is not bound but I am not sure how to bind out the right writer.
Basically I am getting

#error {
 :cause class sci.impl.vars.SciUnbound cannot be cast to class java.io.Writer (sci.impl.vars.SciUnbound is in unnamed module of loader 'app'; java.io.Writer is in module java.base of loader 'bootstrap')
 :via
 [{:type clojure.lang.ExceptionInfo
   :message class sci.impl.vars.SciUnbound cannot be cast to class java.io.Writer (sci.impl.vars.SciUnbound is in unnamed module of loader 'app'; java.io.Writer is in module java.base of loader 'bootstrap') [at line 1, column 1]
   :data {:type :sci/error, :line 1, :column 1, :message class sci.impl.vars.SciUnbound cannot be cast to class java.io.Writer (sci.impl.vars.SciUnbound is in unnamed module of loader 'app'; java.io.Writer is in module java.base of loader 'bootstrap') [at line 1, column 1]}

so then in

babashka.nrepl/src/babashka/nrepl/impl/server.clj

Lines 31 to 32 in 3e97bcb

	(let [result (sci/with-bindings {sci/out pw}
	(eval-form ctx form))]

I am not sure how to get the right print writer I tried sci/err pw but then it sends stderr to stdout and I am not sure how I can bind sci/err to the right writer

[borkdude]

@tzzh I think you need to build another replying-print-writer that sends "err" messages instead of "out" messages:

babashka.nrepl/src/babashka/nrepl/impl/utils.clj

Line 40 in 3e97bcb

;; from https://github.com/nrepl/nrepl/blob/1cc9baae631703c184894559a2232275dc50dff6/src/clojure/nrepl/middleware/print.clj#L99

and bind that to sci/err.

I think it's nicer to make "out" and "err" pluggable as an argument.
Note that the original nREPL also does this:

https://github.com/nrepl/nrepl/blob/1cc9baae631703c184894559a2232275dc50dff6/src/clojure/nrepl/middleware/print.clj#L115

[tzzh]

OK cool I am not super familiar with the nrepl code but I am starting to understand thanks 👍 - I'll try and make a PR for this

[borkdude]

@tzzh The pod protocol was largely inspired by nREPL so you're probably more familiar than you realize :).

[borkdude]

Thanks!