Output should distinguish stdout and stderr

[som-snytt]

Compiler version

3.2.1

Output

javac --version (and help) is written to stdout, and scalac 2 follows that model of reporting only error output to stderr.

scalac 3 writes all output to stderr.

Expectation

Expect javac behavior. Not sure about the summary 19 errors which is echoed to stdout in scala 2. Edit: scala 2 prints summary count to stderr scala/scala#10272

Would expect debug output -Vprint on stdout. That is, stderr is for the tool to tell me why it could not fulfill my request.

Not sure about scala-cli or sbt compile.

[Kordyjan]

I prefer the output of -Vprint to stay in stderr, as it should be considered diagnostic data.
I, however, agree that scalac -version should output to stdout, as the version is the main output of the command, and I can see it being used in scripts.

[som-snytt]

My criterion was "stdout for output I asked for", but "stderr to report why the tool did not do what I requested."

On Scala 2, I chose that summary N errors is stderr output. (PR not accepted yet.) The error summary clearly explains the error.

"Diagnostic data" is an interesting criterion. How is -version not diagnostic in some sense? I would stand by the criterion, "successful completion" versus "error outputs explaining a failure".

What about warnings? If I say -Xlint, then those warnings are "requested", to stdout. Are those warning stdout normally, but stderr if -Werror?

I won't try the permutations just now, but it's not obvious which output to use in all cases. It might be a "style" choice.

[som-snytt]

Also scalac -help 2>&1 | grep color to jog my memory on colorization.

Note javac is on stdout, javac -help | grep proc. It makes sense because that is the successful output I requested.

Scala 2 follows java.

If the compiler were one of those sarcastic robots from science fiction, it would say, "Helpful output is not my primary function."

[ncgl-git]

Very new to scala and decided to start looking into this issue. I see us mapping --version to Repl here, and us defaulting to Console.out here.

Is Console.out not Stdout?

[som-snytt]

I see settings.version used here, but I don't know without looking further whether reporting an Info is output on a channel for info or for errors and warnings.

I'm not sure "diagnostic" is sufficiently diagnostic. Everything that is not a class file (or tasty file) is diagnostic output.

Edit: console output

I don't remember how Scala 2 works, as reporting was reworked so many times.