Scala 2.13 REPL has no color on Windows

[Friendseeker]

Version(s)
1.5.4

Describe the bug
Scala 2.13 REPL has no color on Windows

To Reproduce
scala-cli -S 2.13.15

Expected behaviour
Output should be colored, like sbt console

c.c. @SethTisue

[Gedochao]

@SethTisue @lrytz @philwalk any clue where to look?

[SethTisue]

I wish I had some insight, but I don't.

[philwalk]

I verified that the problem exists in cygwin64 running with mintty, and msys64 running in Windows Terminal.
I'll experiment with it to see if I can get any insights.

[philwalk]

This "feature" seems to be part of scala 2.13 rather than scala-cli (same thing happens in any scala 2.13 REPL session).

The following fix works for me when running either bash or CMD from Windows Terminal:

scala-cli -S 2.13 -Dscala.color=true

When directly running in a CMD session, the following works:

C:\opt\scala-2.13.15\bin>scala-cli -S 2.13 -Dscala.color=true -Djline.terminal=jline.WindowsTerminal

Not sure if these settings could easily be made to be the defaults in those environments.

This works in a cygwin mintty session:

and in a Windows Terminal msys64 bash session:

[SethTisue]

note that scala.color defaults to auto

but in src/library/scala/util/Properties.scala I see:

  private[scala] def coloredOutputEnabled: Boolean = propOrElse("scala.color", "auto") match {
    case "auto" => !isWin && consoleIsTerminal
    case s      => "" == s || "true".equalsIgnoreCase(s)
  }

note that the !isWin, which appears to be the culprit

the history for why this was added is at scala/scala#5663 , which was back in 2017, in 2.12.x days

presumably a Scala 2.13 PR doing something better — not just in the Scala-CLI context — would have a good chance of being accepted

about the native-code angle, we've been on JLine 3 on 2.13.x for ages now, and scala/scala#10898 aligns us with the JLine 3 project's current recommendations on Windows

I'm less confident that makes sense to consider changing 2.12, since with every year that passes we're less and less willing to touch 2.12 (which still uses JLine 2) — in general, but especially when it's something like the REPL that's fragile and requires manual testing

[Gedochao]

@SethTisue to confirm, is this something we should try to address in the Scala 2.13 (or less likely 2.12) REPL, rather than on the side of Scala CLI? Is there a ticket on Scala 2 side to track this, or should we raise one?

Adding -Dscala.color=true by default for REPL on Windows environments for Scala 2.x specifically in Scala CLI is something we could do, I guess... But maybe it's better to fix it at the source.

[SethTisue]

Agree. @Friendseeker @philwalk can I interest you in opening a ticket in scala/bug?

[philwalk]

Yes, the problem originates in the scala 2.13 REPL

…

On Wed, Jan 8, 2025, 02:42 Piotr Chabelski ***@***.***> wrote: @SethTisue <https://github.com/SethTisue> to confirm, is this something we should try to address in the Scala 2.13 (or less likely 2.12) REPL, rather than on the side of Scala CLI? Is there a ticket on Scala 2 side to track this, or should we raise one? Adding -Dscala.color=true by default for REPL on Windows environments for Scala 2.x specifically in Scala CLI is something we could do, I guess... But maybe it's better to fix it at the source. — Reply to this email directly, view it on GitHub <#3394 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAYGLFUHSIJJ6V4MSFPRMAL2JTXI3AVCNFSM6AAAAABUDZ3SZKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNZXGIZDMMRUG4> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[philwalk]

@philwalk can I interest you in opening a ticket in scala/bug?

I'll look into it. Not familiar with the build process for scala 2, but how hard can it be :)
If we change the default from "auto" to "true", people can do -Dscala.color=false if they run into problems.

[SethTisue]

If we change the default from "auto" to "true", people can do -Dscala.color=false if they run into problems

I agree that a PR with only that change might well be accepted, assuming that you show the same manual testing that you showed above

[philwalk]

Here's the bug report: scala/bug#13077