Scala 3.8 REPL support?

[SethTisue]

https://mill-build.org/mill/scalalib/intro.html says

You can also start a standalone Scala REPL with the Bundled Libraries included via ./mill --repl

but when I try it:

% mill --repl
The --repl mode is no longer supported.

the same page says:

 ./mill -i repl       # start an Ammonite Scala REPL within your project

but I tried that in a fresh clone of com-lihaoyi/os-lib and got:

% mill -i repl
[64/64] ============================== repl ============================== 1s
Cannot resolve repl. Try `mill resolve _`, `mill resolve __.repl` to see what's available, or `mill __.repl` to run all `repl` tasks

the reason I was even trying this was that I wondered if Mill's REPL support needed to be updated for Scala 3.8, as already in the 3.8 nightlies the REPL has been split off into a separate jar, and other tools have had to adapt to that:

• Scala 3.8 REPL support sbt/sbt#8348
• Add support for the new Scala 3.8 REPL VirtusLab/scala-cli#3936

but now I'm unsure if Mill's REPL support still exists, to need updating?

[lefou]

We removed the Ammonite based --repl option in Mill 0.11, but lately resurrected it in Mill 1.1.0-RC1 (#5983), this time based on the Scala default REPL and some additional libraries.

[SethTisue]

okay — what about the 3.8 angle, is any work needed there?

[lefou]

I assume, if the REPL of Scala 3.8 is no longer part of the jars, but requires a new jar, we also need to adapt it in Mill.

The two places where Mill uses the Scala REPL are ScalaModule.console and the --repl option, which ultimately also uses the console task of the meta build.

It currently uses the compiler classpath combined with the module's run classpath.

mill/libs/scalalib/src/mill/scalalib/ScalaModule.scala

Lines 416 to 424 in 51a76bd

	Jvm.callProcess(
	mainClass =
	if (JvmWorkerUtil.isDottyOrScala3(scalaVersion()))
	"dotty.tools.repl.Main"
	else
	"scala.tools.nsc.MainGenericRunner",
	classPath = runClasspath().map(_.path) ++ scalaCompilerClasspath().map(
	_.path
	),

The best would be to add a new scalaConsoleClasspath task.

As a workaround, users can add the missing jar either to the scalaCompilerClasspath or the runClasspath via runMvnDeps.

Are there other changes needed, like a change of the main class?

[SethTisue]

Are there other changes needed, like a change of the main class?

the author of scala/scala3#24243 , @hamzaremmal, should be able to advise you on that