Scala REPL based app. fail when file name has no extension '.jar' or '.zip'

repl_ext_jar.md

REPL based application will fail with initialization error of REPL if its jar file name has no extension '.jar' or '.zip'.

import scala.tools.nsc.Settings
import scala.tools.nsc.interpreter.shell.{ILoop, ShellConfig}

object ReplTestMain extends App {
    println("test")
    val settings = new Settings
    settings.usejavacp.value = true
    new TestILoop(ShellConfig(settings)).run(settings)
}

class TestILoop(val shellConfig:ShellConfig) extends ILoop(shellConfig) {
}

In above sample application, we can run REPL as follows.

$ java -jar target/scala-2.13/repl-test-assembly-0.1.0-SNAPSHOT.jar
test
Welcome to Scala 2.13.4 (OpenJDK 64-Bit Server VM, Java 1.8.0_242).
Type in expressions for evaluation. Or try :help.

scala>

But if rename the file to repl-test-assembly-0.1.0-SNAPSHOT, it failed to run as follows.

$ cp target/scala-2.13/repl-test-assembly-0.1.0-SNAPSHOT.jar target/scala-2.13/repl-test-assembly-0.1.0-SNAPSHOT
$ java -jar target/scala-2.13/repl-test-assembly-0.1.0-SNAPSHOT
test
Welcome to Scala 2.13.4 (OpenJDK 64-Bit Server VM, Java 1.8.0_242).
Type in expressions for evaluation. Or try :help.

Failed to initialize compiler: object scala in compiler mirror not found.
** Note that as of 2.8 scala does not assume use of the java classpath.
** For the old behavior pass -usejavacp to scala, or if using a Settings
** object programmatically, settings.usejavacp.value = true.
Exception in thread "main" java.lang.NullPointerException
        at scala.tools.nsc.CompilationUnits$CompilationUnit.<init>(CompilationUnits.scala:44)
        at scala.tools.nsc.CompilationUnits$CompilationUnit.<init>(CompilationUnits.scala:45)
        at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:735)
        at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:554)
        at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:590)
        at scala.tools.nsc.interpreter.IMain.$anonfun$quietBind$1(IMain.scala:589)
        at scala.tools.nsc.interpreter.shell.ReplReporterImpl.withoutPrintingResults(Reporter.scala:64)
        at scala.tools.nsc.interpreter.IMain.quietBind(IMain.scala:589)

The extension .zip is also OK.

build.sbt

lazy val scalaVer = "2.13.4"
ThisBuild / scalaVersion     := scalaVer
ThisBuild / version          := "0.1.0-SNAPSHOT"
ThisBuild / scalacOptions ++= Seq("-deprecation", "-feature")

lazy val root = (project in file("."))
  .settings(
    name := "repl-test",
    test in assembly := {},
    libraryDependencies ++= Seq(
      "org.scala-lang" % "scala-compiler" % scalaVer,
    ),
  )

project/plugins.sbt

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.15.0")