Add support for JShell in repl (#4262)

* Add support for JSHELL in `repl`

* Add support for `--repl-init-script-file` to enable testing JSHELL on Windows

* Extract Jshell integration tests to a dedicated trait

* Test JSHELL with the supported JVMs

* Refactor

* Refactor some more

* Make JSHELL non-experimental

* Refactor some more

* Allow to run pure Java projects in Scala REPL

* Enable usage of Scala dependencies in pure Java projects

* Refactor some more

Author: Gedochao

modules/cli/src/main/scala/scala/cli/commands/repl/JShellRunner.scala

@@ -0,0 +1,110 @@
+package scala.cli.commands.repl
+
+import java.io.File
+
+import scala.build.Logger
+import scala.build.errors.BuildException
+import scala.build.internal.Runner
+import scala.build.options.BuildOptions
+import scala.util.Properties
+
+object JShellRunner {
+  final case class Command(
+    jshellCommand: String,
+    args: Seq[String],
+    extraEnv: Map[String, String]
+  ) {
+    def processCommand: Seq[String]   = Seq(jshellCommand) ++ args
+    def displayedCommand: Seq[String] = Runner.envCommand(extraEnv) ++ processCommand
+  }
+
+  final class JShellUnavailable(message0: String)
+      extends BuildException(message0)
+
+  private def executableExt(isWindows: Boolean): String = if isWindows then ".exe" else ""
+
+  def commandFor(
+    javaHomeInfo: BuildOptions.JavaHomeInfo,
+    javaOpts: Seq[String],
+    classPath: Seq[os.Path],
+    programArgs: Seq[String],
+    initScriptOpt: Option[String],
+    quitAfterInit: Boolean,
+    currentEnv: Map[String, String],
+    isWindows: Boolean = Properties.isWin
+  ): Either[BuildException, Command] =
+    if javaHomeInfo.version < 9 then
+      Left(
+        JShellUnavailable(
+          s"JShell requires JDK >= 9, but the selected JDK is ${javaHomeInfo.version}. Consider using --jvm 17."
+        )
+      )
+    else {
+      val jshellPath    = javaHomeInfo.javaHome / "bin" / s"jshell${executableExt(isWindows)}"
+      val jshellCommand = jshellPath.toString
+      if !os.exists(jshellPath) then
+        Left(
+          JShellUnavailable(
+            s"JShell executable not found at $jshellCommand. Ensure the selected JVM is a full JDK (for example with --jvm 17)."
+          )
+        )
+      else {
+        val classPathArg = classPath.map(_.toString).distinct.mkString(File.pathSeparator)
+        val startupArgs  = initScriptOpt.toSeq.flatMap { script =>
+          val scriptFile = os.temp(
+            prefix = "scala-cli-jshell-init-",
+            suffix = ".jsh",
+            deleteOnExit = false
+          )
+          os.write.over(scriptFile, script + System.lineSeparator())
+          Seq("--startup", "DEFAULT", "--startup", scriptFile.toString)
+        }
+        val quitAfterInitArgs =
+          if quitAfterInit then {
+            val exitFile = os.temp(
+              prefix = "scala-cli-jshell-exit-",
+              suffix = ".jsh",
+              deleteOnExit = false
+            )
+            os.write.over(exitFile, "/exit" + System.lineSeparator())
+            Seq(exitFile.toString)
+          }
+          else Nil
+        val vmArgs = javaOpts.map(opt => s"-J$opt")
+        val args   = Seq("--class-path", classPathArg) ++
+          vmArgs ++
+          startupArgs ++
+          programArgs ++
+          quitAfterInitArgs
+        val extraEnv = javaHomeInfo.envUpdates(currentEnv)
+        Right(Command(jshellCommand, args, extraEnv))
+      }
+    }
+
+  def run(
+    command: Command,
+    logger: Logger,
+    allowExecve: Boolean,
+    dryRun: Boolean
+  ): Either[BuildException, Unit] = {
+    logger.log(
+      s"Running ${command.displayedCommand.mkString(" ")}",
+      "  Running" + System.lineSeparator() +
+        command.displayedCommand.iterator.map(_ + System.lineSeparator()).mkString
+    )
+    if dryRun then {
+      logger.message(s"JShell command: ${command.processCommand.mkString(" ")}")
+      logger.message("Dry run, not running REPL.")
+      Right(())
+    }
+    else {
+      val process =
+        if allowExecve then
+          Runner.maybeExec("jshell", command.processCommand, logger, extraEnv = command.extraEnv)
+        else Runner.run(command.processCommand, logger, extraEnv = command.extraEnv)
+      val retCode = process.waitFor()
+      if retCode == 0 then Right(())
+      else Left(new Repl.ReplError(retCode))
+    }
+  }
+}