Scripting Solution: scala can compile & run *.scala files

Author: anatoliykmetyuk

compiler/src/dotty/tools/repl/Main.scala

@@ -1,7 +1,24 @@
 package dotty.tools.repl
 
+import java.io.File
+
 /** Main entry point to the REPL */
-object Main {
-  def main(args: Array[String]): Unit =
-    new ReplDriver(args).runUntilQuit()
-}
+object Main:
+  def preprocessArgs(args: Array[String]): (Array[String], Option[File], Array[String]) =
+    val scriptIndex = args.lastIndexWhere(_.endsWith(".scala"))
+    if scriptIndex < 0 then (args, None, Array.empty[String])
+    else (args.take(scriptIndex), Some(File(args(scriptIndex))), args.drop(scriptIndex + 1))
+  end preprocessArgs
+
+  def main(args: Array[String]): Unit = preprocessArgs(args) match
+    case (compilerArgs, Some(scriptFile), scriptArgs) =>
+      try ScriptingDriver(compilerArgs, scriptFile, scriptArgs).compileAndRun()
+      catch
+        case ScriptingException(msg) =>
+          println(s"Error: $msg")
+          sys.exit(1)
+    case (compilerArgs, None, scriptArgs) if scriptArgs.isEmpty =>
+      new ReplDriver(args).runUntilQuit()
+    case _ =>
+      throw RuntimeException(s"Incorrect arguments to REPL: ${args.mkString(" ")}")
+end Main

compiler/src/dotty/tools/repl/ScriptingDriver.scala

@@ -0,0 +1,79 @@
+package dotty.tools.repl
+
+import java.nio.file.{ Files, Path }
+import java.io.File
+import java.net.{ URL, URLClassLoader }
+import java.lang.reflect.{ Modifier, Method }
+
+import scala.jdk.CollectionConverters._
+
+import dotty.tools.dotc.{ Driver, Compiler }
+import dotty.tools.dotc.core.Contexts, Contexts.{ Context, ContextBase, ctx }
+import dotty.tools.dotc.config.CompilerCommand
+import dotty.tools.io.{ PlainDirectory, Directory }
+import dotty.tools.dotc.reporting.Reporter
+import dotty.tools.dotc.config.Settings.Setting._
+
+import sys.process._
+
+class ScriptingDriver(compilerArgs: Array[String], scriptFile: File, scriptArgs: Array[String]) extends Driver:
+  def compileAndRun(): Unit =
+    val outDir = Files.createTempDirectory("scala3-scripting")
+    val (toCompile, rootCtx) = setup(compilerArgs :+ scriptFile.getAbsolutePath, initCtx.fresh)
+    given Context = rootCtx.fresh.setSetting(rootCtx.settings.outputDir,
+      new PlainDirectory(Directory(outDir)))
+
+    if doCompile(newCompiler, toCompile).hasErrors then
+      throw ScriptingException("Errors encountered during compilation")
+
+    try detectMainMethod(outDir, ctx.settings.classpath.value).invoke(null, scriptArgs)
+    catch
+      case e: java.lang.reflect.InvocationTargetException =>
+        throw e.getCause
+
+  end compileAndRun
+
+  private def detectMainMethod(outDir: Path, classpath: String): Method =
+    val outDirURL = outDir.toUri.toURL
+    val classpathUrls = classpath.split(":").map(File(_).toURI.toURL)
+    val cl = URLClassLoader(classpathUrls :+ outDirURL)
+
+    def collectMainMethods(target: File, path: String): List[Method] =
+      val nameWithoutExtension = target.getName.takeWhile(_ != '.')
+      val targetPath =
+        if path.nonEmpty then s"${path}.${nameWithoutExtension}"
+        else nameWithoutExtension
+
+      if target.isDirectory then
+        for
+          packageMember <- target.listFiles.toList
+          membersMainMethod <- collectMainMethods(packageMember, targetPath)
+        yield membersMainMethod
+      else if target.getName.endsWith(".class") then
+        val cls = cl.loadClass(targetPath)
+        val method =
+          try cls.getMethod("main", classOf[Array[String]])
+          catch
+            case _: java.lang.NoSuchMethodException => null
+
+        if method != null && Modifier.isStatic(method.getModifiers) then List(method)
+        else Nil
+      else Nil
+    end collectMainMethods
+
+    val candidates = for
+      file <- outDir.toFile.listFiles.toList
+      method <- collectMainMethods(file, "")
+    yield method
+
+    candidates match
+      case Nil =>
+        throw ScriptingException("No main methods detected in your script")
+      case _ :: _ :: _ =>
+        throw ScriptingException("More than one main method detected in your script")
+      case m :: Nil => m
+    end match
+  end detectMainMethod
+end ScriptingDriver
+
+case class ScriptingException(msg: String) extends RuntimeException(msg)