Fix running JARs from scala script

Author: BarkingBad

compiler/src/dotty/tools/MainGenericRunner.scala

@@ -12,6 +12,8 @@ import scala.annotation.internal.sharable
 import dotty.tools.dotc.util.ClasspathFromClassloader
 import dotty.tools.runner.ObjectRunner
 import dotty.tools.dotc.config.Properties.envOrNone
+import java.util.jar._
+import java.util.jar.Attributes.Name
 
 enum ExecuteMode:
   case Guess
@@ -129,7 +131,25 @@ object MainGenericRunner {
       case ExecuteMode.Run =>
         val scalaClasspath = ClasspathFromClassloader(Thread.currentThread().getContextClassLoader).split(classpathSeparator)
         val newClasspath = (settings.classPath ++ scalaClasspath :+ ".").map(File(_).toURI.toURL)
-        errorFn("", ObjectRunner.runAndCatch(newClasspath, settings.residualArgs.head, settings.residualArgs.drop(1)))
+        val res = ObjectRunner.runAndCatch(newClasspath, settings.residualArgs.head, settings.residualArgs.drop(1)).flatMap {
+          case ex: ClassNotFoundException if ex.getMessage == settings.residualArgs.head =>
+            val file = settings.residualArgs.head
+            def withJarInput[T](f: JarInputStream => T): T =
+              val in = new JarInputStream(java.io.FileInputStream(file))
+              try f(in)
+              finally in.close()
+            val manifest = withJarInput(s => Option(s.getManifest))
+            manifest match
+              case None => Some(IllegalArgumentException(s"Cannot find manifest in jar: $file"))
+              case Some(f) =>
+                f.getMainAttributes.get(Name.MAIN_CLASS) match
+                  case mainClass: String =>
+                    ObjectRunner.runAndCatch(newClasspath :+ File(file).toURI.toURL, mainClass, settings.residualArgs)
+                  case _ =>
+                    Some(IllegalArgumentException(s"No main class defined in manifest in jar: $file"))
+          case ex => Some(ex)
+        }
+        errorFn("", res)
       case ExecuteMode.Script =>
         val properArgs =
           List("-classpath", settings.classPath.mkString(classpathSeparator)).filter(Function.const(settings.classPath.nonEmpty))

compiler/test-coursier/dotty/tools/coursier/CoursierScalaTests.scala

@@ -92,6 +92,12 @@ class CoursierScalaTests:
       assertTrue(source.getParentFile.listFiles.find(_.getName == "myfile.jar").isDefined)
     jar()
 
+    def runThatJar() =
+      val source = new File(getClass.getResource("/run/myfile.jar").getPath)
+      val output = CoursierScalaTests.csCmd(source.absPath)
+      assertEquals(output.mkString("\n"), "Hello")
+    runThatJar()
+
 object CoursierScalaTests:
 
   def execCmd(command: String, options: String*): List[String] =