Code review changes: add a warning message about script classes available in context

Author: Gedochao

modules/build/src/main/scala/scala/build/Build.scala

@@ -54,7 +54,10 @@ object Build {
     def outputOpt: Some[os.Path]        = Some(output)
     def fullClassPath: Seq[os.Path]     = Seq(output) ++ sources.resourceDirs ++ artifacts.classPath
     def foundMainClasses(): Seq[String] = MainClass.find(output)
-    def retainedMainClass(mainClasses: Seq[String]): Either[MainClassError, String] = {
+    def retainedMainClass(
+      mainClasses: Seq[String],
+      logger: Logger
+    ): Either[MainClassError, String] = {
       val defaultMainClassOpt = sources.defaultMainClass
         .filter(name => mainClasses.contains(name))
       def foundMainClass =
@@ -77,7 +80,23 @@ object Build {
                 }
             val filteredMainClasses =
               mainClasses.filter(!scriptInferredMainClasses.contains(_))
-            if (filteredMainClasses.length == 1) Right(filteredMainClasses.head)
+            if (filteredMainClasses.length == 1) {
+              val pickedMainClass = filteredMainClasses.head
+              if (scriptInferredMainClasses.nonEmpty) {
+                val firstScript   = scriptInferredMainClasses.head
+                val scriptsString = scriptInferredMainClasses.mkString(", ")
+                logger.message(
+                  s"Running $pickedMainClass. Also detected script main classes: $scriptsString"
+                )
+                logger.message(
+                  s"You can run any one of them by passing option --main-class, i.e. --main-class $firstScript"
+                )
+                logger.message(
+                  "All available main classes can always be listed by passing option --list-main-classes"
+                )
+              }
+              Right(pickedMainClass)
+            }
             else options.interactive
               .chooseOne(
                 "Found several main classes. Which would you like to run?",

modules/cli/src/main/scala/scala/cli/commands/Package.scala

@@ -212,7 +212,7 @@ object Package extends ScalaCommand[PackageOptions] {
           .map(_.stripSuffix("_sc"))
           .map(_ + extension)
       }
-      .orElse(build.retainedMainClass(build.foundMainClasses()).map(
+      .orElse(build.retainedMainClass(build.foundMainClasses(), logger).map(
         _.stripSuffix("_sc") + extension
       ).toOption)
       .orElse(build.sources.paths.collectFirst(_._1.baseName + extension))
@@ -239,7 +239,7 @@ object Package extends ScalaCommand[PackageOptions] {
     def mainClass: Either[BuildException, String] =
       build.options.mainClass match {
         case Some(cls) => Right(cls)
-        case None      => build.retainedMainClass(build.foundMainClasses())
+        case None      => build.retainedMainClass(build.foundMainClasses(), logger)
       }
 
     val packageOptions = build.options.notForBloopOptions.packageOptions

modules/cli/src/main/scala/scala/cli/commands/Run.scala

@@ -183,7 +183,7 @@ object Run extends ScalaCommand[RunOptions] {
       }
     val mainClass = mainClassOpt match {
       case Some(cls) => cls
-      case None      => value(build.retainedMainClass(potentialMainClasses))
+      case None      => value(build.retainedMainClass(potentialMainClasses, logger))
     }
     val verbosity = build.options.internal.verbosity.getOrElse(0).toString
 

modules/cli/src/main/scala/scala/cli/commands/publish/Publish.scala

@@ -385,7 +385,7 @@ object Publish extends ScalaCommand[PublishOptions] {
     val mainJar = {
       val mainClassOpt = build.options.mainClass.orElse {
         val potentialMainClasses = build.foundMainClasses()
-        build.retainedMainClass(potentialMainClasses) match {
+        build.retainedMainClass(potentialMainClasses, logger) match {
           case Left(_: NoMainClassFoundError) => None
           case Left(err) =>
             logger.debug(s"Error while looking for main class: $err")