Completely remove logic to set Main-Class

It never actually worked (see previous commit), we have no tests for it,
and it's only useful for a marginal feature (when the compiler outputs a
jar), better to remove dead code and wait for a usecase to appear.

compiler/src/dotty/tools/backend/jvm/BCodeHelpers.scala

@@ -77,27 +77,12 @@ trait BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
   /*
    * must-single-thread
    */
-  def initBytecodeWriter(entryPoints: List[Symbol]): BytecodeWriter = {
+  def initBytecodeWriter(): BytecodeWriter = {
     getSingleOutput match {
-      case Some(f) if f hasExtension "jar" =>
-        // If no main class was specified, see if there's only one
-        // entry point among the classes going into the jar.
-        if (mainClass.isEmpty) {
-          entryPoints map (_.fullName('.')) match {
-            case Nil =>
-              log("No Main-Class designated or discovered.")
-            case name :: Nil =>
-              log(s"Unique entry point: setting Main-Class to $name")
-              setMainClass(name)
-            case names =>
-              log(s"No Main-Class due to multiple entry points:\n  ${names.mkString("\n  ")}")
-          }
-        }
-        else log(s"Main-Class was specified: ${mainClass.get}")
-
+      case Some(f) if f.hasExtension("jar") =>
         new DirectToJarfileWriter(f.file)
-
-      case _ => factoryNonJarBytecodeWriter()
+      case _ =>
+        factoryNonJarBytecodeWriter()
     }
   }
 

compiler/src/dotty/tools/backend/jvm/BackendInterface.scala

@@ -156,13 +156,11 @@ abstract class BackendInterface extends BackendInterfaceDefinitions {
   /* various configuration options used by backend */
   def emitAsmp: Option[String]
   def dumpClasses: Option[String]
-  def mainClass: Option[String]
   def noForwarders: Boolean
   def debuglevel: Int
   def settings_debug: Boolean
   def targetPlatform: String
   def sourceFileFor(cu: CompilationUnit): String
-  def setMainClass(name: String): Unit
   def informProgress(msg: String): Unit
   def hasLabelDefs: Boolean // whether this compiler uses LabelDefs (i.e., scalac)
 
@@ -508,7 +506,6 @@ abstract class BackendInterface extends BackendInterfaceDefinitions {
     def isNonBottomSubClass(sym: Symbol): Boolean
     def hasAnnotation(sym: Symbol): Boolean
     def shouldEmitForwarders: Boolean
-    def isJavaEntryPoint: Boolean
     def isJavaDefaultMethod: Boolean
     def isClassConstructor: Boolean
     def isSerializable: Boolean

compiler/src/dotty/tools/backend/jvm/BytecodeWriters.scala

@@ -50,9 +50,7 @@ trait BytecodeWriters {
   }
 
   class DirectToJarfileWriter(jfile: JFile) extends BytecodeWriter {
-    val jarMainAttrs = mainClass.map(nm => List(Name.MAIN_CLASS -> nm)).getOrElse(Nil)
-
-    val writer = new Jar(jfile).jarWriter(jarMainAttrs: _*)
+    val writer = new Jar(jfile).jarWriter()
 
     def writeClass(label: String, jclassName: String, jclassBytes: Array[Byte], outfile: AbstractFile): Unit = {
       assert(outfile == null,

compiler/src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -400,12 +400,6 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
     if (ctx.settings.Ydumpclasses.isDefault) None
     else Some(ctx.settings.Ydumpclasses.value)
 
-  def mainClass: Option[String] =
-    if (ctx.settings.XmainClass.isDefault) None
-    else Some(ctx.settings.XmainClass.value)
-  def setMainClass(name: String): Unit = ctx.settings.XmainClass.update(name)
-
-
   def noForwarders: Boolean = ctx.settings.XnoForwarders.value
   def debuglevel: Int = 3 // 0 -> no debug info; 1-> filename; 2-> lines; 3-> varnames
   def settings_debug: Boolean = ctx.settings.Ydebug.value
@@ -700,7 +694,6 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
     def hasAnnotation(ann: Symbol): Boolean = toDenot(sym).hasAnnotation(ann)
     def shouldEmitForwarders: Boolean =
       (sym.is(Flags.Module)) && sym.isStatic
-    def isJavaEntryPoint: Boolean = CollectEntryPoints.isJavaEntryPoint(sym)
     def isEnum = sym.is(Flags.Enum)
 
     def isClassConstructor: Boolean = toDenot(sym).isClassConstructor

compiler/src/dotty/tools/backend/jvm/GenBCode.scala

@@ -32,8 +32,6 @@ import dotty.tools.io._
 
 class GenBCode extends Phase {
   def phaseName: String = GenBCode.name
-  private val entryPoints = new mutable.HashSet[Symbol]()
-  def registerEntryPoint(sym: Symbol): Unit = entryPoints += sym
 
   private val superCallsMap = newMutableSymbolMap[Set[ClassSymbol]]
   def registerSuperCall(sym: Symbol, calls: ClassSymbol): Unit = {
@@ -50,9 +48,8 @@ class GenBCode extends Phase {
   }
 
   def run(implicit ctx: Context): Unit = {
-    new GenBCodePipeline(entryPoints.toList,
-        new DottyBackendInterface(outputDir, superCallsMap.toMap)(ctx))(ctx).run(ctx.compilationUnit.tpdTree)
-    entryPoints.clear()
+    new GenBCodePipeline(new DottyBackendInterface(
+      outputDir, superCallsMap.toMap)(ctx))(ctx).run(ctx.compilationUnit.tpdTree)
   }
 
   override def runOn(units: List[CompilationUnit])(implicit ctx: Context): List[CompilationUnit] = {
@@ -69,7 +66,7 @@ object GenBCode {
   val name: String = "genBCode"
 }
 
-class GenBCodePipeline(val entryPoints: List[Symbol], val int: DottyBackendInterface)(implicit val ctx: Context) extends BCodeSyncAndTry {
+class GenBCodePipeline(val int: DottyBackendInterface)(implicit val ctx: Context) extends BCodeSyncAndTry {
 
   private[this] var tree: Tree = _
 
@@ -474,7 +471,7 @@ class GenBCodePipeline(val entryPoints: List[Symbol], val int: DottyBackendInter
       // Statistics.stopTimer(BackendStats.bcodeInitTimer, initStart)
 
       // initBytecodeWriter invokes fullName, thus we have to run it before the typer-dependent thread is activated.
-      bytecodeWriter  = initBytecodeWriter(entryPoints)
+      bytecodeWriter  = initBytecodeWriter()
       mirrorCodeGen   = new JMirrorBuilder
 
       val needsOutfileForSymbol = bytecodeWriter.isInstanceOf[ClassBytecodeWriter]

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -118,8 +118,6 @@ class Compiler {
          new RestoreScopes,          // Repair scopes rendered invalid by moving definitions in prior phases of the group
          new SelectStatic,           // get rid of selects that would be compiled into GetStatic
          new sjs.JUnitBootstrappers, // Generate JUnit-specific bootstrapper classes for Scala.js (not enabled by default)
-         // FIXME: See comment in CollectEntryPoints
-         // new CollectEntryPoints,     // Find classes with main methods
          new CollectSuperCalls) ::   // Find classes that are called with super
     Nil
 

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -77,7 +77,6 @@ class ScalaSettings extends Settings.SettingGroup {
   val XprintDiffDel: Setting[Boolean] = BooleanSetting("-Xprint-diff-del", "Print changed parts of the tree since last print including deleted parts.")
   val XprintInline: Setting[Boolean] = BooleanSetting("-Xprint-inline", "Show  where inlined code comes from")
   val Xprompt: Setting[Boolean] = BooleanSetting("-Xprompt", "Display a prompt after each error (debugging option).")
-  val XmainClass: Setting[String] = StringSetting("-Xmain-class", "path", "Class for manifest's Main-Class entry (only useful with -d <jar>)", "")
   val XnoValueClasses: Setting[Boolean] = BooleanSetting("-Xno-value-classes", "Do not use value classes. Helps debugging.")
   val XreplLineWidth: Setting[Int] = IntSetting("-Xrepl-line-width", "Maximal number of columns per line for REPL output", 390)
   val XfatalWarnings: Setting[Boolean] = BooleanSetting("-Xfatal-warnings", "Fail the compilation if there are any warnings.")