Resurrect the Scala.js backend

This partially reverts 06a3d47 to bring
back Dotty.js from the dead. Many things are broken still, but this is
enough to do some experiments:
- The backend was initially removed because of #1574, I don't see why
  GetClass has a requirement on FunctionalInterfaces, so I just removed
  it ¯\_(ツ)_/¯
- Scala.js was upgraded to 0.6.19. More recent versions of Scala.js cannot be
  used because they require sbt 0.13.16 and we're blocked by
  sbt/sbt#3460, this won't be an issue anymore
  once we switch to sbt 1 (see #3441)
- GenSJSIR was hacked to compile with 0.6.19 but is missing most of the
  changes to the Scala.js backend phase for Scala 2 that happened
  since it was initially ported to Dotty from Scala.js 0.6.8
- scalajs-ir does not compile with Dotty anymore, see comments in Build.scala
- The Scala.js backend explodes when extending a Scala 2 trait because
  of the way LinkScala2Impls transforms supercalls to these traits.
  Luckily, we don't need to extend js.JSApp anymore to make a Hello World :P.

I verified that the following works:
    sbt sjsSandbox/run
But I don't know if anything else does!

Author: smarter

compiler/sjs/backend/sjs/GenSJSIR.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/GenSJSIR.scala

@@ -185,7 +185,7 @@ class JSCodeGen()(implicit ctx: Context) {
     import dotty.tools.io._
 
     val outputDirectory: AbstractFile = // TODO Support virtual files
-      new PlainDirectory(new Directory(new java.io.File(ctx.settings.d.value)))
+      new PlainDirectory(ctx.settings.outputDir.value)
 
     val pathParts = sym.fullName.toString.split("[./]")
     val dir = (outputDirectory /: pathParts.init)(_.subdirectoryNamed(_))
@@ -285,9 +285,9 @@ class JSCodeGen()(implicit ctx: Context) {
           js.ModuleExportDef("hello.world"),
           js.MethodDef(static = false, js.StringLiteral("main"),
               Nil, jstpe.AnyType,
-              js.Block(List(
+              Some(js.Block(List(
                 js.Apply(js.This()(jstpe.ClassType(classIdent.name)), js.Ident("main__V"), Nil)(jstpe.NoType),
-                js.Undefined())))(
+                js.Undefined()))))(
               OptimizerHints.empty, None))
       } else {
         /*
@@ -339,17 +339,22 @@ class JSCodeGen()(implicit ctx: Context) {
     implicit val pos = sym.pos
 
     val classIdent = encodeClassFullNameIdent(sym)
+    val kind = {
+      if (sym.is(Trait)) ClassKind.AbstractJSType
+      else if (sym.is(ModuleClass)) ClassKind.NativeJSModuleClass
+      else ClassKind.NativeJSClass
+    }
     val superClass =
       if (sym.is(Trait)) None
       else Some(encodeClassFullNameIdent(sym.superClass))
-    val jsName =
-      if (sym.is(Trait) || sym.is(ModuleClass)) None
-      else Some(fullJSNameOf(sym))
+    val jsNativeLoadSpec =
+      if (sym.is(Trait)) None
+      else Some(js.JSNativeLoadSpec.Global(fullJSNameOf(sym).split('.').toList))
 
-    js.ClassDef(classIdent, ClassKind.RawJSType,
+    js.ClassDef(classIdent, kind,
         superClass,
         genClassInterfaces(sym),
-        jsName,
+        jsNativeLoadSpec,
         Nil)(
         OptimizerHints.empty)
   }
@@ -404,10 +409,7 @@ class JSCodeGen()(implicit ctx: Context) {
         "genClassFields called with a ClassDef other than the current one")
 
     // Non-method term members are fields
-    (for {
-      f <- classSym.info.decls
-      if !f.is(Method) && f.isTerm
-    } yield {
+    classSym.info.decls.filter(f => !f.is(Method) && f.isTerm).map({ f =>
       implicit val pos = f.pos
 
       val name =
@@ -451,7 +453,7 @@ class JSCodeGen()(implicit ctx: Context) {
         }
       }*/
 
-      js.FieldDef(name, irTpe, f.is(Mutable))
+      js.FieldDef(static = false, name, irTpe, f.is(Mutable))
     }).toList
   }
 
@@ -510,7 +512,7 @@ class JSCodeGen()(implicit ctx: Context) {
         None
       } else*/ if (sym.is(Deferred)) {
         Some(js.MethodDef(static = false, methodName,
-            jsParams, toIRType(patchedResultType(sym)), js.EmptyTree)(
+            jsParams, toIRType(patchedResultType(sym)), None)(
             OptimizerHints.empty, None))
       } else /*if (isJSNativeCtorDefaultParam(sym)) {
         None
@@ -549,7 +551,7 @@ class JSCodeGen()(implicit ctx: Context) {
           } else*/ if (sym.isConstructor) {
             js.MethodDef(static = false, methodName,
                 jsParams, jstpe.NoType,
-                genStat(rhs))(optimizerHints, None)
+                Some(genStat(rhs)))(optimizerHints, None)
           } else {
             val resultIRType = toIRType(patchedResultType(sym))
             genMethodDef(static = false, methodName,
@@ -576,7 +578,7 @@ class JSCodeGen()(implicit ctx: Context) {
       tree: Tree, optimizerHints: OptimizerHints): js.MethodDef = {
     implicit val pos = tree.pos
 
-    ctx.debuglog("genMethod " + methodName.name)
+    ctx.debuglog("genMethod " + methodName.encodedName)
     ctx.debuglog("")
 
     val jsParams = for (param <- paramsSyms) yield {
@@ -590,7 +592,7 @@ class JSCodeGen()(implicit ctx: Context) {
       else genExpr(tree)
 
     //if (!isScalaJSDefinedJSClass(currentClassSym)) {
-      js.MethodDef(static, methodName, jsParams, resultIRType, genBody())(
+      js.MethodDef(static, methodName, jsParams, resultIRType, Some(genBody()))(
           optimizerHints, None)
     /*} else {
       assert(!static, tree.pos)
@@ -1006,7 +1008,7 @@ class JSCodeGen()(implicit ctx: Context) {
 
   /** Gen JS code for a primitive method call. */
   private def genPrimitiveOp(tree: Apply, isStat: Boolean): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
     implicit val pos = tree.pos
 
@@ -1046,7 +1048,7 @@ class JSCodeGen()(implicit ctx: Context) {
 
   /** Gen JS code for a simple unary operation. */
   private def genSimpleUnaryOp(tree: Apply, arg: Tree, code: Int): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
     implicit val pos = tree.pos
 
@@ -1087,7 +1089,7 @@ class JSCodeGen()(implicit ctx: Context) {
 
   /** Gen JS code for a simple binary operation. */
   private def genSimpleBinaryOp(tree: Apply, lhs: Tree, rhs: Tree, code: Int): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
     import js.UnaryOp._
 
     /* Codes for operation types, in an object so that they can be 'final val'
@@ -1265,7 +1267,7 @@ class JSCodeGen()(implicit ctx: Context) {
   private def genUniversalEqualityOp(lhs: Tree, rhs: Tree, code: Int)(
       implicit pos: Position): js.Tree = {
 
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
     val genLhs = genExpr(lhs)
     val genRhs = genExpr(rhs)
@@ -1394,7 +1396,7 @@ class JSCodeGen()(implicit ctx: Context) {
 
   /** Gen JS code for an array operation (get, set or length) */
   private def genArrayOp(tree: Tree, code: Int): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
     implicit val pos = tree.pos
 
@@ -1408,8 +1410,9 @@ class JSCodeGen()(implicit ctx: Context) {
       case defn.ArrayOf(el)  => el
       case JavaArrayType(el) => el
       case tpe =>
-        ctx.error(s"expected Array $tpe")
-        ErrorType
+        val msg = ex"expected Array $tpe"
+        ctx.error(msg)
+        ErrorType(msg)
     }
 
     def genSelect(): js.Tree =
@@ -1457,7 +1460,7 @@ class JSCodeGen()(implicit ctx: Context) {
 
   /** Gen JS code for a coercion */
   private def genCoercion(tree: Apply, receiver: Tree, code: Int): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
+    import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
     implicit val pos = tree.pos
 
@@ -1866,7 +1869,7 @@ class JSCodeGen()(implicit ctx: Context) {
     }.unzip
 
     val formalParamNames = sym.info.paramNamess.flatten.drop(envSize)
-    val formalParamTypes = sym.info.paramTypess.flatten.drop(envSize)
+    val formalParamTypes = sym.info.paramInfoss.flatten.drop(envSize)
     val (formalParams, actualParams) = formalParamNames.zip(formalParamTypes).map {
       case (name, tpe) =>
         val formalParam = js.ParamDef(freshLocalIdent(name.toString),
@@ -2160,7 +2163,7 @@ class JSCodeGen()(implicit ctx: Context) {
       implicit pos: Position): List[js.Tree] = {
 
     def paramNamesAndTypes(implicit ctx: Context): List[(Names.TermName, Type)] =
-      sym.info.paramNamess.flatten.zip(sym.info.paramTypess.flatten)
+      sym.info.paramNamess.flatten.zip(sym.info.paramInfoss.flatten)
 
     val wereRepeated = ctx.atPhase(ctx.elimRepeatedPhase) { implicit ctx =>
       for ((name, tpe) <- paramNamesAndTypes)

compiler/sjs/backend/sjs/JSCodeGen.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSCodeGen.scala

@@ -183,17 +183,15 @@ final class JSDefinitions()(implicit ctx: Context) {
    *
    *  This is similar to `isVarArityClass` in `Definitions.scala`.
    */
-  private def isScalaJSVarArityClass(cls: Symbol, prefix: Name): Boolean = {
+  private def isScalaJSVarArityClass(cls: Symbol, prefix: String): Boolean = {
     val name = scalajsClassName(cls)
-    name.startsWith(prefix) && name.drop(prefix.length).forall(_.isDigit)
+    name.startsWith(prefix) && name.toString.drop(prefix.length).forall(_.isDigit)
   }
 
   def isJSFunctionClass(cls: Symbol): Boolean =
-    isScalaJSVarArityClass(cls, nme.Function)
-
-  private val ThisFunctionName = termName("ThisFunction")
+    isScalaJSVarArityClass(cls, str.Function)
 
   def isJSThisFunctionClass(cls: Symbol): Boolean =
-    isScalaJSVarArityClass(cls, ThisFunctionName)
+    isScalaJSVarArityClass(cls, "ThisFunction")
 
 }

compiler/sjs/backend/sjs/JSDefinitions.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSDefinitions.scala

@@ -209,7 +209,7 @@ object JSEncoding {
   }
 
   def foreignIsImplClass(sym: Symbol)(implicit ctx: Context): Boolean =
-    sym.name.isImplClassName
+    sym.name.endsWith(nme.IMPL_CLASS_SUFFIX.toString)
 
   def encodeClassType(sym: Symbol)(implicit ctx: Context): jstpe.Type = {
     if (sym == defn.ObjectClass) jstpe.AnyType

compiler/sjs/backend/sjs/JSEncoding.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSEncoding.scala

@@ -6,6 +6,7 @@ import Flags._
 import Symbols._
 import NameOps._
 import StdNames._
+import NameKinds.DefaultGetterName
 
 import JSDefinitions._
 
@@ -66,11 +67,17 @@ object JSInterop {
    *  is a JS type.
    */
   def isJSDefaultParam(sym: Symbol)(implicit ctx: Context): Boolean = {
-    sym.name.isDefaultGetterName && {
+    sym.name.is(DefaultGetterName) && {
       val owner = sym.owner
-      if (owner.is(ModuleClass) &&
-          sym.name.asTermName.defaultGetterToMethod == nme.CONSTRUCTOR) {
-        isJSType(owner.linkedClass)
+      if (owner.is(ModuleClass)) {
+        val isConstructor = sym.name match {
+          case DefaultGetterName(methName, _) => methName == nme.CONSTRUCTOR
+          case _ => false
+        }
+        if (isConstructor)
+          isJSType(owner.linkedClass)
+        else
+          isJSType(owner)
       } else {
         isJSType(owner)
       }

compiler/sjs/backend/sjs/JSInterop.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSInterop.scala

@@ -43,7 +43,7 @@ object JSPrimitives {
 
 class JSPrimitives(ctx: Context) extends DottyPrimitives(ctx) {
   import JSPrimitives._
-  import scala.tools.nsc.backend.ScalaPrimitives._
+  import scala.tools.nsc.backend.ScalaPrimitivesOps._
 
   private lazy val jsPrimitives: Map[Symbol, Int] = initJSPrimitives(ctx)
 

compiler/sjs/backend/sjs/JSPositions.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSPositions.scala

@@ -5,7 +5,7 @@ import language.implicitConversions
 class ScopedVar[A](init: A) {
   import ScopedVar.Assignment
 
-  private[this] var value = init
+  private[ScopedVar] var value = init
 
   def this()(implicit ev: Null <:< A) = this(ev(null))
 

compiler/sjs/backend/sjs/JSPrimitives.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/JSPrimitives.scala

@@ -15,6 +15,7 @@ import util.FreshNameCreator
 import core.DenotTransformers.DenotTransformer
 import core.Denotations.SingleDenotation
 import dotty.tools.backend.jvm.{CollectSuperCalls, GenBCode}
+import dotty.tools.backend.sjs
 import dotty.tools.dotc.transform.localopt.StringInterpolatorOpt
 
 /** The central class of the dotc compiler. The job of a compiler is to create
@@ -122,6 +123,7 @@ class Compiler {
 
   /** Generate the output of the compilation */
   protected def backendPhases: List[List[Phase]] =
+    List(new sjs.GenSJSIR) ::        // Generate .sjsir files for Scala.js (not enabled by default)
     List(new GenBCode) ::            // Generate JVM bytecode
     Nil
 

compiler/sjs/backend/sjs/ScopedVar.scala renamed to compiler/src/dotty/tools/backend/backend/sjs/ScopedVar.scala

@@ -30,6 +30,7 @@ import scala.annotation.tailrec
 import dotty.tools.io.VirtualFile
 
 import scala.util.control.NonFatal
+import dotty.tools.backend.sjs
 
 /** A compiler run. Exports various methods to compile source files */
 class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with ConstraintRunInfo {
@@ -44,7 +45,23 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
    */
   protected[this] def rootContext(implicit ctx: Context): Context = {
     ctx.initialize()(ctx)
-    ctx.base.setPhasePlan(comp.phases)
+
+    val actualPhases = if (ctx.settings.scalajs.value) {
+      // Remove phases that Scala.js does not want
+      comp.phases.mapConserve(_.filter {
+        case _: transform.FunctionalInterfaces => false
+        case _ => true
+      }).filter(_.nonEmpty)
+    } else {
+      // Remove Scala.js-related phases
+      comp.phases.mapConserve(_.filter {
+        case _: sjs.GenSJSIR => false
+        case _ => true
+      }).filter(_.nonEmpty)
+    }
+
+    ctx.base.setPhasePlan(actualPhases)
+
     val rootScope = new MutableScope
     val bootstrap = ctx.fresh
       .setPeriod(Period(comp.nextRunId, FirstPhaseId))

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

@@ -35,6 +35,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val color = ChoiceSetting("-color", "mode", "Colored output", List("always", "never"/*, "auto"*/), "always"/* "auto"*/)
   val target = ChoiceSetting("-target", "target", "Target platform for object files. All JVM 1.5 targets are deprecated.",
     List("jvm-1.5", "jvm-1.5-fjbg", "jvm-1.5-asm", "jvm-1.6", "jvm-1.7", "jvm-1.8", "msil"), "jvm-1.8")
+  val scalajs = BooleanSetting("-scalajs", "Compile in Scala.js mode (requires scalajs-library.jar on the classpath).")
   val unchecked = BooleanSetting("-unchecked", "Enable additional warnings where generated code depends on assumptions.")
   val uniqid = BooleanSetting("-uniqid", "Uniquely tag all identifiers in debugging output.")
   val usejavacp = BooleanSetting("-usejavacp", "Utilize the java.class.path in classpath resolution.")

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

@@ -27,7 +27,7 @@ import reporting.diagnostic.Message
 import collection.mutable
 import collection.immutable.BitSet
 import printing._
-import config.{JavaPlatform, Platform, ScalaSettings, Settings}
+import config.{JavaPlatform, SJSPlatform, Platform, ScalaSettings, Settings}
 
 import scala.annotation.internal.sharable
 
@@ -596,7 +596,8 @@ object Contexts {
     }
 
     protected def newPlatform(implicit ctx: Context): Platform =
-      new JavaPlatform
+      if (settings.scalajs.value) new SJSPlatform
+      else new JavaPlatform
 
     /** The loader that loads the members of _root_ */
     def rootLoader(root: TermSymbol)(implicit ctx: Context): SymbolLoader = platform.rootLoader(root)

compiler/sjs/tools/dotc/config/SJSPlatform.scala renamed to compiler/src/dotty/tools/dotc/config/SJSPlatform.scala

@@ -21,7 +21,7 @@ class GetClass extends MiniPhase {
   override def phaseName: String = "getClass"
 
   // getClass transformation should be applied to specialized methods
-  override def runsAfter = Set(Erasure.name, FunctionalInterfaces.name)
+  override def runsAfter = Set(Erasure.name)
 
   override def transformApply(tree: Apply)(implicit ctx: Context): Tree = {
     import ast.Trees._