Fix #1167: Remove the magic from Arrays.newRefArray.

Previously, the method `Arrays.newRefArray` was one of the only 3
methods that are kept generic after erasure. This commit removes
this magic, by making it take an actual `j.l.Class[T]` as
parameter.

Moreover, the methods `newXArray` all receive an actual body,
implemented on top of Java reflection, which means that a back-end
does not *have to* special-case those methods for correctness.
It might still be required for performance, though, depending on
the back-end.

The JVM back-end is made non-optimal in this commit, precisely
because it does not specialize that method anymore. Doing so
requires modifying the fork of scalac that we use, which should
be done separately.

The JS back-end is adapted simply by doing nothing at all on any
of the newXArray methods. It will normally call the user-space
implementations which use reflection. The Scala.js optimizer will
inline and intrinsify the reflective calls, producing optimal
code, at the end of the day.

Author: sjrd

src/dotty/runtime/Arrays.scala

@@ -2,6 +2,8 @@ package dotty.runtime
 
 import scala.reflect.ClassTag
 
+import java.lang.{reflect => jlr}
+
 /** All but the first two operations should be short-circuited and implemented specially by
  *  the backend.
  */
@@ -22,35 +24,44 @@ object Arrays {
     arr
   }
 
-  /** Create an array of type T. T must be of form Array[E], with
-   *  E being a reference type.
+  /** Create an array of a reference type T.
    */
-  def newRefArray[T](length: Int): T = ???
+  def newRefArray[T](componentType: Class[T])(length: Int): Array[T] =
+    jlr.Array.newInstance(componentType, length).asInstanceOf[Array[T]]
 
   /** Create a Byte[] array */
-  def newByteArray(length: Int): Array[Byte] = ???
+  def newByteArray(length: Int): Array[Byte] =
+    jlr.Array.newInstance(classOf[Byte], length).asInstanceOf[Array[Byte]]
 
   /** Create a Short[] array */
-  def newShortArray(length: Int): Array[Short] = ???
+  def newShortArray(length: Int): Array[Short] =
+    jlr.Array.newInstance(classOf[Short], length).asInstanceOf[Array[Short]]
 
   /** Create a Char[] array */
-  def newCharArray(length: Int): Array[Char] = ???
+  def newCharArray(length: Int): Array[Char] =
+    jlr.Array.newInstance(classOf[Char], length).asInstanceOf[Array[Char]]
 
   /** Create an Int[] array */
-  def newIntArray(length: Int): Array[Int] = ???
+  def newIntArray(length: Int): Array[Int] =
+    jlr.Array.newInstance(classOf[Int], length).asInstanceOf[Array[Int]]
 
   /** Create a Long[] array */
-  def newLongArray(length: Int): Array[Long] = ???
+  def newLongArray(length: Int): Array[Long] =
+    jlr.Array.newInstance(classOf[Long], length).asInstanceOf[Array[Long]]
 
   /** Create a Float[] array */
-  def newFloatArray(length: Int): Array[Float] = ???
+  def newFloatArray(length: Int): Array[Float] =
+    jlr.Array.newInstance(classOf[Float], length).asInstanceOf[Array[Float]]
 
   /** Create a Double[] array */
-  def newDoubleArray(length: Int): Array[Double] = ???
+  def newDoubleArray(length: Int): Array[Double] =
+    jlr.Array.newInstance(classOf[Double], length).asInstanceOf[Array[Double]]
 
   /** Create a Boolean[] array */
-  def newBooleanArray(length: Int): Array[Boolean] = ???
+  def newBooleanArray(length: Int): Array[Boolean] =
+    jlr.Array.newInstance(classOf[Boolean], length).asInstanceOf[Array[Boolean]]
 
   /** Create a scala.runtime.BoxedUnit[] array */
-  def newUnitArray(length: Int): Array[Unit] = ???
+  def newUnitArray(length: Int): Array[Unit] =
+    jlr.Array.newInstance(classOf[scala.runtime.BoxedUnit], length).asInstanceOf[Array[Unit]]
 }

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

@@ -153,7 +153,7 @@ class DottyBackendInterface(outputDirectory: AbstractFile)(implicit ctx: Context
   }.toMap
   def unboxMethods: Map[Symbol, Symbol] = defn.ScalaValueClasses().map(x => (x, Erasure.Boxing.unboxMethod(x.asClass))).toMap
 
-  private val mkArrayNames: Set[Name] = Set("Byte", "Float", "Char", "Double", "Boolean", "Unit", "Long", "Int", "Short", "Ref").map{ x=>
+  private val mkArrayNames: Set[Name] = Set("Byte", "Float", "Char", "Double", "Boolean", "Unit", "Long", "Int", "Short"/*, "Ref"*/).map{ x=>
     ("new" + x + "Array").toTermName
   }
 

src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -1036,8 +1036,6 @@ class JSCodeGen()(implicit ctx: Context) {
       genStringConcat(tree, receiver, args)
     else if (code == HASH)
       genScalaHash(tree, receiver)
-    else if (isArrayNew(code))
-      genArrayNew(tree, code)
     else if (isArrayOp(code))
       genArrayOp(tree, code)
     else if (code == SYNCHRONIZED)
@@ -1409,24 +1407,6 @@ class JSCodeGen()(implicit ctx: Context) {
         List(genExpr(receiver)))
   }
 
-  /** Gen JS code for a new array operation. */
-  private def genArrayNew(tree: Tree, code: Int): js.Tree = {
-    import scala.tools.nsc.backend.ScalaPrimitives._
-
-    implicit val pos: Position = tree.pos
-
-    val Apply(fun, args) = tree
-    val genLength = genExpr(args.head)
-
-    toIRType(tree.tpe) match {
-      case arrayType: jstpe.ArrayType =>
-        js.NewArray(arrayType, List(genLength))
-
-      case irTpe =>
-        throw new FatalError(s"ArrayNew $tree must have an array type but was $irTpe")
-    }
-  }
-
   /** 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._

src/dotty/tools/backend/sjs/JSPrimitives.scala

@@ -80,18 +80,6 @@ class JSPrimitives(ctx: Context) extends DottyPrimitives(ctx) {
 
     val jsdefn = JSDefinitions.jsdefn
 
-    // For some reason, the JVM primitive set does not register those
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newBooleanArray")), NEW_ZARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newByteArray")), NEW_BARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newShortArray")), NEW_SARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newCharArray")), NEW_CARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newIntArray")), NEW_IARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newLongArray")), NEW_LARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newFloatArray")), NEW_FARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newDoubleArray")), NEW_DARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newRefArray")), NEW_OARRAY)
-    addPrimitive(defn.DottyArraysModule.requiredMethod(Names.termName("newUnitArray")), NEW_OARRAY)
-
     addPrimitive(defn.Any_getClass, GETCLASS)
 
     for (i <- 0 to 22)

src/dotty/tools/dotc/ast/tpd.scala

@@ -372,9 +372,12 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       newArr("Generic").appliedToTypeTrees(typeArg :: Nil)
     else if (elemClass.isPrimitiveValueClass)
       newArr(elemClass.name.toString)
-    else
-      newArr("Ref").appliedToTypeTrees(
-        TypeTree(defn.ArrayOf(elemType)).withPos(typeArg.pos) :: Nil)
+    else {
+      val typeApplied = newArr("Ref").appliedToTypeTrees(typeArg :: Nil)
+      val classOfArg =
+        ref(defn.Predef_classOf).appliedToTypeTrees(typeArg :: Nil)
+      Apply(typeApplied, classOfArg :: Nil).withPos(typeArg.pos)
+    }
   }
 
   // ------ Creating typed equivalents of trees that exist only in untyped form -------

src/dotty/tools/dotc/core/Definitions.scala

@@ -247,8 +247,6 @@ class Definitions {
   lazy val DottyArraysModuleRef = ctx.requiredModuleRef("dotty.runtime.Arrays")
   def DottyArraysModule(implicit ctx: Context) = DottyArraysModuleRef.symbol
 
-    def newRefArrayMethod(implicit ctx: Context) = DottyArraysModule.requiredMethod("newRefArray")
-
   lazy val NilModuleRef = ctx.requiredModuleRef("scala.collection.immutable.Nil")
   def NilModule(implicit ctx: Context) = NilModuleRef.symbol
 
@@ -620,7 +618,7 @@ class Definitions {
   lazy val PhantomClasses = Set[Symbol](AnyClass, AnyValClass, NullClass, NothingClass)
 
   def isPolymorphicAfterErasure(sym: Symbol) =
-     (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf) || (sym eq newRefArrayMethod)
+     (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf)
 
   def isTupleType(tp: Type)(implicit ctx: Context) = {
     val arity = tp.dealias.argInfos.length

src/dotty/tools/dotc/transform/Erasure.scala

@@ -467,28 +467,18 @@ object Erasure extends TypeTestsCasts{
         tpt = untpd.TypedSplice(TypeTree(sym.info).withPos(vdef.tpt.pos))), sym)
 
     override def typedDefDef(ddef: untpd.DefDef, sym: Symbol)(implicit ctx: Context) = {
-      var effectiveSym = sym
-      if (sym == defn.newRefArrayMethod) {
-        // newRefArray is treated specially: It's the only source-defined method
-        // that has a polymorphic type after erasure. But treating its (dummy) definition
-        // with a polymorphic type at and after erasure is an awkward special case.
-        // We therefore rewrite the method definition with a new Symbol of type
-        // (length: Int)Object
-        val MethodType(pnames, ptypes) = sym.info.resultType
-        effectiveSym = sym.copy(info = MethodType(pnames, ptypes, defn.ObjectType))
-      }
       val restpe =
-        if (effectiveSym.isConstructor) defn.UnitType
-        else effectiveSym.info.resultType
+        if (sym.isConstructor) defn.UnitType
+        else sym.info.resultType
       val ddef1 = untpd.cpy.DefDef(ddef)(
         tparams = Nil,
-        vparamss = (outer.paramDefs(effectiveSym) ::: ddef.vparamss.flatten) :: Nil,
+        vparamss = (outer.paramDefs(sym) ::: ddef.vparamss.flatten) :: Nil,
         tpt = untpd.TypedSplice(TypeTree(restpe).withPos(ddef.tpt.pos)),
         rhs = ddef.rhs match {
           case id @ Ident(nme.WILDCARD) => untpd.TypedSplice(id.withType(restpe))
           case _ => ddef.rhs
         })
-      super.typedDefDef(ddef1, effectiveSym)
+      super.typedDefDef(ddef1, sym)
     }
 
     /** After erasure, we may have to replace the closure method by a bridge.

src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -277,8 +277,7 @@ class TreeChecker extends Phase with SymTransformer {
       def isNonMagicalMethod(x: Symbol) =
         x.is(Method) &&
           !x.isCompanionMethod &&
-          !x.isValueClassConvertMethod &&
-          x != defn.newRefArrayMethod
+          !x.isValueClassConvertMethod
 
       val symbolsNotDefined = cls.classInfo.decls.toSet.filter(isNonMagicalMethod) -- impl.body.map(_.symbol) - constr.symbol