Special case pattern matching against abstract types with class tags

src/dotty/DottyPredef.scala

@@ -1,37 +1,13 @@
 package dotty
 
-import scala.reflect.ClassTag
 import scala.reflect.runtime.universe.TypeTag
+import scala.reflect.ClassTag
 import scala.Predef.???
 
-abstract class I1 {
-  implicit def classTag[T]: ClassTag[T] = ???
+/** unimplemented implicit for TypeTag */
+object DottyPredef {
   implicit def typeTag[T]: TypeTag[T] = ???
-  implicit val DoubleClassTag: ClassTag[Double]   = ClassTag.Double
-}
-abstract class I2 extends I1 {
-  implicit val FloatClassTag: ClassTag[Double]   = ClassTag.Double
-}
-abstract class I3 extends I2 {
-  implicit val LongClassTag: ClassTag[Long]       = ClassTag.Long
-}
-abstract class I4 extends I3 {
-  implicit val IntClassTag: ClassTag[Int]         = ClassTag.Int
-}
-abstract class I5 extends I4 {
-  implicit val ShortClassTag: ClassTag[Short]     = ClassTag.Short
-}
-abstract class I6 extends I5 {
-  implicit val ByteClassTag: ClassTag[Byte]       = ClassTag.Byte
-  implicit val CharClassTag: ClassTag[Char]       = ClassTag.Char
-  implicit val BooleanClassTag: ClassTag[Boolean] = ClassTag.Boolean
-  implicit val UnitClassTag: ClassTag[Unit]       = ClassTag.Unit
-  implicit val NullClassTag: ClassTag[Null]       = ClassTag.Null
-}
-
-/** implicits for ClassTag and TypeTag. Should be implemented with macros */
-object DottyPredef extends I6 {
 
-  /** ClassTags for final classes */
-  implicit val NothingClassTag: ClassTag[Nothing] = ClassTag.Nothing
+  implicit def arrayTag[T](implicit ctag: ClassTag[T]): ClassTag[Array[T]] =
+    ctag.wrap
 }

src/dotty/tools/dotc/Compiler.scala

@@ -59,7 +59,6 @@ class Compiler {
            new SeqLiterals,
            new InterceptedMethods,
            new Getters,
-           new ClassTags,
            new ElimByName,
            new AugmentScala2Traits,
            new ResolveSuper),

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

@@ -147,18 +147,7 @@ object desugar {
         tparam
     }
 
-    val meth1 = epbuf.toList match {
-      case Nil =>
-        meth
-      case evidenceParams =>
-        val vparamss1 = vparamss.reverse match {
-          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
-            ((vparams ++ evidenceParams) :: rvparamss).reverse
-          case _ =>
-            vparamss :+ evidenceParams
-        }
-        cpy.DefDef(meth)(tparams = tparams1, vparamss = vparamss1)
-    }
+    val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
 
     /** The longest prefix of parameter lists in vparamss whose total length does not exceed `n` */
     def takeUpTo(vparamss: List[List[ValDef]], n: Int): List[List[ValDef]] = vparamss match {
@@ -204,6 +193,30 @@ object desugar {
     }
   }
 
+  // Add all evidence parameters in `params` as implicit parameters to `meth` */
+  private def addEvidenceParams(meth: DefDef, params: List[ValDef])(implicit ctx: Context): DefDef =
+    params match {
+      case Nil =>
+        meth
+      case evidenceParams =>
+        val vparamss1 = meth.vparamss.reverse match {
+          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
+            ((vparams ++ evidenceParams) :: rvparamss).reverse
+          case _ =>
+            meth.vparamss :+ evidenceParams
+        }
+        cpy.DefDef(meth)(vparamss = vparamss1)
+    }
+
+  /** The implicit evidence parameters of `meth`, as generated by `desugar.defDef` */
+  private def evidenceParams(meth: DefDef)(implicit ctx: Context): List[ValDef] =
+    meth.vparamss.reverse match {
+      case (vparams @ (vparam :: _)) :: _ if vparam.mods is Implicit =>
+        vparams.dropWhile(!_.name.startsWith(nme.EVIDENCE_PARAM_PREFIX))
+      case _ =>
+        Nil
+    }
+
   /** Fill in empty type bounds with Nothing/Any. Expand private local type parameters as follows:
    *
    *     class C[v T]
@@ -256,10 +269,13 @@ object desugar {
       else constr1.vparamss.nestedMap(toDefParam)
     val constr = cpy.DefDef(constr1)(tparams = constrTparams, vparamss = constrVparamss)
 
-    // Add constructor type parameters to auxiliary constructors
+    // Add constructor type parameters and evidence implicit parameters
+    // to auxiliary constructors
     val normalizedBody = impl.body map {
       case ddef: DefDef if ddef.name.isConstructorName =>
-        cpy.DefDef(ddef)(tparams = constrTparams)
+        addEvidenceParams(
+          cpy.DefDef(ddef)(tparams = constrTparams),
+          evidenceParams(constr1).map(toDefParam))
       case stat =>
         stat
     }

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

@@ -777,27 +777,6 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       }
       else Assign(tree, rhs)
 
-    /** A tree in place of this tree that represents the class of type `tp`.
-     *  Contains special handling if the class is a primitive value class
-     *  and invokes a `default` method otherwise.
-     */
-    def clsOf(tp: Type, default: => Tree)(implicit ctx: Context): Tree = {
-      def TYPE(module: TermSymbol) =
-        ref(module).select(nme.TYPE_).ensureConforms(tree.tpe).withPos(tree.pos)
-      defn.scalaClassName(tp) match {
-        case tpnme.Boolean => TYPE(defn.BoxedBooleanModule)
-        case tpnme.Byte => TYPE(defn.BoxedByteModule)
-        case tpnme.Short => TYPE(defn.BoxedShortModule)
-        case tpnme.Char => TYPE(defn.BoxedCharModule)
-        case tpnme.Int => TYPE(defn.BoxedIntModule)
-        case tpnme.Long => TYPE(defn.BoxedLongModule)
-        case tpnme.Float => TYPE(defn.BoxedFloatModule)
-        case tpnme.Double => TYPE(defn.BoxedDoubleModule)
-        case tpnme.Unit => TYPE(defn.BoxedUnitModule)
-        case _ => default
-      }
-    }
-
     // --- Higher order traversal methods -------------------------------
 
     /** Apply `f` to each subtree of this tree */
@@ -842,6 +821,23 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     }
   }
 
+  /** A tree that represents the class of the erasure of type `tp`. */
+  def clsOf(tp: Type)(implicit ctx: Context): Tree = {
+    def TYPE(module: TermSymbol) = ref(module).select(nme.TYPE_)
+    defn.scalaClassName(tp) match {
+      case tpnme.Boolean => TYPE(defn.BoxedBooleanModule)
+      case tpnme.Byte => TYPE(defn.BoxedByteModule)
+      case tpnme.Short => TYPE(defn.BoxedShortModule)
+      case tpnme.Char => TYPE(defn.BoxedCharModule)
+      case tpnme.Int => TYPE(defn.BoxedIntModule)
+      case tpnme.Long => TYPE(defn.BoxedLongModule)
+      case tpnme.Float => TYPE(defn.BoxedFloatModule)
+      case tpnme.Double => TYPE(defn.BoxedDoubleModule)
+      case tpnme.Unit => TYPE(defn.BoxedUnitModule)
+      case _ => Literal(Constant(TypeErasure.erasure(tp)))
+    }
+  }
+
   def applyOverloaded(receiver: Tree, method: TermName, args: List[Tree], targs: List[Type], expectedType: Type, isAnnotConstructor: Boolean = false)(implicit ctx: Context): Tree = {
     val typer = ctx.typer
     val proto = new FunProtoTyped(args, expectedType, typer)

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

@@ -221,6 +221,8 @@ class Definitions {
 
     lazy val Predef_conformsR = ScalaPredefModule.requiredMethodRef("$conforms")
     def Predef_conforms(implicit ctx: Context) = Predef_conformsR.symbol
+    lazy val Predef_classOfR = ScalaPredefModule.requiredMethodRef("classOf")
+    def Predef_classOf(implicit ctx: Context) = Predef_classOfR.symbol
 
   lazy val ScalaRuntimeModuleRef = ctx.requiredModuleRef("scala.runtime.ScalaRunTime")
   def ScalaRuntimeModule(implicit ctx: Context) = ScalaRuntimeModuleRef.symbol
@@ -419,6 +421,9 @@ class Definitions {
   lazy val LanguageModuleRef          = ctx.requiredModule("dotty.language")
   def LanguageModuleClass(implicit ctx: Context) = LanguageModuleRef.symbol.moduleClass.asClass
   lazy val NonLocalReturnControlType: TypeRef   = ctx.requiredClassRef("scala.runtime.NonLocalReturnControl")
+  lazy val ClassTagType = ctx.requiredClassRef("scala.reflect.ClassTag")
+  def ClassTagClass(implicit ctx: Context) = ClassTagType.symbol.asClass
+  def ClassTagModule(implicit ctx: Context) = ClassTagClass.companionModule
 
   // Annotation base classes
   lazy val AnnotationType              = ctx.requiredClassRef("scala.annotation.Annotation")

src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -290,6 +290,8 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
           ConstantType(Constant(readName().toString))
         case NULLconst =>
           ConstantType(Constant(null))
+        case CLASSconst =>
+          ConstantType(Constant(readType()))
         case BYNAMEtype =>
           ExprType(readType())
       }

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

@@ -21,17 +21,10 @@ class ClassOf extends MiniPhaseTransform {
 
   override def phaseName: String = "classOf"
 
-  private var classOfMethod: TermSymbol = _
-
-  override def prepareForUnit(tree: tpd.Tree)(implicit ctx: Context): TreeTransform = {
-    classOfMethod = defn.ScalaPredefModule.requiredMethod(nme.classOf)
-    this
-  }
-
   override def transformTypeApply(tree: TypeApply)(implicit ctx: Context, info: TransformerInfo): Tree =
-    if (tree.symbol eq classOfMethod) {
+    if (tree.symbol eq defn.Predef_classOf) {
       val targ = tree.args.head.tpe
-      tree.clsOf(targ, Literal(Constant(TypeErasure.erasure(targ))))
+      clsOf(targ).ensureConforms(tree.tpe).withPos(tree.pos)
     }
     else tree
 }

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

@@ -5,6 +5,7 @@ import ast.tpd
 import core.Contexts.Context
 import core.StdNames.nme
 import core.Phases.Phase
+import TypeUtils._
 import TreeTransforms.{MiniPhaseTransform, TransformerInfo}
 
 /** Rewrite `getClass` calls as follow:
@@ -24,7 +25,8 @@ class GetClass extends MiniPhaseTransform {
   override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo): Tree = {
     import ast.Trees._
     tree match {
-      case Apply(Select(qual, nme.getClass_), Nil) => tree.clsOf(qual.tpe.widen, tree)
+      case Apply(Select(qual, nme.getClass_), Nil) if qual.tpe.widen.isPrimitiveValueType =>
+        clsOf(qual.tpe.widen).withPos(tree.pos)
       case _ => tree
     }
   }

src/dotty/tools/dotc/typer/Applications.scala

@@ -617,6 +617,10 @@ trait Applications extends Compatibility { self: Typer =>
       case pt: PolyType =>
         if (typedArgs.length <= pt.paramBounds.length && !isNamed)
           typedArgs = typedArgs.zipWithConserve(pt.paramBounds)(adaptTypeArg)
+          if (typedFn.symbol == defn.Predef_classOf && typedArgs.nonEmpty) {
+            val arg = typedArgs.head
+            checkClassType(arg.tpe, arg.pos, traitReq = false, stablePrefixReq = false)
+          }
       case _ =>
     }
     assignType(cpy.TypeApply(tree)(typedFn, typedArgs), typedFn, typedArgs)

src/dotty/tools/dotc/typer/Checking.scala

@@ -394,16 +394,17 @@ trait Checking {
       ctx.error(i"$tp cannot be instantiated since it${rstatus.msg}", pos)
   }
 
- /**  Check that `tp` is a class type with a stable prefix. Also, if `traitReq` is
-   *  true check that `tp` is a trait.
-   *  Stability checking is disabled in phases after RefChecks.
+ /**  Check that `tp` is a class type.
+  *   Also, if `traitReq` is true, check that `tp` is a trait.
+  *   Also, if `stablePrefixReq` is true and phase is not after RefChecks,
+  *   check that class prefix is stable.
    *  @return  `tp` itself if it is a class or trait ref, ObjectType if not.
    */
-  def checkClassTypeWithStablePrefix(tp: Type, pos: Position, traitReq: Boolean)(implicit ctx: Context): Type =
+  def checkClassType(tp: Type, pos: Position, traitReq: Boolean, stablePrefixReq: Boolean)(implicit ctx: Context): Type =
     tp.underlyingClassRef(refinementOK = false) match {
       case tref: TypeRef =>
-        if (ctx.phase <= ctx.refchecksPhase) checkStable(tref.prefix, pos)
         if (traitReq && !(tref.symbol is Trait)) ctx.error(d"$tref is not a trait", pos)
+        if (stablePrefixReq && ctx.phase <= ctx.refchecksPhase) checkStable(tref.prefix, pos)
         tp
       case _ =>
         ctx.error(d"$tp is not a class type", pos)
@@ -506,7 +507,7 @@ trait NoChecking extends Checking {
   override def checkNonCyclic(sym: Symbol, info: TypeBounds, reportErrors: Boolean)(implicit ctx: Context): Type = info
   override def checkValue(tree: Tree, proto: Type)(implicit ctx: Context): tree.type = tree
   override def checkStable(tp: Type, pos: Position)(implicit ctx: Context): Unit = ()
-  override def checkClassTypeWithStablePrefix(tp: Type, pos: Position, traitReq: Boolean)(implicit ctx: Context): Type = tp
+  override def checkClassType(tp: Type, pos: Position, traitReq: Boolean, stablePrefixReq: Boolean)(implicit ctx: Context): Type = tp
   override def checkImplicitParamsNotSingletons(vparamss: List[List[ValDef]])(implicit ctx: Context): Unit = ()
   override def checkFeasible(tp: Type, pos: Position, where: => String = "")(implicit ctx: Context): Type = tp
   override def checkNoDoubleDefs(cls: Symbol)(implicit ctx: Context): Unit = ()

src/dotty/tools/dotc/typer/Namer.scala

@@ -603,7 +603,8 @@ class Namer { typer: Typer =>
         val ptype = parentType(parent)(ctx.superCallContext)
         if (cls.isRefinementClass) ptype
         else {
-          val pt = checkClassTypeWithStablePrefix(ptype, parent.pos, traitReq = parent ne parents.head)
+          val pt = checkClassType(ptype, parent.pos,
+              traitReq = parent ne parents.head, stablePrefixReq = true)
           if (pt.derivesFrom(cls)) {
             val addendum = parent match {
               case Select(qual: Super, _) if ctx.scala2Mode =>