ClassTags: New phase which synthesises class tags.

src/dotty/tools/dotc/Compiler.scala

@@ -54,6 +54,7 @@ class Compiler {
            new InterceptedMethods,
            new Literalize,
            new Getters,
+           new ClassTags,
            new ElimByName,
            new ResolveSuper),
       List(new Erasure),

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

@@ -149,8 +149,10 @@ object StdNames {
     final val Seq: N        = "Seq"
     final val Symbol: N     = "Symbol"
     final val ClassTag: N   = "ClassTag"
+    final val classTag: N   = "classTag"
     final val WeakTypeTag: N = "WeakTypeTag"
     final val TypeTag : N   = "TypeTag"
+    final val typeTag: N    = "typeTag"
     final val Expr: N       = "Expr"
     final val String: N     = "String"
     final val Annotation: N = "Annotation"

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

@@ -1346,7 +1346,7 @@ object SymDenotations {
           // than this is a scope that will eventually become decls of this symbol.
           // And this should only happen if this is first time the scope of symbol
           // is computed, ie symbol yet has no future.
-          assert(this.nextInRun == this)
+          assert(this.nextInRun.validFor.code <= this.validFor.code)
           scope
         case _ => unforcedDecls.openForMutations
       }
@@ -1367,7 +1367,7 @@ object SymDenotations {
 
     /** Enter a symbol in given `scope` without potentially replacing the old copy. */
     def enterNoReplace(sym: Symbol, scope: MutableScope)(implicit ctx: Context): Unit = {
-      require((sym.denot.flagsUNSAFE is Private) ||  !(this is Frozen))
+      require((sym.denot.flagsUNSAFE is Private) ||  !(this is Frozen) || (scope ne this.unforcedDecls))
       scope.enter(sym)
 
       if (myMemberFingerPrint != FingerPrint.unknown)

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

@@ -0,0 +1,65 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import TreeTransforms._
+import Contexts.Context
+import Flags._
+import SymUtils._
+import Symbols._
+import SymDenotations._
+import Types._
+import Decorators._
+import DenotTransformers._
+import StdNames._
+import NameOps._
+import ast.Trees._
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc.core.Constants.Constant
+import util.Positions._
+import Names._
+import collection.mutable
+
+/** This phase replaces calls to DottyPredef.classTag by code that synthesizes appropriate ClassTag
+  */
+class ClassTags extends MiniPhaseTransform with IdentityDenotTransformer { thisTransform =>
+  import ast.tpd._
+
+  private var classTagCache: Symbol = null
+  private var typeTagCache: Symbol  = null
+  private var scala2ClassTagModule: Symbol = null
+
+
+  override def prepareForUnit(tree: tpd.Tree)(implicit ctx: Context): TreeTransform = {
+    val predefClass = defn.DottyPredefModule.moduleClass.asClass
+    classTagCache = ctx.requiredMethod(predefClass, nme.classTag)
+    typeTagCache = ctx.requiredMethod(predefClass, nme.typeTag)
+    scala2ClassTagModule = ctx.requiredModule("scala.reflect.ClassTag")
+    this
+  }
+
+  override def phaseName: String = "classTags"
+
+  override def transformTypeApply(tree: tpd.TypeApply)(implicit ctx: Context, info: TransformerInfo): tpd.Tree =
+    if (tree.fun.symbol eq classTagCache) {
+      val tp = tree.args.head.tpe
+      val defn = ctx.definitions
+      val (elemType, ndims) = tp match {
+        case defn.MultiArrayType(elem, ndims) => (elem, ndims)
+        case _ => (tp, 0)
+      }
+
+      val claz = tp.classSymbol
+      val elemClaz = elemType.classSymbol
+      assert(!claz.isPrimitiveValueClass) // should be inserted by typer
+      val elemTag = if (defn.ScalaValueClasses.contains(elemClaz) || elemClaz == defn.NothingClass || elemClaz == defn.NullClass)
+          ref(defn.DottyPredefModule).select(s"${elemClaz.name}ClassTag".toTermName)
+        else if (ValueClasses.isDerivedValueClass(elemClaz)) ref(claz.companionModule)
+        else if (elemClaz eq defn.AnyClass) ref(scala2ClassTagModule).select(nme.Any)
+        else {
+          val erazedTp = TypeErasure.erasure(elemType).classSymbol.typeRef
+          ref(scala2ClassTagModule).select(nme.apply).appliedToType(erazedTp).appliedTo(Literal(Constant(erazedTp)))
+        }
+      (1 to ndims).foldLeft(elemTag)((arr, level) => Select(arr, nme.wrap).ensureApplied).ensureConforms(tree.tpe)
+    } else tree
+}

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

@@ -46,35 +46,56 @@ class ExtensionMethods extends MiniPhaseTransform with DenotTransformer with Ful
   override def runsAfterGroupsOf = Set(classOf[FirstTransform]) // need companion objects to exist
 
   override def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation = ref match {
-    case ref: ClassDenotation if ref is ModuleClass =>
-      ref.linkedClass match {
-        case origClass: ClassSymbol if isDerivedValueClass(origClass) =>
-          val cinfo = ref.classInfo
+    case moduleClassSym: ClassDenotation if moduleClassSym is ModuleClass =>
+      moduleClassSym.linkedClass match {
+        case valueClass: ClassSymbol if isDerivedValueClass(valueClass) =>
+          val cinfo = moduleClassSym.classInfo
           val decls1 = cinfo.decls.cloneScope
+          val moduleSym = moduleClassSym.symbol.asClass
+
+          var newSuperClass: Type = null
+
           ctx.atPhase(thisTransformer.next) { implicit ctx =>
             // In Scala 2, extension methods are added before pickling so we should
             // not generate them again.
-            if (!(origClass is Scala2x)) ctx.atPhase(thisTransformer) { implicit ctx =>
-              for (decl <- origClass.classInfo.decls) {
+            if (!(valueClass is Scala2x)) ctx.atPhase(thisTransformer) { implicit ctx =>
+              for (decl <- valueClass.classInfo.decls) {
                 if (isMethodWithExtension(decl))
-                  decls1.enter(createExtensionMethod(decl, ref.symbol))
+                  decls1.enter(createExtensionMethod(decl, moduleClassSym.symbol))
               }
             }
 
-            val sym = ref.symbol
-            val underlying = erasure(underlyingOfValueClass(origClass))
-            val evt = ErasedValueType(origClass, underlying)
-            val u2evtSym = ctx.newSymbol(sym, nme.U2EVT, Synthetic | Method,
+            val underlying = erasure(underlyingOfValueClass(valueClass))
+            val evt = ErasedValueType(valueClass, underlying)
+            val u2evtSym = ctx.newSymbol(moduleSym, nme.U2EVT, Synthetic | Method,
               MethodType(List(nme.x_0), List(underlying), evt))
-            val evt2uSym = ctx.newSymbol(sym, nme.EVT2U, Synthetic | Method,
+            val evt2uSym = ctx.newSymbol(moduleSym, nme.EVT2U, Synthetic | Method,
               MethodType(List(nme.x_0), List(evt), underlying))
+
+            val defn = ctx.definitions
+
+            val underlyingCls = underlying.classSymbol
+            val underlyingClsName =
+              if (defn.ScalaNumericValueClasses.contains(underlyingCls) ||
+                underlyingCls == defn.BooleanClass) underlyingCls.name else nme.Object
+
+
+            val syp = ctx.requiredClass(s"dotty.runtime.vc.VC${underlyingClsName}Companion").asClass
+
+            newSuperClass = tpd.ref(syp).select(nme.CONSTRUCTOR).appliedToType(valueClass.typeRef).tpe.resultType
+
             decls1.enter(u2evtSym)
             decls1.enter(evt2uSym)
           }
-          if (decls1.isEmpty) ref
-          else ref.copySymDenotation(info = cinfo.derivedClassInfo(decls = decls1))
+
+          // add a VCXXXCompanion superclass
+
+          moduleClassSym.copySymDenotation(info =
+            cinfo.derivedClassInfo(
+              classParents = ctx.normalizeToClassRefs(List(newSuperClass), moduleSym, decls1),
+              decls = decls1))
         case _ =>
-          ref
+          moduleClassSym
       }
     case ref: SymDenotation
     if isMethodWithExtension(ref) && ref.hasAnnotation(defn.TailrecAnnotationClass) =>