Reworked erasure denotation transformer

Now works for all combinations of

    java/scala
    sue ErasedValueClass/go directly to underlying type
    constructors/others
    wildcards ok/not

Signatures had to be refined as well, because the signature depends
on whether a type comes form Java or Scala (handling of intersections
is different).

Also, replaced splitArray method in TypeApplication by extractors for
single- and multi-dimensional array types in definitions.

1 files changed, 172 insertions, 64 deletions

diff --git a/src/dotty/tools/dotc/core/transform/Erasure.scala b/src/dotty/tools/dotc/core/transform/Erasure.scala
index 093b59ae8..89a504ac6 100644
--- a/src/dotty/tools/dotc/core/transform/Erasure.scala
+++ b/src/dotty/tools/dotc/core/transform/Erasure.scala
@@ -2,10 +2,89 @@ package dotty.tools.dotc
 package core
 package transform
 
-import Symbols._, Types._, Contexts._, Flags._, Names._, StdNames._
+import Symbols._, Types._, Contexts._, Flags._, Names._, StdNames._, Flags.JavaDefined
+import util.DotClass
 
 object Erasure {
 
+  private def erasureIdx(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcardOK: Boolean) =
+    (if (isJava) 1 else 0) +
+    (if (isSemi) 2 else 0) +
+    (if (isConstructor) 4 else 0) +
+    (if (wildcardOK) 8 else 0)
+
+  private var erasures = new Array[Erasure](16)
+
+  for {
+    isJava <- List(false, true)
+    isSemi <- List(false, true)
+    isConstructor <- List(false, true)
+    wildcardOK <- List(false, true)
+  } erasures(erasureIdx(isJava, isSemi, isConstructor, wildcardOK)) =
+    new Erasure(isJava, isSemi, isConstructor, wildcardOK)
+
+  /** Produces an erasure function.
+   *  @param isJava        Arguments should be treated the way Java does it
+   *  @param isSemi        Value classes are mapped in an intermediate step to
+   *                       ErasedValueClass types, instead of going directly to
+   *                       the erasure of the underlying type.
+   *  @param isConstructor Argument forms part of the type of a constructor
+   *  @param wildcardOK    Wildcards are acceptable (true when using the erasure
+   *                       for computing a signature name).
+   */
+  private def erasureFn(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcardOK: Boolean): Erasure =
+    erasures(erasureIdx(isJava, isSemi, isConstructor, wildcardOK))
+
+  private val scalaErasureFn = erasureFn(isJava = false, isSemi = false, isConstructor = false, wildcardOK = false)
+  private val scalaSigFn = erasureFn(isJava = false, isSemi = false, isConstructor = false, wildcardOK = true)
+  private val javaSigFn = erasureFn(isJava = true, isSemi = false, isConstructor = false, wildcardOK = true)
+  private val semiErasureFn = erasureFn(isJava = false, isSemi = true, isConstructor = false, wildcardOK = false)
+
+  def erasure(tp: Type)(implicit ctx: Context): Type = scalaErasureFn(tp)
+  def semiErasure(tp: Type)(implicit ctx: Context): Type = semiErasureFn(tp)
+  def sigName(tp: Type, isJava: Boolean)(implicit ctx: Context): TypeName =
+    (if (isJava) javaSigFn else scalaSigFn).sigName(tp)
+
+  /**  The symbol's erased info. This is the type's erasure, except for the following symbols:
+   *
+   *   - For $asInstanceOf           : [T]T
+   *   - For $isInstanceOf           : [T]scala#Boolean
+   *   - For Array[T].<init>         : [T]{scala#Int)Array[T]
+   *   - For type members of Array   : The original info
+   *   - For all other abstract types: = ?
+   *   - For all other symbols       : the semi-erasure of their types, with
+   *                                   isJava, isConstructor set according to symbol.
+   */
+  def transformInfo(sym: Symbol, tp: Type)(implicit ctx: Context): Type = {
+    val erase = erasureFn(sym is JavaDefined, isSemi = true, sym.isConstructor, wildcardOK = false)
+    if ((sym eq defn.Object_asInstanceOf) || sym.isType && (sym.owner eq defn.ArrayClass))
+      sym.info
+    else if ((sym eq defn.Object_isInstanceOf) || (sym eq defn.ArrayClass.primaryConstructor)) {
+      val tp @ PolyType(pnames) = sym.info
+      tp.derivedPolyType(pnames, TypeBounds.empty :: Nil, erase(tp.resultType))
+    }
+    else if (sym.isAbstractType)
+      TypeAlias(WildcardType)
+    else
+      erase(tp)
+  }
+
+  def isUnboundedGeneric(tp: Type)(implicit ctx: Context) = !(
+    (tp derivesFrom defn.ObjectClass) ||
+    tp.classSymbol.isPrimitiveValueClass ||
+    (tp.typeSymbol is JavaDefined))
+
+}
+import Erasure._
+
+/**
+ *  This is used as the Scala erasure during the erasure phase itself
+   *  It differs from normal erasure in that value classes are erased to ErasedValueTypes which
+   *  are then later converted to the underlying parameter type in phase posterasure.
+ *
+ */
+class Erasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wildcardOK: Boolean) extends DotClass {
+
   /**  The erasure |T| of a type T. This is:
    *
    *   - For a refined type scala.Array+[T]:
@@ -15,8 +94,9 @@ object Erasure {
    *      - otherwise, Object
    *   - For a constant type, NoType or NoPrefix, the type itself.
    *   - For all other type proxies: The erasure of the underlying type.
-   *   - For a typeref scala.Any, scala.AnyVal, scala.Singleon or scala.NotNull, java.lang.Object.
+   *   - For a typeref scala.Any, scala.AnyVal, scala.Singleon or scala.NotNull: java.lang.Object.
    *   - For a typeref scala.Unit, scala.runtime.BoxedUnit.
+   *   - For a typeref whose symbol is owned by Array: The typeref itself
    *   - For a typeref P.C where C refers to a toplevel class, P.C.
    *   - For a typeref P.C where C refers to a nested class, |P|.C.
    *   - For a typeref P.C where C refers to an alias type, the erasure of C's alias.
@@ -32,56 +112,73 @@ object Erasure {
    *     parents |Ps|, but with duplicate references of Object removed.
    *   - For any other type, exception.
    */
-  def erasure(tp: Type)(implicit ctx: Context): Type = tp match {
+  def apply(tp: Type)(implicit ctx: Context): Type = tp match {
     case tp: TypeRef =>
       val sym = tp.symbol
-      if (sym.isClass)
-        /*if (sym.isDerivedValueClass) eraseDerivedValueClassRef(tref)
-        else */if (sym.owner is Package) normalizeClass(sym.asClass).typeRef
-        else tp.derivedSelect(erasure(tp.prefix))
-      else erasure(tp.info)
+      if (!sym.isClass)
+        if (sym.owner eq defn.ArrayClass) tp else this(tp.info)
+      else if (sym.isDerivedValueClass) eraseDerivedValueClassRef(tp)
+      else eraseNormalClassRef(tp)
     case tp: RefinedType =>
       val parent = tp.parent
       if (parent isRef defn.ArrayClass) eraseArray(tp)
-      else erasure(parent)
-    case ConstantType(_) | NoType | NoPrefix =>
+      else this(parent)
+    case tp: ConstantType =>
       tp
     case tp: TypeProxy =>
-      erasure(tp.underlying)
+       this(tp.underlying)
     case AndType(tp1, tp2) =>
-      erasure(tp1)
+      mergeAnd(this(tp1), this(tp2))
     case OrType(tp1, tp2) =>
-      erasure(tp.baseTypeRef(lubClass(tp1, tp2)))
+      this(tp.baseTypeRef(lubClass(tp1, tp2)))
     case tp: MethodType =>
+      val paramErasure = erasureFn(tp.isJava, isSemi, isConstructor, wildcardOK)(_)
       tp.derivedMethodType(
-        tp.paramNames, tp.paramTypes.mapConserve(erasure), resultErasure(tp.resultType))
+        tp.paramNames, tp.paramTypes.mapConserve(paramErasure), eraseResult(tp.resultType))
     case tp: PolyType =>
-      erasure(tp.resultType)
+      this(tp.resultType)
     case tp @ ClassInfo(pre, cls, classParents, decls, _) =>
+      def eraseTypeRef = this.asInstanceOf[TypeRef => TypeRef]
       val parents: List[TypeRef] =
-        if (cls == defn.ObjectClass || cls.isPrimitiveValueClass) Nil
-        else if (cls == defn.ArrayClass) defn.ObjectClass.typeRef :: Nil
-        else removeLaterObjects(classParents mapConserve (erasure(_).asInstanceOf[TypeRef]))
-      tp.derivedClassInfo(erasure(pre), parents, NoType)
-    case ErrorType =>
+        if ((cls eq defn.ObjectClass) || cls.isPrimitiveValueClass) Nil
+        else if (cls eq defn.ArrayClass) defn.ObjectClass.typeRef :: Nil
+        else removeLaterObjects(classParents.mapConserve(eraseTypeRef))
+      tp.derivedClassInfo(this(pre), parents, NoType)
+    case NoType | NoPrefix | ErrorType =>
+      tp
+    case tp: WildcardType if wildcardOK =>
       tp
   }
 
-  def eraseArray(tp: RefinedType)(implicit ctx: Context) = {
-    val (n, elemtp) = tp.splitArray
-    val elemCls = elemtp.classSymbol
-    if (elemCls.isSubClass(defn.NullClass))
-      defn.ObjectArrayType
-    else if (elemCls.isSubClass(defn.ObjectClass) || elemCls.isPrimitiveValueClass)
-      (erasure(elemtp) /: (0 until n))((erased, _) =>
-        defn.ArrayType.appliedTo(erased))
-    else if (elemtp.typeSymbol is JavaDefined)
-      defn.ObjectArrayType
-    else
-      defn.ObjectType
+  private def eraseArray(tp: RefinedType)(implicit ctx: Context) = {
+    val defn.ArrayType(elemtp) = tp
+    if (elemtp derivesFrom defn.NullClass) defn.ObjectArrayType
+    else if (isUnboundedGeneric(elemtp)) defn.ObjectType
+    else defn.ArrayType(this(elemtp))
+  }
+
+  private def eraseDerivedValueClassRef(tref: TypeRef)(implicit ctx: Context): Type =
+    unsupported("eraseDerivedValueClass")
+
+  private def eraseNormalClassRef(tref: TypeRef)(implicit ctx: Context): Type = {
+    val sym = tref.symbol
+    if (sym.owner is Package) normalizeClass(sym.asClass).typeRef
+    else tref.derivedSelect(this(tref.prefix))
   }
 
-  def normalizeClass(cls: ClassSymbol)(implicit ctx: Context): ClassSymbol = {
+  private def eraseResult(tp: Type)(implicit ctx: Context): Type = tp match {
+    case tp: TypeRef =>
+      val sym = tp.typeSymbol
+      if (sym eq defn.UnitClass) sym.typeRef
+      else if (sym.isDerivedValueClass) eraseNormalClassRef(tp)
+      else this(tp)
+    case RefinedType(parent, _) if !(parent isRef defn.ArrayClass) =>
+      eraseResult(parent)
+    case _ =>
+      this(tp)
+  }
+
+  private def normalizeClass(cls: ClassSymbol)(implicit ctx: Context): ClassSymbol = {
     if (cls.owner == defn.ScalaPackageClass) {
       if (cls == defn.AnyClass || cls == defn.AnyValClass || cls == defn.SingletonClass || cls == defn.NotNullClass)
         return defn.ObjectClass
@@ -91,7 +188,7 @@ object Erasure {
     cls
   }
 
-  def lubClass(tp1: Type, tp2: Type)(implicit ctx: Context): ClassSymbol = {
+  private def lubClass(tp1: Type, tp2: Type)(implicit ctx: Context): ClassSymbol = {
     var bcs1 = tp1.baseClasses
     val bc2 = tp2.baseClasses.head
     while (bcs1.nonEmpty && !bc2.derivesFrom(bcs1.head))
@@ -99,44 +196,55 @@ object Erasure {
     if (bcs1.isEmpty) defn.ObjectClass else bcs1.head
   }
 
+  private def removeLaterObjects(trs: List[TypeRef])(implicit ctx: Context): List[TypeRef] = trs match {
+    case tr :: trs1 => tr :: trs1.filterNot(_ isRef defn.ObjectClass)
+    case nil => nil
+  }
+
+  private def mergeAnd(tp1: Type, tp2: Type)(implicit ctx: Context): Type = tp1 match {
+    case defn.ArrayType(elem1) =>
+      tp2 match {
+        case defn.ArrayType(elem2) => defn.ArrayType(mergeAnd(elem1, elem2))
+        case _ => defn.ObjectType
+      }
+    case _ =>
+      tp2 match {
+        case defn.ArrayType(_) => defn.ObjectType
+        case _ =>
+          val tsym1 = tp1.typeSymbol
+          val tsym2 = tp2.typeSymbol
+          if (!tsym2.exists) tp1
+          else if (!tsym1.exists) tp2
+          else if (!isJava && tsym1.derivesFrom(tsym2)) tp1
+          else if (!isJava && tsym2.derivesFrom(tsym1)) tp2
+          else if (tp1.typeSymbol.isRealClass) tp1
+          else if (tp2.typeSymbol.isRealClass) tp2
+          else tp1
+      }
+  }
+
   /** The name of the type as it is used in `Signature`s.
    *  Need to ensure correspondence with erasure!
    */
   def sigName(tp: Type)(implicit ctx: Context): TypeName = tp match {
     case tp: TypeRef =>
       val sym = tp.symbol
-      if (sym.isClass)
-        /*if (sym.isDerivedValueClass) eraseDerivedValueClassRef(tref)
-        else */if (sym.owner is Package) normalizeClass(sym.asClass).fullName.asTypeName
-        else sym.asClass.fullName.asTypeName
-      else sigName(tp.info)
-    case tp: RefinedType =>
-      val parent = tp.parent
-      if (parent isRef defn.ArrayClass)
-        eraseArray(tp) match {
-          case tp1: RefinedType if tp1.parent isRef defn.ArrayClass =>
-            sigName(tp1.refinedInfo) ++ "[]"
-          case tp1 =>
-            sigName(tp1)
-        }
-      else sigName(parent)
+      if (!sym.isClass) sigName(tp.info)
+      else if (sym.isDerivedValueClass) sigName(eraseDerivedValueClassRef(tp))
+      else normalizeClass(sym.asClass).fullName.asTypeName
+    case defn.ArrayType(elem) =>
+      sigName(elem) ++ "[]"
+    case tp: TypeBounds =>
+      sigName(tp.hi)
     case tp: TypeProxy =>
       sigName(tp.underlying)
-    case AndType(tp1, tp2) =>
-      sigName(tp1)
-    case OrType(tp1, tp2) =>
-      lubClass(tp1, tp2).name
-    case tp: WildcardType =>
+    case ErrorType | WildcardType =>
       tpnme.WILDCARD
-    case ErrorType =>
-      tpnme.WILDCARD
-  }
-
-  def resultErasure(tp: Type)(implicit ctx: Context) =
-    if (tp isRef defn.UnitClass) tp else erasure(tp)
-
-  def removeLaterObjects(trs: List[TypeRef])(implicit ctx: Context): List[TypeRef] = trs match {
-    case tr :: trs1 => tr :: trs1.filterNot(_ isRef defn.ObjectClass)
-    case nil => nil
+    case tp: WildcardType =>
+      sigName(tp.optBounds)
+    case _ =>
+      val erased = this(tp)
+      assert(erased ne tp)
+      sigName(erased)
   }
 }