Merge pull request #3410 from dotty-staging/make-phantoms-unused

Remove scala.Phantom (replaced by `unused`)

Author: odersky

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

@@ -80,8 +80,7 @@ class Compiler {
          new ShortcutImplicits,      // Allow implicit functions without creating closures
          new CrossCastAnd,           // Normalize selections involving intersection types.
          new Splitter) ::            // Expand selections involving union types into conditionals
-    List(new PhantomArgLift,         // Extracts the evaluation of phantom arguments placing them before the call.
-         new UnusedDecls,            // Removes all unused defs and vals decls (except for parameters)
+    List(new UnusedDecls,            // Removes all unused defs and vals decls (except for parameters)
          new VCInlineMethods,        // Inlines calls to value class methods
          new SeqLiterals,            // Express vararg arguments as arrays
          new InterceptedMethods,     // Special handling of `==`, `|=`, `getClass` methods

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

@@ -1161,8 +1161,7 @@ class Definitions {
     NullClass,
     NothingClass,
     SingletonClass,
-    EqualsPatternClass,
-    PhantomClass)
+    EqualsPatternClass)
 
   lazy val syntheticCoreClasses = syntheticScalaClasses ++ List(
     EmptyPackageVal,
@@ -1191,28 +1190,4 @@ class Definitions {
     }
   }
 
-  // ----- Phantoms ---------------------------------------------------------
-
-  lazy val PhantomClass: ClassSymbol = {
-    val cls = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.Phantom, NoInitsTrait, List(AnyType)))
-
-    val any = enterCompleteClassSymbol(cls, tpnme.Any, Protected | Final | NoInitsTrait, Nil)
-    val nothing = enterCompleteClassSymbol(cls, tpnme.Nothing, Protected | Final | NoInitsTrait, List(any.typeRef))
-    enterMethod(cls, nme.assume_, ExprType(nothing.typeRef), Protected | Final | Method)
-
-    cls
-  }
-  lazy val Phantom_AnyClass = PhantomClass.unforcedDecls.find(_.name eq tpnme.Any).asClass
-  lazy val Phantom_NothingClass = PhantomClass.unforcedDecls.find(_.name eq tpnme.Nothing).asClass
-  lazy val Phantom_assume = PhantomClass.unforcedDecls.find(_.name eq nme.assume_)
-
-  /** If the symbol is of the class scala.Phantom.Any or scala.Phantom.Nothing */
-  def isPhantomTerminalClass(sym: Symbol) = (sym eq Phantom_AnyClass) || (sym eq Phantom_NothingClass)
-
-
-  lazy val ErasedPhantomType: TypeRef = ctx.requiredClassRef("dotty.runtime.ErasedPhantom")
-  def ErasedPhantomClass(implicit ctx: Context) = ErasedPhantomType.symbol.asClass
-
-  def ErasedPhantom_UNIT(implicit ctx: Context) = ErasedPhantomClass.linkedClass.requiredValue("UNIT")
-
 }

compiler/src/dotty/tools/dotc/core/PhantomErasure.scala

@@ -84,7 +84,7 @@ case class Signature(paramsSig: List[TypeName], resSig: TypeName) {
    *  to the parameter part of this signature.
    */
   def prepend(params: List[Type], isJava: Boolean)(implicit ctx: Context) =
-    Signature(params.collect { case p if !p.isPhantom => sigName(p, isJava) } ++ paramsSig, resSig)
+    Signature(params.map(p => sigName(p, isJava)) ++ paramsSig, resSig)
 
   /** A signature is under-defined if its paramsSig part contains at least one
    *  `tpnme.Uninstantiated`. Under-defined signatures arise when taking a signature

compiler/src/dotty/tools/dotc/core/Signature.scala

@@ -241,7 +241,6 @@ object StdNames {
     final val SourceFileATTR: N             = "SourceFile"
     final val SyntheticATTR: N              = "Synthetic"
 
-    final val Phantom: N = "Phantom"
 
 // ----- Term names -----------------------------------------
 

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

@@ -667,7 +667,7 @@ object SymDenotations {
 
     /** Is this symbol a class references to which that are supertypes of null? */
     final def isNullableClass(implicit ctx: Context): Boolean =
-      isClass && !isValueClass && !(this is ModuleClass) && symbol != defn.NothingClass && !defn.isPhantomTerminalClass(symbol)
+      isClass && !isValueClass && !(this is ModuleClass) && symbol != defn.NothingClass
 
     /** Is this definition accessible as a member of tree with type `pre`?
      *  @param pre          The type of the tree from which the selection is made

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

@@ -50,7 +50,6 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
   private[this] var myAnyClass: ClassSymbol = null
   private[this] var myNothingClass: ClassSymbol = null
   private[this] var myNullClass: ClassSymbol = null
-  private[this] var myPhantomNothingClass: ClassSymbol = null
   private[this] var myObjectClass: ClassSymbol = null
   private[this] var myAnyType: TypeRef = null
   private[this] var myNothingType: TypeRef = null
@@ -67,10 +66,6 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     if (myNullClass == null) myNullClass = defn.NullClass
     myNullClass
   }
-  def PhantomNothingClass = {
-    if (myPhantomNothingClass == null) myPhantomNothingClass = defn.Phantom_NothingClass
-    myPhantomNothingClass
-  }
   def ObjectClass = {
     if (myObjectClass == null) myObjectClass = defn.ObjectClass
     myObjectClass
@@ -287,7 +282,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
             if (recur(info1.alias, tp2)) return true
             if (tp1.prefix.isStable) return false
           case _ =>
-            if (tp1 eq NothingType) return tp1 == tp2.bottomType
+            if (tp1 eq NothingType) return true
         }
         thirdTry
       case tp1: TypeParamRef =>
@@ -586,9 +581,8 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
               case _ => false
             }
             val sym1 = tp1.symbol
-            (sym1 eq NothingClass) && tp2.isValueTypeOrLambda && !tp2.isPhantom ||
-            (sym1 eq NullClass) && isNullable(tp2) ||
-            (sym1 eq PhantomNothingClass) && tp1.topType == tp2.topType
+            (sym1 eq NothingClass) && tp2.isValueTypeOrLambda ||
+            (sym1 eq NullClass) && isNullable(tp2)
         }
       case tp1 @ AppliedType(tycon1, args1) =>
         compareAppliedType1(tp1, tycon1, args1)

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -380,8 +380,6 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
       else if (semiEraseVCs && isDerivedValueClass(sym)) eraseDerivedValueClassRef(tp)
       else if (sym == defn.ArrayClass) apply(tp.appliedTo(TypeBounds.empty)) // i966 shows that we can hit a raw Array type.
       else if (defn.isSyntheticFunctionClass(sym)) defn.erasedFunctionType(sym)
-      else if (defn.isPhantomTerminalClass(sym)) PhantomErasure.erasedPhantomType
-      else if (sym eq defn.PhantomClass) defn.ObjectType // To erase the definitions of Phantom.{assume, Any, Nothing}
       else eraseNormalClassRef(tp)
     case tp: AppliedType =>
       if (tp.tycon.isRef(defn.ArrayClass)) eraseArray(tp)
@@ -401,10 +399,7 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
     case tp: MethodType =>
       def paramErasure(tpToErase: Type) =
         erasureFn(tp.isJavaMethod, semiEraseVCs, isConstructor, wildcardOK)(tpToErase)
-      val (names, formals0) =
-        if (tp.isUnusedMethod) (Nil, Nil)
-        else if (tp.paramInfos.exists(_.isPhantom)) tp.paramNames.zip(tp.paramInfos).filterNot(_._2.isPhantom).unzip
-        else (tp.paramNames, tp.paramInfos)
+      val (names, formals0) = if (tp.isUnusedMethod) (Nil, Nil) else (tp.paramNames, tp.paramInfos)
       val formals = formals0.mapConserve(paramErasure)
       eraseResult(tp.resultType) match {
         case rt: MethodType =>
@@ -527,8 +522,6 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
         }
         if (defn.isSyntheticFunctionClass(sym))
           sigName(defn.erasedFunctionType(sym))
-        else if (defn.isPhantomTerminalClass(tp.symbol))
-          sigName(PhantomErasure.erasedPhantomType)
         else
           normalizeClass(sym.asClass).fullName.asTypeName
       case tp: AppliedType =>

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -42,7 +42,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
           case pre: SuperType => toPrefix(pre.thistpe, cls, thiscls)
           case _ =>
             if (thiscls.derivesFrom(cls) && pre.baseType(thiscls).exists)
-              if (variance <= 0 && !isLegalPrefix(pre)) range(pre.bottomType, pre)
+              if (variance <= 0 && !isLegalPrefix(pre)) range(defn.NothingType, pre)
               else pre
             else if ((pre.termSymbol is Package) && !(thiscls is Package))
               toPrefix(pre.select(nme.PACKAGE), cls, thiscls)

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -193,59 +193,18 @@ object Types {
         }
       }
 
-    /** Returns true if the type is a phantom type
-     *   - true if XYZ extends scala.Phantom and this type is upper bounded XYZ.Any
-     *   - false otherwise
-     */
-    final def isPhantom(implicit ctx: Context): Boolean = phantomLatticeType.exists
-
-    /** Returns the top type of the lattice
-     *   - XYX.Any if XYZ extends scala.Phantom and this type is upper bounded XYZ.Any
-     *   - scala.Any otherwise
-     */
-    final def topType(implicit ctx: Context): Type = {
-      val lattice = phantomLatticeType
-      if (lattice.exists) lattice.select(tpnme.Any)
-      else defn.AnyType
-    }
-
-    /** Returns the bottom type of the lattice
-     *   - XYZ.Nothing if XYZ extends scala.Phantom and this type is upper bounded XYZ.Any
-     *   - scala.Nothing otherwise
-     */
-    final def bottomType(implicit ctx: Context): Type = {
-      val lattice = phantomLatticeType
-      if (lattice.exists) lattice.select(tpnme.Nothing)
-      else defn.NothingType
-    }
-
     /** Is this type exactly Nothing (no vars, aliases, refinements etc allowed)? */
     def isBottomType(implicit ctx: Context): Boolean = this match {
-      case tp: TypeRef =>
-        val sym = tp.symbol
-        (sym eq defn.NothingClass) || (sym eq defn.Phantom_NothingClass)
+      case tp: TypeRef => tp.symbol eq defn.NothingClass
       case _ => false
     }
 
       /** Is this type exactly Any (no vars, aliases, refinements etc allowed)? */
     def isTopType(implicit ctx: Context): Boolean = this match {
-      case tp: TypeRef =>
-        val sym = tp.symbol
-        (sym eq defn.AnyClass) || (sym eq defn.Phantom_AnyClass)
+      case tp: TypeRef => tp.symbol eq defn.AnyClass
       case _ => false
     }
 
-    /** Returns the type of the phantom lattice (i.e. the prefix of the phantom type)
-      *   - XYZ if XYZ extends scala.Phantom and this type is upper bounded XYZ.Any
-      *   - NoType otherwise
-      */
-    private final def phantomLatticeType(implicit ctx: Context): Type = widen match {
-      case tp: ClassInfo if defn.isPhantomTerminalClass(tp.classSymbol) => tp.prefix
-      case tp: TypeProxy => tp.underlying.phantomLatticeType
-      case tp: AndOrType => tp.tp1.phantomLatticeType
-      case _ => NoType
-    }
-
     /** Is this type a (possibly aliased) singleton type? */
     def isSingleton(implicit ctx: Context) = dealias.isInstanceOf[SingletonType]
 
@@ -2860,7 +2819,7 @@ object Types {
         val dropDependencies = new ApproximatingTypeMap {
           def apply(tp: Type) = tp match {
             case tp @ TermParamRef(thisLambdaType, _) =>
-              range(tp.bottomType, atVariance(1)(apply(tp.underlying)))
+              range(defn.NothingType, atVariance(1)(apply(tp.underlying)))
             case _ => mapOver(tp)
           }
         }
@@ -4177,7 +4136,7 @@ object Types {
             case Range(infoLo: TypeBounds, infoHi: TypeBounds) =>
               assert(variance == 0)
               if (!infoLo.isAlias && !infoHi.isAlias) propagate(infoLo, infoHi)
-              else range(tp.bottomType, tp.parent)
+              else range(defn.NothingType, tp.parent)
             case Range(infoLo, infoHi) =>
               propagate(infoLo, infoHi)
             case _ =>
@@ -4209,7 +4168,7 @@ object Types {
       else tp.derivedTypeBounds(lo, hi)
 
     override protected def derivedSuperType(tp: SuperType, thistp: Type, supertp: Type) =
-      if (isRange(thistp) || isRange(supertp)) range(thistp.bottomType, thistp.topType)
+      if (isRange(thistp) || isRange(supertp)) range(defn.NothingType, defn.AnyType)
       else tp.derivedSuperType(thistp, supertp)
 
     override protected def derivedAppliedType(tp: AppliedType, tycon: Type, args: List[Type]): Type =
@@ -4246,7 +4205,7 @@ object Types {
               if (distributeArgs(args, tp.typeParams))
                 range(tp.derivedAppliedType(tycon, loBuf.toList),
                       tp.derivedAppliedType(tycon, hiBuf.toList))
-              else range(tp.bottomType, tp.topType)
+              else range(defn.NothingType, defn.AnyType)
                 // TODO: can we give a better bound than `topType`?
             }
           }

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -131,7 +131,7 @@ class Constructors extends MiniPhase with IdentityDenotTransformer { thisPhase =
     // Produce aligned accessors and constructor parameters. We have to adjust
     // for any outer parameters, which are last in the sequence of original
     // parameter accessors but come first in the constructor parameter list.
-    val accessors = cls.paramAccessors.filterNot(x => x.isSetter || x.info.resultType.classSymbol == defn.ErasedPhantomClass)
+    val accessors = cls.paramAccessors.filterNot(x => x.isSetter)
     val vparamsWithOuterLast = vparams match {
       case vparam :: rest if vparam.name == nme.OUTER => rest ::: vparam :: Nil
       case _ => vparams

compiler/src/dotty/tools/dotc/transform/Constructors.scala

@@ -28,7 +28,6 @@ import ValueClasses._
 import TypeUtils._
 import ExplicitOuter._
 import core.Mode
-import core.PhantomErasure
 import reporting.trace
 
 class Erasure extends Phase with DenotTransformer {
@@ -213,8 +212,6 @@ object Erasure {
           val tree1 =
             if (tree.tpe isRef defn.NullClass)
               adaptToType(tree, underlying)
-            else if (wasPhantom(underlying))
-              PhantomErasure.erasedParameterRef
             else if (!(tree.tpe <:< tycon)) {
               assert(!(tree.tpe.typeSymbol.isPrimitiveValueClass))
               val nullTree = Literal(Constant(null))
@@ -437,16 +434,9 @@ object Erasure {
         }
       }
 
-      if ((origSym eq defn.Phantom_assume) || (origSym.is(Flags.ParamAccessor) && wasPhantom(pt)))
-        PhantomErasure.erasedAssume
-      else recur(typed(tree.qualifier, AnySelectionProto))
+      recur(typed(tree.qualifier, AnySelectionProto))
     }
 
-    override def typedIdent(tree: untpd.Ident, pt: Type)(implicit ctx: Context): tpd.Tree =
-      if (tree.symbol eq defn.Phantom_assume) PhantomErasure.erasedAssume
-      else if (tree.symbol.is(Flags.Param) && wasPhantom(tree.typeOpt)) PhantomErasure.erasedParameterRef
-      else super.typedIdent(tree, pt)
-
     override def typedThis(tree: untpd.This)(implicit ctx: Context): Tree =
       if (tree.symbol == ctx.owner.lexicallyEnclosingClass || tree.symbol.isStaticOwner) promote(tree)
       else {
@@ -507,11 +497,9 @@ object Erasure {
                   .withType(defn.ArrayOf(defn.ObjectType))
                 args0 = bunchedArgs :: Nil
               }
-              // Arguments are phantom if an only if the parameters are phantom, guaranteed by the separation of type lattices
-              val args1 = args0.filterConserve(arg => !wasPhantom(arg.typeOpt))
-              assert(args1 hasSameLengthAs mt.paramInfos)
-              val args2 = args1.zipWithConserve(mt.paramInfos)(typedExpr)
-              untpd.cpy.Apply(tree)(fun1, args2) withType mt.resultType
+              assert(args0 hasSameLengthAs mt.paramInfos)
+              val args1 = args0.zipWithConserve(mt.paramInfos)(typedExpr)
+              untpd.cpy.Apply(tree)(fun1, args1) withType mt.resultType
             case _ =>
               throw new MatchError(i"tree $tree has unexpected type of function ${fun1.tpe.widen}, was ${fun.typeOpt.widen}")
           }
@@ -572,11 +560,6 @@ object Erasure {
         rhs1 = untpd.Block(paramDefs, rhs1)
       }
       vparamss1 = vparamss1.mapConserve(_.filterConserve(!_.symbol.is(Flags.Unused)))
-      vparamss1 = vparamss1.mapConserve(_.filterConserve(vparam => !wasPhantom(vparam.tpe)))
-      if (sym.is(Flags.ParamAccessor) && wasPhantom(ddef.tpt.tpe)) {
-        sym.resetFlag(Flags.ParamAccessor)
-        rhs1 = PhantomErasure.erasedParameterRef
-      }
       val ddef1 = untpd.cpy.DefDef(ddef)(
         tparams = Nil,
         vparamss = vparamss1,
@@ -703,7 +686,4 @@ object Erasure {
 
   def takesBridges(sym: Symbol)(implicit ctx: Context) =
     sym.isClass && !sym.is(Flags.Trait | Flags.Package)
-
-  private def wasPhantom(tp: Type)(implicit ctx: Context): Boolean =
-    tp.widenDealias.classSymbol eq defn.ErasedPhantomClass
 }

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

@@ -161,14 +161,6 @@ class FirstTransform extends MiniPhase with InfoTransformer { thisPhase =>
     } else ddef
   }
 
-  override def transformValDef(vdef: tpd.ValDef)(implicit ctx: Context): tpd.Tree = {
-    if (vdef.tpt.tpe.isPhantom) {
-      if (vdef.symbol.is(Mutable)) ctx.error("var fields cannot have Phantom types", vdef.pos)
-      else if (vdef.symbol.hasAnnotation(defn.VolatileAnnot)) ctx.error("Phantom fields cannot be @volatile", vdef.pos)
-    }
-    vdef
-  }
-
   override def transformStats(trees: List[Tree])(implicit ctx: Context): List[Tree] =
     ast.Trees.flatten(reorderAndComplete(trees)(ctx.withPhase(thisPhase.next)))
 

compiler/src/dotty/tools/dotc/transform/FirstTransform.scala

@@ -212,8 +212,6 @@ object GenericSignatures {
             else
               jsig(unboxedSeen, toplevel, primitiveOK)
           }
-          else if (tp.isPhantom)
-            jsig(defn.ErasedPhantomType)
           else if (sym.isClass)
             classSig
           else
@@ -242,7 +240,7 @@ object GenericSignatures {
           // unused method parameters do not make it to the bytecode.
           def effectiveParamInfoss(t: Type)(implicit ctx: Context): List[List[Type]] = t match {
             case t: MethodType if t.isUnusedMethod => effectiveParamInfoss(t.resType)
-            case t: MethodType => t.paramInfos.filterNot(_.isPhantom) :: effectiveParamInfoss(t.resType)
+            case t: MethodType => t.paramInfos :: effectiveParamInfoss(t.resType)
             case _ => Nil
           }
           val params = effectiveParamInfoss(mtpe).flatten