Implement enum desugaring

6 files changed, 215 insertions, 36 deletions

diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 87994a87b..863c10cb0 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -14,6 +14,7 @@ import reporting.diagnostic.messages._
 
 object desugar {
   import untpd._
+  import DesugarEnums._
 
   /** Tags a .withFilter call generated by desugaring a for expression.
    *  Such calls can alternatively be rewritten to use filter.
@@ -263,7 +264,9 @@ object desugar {
     val className = checkNotReservedName(cdef).asTypeName
     val impl @ Template(constr0, parents, self, _) = cdef.rhs
     val mods = cdef.mods
-    val companionMods = mods.withFlags((mods.flags & AccessFlags).toCommonFlags)
+    val companionMods = mods
+        .withFlags((mods.flags & AccessFlags).toCommonFlags)
+        .withMods(mods.mods.filter(!_.isInstanceOf[Mod.EnumCase]))
 
     val (constr1, defaultGetters) = defDef(constr0, isPrimaryConstructor = true) match {
       case meth: DefDef => (meth, Nil)
@@ -288,17 +291,22 @@ object desugar {
     }
 
     val isCaseClass = mods.is(Case) && !mods.is(Module)
+    val isEnum = mods.hasMod[Mod.Enum]
+    val isEnumCase = isLegalEnumCase(cdef)
     val isValueClass = parents.nonEmpty && isAnyVal(parents.head)
       // This is not watertight, but `extends AnyVal` will be replaced by `inline` later.
 
-    val constrTparams = constr1.tparams map toDefParam
+    val originalTparams =
+      if (isEnumCase && parents.isEmpty) reconstitutedEnumTypeParams(cdef.pos.startPos)
+      else constr1.tparams
+    val originalVparamss = constr1.vparamss
+    val constrTparams = originalTparams.map(toDefParam)
     val constrVparamss =
-      if (constr1.vparamss.isEmpty) { // ensure parameter list is non-empty
-        if (isCaseClass)
-          ctx.error(CaseClassMissingParamList(cdef), cdef.namePos)
+      if (originalVparamss.isEmpty) { // ensure parameter list is non-empty
+        if (isCaseClass) ctx.error(CaseClassMissingParamList(cdef), cdef.namePos)
         ListOfNil
       }
-      else constr1.vparamss.nestedMap(toDefParam)
+      else originalVparamss.nestedMap(toDefParam)
     val constr = cpy.DefDef(constr1)(tparams = constrTparams, vparamss = constrVparamss)
 
     // Add constructor type parameters and evidence implicit parameters
@@ -312,21 +320,22 @@ object desugar {
         stat
     }
 
-    val derivedTparams = constrTparams map derivedTypeParam
+    val derivedTparams =
+      if (isEnumCase) constrTparams else constrTparams map derivedTypeParam
     val derivedVparamss = constrVparamss nestedMap derivedTermParam
     val arity = constrVparamss.head.length
 
-    var classTycon: Tree = EmptyTree
+    val classTycon: Tree = new TypeRefTree // watching is set at end of method
 
-    // a reference to the class type, with all parameters given.
-    val classTypeRef/*: Tree*/ = {
-        // -language:keepUnions difference: classTypeRef needs type annotation, otherwise
-        // infers Ident | AppliedTypeTree, which
-        // renders the :\ in companions below untypable.
-      classTycon = (new TypeRefTree) withPos cdef.pos.startPos // watching is set at end of method
-      val tparams = impl.constr.tparams
-      if (tparams.isEmpty) classTycon else AppliedTypeTree(classTycon, tparams map refOfDef)
-    }
+    def appliedRef(tycon: Tree) =
+      (if (constrTparams.isEmpty) tycon
+       else AppliedTypeTree(tycon, constrTparams map refOfDef))
+       .withPos(cdef.pos.startPos)
+
+    // a reference to the class type bound by `cdef`, with type parameters coming from the constructor
+    val classTypeRef = appliedRef(classTycon)
+    // a refereence to `enumClass`, with type parameters coming from the constructor
+    lazy val enumClassTypeRef = appliedRef(enumClassRef)
 
     // new C[Ts](paramss)
     lazy val creatorExpr = New(classTypeRef, constrVparamss nestedMap refOfDef)
@@ -374,7 +383,9 @@ object desugar {
             DefDef(nme.copy, derivedTparams, copyFirstParams :: copyRestParamss, TypeTree(), creatorExpr)
               .withMods(synthetic) :: Nil
           }
-        copyMeths ::: productElemMeths.toList
+
+        val enumTagMeths = if (isEnumCase) enumTagMeth :: Nil else Nil
+        copyMeths ::: enumTagMeths ::: productElemMeths.toList
       }
       else Nil
 
@@ -387,8 +398,12 @@ object desugar {
 
     // Case classes and case objects get a ProductN parent
     var parents1 = parents
+    if (isEnumCase && parents.isEmpty)
+      parents1 = enumClassTypeRef :: Nil
     if (mods.is(Case) && arity <= Definitions.MaxTupleArity)
-      parents1 = parents1 :+ productConstr(arity)
+      parents1 = parents1 :+ productConstr(arity) // TODO: This also adds Product0 to caes objects. Do we want that?
+    if (isEnum)
+      parents1 = parents1 :+ ref(defn.EnumType)
 
     // The thicket which is the desugared version of the companion object
     //     synthetic object C extends parentTpt { defs }
@@ -419,9 +434,11 @@ object desugar {
           else (constrVparamss :\ classTypeRef) ((vparams, restpe) => Function(vparams map (_.tpt), restpe))
         val applyMeths =
           if (mods is Abstract) Nil
-          else
-            DefDef(nme.apply, derivedTparams, derivedVparamss, TypeTree(), creatorExpr)
+          else {
+            val restpe = if (isEnumCase) enumClassTypeRef else TypeTree()
+            DefDef(nme.apply, derivedTparams, derivedVparamss, restpe, creatorExpr)
               .withFlags(Synthetic | (constr1.mods.flags & DefaultParameterized)) :: Nil
+          }
         val unapplyMeth = {
           val unapplyParam = makeSyntheticParameter(tpt = classTypeRef)
           val unapplyRHS = if (arity == 0) Literal(Constant(true)) else Ident(unapplyParam.name)
@@ -464,15 +481,15 @@ object desugar {
       else cpy.ValDef(self)(tpt = selfType).withMods(self.mods | SelfName)
     }
 
-    val cdef1 = {
-      val originalTparams = constr1.tparams.toIterator
-      val originalVparams = constr1.vparamss.toIterator.flatten
-      val tparamAccessors = derivedTparams.map(_.withMods(originalTparams.next.mods))
+    val cdef1 = addEnumFlags {
+      val originalTparamsIt = originalTparams.toIterator
+      val originalVparamsIt = originalVparamss.toIterator.flatten
+      val tparamAccessors = derivedTparams.map(_.withMods(originalTparamsIt.next.mods))
       val caseAccessor = if (isCaseClass) CaseAccessor else EmptyFlags
       val vparamAccessors = derivedVparamss match {
         case first :: rest =>
-          first.map(_.withMods(originalVparams.next.mods | caseAccessor)) ++
-          rest.flatten.map(_.withMods(originalVparams.next.mods))
+          first.map(_.withMods(originalVparamsIt.next.mods | caseAccessor)) ++
+          rest.flatten.map(_.withMods(originalVparamsIt.next.mods))
         case _ =>
           Nil
       }
@@ -503,23 +520,26 @@ object desugar {
    */
   def moduleDef(mdef: ModuleDef)(implicit ctx: Context): Tree = {
     val moduleName = checkNotReservedName(mdef).asTermName
-    val tmpl = mdef.impl
+    val impl = mdef.impl
     val mods = mdef.mods
+    lazy val isEnumCase = isLegalEnumCase(mdef)
     if (mods is Package)
-      PackageDef(Ident(moduleName), cpy.ModuleDef(mdef)(nme.PACKAGE, tmpl).withMods(mods &~ Package) :: Nil)
+      PackageDef(Ident(moduleName), cpy.ModuleDef(mdef)(nme.PACKAGE, impl).withMods(mods &~ Package) :: Nil)
+    else if (isEnumCase)
+      expandEnumModule(moduleName, impl, mods, mdef.pos)
     else {
       val clsName = moduleName.moduleClassName
       val clsRef = Ident(clsName)
       val modul = ValDef(moduleName, clsRef, New(clsRef, Nil))
         .withMods(mods | ModuleCreationFlags | mods.flags & AccessFlags)
         .withPos(mdef.pos)
-      val ValDef(selfName, selfTpt, _) = tmpl.self
-      val selfMods = tmpl.self.mods
-      if (!selfTpt.isEmpty) ctx.error(ObjectMayNotHaveSelfType(mdef), tmpl.self.pos)
-      val clsSelf = ValDef(selfName, SingletonTypeTree(Ident(moduleName)), tmpl.self.rhs)
+      val ValDef(selfName, selfTpt, _) = impl.self
+      val selfMods = impl.self.mods
+      if (!selfTpt.isEmpty) ctx.error(ObjectMayNotHaveSelfType(mdef), impl.self.pos)
+      val clsSelf = ValDef(selfName, SingletonTypeTree(Ident(moduleName)), impl.self.rhs)
         .withMods(selfMods)
-        .withPos(tmpl.self.pos orElse tmpl.pos.startPos)
-      val clsTmpl = cpy.Template(tmpl)(self = clsSelf, body = tmpl.body)
+        .withPos(impl.self.pos orElse impl.pos.startPos)
+      val clsTmpl = cpy.Template(impl)(self = clsSelf, body = impl.body)
       val cls = TypeDef(clsName, clsTmpl)
         .withMods(mods.toTypeFlags & RetainedModuleClassFlags | ModuleClassCreationFlags)
       Thicket(modul, classDef(cls).withPos(mdef.pos))
diff --git a/compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala b/compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala
new file mode 100644
index 000000000..4317c8183
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala
@@ -0,0 +1,124 @@
+package dotty.tools
+package dotc
+package ast
+
+import core._
+import util.Positions._, Types._, Contexts._, Constants._, Names._, NameOps._, Flags._
+import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._
+import Decorators._
+import collection.mutable.ListBuffer
+import util.Property
+import reporting.diagnostic.messages._
+
+object DesugarEnums {
+  import untpd._
+  import desugar.DerivedFromParamTree
+
+  val EnumCaseCount = new Property.Key[Int]
+
+  def enumClass(implicit ctx: Context) = ctx.owner.linkedClass
+
+  def nextEnumTag(implicit ctx: Context): Int = {
+    val result = ctx.tree.removeAttachment(EnumCaseCount).getOrElse(0)
+    ctx.tree.pushAttachment(EnumCaseCount, result + 1)
+    result
+  }
+
+  def isLegalEnumCase(tree: MemberDef)(implicit ctx: Context): Boolean = {
+    tree.mods.hasMod[Mod.EnumCase] &&
+    (  ctx.owner.is(ModuleClass) && enumClass.derivesFrom(defn.EnumClass)
+    || { ctx.error(em"case not allowed here, since owner ${ctx.owner} is not an `enum' object", tree.pos)
+         false
+       }
+    )
+  }
+
+  /** Type parameters reconstituted from the constructor
+   *  of the `enum' class corresponding to an enum case
+   */
+  def reconstitutedEnumTypeParams(pos: Position)(implicit ctx: Context) = {
+    val tparams = enumClass.primaryConstructor.info match {
+      case info: PolyType =>
+        ctx.newTypeParams(ctx.newLocalDummy(enumClass), info.paramNames, EmptyFlags, info.instantiateBounds)
+      case _ =>
+        Nil
+    }
+    for (tparam <- tparams) yield {
+      val tbounds = new DerivedFromParamTree
+      tbounds.pushAttachment(OriginalSymbol, tparam)
+      TypeDef(tparam.name, tbounds)
+        .withFlags(Param | PrivateLocal).withPos(pos)
+    }
+  }
+
+  def enumTagMeth(implicit ctx: Context) =
+    DefDef(nme.enumTag, Nil, Nil, TypeTree(), Literal(Constant(nextEnumTag)))
+
+  def enumClassRef(implicit ctx: Context) = TypeTree(enumClass.typeRef)
+
+  def addEnumFlags(cdef: TypeDef)(implicit ctx: Context) =
+    if (cdef.mods.hasMod[Mod.Enum]) cdef.withFlags(cdef.mods.flags | Abstract | Sealed)
+    else if (isLegalEnumCase(cdef)) cdef.withFlags(cdef.mods.flags | Final)
+    else cdef
+
+  /**  The following lists of definitions for an enum type E:
+   *
+   *   private val $values = new EnumValues[E]
+   *   def valueOf: Int => E = $values
+   *   def values = $values.values
+	 *
+   *   private def $new(tag: Int, name: String) = new E {
+   *     def enumTag = tag
+   *     override def toString = name
+   *     $values.register(this)
+   *   }
+   */
+  private def enumScaffolding(implicit ctx: Context): List[Tree] = {
+    val valsRef = Ident(nme.DOLLAR_VALUES)
+    def param(name: TermName, typ: Type) =
+      ValDef(name, TypeTree(typ), EmptyTree).withFlags(Param)
+    val privateValuesDef =
+      ValDef(nme.DOLLAR_VALUES, TypeTree(),
+             New(TypeTree(defn.EnumValuesType.appliedTo(enumClass.typeRef :: Nil)), ListOfNil))
+        .withFlags(Private)
+    val valueOfDef =
+      DefDef(nme.valueOf, Nil, Nil,
+          TypeTree(defn.FunctionOf(defn.IntType :: Nil, enumClass.typeRef)), valsRef)
+    val valuesDef =
+      DefDef(nme.values, Nil, Nil, TypeTree(), Select(valsRef, nme.values))
+    val enumTagDef =
+      DefDef(nme.enumTag, Nil, Nil, TypeTree(), Ident(nme.tag))
+    val toStringDef =
+      DefDef(nme.toString_, Nil, Nil, TypeTree(), Ident(nme.name))
+        .withFlags(Override)
+    val registerStat =
+      Apply(Select(valsRef, nme.register), This(EmptyTypeIdent) :: Nil)
+    def creator = New(Template(emptyConstructor, enumClassRef :: Nil, EmptyValDef,
+        List(enumTagDef, toStringDef, registerStat)))
+    val newDef =
+      DefDef(nme.DOLLAR_NEW, Nil,
+          List(List(param(nme.tag, defn.IntType), param(nme.name, defn.StringType))),
+          TypeTree(), creator)
+    List(privateValuesDef, valueOfDef, valuesDef, newDef)
+  }
+
+  def expandEnumModule(name: TermName, impl: Template, mods: Modifiers, pos: Position)(implicit ctx: Context): Tree = {
+    def nameLit = Literal(Constant(name.toString))
+    if (impl.parents.isEmpty) {
+      if (reconstitutedEnumTypeParams(pos).nonEmpty)
+        ctx.error(i"illegal enum value of generic $enumClass: an explicit `extends' clause is needed", pos)
+      val tag = nextEnumTag
+      val prefix = if (tag == 0) enumScaffolding else Nil
+      val creator = Apply(Ident(nme.DOLLAR_NEW), List(Literal(Constant(tag)), nameLit))
+      val vdef = ValDef(name, enumClassRef, creator).withMods(mods | Final).withPos(pos)
+      flatTree(prefix ::: vdef :: Nil).withPos(pos.startPos)
+    } else {
+      def toStringMeth =
+        DefDef(nme.toString_, Nil, Nil, TypeTree(defn.StringType), nameLit)
+          .withFlags(Override)
+      val impl1 = cpy.Template(impl)(body =
+        impl.body ++ List(enumTagMeth, toStringMeth))
+      ValDef(name, TypeTree(), New(impl1)).withMods(mods | Final).withPos(pos)
+    }
+  }
+}
diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 4d4350f98..39b46cbfe 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -512,6 +512,10 @@ class Definitions {
   def DynamicClass(implicit ctx: Context) = DynamicType.symbol.asClass
   lazy val OptionType: TypeRef                  = ctx.requiredClassRef("scala.Option")
   def OptionClass(implicit ctx: Context) = OptionType.symbol.asClass
+  lazy val EnumType: TypeRef                    = ctx.requiredClassRef("scala.Enum")
+  def EnumClass(implicit ctx: Context) = EnumType.symbol.asClass
+  lazy val EnumValuesType: TypeRef              = ctx.requiredClassRef("scala.runtime.EnumValues")
+  def EnumValuesClass(implicit ctx: Context) = EnumValuesType.symbol.asClass
   lazy val ProductType: TypeRef                 = ctx.requiredClassRef("scala.Product")
   def ProductClass(implicit ctx: Context) = ProductType.symbol.asClass
     lazy val Product_canEqualR = ProductClass.requiredMethodRef(nme.canEqual_)
diff --git a/compiler/src/dotty/tools/dotc/core/StdNames.scala b/compiler/src/dotty/tools/dotc/core/StdNames.scala
index 5b7dc3d1d..ff3ddbad7 100644
--- a/compiler/src/dotty/tools/dotc/core/StdNames.scala
+++ b/compiler/src/dotty/tools/dotc/core/StdNames.scala
@@ -132,6 +132,8 @@ object StdNames {
     val TRAIT_SETTER_SEPARATOR: N     = "$_setter_$"
     val DIRECT_SUFFIX: N              = "$direct"
     val LAZY_IMPLICIT_PREFIX: N       = "$lazy_implicit$"
+    val DOLLAR_VALUES: N              = "$values"
+    val DOLLAR_NEW: N                 = "$new"
 
     // value types (and AnyRef) are all used as terms as well
     // as (at least) arguments to the @specialize annotation.
@@ -395,6 +397,7 @@ object StdNames {
     val elem: N                 = "elem"
     val emptyValDef: N          = "emptyValDef"
     val ensureAccessible : N    = "ensureAccessible"
+    val enumTag: N              = "enumTag"
     val eq: N                   = "eq"
     val equalsNumChar : N       = "equalsNumChar"
     val equalsNumNum : N        = "equalsNumNum"
@@ -474,6 +477,7 @@ object StdNames {
     val productPrefix: N        = "productPrefix"
     val readResolve: N          = "readResolve"
     val reflect : N             = "reflect"
+    val register: N             = "register"
     val reify : N               = "reify"
     val rootMirror : N          = "rootMirror"
     val runOrElse: N            = "runOrElse"
@@ -499,6 +503,7 @@ object StdNames {
     val staticModule : N        = "staticModule"
     val staticPackage : N       = "staticPackage"
     val synchronized_ : N       = "synchronized"
+    val tag: N                  = "tag"
     val tail: N                 = "tail"
     val `then` : N              = "then"
     val this_ : N               = "this"
@@ -523,7 +528,7 @@ object StdNames {
     val updateDynamic: N        = "updateDynamic"
     val value: N                = "value"
     val valueOf : N             = "valueOf"
-    val values : N              = "values"
+    val values: N               = "values"
     val view_ : N               = "view"
     val wait_ : N               = "wait"
     val withFilter: N           = "withFilter"
diff --git a/library/src/scala/Enum.scala b/library/src/scala/Enum.scala
new file mode 100644
index 000000000..7d2eefb3d
--- /dev/null
+++ b/library/src/scala/Enum.scala
@@ -0,0 +1,8 @@
+package scala
+
+/** A base trait of all enum classes */
+trait Enum {
+
+  /** A number uniquely identifying a case of an enum */
+  def enumTag: Int
+}
diff --git a/library/src/scala/runtime/EnumValues.scala b/library/src/scala/runtime/EnumValues.scala
new file mode 100644
index 000000000..6d2e56cf3
--- /dev/null
+++ b/library/src/scala/runtime/EnumValues.scala
@@ -0,0 +1,18 @@
+package scala.runtime
+
+import scala.collection.immutable.Seq
+import scala.collection.mutable.ResizableArray
+
+class EnumValues[E <: Enum] extends ResizableArray[E] {
+  private var valuesCache: List[E] = Nil
+  def register(v: E) = {
+    ensureSize(v.enumTag + 1)
+    size0 = size0 max (v.enumTag + 1)
+    array(v.enumTag) = v
+    valuesCache = null
+  }
+  def values: Seq[E] = {
+    if (valuesCache == null) valuesCache = array.filter(_ != null).toList.asInstanceOf[scala.List[E]]
+    valuesCache
+  }
+}