Move EnumValue to scala.runtime

It is no longer visible in the types of enum constants, so no need to
keep it in Scala.

Also, update doc pages to match the new scheme.

Author: odersky

compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala

@@ -124,7 +124,7 @@ object DesugarEnums {
 
   /** A creation method for a value of enum type `E`, which is defined as follows:
    *
-   *   private def $new(_$ordinal: Int, $name: String) = new E with EnumValue {
+   *   private def $new(_$ordinal: Int, $name: String) = new E with scala.runtime.EnumValue {
    *     def $ordinal = $tag
    *     override def toString = $name
    *     $values.register(this)
@@ -135,7 +135,7 @@ object DesugarEnums {
     val toStringDef = toStringMeth(Ident(nme.nameDollar))
     val creator = New(Template(
       constr = emptyConstructor,
-      parents = enumClassRef :: scalaDot(str.EnumValue.toTypeName) :: Nil,
+      parents = enumClassRef :: scalaRuntimeDot(tpnme.EnumValue) :: Nil,
       derived = Nil,
       self = EmptyValDef,
       body = List(ordinalDef, toStringDef) ++ registerCall
@@ -287,7 +287,7 @@ object DesugarEnums {
       val ordinalDef = ordinalMethLit(tag)
       val toStringDef = toStringMethLit(name.toString)
       val impl1 = cpy.Template(impl)(
-        parents = impl.parents :+ scalaDot(str.EnumValue.toTypeName),
+        parents = impl.parents :+ scalaRuntimeDot(tpnme.EnumValue),
         body = List(ordinalDef, toStringDef) ++ registerCall)
         .withAttachment(ExtendsSingletonMirror, ())
       val vdef = ValDef(name, TypeTree(), New(impl1)).withMods(mods.withAddedFlags(EnumValue, span))

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -450,6 +450,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def rootDot(name: Name)(implicit src: SourceFile): Select = Select(Ident(nme.ROOTPKG), name)
   def scalaDot(name: Name)(implicit src: SourceFile): Select = Select(rootDot(nme.scala), name)
   def scalaAnnotationDot(name: Name)(using SourceFile): Select = Select(scalaDot(nme.annotation), name)
+  def scalaRuntimeDot(name: Name)(using SourceFile): Select = Select(scalaDot(nme.runtime), name)
   def scalaUnit(implicit src: SourceFile): Select = scalaDot(tpnme.Unit)
   def scalaAny(implicit src: SourceFile): Select = scalaDot(tpnme.Any)
   def javaDotLangDot(name: Name)(implicit src: SourceFile): Select = Select(Select(Ident(nme.java), nme.lang), name)

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

@@ -639,7 +639,7 @@ class Definitions {
   @tu lazy val EnumClass: ClassSymbol = ctx.requiredClass("scala.Enum")
     @tu lazy val Enum_ordinal: Symbol = EnumClass.requiredMethod(nme.ordinal)
 
-  @tu lazy val EnumValueClass: ClassSymbol = ctx.requiredClass("scala.EnumValue")
+  @tu lazy val EnumValueClass: ClassSymbol = ctx.requiredClass("scala.runtime.EnumValue")
   @tu lazy val EnumValuesClass: ClassSymbol = ctx.requiredClass("scala.runtime.EnumValues")
   @tu lazy val ProductClass: ClassSymbol = ctx.requiredClass("scala.Product")
     @tu lazy val Product_canEqual          : Symbol = ProductClass.requiredMethod(nme.canEqual_)

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

@@ -33,7 +33,6 @@ object StdNames {
 
     final val MODULE_INSTANCE_FIELD      = "MODULE$"
 
-    final val EnumValue                  = "EnumValue"
     final val Function                   = "Function"
     final val ErasedFunction             = "ErasedFunction"
     final val ContextFunction            = "ContextFunction"
@@ -358,15 +357,14 @@ object StdNames {
     val CAP: N                  = "CAP"
     val Constant: N             = "Constant"
     val ConstantType: N         = "ConstantType"
-    val doubleHash: N           = "doubleHash"
+    val EnumValue: N            = "EnumValue"
     val ExistentialTypeTree: N  = "ExistentialTypeTree"
     val Flag : N                = "Flag"
     val floatHash: N            = "floatHash"
     val Ident: N                = "Ident"
     val Import: N               = "Import"
     val Literal: N              = "Literal"
     val LiteralAnnotArg: N      = "LiteralAnnotArg"
-    val longHash: N             = "longHash"
     val MatchCase: N            = "MatchCase"
     val MirroredElemTypes: N    = "MirroredElemTypes"
     val MirroredElemLabels: N   = "MirroredElemLabels"
@@ -444,6 +442,7 @@ object StdNames {
     val delayedInitArg: N       = "delayedInit$body"
     val derived: N              = "derived"
     val derives: N              = "derives"
+    val doubleHash: N           = "doubleHash"
     val drop: N                 = "drop"
     val dynamics: N             = "dynamics"
     val elem: N                 = "elem"
@@ -506,6 +505,7 @@ object StdNames {
     val language: N             = "language"
     val length: N               = "length"
     val lengthCompare: N        = "lengthCompare"
+    val longHash: N             = "longHash"
     val macroThis : N           = "_this"
     val macroContext : N        = "c"
     val main: N                 = "main"

docs/docs/reference/enums/desugarEnums.md

@@ -126,7 +126,9 @@ map into `case class`es or `val`s.
    where `n` is the ordinal number of the case in the companion object,
    starting from 0.  The statement `$values.register(this)` registers the value
    as one of the `values` of the enumeration (see below). `$values` is a
-   compiler-defined private value in the companion object.
+   compiler-defined private value in the companion object. The anonymous class also
+   implements the abstract `Product` methods that it inherits from `Enum`.
+
 
    It is an error if a value case refers to a type parameter of the enclosing `enum`
    in a type argument of `<parents>`.
@@ -178,6 +180,7 @@ Companion objects of enumerations that contain at least one simple case define i
      }
      ```
 
+The anonymous class also implements the abstract `Product` methods that it inherits from `Enum`.
 The `$ordinal` method above is used to generate the `ordinal` method if the enum does not extend a `java.lang.Enum` (as Scala enums do not extend `java.lang.Enum`s unless explicitly specified). In case it does, there is no need to generate `ordinal` as `java.lang.Enum` defines it.
 
 ### Scopes for Enum Cases

docs/docs/reference/enums/enums.md

@@ -95,7 +95,7 @@ If you want to use the Scala-defined enums as Java enums, you can do so by exten
 enum Color extends java.lang.Enum[Color] { case Red, Green, Blue }
 ```
 
-The type parameter comes from the Java enum [definition](https://docs.oracle.com/javase/8/docs/api/index.html?java/lang/Enum.html) and should be the same as the type of the enum. 
+The type parameter comes from the Java enum [definition](https://docs.oracle.com/javase/8/docs/api/index.html?java/lang/Enum.html) and should be the same as the type of the enum.
 There is no need to provide constructor arguments (as defined in the Java API docs) to `java.lang.Enum` when extending it – the compiler will generate them automatically.
 
 After defining `Color` like that, you can use it like you would a Java enum:
@@ -116,7 +116,7 @@ This trait defines a single public method, `ordinal`:
 package scala
 
 /** A base trait of all enum classes */
-trait Enum {
+trait Enum extends Product with Serializable {
 
   /** A number uniquely identifying a case of an enum */
   def ordinal: Int

library/src/scala/EnumValue.scala renamed to library/src/scala/runtime/EnumValue.scala

@@ -1,4 +1,4 @@
-package scala
+package scala.runtime
 
 trait EnumValue extends Product, Serializable:
   override def canEqual(that: Any) = this eq that.asInstanceOf[AnyRef]

tests/neg/enumvalues.scala

@@ -1,11 +1,15 @@
 enum Color:
   case Red, Green, Blue
 
+enum Option[+T]
+  case None extends Option[Nothing]
+
+import scala.runtime.EnumValue
+
 @main def Test(c: Boolean) =
-  // These currently give errors. But maybe we should make the actual
-  // enum values carry the `EnumValue` trait, and only strip it from
-  // user-defined vals and defs?
+  // Verify that enum constants don't leak the scala.runtime.EnumValue trait
   val x: EnumValue = if c then Color.Red else Color.Blue // error // error
   val y: EnumValue = Color.Green        // error
+  val z: EnumValue = Option.None        // error
 
 

tests/pos/enum-List-control.scala

@@ -11,7 +11,7 @@ object List {
   object Cons {
     def apply[T](x: T, xs: List[T]): List[T] = new Cons(x, xs)
   }
-  final class Nil[T]() extends List[T], EnumValue {
+  final class Nil[T]() extends List[T], runtime.EnumValue {
     def $ordinal = 1
   }
   object Nil {