make fromOrdinal public and always available

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

@@ -154,22 +154,29 @@ object DesugarEnums {
   private def enumLookupMethods(constraints: EnumConstraints)(using Context): List[Tree] =
     def scaffolding: List[Tree] = if constraints.cached then enumScaffolding(constraints.enumCases.map(_._2)) else Nil
     def valueCtor: List[Tree] = if constraints.requiresCreator then enumValueCreator :: Nil else Nil
-    def byOrdinal: List[Tree] =
-      if isJavaEnum || !constraints.cached then Nil
+    def fromOrdinal: Tree =
+      def throwArg(ordinal: Tree) =
+        Throw(New(TypeTree(defn.NoSuchElementExceptionType), List(Select(ordinal, nme.toString_) :: Nil)))
+      if !constraints.cached then
+        fromOrdinalMeth(throwArg)
       else
-        val defaultCase =
-          val ord = Ident(nme.ordinal)
-          val err = Throw(New(TypeTree(defn.IndexOutOfBoundsException.typeRef), List(Select(ord, nme.toString_) :: Nil)))
-          CaseDef(ord, EmptyTree, err)
-        val valueCases = constraints.enumCases.map((i, enumValue) =>
-          CaseDef(Literal(Constant(i)), EmptyTree, enumValue)
-        ) ::: defaultCase :: Nil
-        val fromOrdinalDef = DefDef(nme.fromOrdinalDollar, Nil, List(param(nme.ordinalDollar_, defn.IntType) :: Nil),
-          rawRef(enumClass.typeRef), Match(Ident(nme.ordinalDollar_), valueCases))
-            .withFlags(Synthetic | Private)
-        fromOrdinalDef :: Nil
-
-    scaffolding ::: valueCtor ::: byOrdinal
+        def default(ordinal: Tree) =
+          CaseDef(Ident(nme.WILDCARD), EmptyTree, throwArg(ordinal))
+        if constraints.isEnumeration then
+          fromOrdinalMeth(ordinal =>
+            Try(Apply(valuesDot(nme.apply), ordinal), default(ordinal) :: Nil, EmptyTree))
+        else
+          fromOrdinalMeth(ordinal =>
+            Match(ordinal,
+              constraints.enumCases.map((i, enumValue) => CaseDef(Literal(Constant(i)), EmptyTree, enumValue))
+              :+ default(ordinal)))
+
+    if !enumClass.exists then
+      // in the case of a double definition of an enum that only defines class cases (see tests/neg/i4470c.scala)
+      // it seems `enumClass` might be `NoSymbol`; in this case we provide no scaffolding.
+      Nil
+    else
+      scaffolding ::: valueCtor ::: fromOrdinal :: Nil
   end enumLookupMethods
 
   /** A creation method for a value of enum type `E`, which is defined as follows:
@@ -278,6 +285,10 @@ object DesugarEnums {
   def ordinalMethLit(ord: Int)(using Context): DefDef =
     ordinalMeth(Literal(Constant(ord)))
 
+  def fromOrdinalMeth(body: Tree => Tree)(using Context): DefDef =
+    DefDef(nme.fromOrdinal, Nil, (param(nme.ordinal, defn.IntType) :: Nil) :: Nil,
+      rawRef(enumClass.typeRef), body(Ident(nme.ordinal))).withFlags(Synthetic)
+
   /** Expand a module definition representing a parameterless enum case */
   def expandEnumModule(name: TermName, impl: Template, mods: Modifiers, definesLookups: Boolean, span: Span)(using Context): Tree = {
     assert(impl.body.isEmpty)

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

@@ -617,7 +617,7 @@ object StdNames {
     val using: N                = "using"
     val value: N                = "value"
     val valueOf : N             = "valueOf"
-    val fromOrdinalDollar: N    = "$fromOrdinal"
+    val fromOrdinal: N          = "fromOrdinal"
     val values: N               = "values"
     val view_ : N               = "view"
     val wait_ : N               = "wait"

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

@@ -429,7 +429,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
    *  and not deriving from `java.lang.Enum` add the method:
    *
    *      private def readResolve(): AnyRef =
-   *        MyEnum.$fromOrdinal(this.ordinal)
+   *        MyEnum.fromOrdinal(this.ordinal)
    *
    *  unless an implementation already exists, otherwise do nothing.
    */
@@ -443,7 +443,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
       List(
         DefDef(readResolveDef(clazz),
           _ => ref(clazz.owner.owner.sourceModule)
-                .select(nme.fromOrdinalDollar)
+                .select(nme.fromOrdinal)
                 .appliedTo(This(clazz).select(nme.ordinal).ensureApplied))
           .withSpan(ctx.owner.span.focus))
     else

tests/neg/i4470c.scala

@@ -1,9 +1,31 @@
 object DuplicatedEnum {
+
   enum Maybe[+T] { // error
     case Some[T](x: T) extends Maybe[T]
   }
 
   enum Maybe[+T] { // error
     case Some[T](x: T) extends Maybe[T]
   }
+
+  enum Color { // error
+    case Red, Green, Blue
+  }
+
+  enum Color { // error
+    case Red, Green, Blue
+  }
+
+  enum Tag[T] { // error
+    case Int extends Tag[Int]
+    case OfClass[T]()(using val tag: reflect.ClassTag[T]) extends Tag[T] // mix order of class and value
+    case String extends Tag[String]
+  }
+
+  enum Tag[T] { // error
+    case Int extends Tag[Int]
+    case OfClass[T]()(using val tag: reflect.ClassTag[T]) extends Tag[T] // mix order of class and value
+    case String extends Tag[String]
+  }
+
 }

tests/run/enum-values.scala

@@ -1,10 +1,16 @@
+import reflect.Selectable.reflectiveSelectable
+import deriving.Mirror
+
 enum Color:
   case Red, Green, Blue
 
+enum Suits extends java.lang.Enum[Suits]:
+  case Clubs, Spades, Diamonds, Hearts
+
 enum Tag[T]:
   case Int extends Tag[Int]
+  case OfClass[T]()(using val tag: reflect.ClassTag[T]) extends Tag[T] // mix order of class and value
   case String extends Tag[String]
-  case OfClass[T]()(using val tag: reflect.ClassTag[T]) extends Tag[T]
 
 enum Expr[-T >: Null]:
   case EmptyTree extends Expr[Null]
@@ -16,18 +22,64 @@ enum ListLike[+T]:
 
 enum TypeCtorsK[F[_]]:
   case List       extends TypeCtorsK[List]
+  case Const[T]() extends TypeCtorsK[[U] =>> T] // mix order of class and value
   case Option     extends TypeCtorsK[Option]
-  case Const[T]() extends TypeCtorsK[[U] =>> T]
 
 enum MixedParams[F[_], G[X,Y] <: collection.Map[X,Y], T]:
   case Foo extends MixedParams[List, collection.mutable.LinkedHashMap, Unit]
 
+enum ClassOnly: // this should still generate the `ordinal` and `fromOrdinal` companion methods
+  case BranchProd(i: Int)
+
 @main def Test: Unit =
-  import Color._, Tag._, Expr._, ListLike._, TypeCtorsK._, MixedParams._
-  import reflect.Selectable.reflectiveSelectable
+  import Color._, Suits._, Tag._, Expr._, ListLike._, TypeCtorsK._, MixedParams._, ClassOnly._
+
+  type FromOrdinal[T] = {
+    def fromOrdinal(ordinal: Int): T
+  }
+
+  type ValueOf[T] = {
+    def valueOf(s: String): T
+  }
 
   extension [A](t: A) def show = runtime.ScalaRunTime.stringOf(t)
 
+  def fetchFromOrdinal[T <: AnyRef & reflect.Enum](companion: FromOrdinal[T], compare: T*): Unit =
+    for c <- compare do
+      assert(companion.fromOrdinal(c.ordinal) eq c,
+        s"$c does not `eq` companion.fromOrdinal(${c.ordinal}), got ${companion.fromOrdinal(c.ordinal)}")
+
+  def notFromOrdinal[T <: AnyRef & reflect.Enum](companion: FromOrdinal[T], compare: T): Unit =
+    cantFind(companion, compare.ordinal)
+
+  def cantFind[T](companion: FromOrdinal[T], ordinal: Int): Unit =
+    try
+      companion.fromOrdinal(ordinal)
+      assertFail(s"$companion.fromOrdinal(${ordinal}) did not fail")
+    catch
+      case e: java.lang.reflect.InvocationTargetException => // TODO: maybe reflect.Selectable should catch this?
+        assert(e.getCause.isInstanceOf[java.util.NoSuchElementException]
+          && e.getCause.getMessage == ordinal.toString)
+
+  fetchFromOrdinal(companion = Color,       compare = Red, Green, Blue)
+  fetchFromOrdinal(companion = Suits,       compare = Clubs, Spades, Diamonds, Hearts)
+  fetchFromOrdinal(companion = Tag,         compare = Int, String)
+  fetchFromOrdinal(companion = Expr,        compare = EmptyTree, AnyTree)
+  fetchFromOrdinal(companion = ListLike,    compare = EmptyListLike)
+  fetchFromOrdinal(companion = TypeCtorsK,  compare = List, Option)
+  fetchFromOrdinal(companion = MixedParams, compare = Foo)
+
+  notFromOrdinal(companion = Tag,        compare = OfClass[String]())
+  notFromOrdinal(companion = TypeCtorsK, compare = Const[String]())
+  notFromOrdinal(companion = ClassOnly,  compare = BranchProd(1)) // ClassOnly has the `fromOrdinal` method
+
+  cantFind(companion = Color,     ordinal = 500) // test default case for enumeration
+  cantFind(companion = Suits,     ordinal = 500) // test default case for Java style enumeration
+  cantFind(companion = Tag,       ordinal = 500) // test default case for mixed adt with non-simple values
+  cantFind(companion = ClassOnly, ordinal = 500) // should always throw
+
+  assert(summon[Mirror.SumOf[ClassOnly]].ordinal(BranchProd(1)) == 0)
+
   val colors: Array[Color]             = Color.values
   val tags: Array[Tag[?]]              = Tag.values
   val exprs: Array[Expr[? >: Null]]    = Expr.values
@@ -46,7 +98,7 @@ enum MixedParams[F[_], G[X,Y] <: collection.Map[X,Y], T]:
   sameAs(typeCtorsK,  List, Option)
   sameAs(mixedParams, Foo)
 
-  def singleton[E <: AnyRef](value: E, name: String, companion: { def valueOf(s: String): E}) =
+  def singleton[E <: AnyRef](value: E, name: String, companion: ValueOf[E]) =
     val lookup = companion.valueOf(name)
     assert(value eq lookup, s"${value.show} is not identical to ${lookup.show}")
 

tests/semanticdb/metac.expect

@@ -641,7 +641,7 @@ Schema => SemanticDB v4
 Uri => Enums.scala
 Text => empty
 Language => Scala
-Symbols => 181 entries
+Symbols => 185 entries
 Occurrences => 203 entries
 
 Symbols:
@@ -651,37 +651,35 @@ _empty_/Enums.Coin#`<init>`(). => primary ctor <init>
 _empty_/Enums.Coin#`<init>`().(value) => param value
 _empty_/Enums.Coin#value. => val method value
 _empty_/Enums.Coin. => final object Coin
-_empty_/Enums.Coin.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Coin.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Coin.$values. => val method $values
 _empty_/Enums.Coin.Dime. => case val static enum method Dime
 _empty_/Enums.Coin.Dollar. => case val static enum method Dollar
 _empty_/Enums.Coin.Nickel. => case val static enum method Nickel
 _empty_/Enums.Coin.Penny. => case val static enum method Penny
 _empty_/Enums.Coin.Quarter. => case val static enum method Quarter
+_empty_/Enums.Coin.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Coin.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Coin.valueOf(). => method valueOf
 _empty_/Enums.Coin.valueOf().($name) => param $name
 _empty_/Enums.Coin.values(). => method values
 _empty_/Enums.Colour# => abstract sealed enum class Colour
 _empty_/Enums.Colour#`<init>`(). => primary ctor <init>
 _empty_/Enums.Colour. => final object Colour
-_empty_/Enums.Colour.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Colour.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Colour.$new(). => method $new
 _empty_/Enums.Colour.$new().($name) => param $name
 _empty_/Enums.Colour.$new().(_$ordinal) => param _$ordinal
 _empty_/Enums.Colour.$values. => val method $values
 _empty_/Enums.Colour.Blue. => case val static enum method Blue
 _empty_/Enums.Colour.Green. => case val static enum method Green
 _empty_/Enums.Colour.Red. => case val static enum method Red
+_empty_/Enums.Colour.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Colour.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Colour.valueOf(). => method valueOf
 _empty_/Enums.Colour.valueOf().($name) => param $name
 _empty_/Enums.Colour.values(). => method values
 _empty_/Enums.Directions# => abstract sealed enum class Directions
 _empty_/Enums.Directions#`<init>`(). => primary ctor <init>
 _empty_/Enums.Directions. => final object Directions
-_empty_/Enums.Directions.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Directions.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Directions.$new(). => method $new
 _empty_/Enums.Directions.$new().($name) => param $name
 _empty_/Enums.Directions.$new().(_$ordinal) => param _$ordinal
@@ -690,15 +688,15 @@ _empty_/Enums.Directions.East. => case val static enum method East
 _empty_/Enums.Directions.North. => case val static enum method North
 _empty_/Enums.Directions.South. => case val static enum method South
 _empty_/Enums.Directions.West. => case val static enum method West
+_empty_/Enums.Directions.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Directions.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Directions.valueOf(). => method valueOf
 _empty_/Enums.Directions.valueOf().($name) => param $name
 _empty_/Enums.Directions.values(). => method values
 _empty_/Enums.Maybe# => abstract sealed enum class Maybe
 _empty_/Enums.Maybe#[A] => covariant typeparam A
 _empty_/Enums.Maybe#`<init>`(). => primary ctor <init>
 _empty_/Enums.Maybe. => final object Maybe
-_empty_/Enums.Maybe.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Maybe.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Maybe.$values. => val method $values
 _empty_/Enums.Maybe.Just# => final case enum class Just
 _empty_/Enums.Maybe.Just#[A] => covariant typeparam A
@@ -721,6 +719,8 @@ _empty_/Enums.Maybe.Just.unapply(). => method unapply
 _empty_/Enums.Maybe.Just.unapply().(x$1) => param x$1
 _empty_/Enums.Maybe.Just.unapply().[A] => typeparam A
 _empty_/Enums.Maybe.None. => case val static enum method None
+_empty_/Enums.Maybe.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Maybe.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Maybe.valueOf(). => method valueOf
 _empty_/Enums.Maybe.valueOf().($name) => param $name
 _empty_/Enums.Maybe.values(). => method values
@@ -744,14 +744,14 @@ _empty_/Enums.Planet.Neptune. => case val static enum method Neptune
 _empty_/Enums.Planet.Saturn. => case val static enum method Saturn
 _empty_/Enums.Planet.Uranus. => case val static enum method Uranus
 _empty_/Enums.Planet.Venus. => case val static enum method Venus
+_empty_/Enums.Planet.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Planet.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Planet.valueOf(). => method valueOf
 _empty_/Enums.Planet.valueOf().($name) => param $name
 _empty_/Enums.Planet.values(). => method values
 _empty_/Enums.Suits# => abstract sealed enum class Suits
 _empty_/Enums.Suits#`<init>`(). => primary ctor <init>
 _empty_/Enums.Suits. => final object Suits
-_empty_/Enums.Suits.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Suits.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Suits.$new(). => method $new
 _empty_/Enums.Suits.$new().($name) => param $name
 _empty_/Enums.Suits.$new().(_$ordinal) => param _$ordinal
@@ -765,26 +765,26 @@ _empty_/Enums.Suits.extension_isBlack(). => method extension_isBlack
 _empty_/Enums.Suits.extension_isBlack().(suit) => param suit
 _empty_/Enums.Suits.extension_isRed(). => method extension_isRed
 _empty_/Enums.Suits.extension_isRed().(suit) => param suit
+_empty_/Enums.Suits.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Suits.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Suits.valueOf(). => method valueOf
 _empty_/Enums.Suits.valueOf().($name) => param $name
 _empty_/Enums.Suits.values(). => method values
 _empty_/Enums.Tag# => abstract sealed enum class Tag
 _empty_/Enums.Tag#[A] => typeparam A
 _empty_/Enums.Tag#`<init>`(). => primary ctor <init>
 _empty_/Enums.Tag. => final object Tag
-_empty_/Enums.Tag.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.Tag.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.Tag.$values. => val method $values
 _empty_/Enums.Tag.BooleanTag. => case val static enum method BooleanTag
 _empty_/Enums.Tag.IntTag. => case val static enum method IntTag
+_empty_/Enums.Tag.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.Tag.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.Tag.valueOf(). => method valueOf
 _empty_/Enums.Tag.valueOf().($name) => param $name
 _empty_/Enums.Tag.values(). => method values
 _empty_/Enums.WeekDays# => abstract sealed enum class WeekDays
 _empty_/Enums.WeekDays#`<init>`(). => primary ctor <init>
 _empty_/Enums.WeekDays. => final object WeekDays
-_empty_/Enums.WeekDays.$fromOrdinal(). => method $fromOrdinal
-_empty_/Enums.WeekDays.$fromOrdinal().(_$ordinal) => param _$ordinal
 _empty_/Enums.WeekDays.$new(). => method $new
 _empty_/Enums.WeekDays.$new().($name) => param $name
 _empty_/Enums.WeekDays.$new().(_$ordinal) => param _$ordinal
@@ -796,6 +796,8 @@ _empty_/Enums.WeekDays.Sunday. => case val static enum method Sunday
 _empty_/Enums.WeekDays.Thursday. => case val static enum method Thursday
 _empty_/Enums.WeekDays.Tuesday. => case val static enum method Tuesday
 _empty_/Enums.WeekDays.Wednesday. => case val static enum method Wednesday
+_empty_/Enums.WeekDays.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.WeekDays.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.WeekDays.valueOf(). => method valueOf
 _empty_/Enums.WeekDays.valueOf().($name) => param $name
 _empty_/Enums.WeekDays.values(). => method values
@@ -817,6 +819,8 @@ _empty_/Enums.`<:<`.Refl.toString(). => method toString
 _empty_/Enums.`<:<`.Refl.unapply(). => method unapply
 _empty_/Enums.`<:<`.Refl.unapply().(x$1) => param x$1
 _empty_/Enums.`<:<`.Refl.unapply().[C] => typeparam C
+_empty_/Enums.`<:<`.fromOrdinal(). => method fromOrdinal
+_empty_/Enums.`<:<`.fromOrdinal().(ordinal) => param ordinal
 _empty_/Enums.`<:<`.given_T(). => final implicit method given_T
 _empty_/Enums.`<:<`.given_T().[T] => typeparam T
 _empty_/Enums.extension_unwrap(). => method extension_unwrap