Merge pull request #9539 from dotty-staging/topic/enum-reduce-bytecode

remove dollar ordinal from Enum

Author: bishabosha

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

@@ -125,20 +125,24 @@ 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 scala.runtime.EnumValue {
-   *     def $ordinal = $tag
-   *     override def toString = $name
+   *     def ordinal = _$ordinal       // if `E` does not derive from jl.Enum
+   *     override def toString = $name // if `E` does not derive from jl.Enum
    *     $values.register(this)
    *   }
    */
   private def enumValueCreator(using Context) = {
-    val ordinalDef = ordinalMeth(Ident(nme.ordinalDollar_))
-    val toStringDef = toStringMeth(Ident(nme.nameDollar))
+    val fieldMethods =
+        if isJavaEnum then Nil
+        else
+          val ordinalDef  = ordinalMeth(Ident(nme.ordinalDollar_))
+          val toStringDef = toStringMeth(Ident(nme.nameDollar))
+          List(ordinalDef, toStringDef)
     val creator = New(Template(
       constr = emptyConstructor,
       parents = enumClassRef :: scalaRuntimeDot(tpnme.EnumValue) :: Nil,
       derived = Nil,
       self = EmptyValDef,
-      body = ordinalDef :: toStringDef :: registerCall :: Nil
+      body = fieldMethods ::: registerCall :: Nil
     ).withAttachment(ExtendsSingletonMirror, ()))
     DefDef(nme.DOLLAR_NEW, Nil,
         List(List(param(nme.ordinalDollar_, defn.IntType), param(nme.nameDollar, defn.StringType))),
@@ -264,8 +268,10 @@ object DesugarEnums {
   def param(name: TermName, typ: Type)(using Context) =
     ValDef(name, TypeTree(typ), EmptyTree).withFlags(Param)
 
+  private def isJavaEnum(using Context): Boolean = ctx.owner.linkedClass.derivesFrom(defn.JavaEnumClass)
+
   def ordinalMeth(body: Tree)(using Context): DefDef =
-    DefDef(nme.ordinalDollar, Nil, Nil, TypeTree(defn.IntType), body)
+    DefDef(nme.ordinal, Nil, Nil, TypeTree(defn.IntType), body)
 
   def toStringMeth(body: Tree)(using Context): DefDef =
     DefDef(nme.toString_, Nil, Nil, TypeTree(defn.StringType), body).withFlags(Override)
@@ -284,12 +290,16 @@ object DesugarEnums {
       expandSimpleEnumCase(name, mods, span)
     else {
       val (tag, scaffolding) = nextOrdinal(CaseKind.Object)
-      val ordinalDef = ordinalMethLit(tag)
-      val toStringDef = toStringMethLit(name.toString)
+      val fieldMethods =
+        if isJavaEnum then Nil
+        else
+          val ordinalDef  = ordinalMethLit(tag)
+          val toStringDef = toStringMethLit(name.toString)
+          List(ordinalDef, toStringDef)
       val impl1 = cpy.Template(impl)(
         parents = impl.parents :+ scalaRuntimeDot(tpnme.EnumValue),
-        body = ordinalDef :: toStringDef :: registerCall :: Nil
-      ).withAttachment(ExtendsSingletonMirror, ())
+        body = fieldMethods ::: registerCall :: Nil)
+        .withAttachment(ExtendsSingletonMirror, ())
       val vdef = ValDef(name, TypeTree(), New(impl1)).withMods(mods.withAddedFlags(EnumValue, span))
       flatTree(scaffolding ::: vdef :: Nil).withSpan(span)
     }

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

@@ -15,6 +15,8 @@ import DenotTransformers._
 import dotty.tools.dotc.ast.Trees._
 import SymUtils._
 
+import annotation.threadUnsafe
+
 object CompleteJavaEnums {
   val name: String = "completeJavaEnums"
 
@@ -62,9 +64,10 @@ class CompleteJavaEnums extends MiniPhase with InfoTransformer { thisPhase =>
   /** The list of parameter definitions `$name: String, $ordinal: Int`, in given `owner`
    *  with given flags (either `Param` or `ParamAccessor`)
    */
-  private def addedParams(owner: Symbol, flag: FlagSet)(using Context): List[ValDef] = {
-    val nameParam = newSymbol(owner, nameParamName, flag | Synthetic, defn.StringType, coord = owner.span)
-    val ordinalParam = newSymbol(owner, ordinalParamName, flag | Synthetic, defn.IntType, coord = owner.span)
+  private def addedParams(owner: Symbol, isLocal: Boolean, flag: FlagSet)(using Context): List[ValDef] = {
+    val flags = flag | Synthetic | (if isLocal then Private | Deferred else EmptyFlags)
+    val nameParam = newSymbol(owner, nameParamName, flags, defn.StringType, coord = owner.span)
+    val ordinalParam = newSymbol(owner, ordinalParamName, flags, defn.IntType, coord = owner.span)
     List(ValDef(nameParam), ValDef(ordinalParam))
   }
 
@@ -85,7 +88,7 @@ class CompleteJavaEnums extends MiniPhase with InfoTransformer { thisPhase =>
     val sym = tree.symbol
     if (sym.isConstructor && sym.owner.derivesFromJavaEnum)
       val tree1 = cpy.DefDef(tree)(
-        vparamss = tree.vparamss.init :+ (tree.vparamss.last ++ addedParams(sym, Param)))
+        vparamss = tree.vparamss.init :+ (tree.vparamss.last ++ addedParams(sym, isLocal=false, Param)))
       sym.setParamssFromDefs(tree1.tparams, tree1.vparamss)
       tree1
     else tree
@@ -107,47 +110,68 @@ class CompleteJavaEnums extends MiniPhase with InfoTransformer { thisPhase =>
     }
   }
 
+  private def isJavaEnumValueImpl(cls: Symbol)(using Context): Boolean =
+    cls.isAnonymousClass
+    && (((cls.owner.name eq nme.DOLLAR_NEW) && cls.owner.isAllOf(Private|Synthetic)) || cls.owner.isAllOf(EnumCase))
+    && cls.owner.owner.linkedClass.derivesFromJavaEnum
+
+  private val enumCaseOrdinals: MutableSymbolMap[Int] = newMutableSymbolMap
+
+  private def registerEnumClass(cls: Symbol)(using Context): Unit =
+    cls.children.zipWithIndex.foreach(enumCaseOrdinals.put)
+
+  private def ordinalFor(enumCase: Symbol): Int =
+    enumCaseOrdinals.remove(enumCase).get
+
   /** 1. If this is an enum class, add $name and $ordinal parameters to its
    *     parameter accessors and pass them on to the java.lang.Enum constructor.
    *
-   *  2. If this is an anonymous class that implement a value enum case,
+   *  2. If this is an anonymous class that implement a singleton enum case,
    *     pass $name and $ordinal parameters to the enum superclass. The class
    *     looks like this:
    *
    *       class $anon extends E(...) {
    *          ...
-   *          def ordinal = N
-   *          def toString = S
-   *          ...
    *       }
    *
    *     After the transform it is expanded to
    *
-   *       class $anon extends E(..., N, S) {
-   *         "same as before"
+   *       class $anon extends E(..., $name, _$ordinal) { // if class implements a simple enum case
+   *          "same as before"
+   *       }
+   *
+   *       class $anon extends E(..., "A", 0) { // if class implements a value enum case `A` with ordinal 0
+   *          "same as before"
    *       }
    */
-  override def transformTemplate(templ: Template)(using Context): Template = {
+  override def transformTemplate(templ: Template)(using Context): Tree = {
     val cls = templ.symbol.owner
-    if (cls.derivesFromJavaEnum) {
+    if cls.derivesFromJavaEnum then
+      registerEnumClass(cls) // invariant: class is visited before cases: see tests/pos/enum-companion-first.scala
       val (params, rest) = decomposeTemplateBody(templ.body)
-      val addedDefs = addedParams(cls, ParamAccessor)
+      val addedDefs = addedParams(cls, isLocal=true, ParamAccessor)
       val addedSyms = addedDefs.map(_.symbol.entered)
       val addedForwarders = addedEnumForwarders(cls)
       cpy.Template(templ)(
         parents = addEnumConstrArgs(defn.JavaEnumClass, templ.parents, addedSyms.map(ref)),
         body = params ++ addedDefs ++ addedForwarders ++ rest)
-    }
-    else if (cls.isAnonymousClass && ((cls.owner.name eq nme.DOLLAR_NEW) || cls.owner.isAllOf(EnumCase)) &&
-             cls.owner.owner.linkedClass.derivesFromJavaEnum) {
-      def rhsOf(name: TermName) =
-        templ.body.collect {
-          case mdef: DefDef if mdef.name == name => mdef.rhs
-        }.head
-      val args = List(rhsOf(nme.toString_), rhsOf(nme.ordinalDollar))
+    else if isJavaEnumValueImpl(cls) then
+      def creatorParamRef(name: TermName) =
+        ref(cls.owner.paramSymss.head.find(_.name == name).get)
+      val args =
+        if cls.owner.isAllOf(EnumCase) then
+          List(Literal(Constant(cls.owner.name.toString)), Literal(Constant(ordinalFor(cls.owner))))
+        else
+          List(creatorParamRef(nme.nameDollar), creatorParamRef(nme.ordinalDollar_))
       cpy.Template(templ)(
-        parents = addEnumConstrArgs(cls.owner.owner.linkedClass, templ.parents, args))
-    }
+        parents = addEnumConstrArgs(cls.owner.owner.linkedClass, templ.parents, args),
+      )
+    else if cls.linkedClass.derivesFromJavaEnum then
+      enumCaseOrdinals.clear() // remove simple cases // invariant: companion is visited after cases
+      templ
     else templ
   }
+
+  override def checkPostCondition(tree: Tree)(using Context): Unit =
+    assert(enumCaseOrdinals.isEmpty, "Java based enum ordinal cache was not cleared")
 }

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

@@ -57,7 +57,6 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
   private var myValueSymbols: List[Symbol] = Nil
   private var myCaseSymbols: List[Symbol] = Nil
   private var myCaseModuleSymbols: List[Symbol] = Nil
-  private var myEnumCaseSymbols: List[Symbol] = Nil
 
   private def initSymbols(using Context) =
     if (myValueSymbols.isEmpty) {
@@ -66,13 +65,11 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
         defn.Product_productArity, defn.Product_productPrefix, defn.Product_productElement,
         defn.Product_productElementName)
       myCaseModuleSymbols = myCaseSymbols.filter(_ ne defn.Any_equals)
-      myEnumCaseSymbols = List(defn.Enum_ordinal)
     }
 
   def valueSymbols(using Context): List[Symbol] = { initSymbols; myValueSymbols }
   def caseSymbols(using Context): List[Symbol] = { initSymbols; myCaseSymbols }
   def caseModuleSymbols(using Context): List[Symbol] = { initSymbols; myCaseModuleSymbols }
-  def enumCaseSymbols(using Context): List[Symbol] = { initSymbols; myEnumCaseSymbols }
 
   private def existingDef(sym: Symbol, clazz: ClassSymbol)(using Context): Symbol = {
     val existing = sym.matchingMember(clazz.thisType)
@@ -96,9 +93,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
     val symbolsToSynthesize: List[Symbol] =
       if (clazz.is(Case))
         if (clazz.is(Module)) caseModuleSymbols
-        else if (isEnumCase) caseSymbols ++ enumCaseSymbols
         else caseSymbols
-      else if (isEnumCase) enumCaseSymbols
       else if (isDerivedValueClass(clazz)) valueSymbols
       else Nil
 
@@ -128,7 +123,6 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
         case nme.productPrefix => ownName
         case nme.productElement => productElementBody(accessors.length, vrefss.head.head)
         case nme.productElementName => productElementNameBody(accessors.length, vrefss.head.head)
-        case nme.ordinal => Select(This(clazz), nme.ordinalDollar)
       }
       report.log(s"adding $synthetic to $clazz at ${ctx.phase}")
       synthesizeDef(synthetic, syntheticRHS)

docs/docs/reference/enums/desugarEnums.md

@@ -36,8 +36,8 @@ map into `case class`es or `val`s.
    ```
    expands to a `sealed abstract` class that extends the `scala.Enum` trait and
    an associated companion object that contains the defined cases, expanded according
-   to rules (2 - 8). The enum trait starts with a compiler-generated import that imports
-   the names `<caseIds>` of all cases so that they can be used without prefix in the trait.
+   to rules (2 - 8). The enum class starts with a compiler-generated import that imports
+   the names `<caseIds>` of all cases so that they can be used without prefix in the class.
    ```scala
    sealed abstract class E ... extends <parents> with scala.Enum {
      import E.{ <caseIds> }
@@ -174,13 +174,15 @@ If `E` contains at least one simple case, its companion object will define in ad
      follows.
      ```scala
      private def $new(_$ordinal: Int, $name: String) = new E with runtime.EnumValue {
-       def $ordinal = $_ordinal
-       override def toString = $name
+       def ordinal = _$ordinal       // if `E` does not have `java.lang.Enum` as a parent
+       override def toString = $name // if `E` does not have `java.lang.Enum` as a parent
        $values.register(this) // register enum value so that `valueOf` and `values` can return it.
      }
      ```
 
-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.
+The anonymous class also implements the abstract `Product` methods that it inherits from `Enum`.
+The `ordinal` method is only generated if the enum does not extend from `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. Similarly there is no need to override `toString` as that is defined in terms of `name` in
+`java.lang.Enum`.
 
 ### Scopes for Enum Cases
 

library/src-bootstrapped/scala/Enum.scala

@@ -5,5 +5,3 @@ trait Enum extends Product, Serializable:
 
   /** A number uniquely identifying a case of an enum */
   def ordinal: Int
-  protected def $ordinal: Int
-

library/src-non-bootstrapped/scala/Enum.scala

@@ -1,7 +1,7 @@
 package scala
 
 /** A base trait of all enum classes */
-trait Enum:
+trait Enum extends Product, Serializable:
 
   /** A number uniquely identifying a case of an enum */
   def ordinal: Int

tests/pos/enum-List-control.scala

@@ -1,7 +1,7 @@
 abstract sealed class List[T] extends Enum
 object List {
   final class Cons[T](x: T, xs: List[T]) extends List[T] {
-    def $ordinal = 0
+    def ordinal = 0
     def canEqual(that: Any): Boolean = that.isInstanceOf[Cons[_]]
     def productArity: Int = 2
     def productElement(n: Int): Any = n match
@@ -12,7 +12,7 @@ object List {
     def apply[T](x: T, xs: List[T]): List[T] = new Cons(x, xs)
   }
   final class Nil[T]() extends List[T], runtime.EnumValue {
-    def $ordinal = 1
+    def ordinal = 1
   }
   object Nil {
     def apply[T](): List[T] = new Nil()

tests/pos/enum-companion-first.scala

@@ -0,0 +1,9 @@
+object Planet:
+  final val G = 6.67300E-11
+
+enum Planet(mass: Double, radius: Double) extends java.lang.Enum[Planet]:
+  def surfaceGravity = Planet.G * mass / (radius * radius)
+  def surfaceWeight(otherMass: Double) =  otherMass * surfaceGravity
+
+  case Mercury extends Planet(3.303e+23, 2.4397e6)
+  case Venus   extends Planet(4.869e+24, 6.0518e6)

tests/run/enum-ordinal-java/Lib.scala

@@ -0,0 +1,5 @@
+object Lib1:
+  trait MyJavaEnum[E <: java.lang.Enum[E]] extends java.lang.Enum[E]
+
+object Lib2:
+  type JavaEnumAlias[E <: java.lang.Enum[E]] = java.lang.Enum[E]

tests/run/enum-ordinal-java/Test.scala

@@ -0,0 +1,9 @@
+enum Color1 extends Lib1.MyJavaEnum[Color1]:
+  case Red, Green, Blue
+
+enum Color2 extends Lib2.JavaEnumAlias[Color2]:
+    case Red, Green, Blue
+
+@main def Test =
+  assert(Color1.Green.ordinal == 1)
+  assert(Color2.Blue.ordinal == 2)