Fix #2663: More refined handling of enum case apply results

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

@@ -40,7 +40,11 @@ object desugar {
     def derivedType(sym: Symbol)(implicit ctx: Context) = sym.typeRef
   }
 
-  class DerivedFromParamTree extends DerivedTypeTree {
+  /** A type tree that computes its type from an existing parameter.
+   *  @param suffix  String difference between existing parameter (call it `P`) and parameter owning the
+   *                 DerivedTypeTree (call it `O`). We have: `O.name == P.name + suffix`.
+   */
+  class DerivedFromParamTree(suffix: String) extends DerivedTypeTree {
 
     /** Make sure that for all enclosing module classes their companion lasses
      *  are completed. Reason: We need the constructor of such companion classes to
@@ -58,24 +62,28 @@ object desugar {
 
     /** Return info of original symbol, where all references to siblings of the
      *  original symbol (i.e. sibling and original symbol have the same owner)
-     *  are rewired to same-named parameters or accessors in the scope enclosing
+     *  are rewired to like-named* parameters or accessors in the scope enclosing
      *  the current scope. The current scope is the scope owned by the defined symbol
      *  itself, that's why we have to look one scope further out. If the resulting
      *  type is an alias type, dealias it. This is necessary because the
      *  accessor of a type parameter is a private type alias that cannot be accessed
      *  from subclasses.
+     *
+     *  (*) like-named means:
+     *
+     *       parameter name  ==  reference name ++ suffix
      */
     def derivedType(sym: Symbol)(implicit ctx: Context) = {
       val relocate = new TypeMap {
         val originalOwner = sym.owner
         def apply(tp: Type) = tp match {
           case tp: NamedType if tp.symbol.exists && (tp.symbol.owner eq originalOwner) =>
             val defctx = ctx.outersIterator.dropWhile(_.scope eq ctx.scope).next()
-            var local = defctx.denotNamed(tp.name).suchThat(_.isParamOrAccessor).symbol
+            var local = defctx.denotNamed(tp.name ++ suffix).suchThat(_.isParamOrAccessor).symbol
             if (local.exists) (defctx.owner.thisType select local).dealias
             else {
               def msg =
-                s"no matching symbol for ${tp.symbol.showLocated} in ${defctx.owner} / ${defctx.effectiveScope}"
+                s"no matching symbol for ${tp.symbol.showLocated} in ${defctx.owner} / ${defctx.effectiveScope.toList}"
               if (ctx.reporter.errorsReported) ErrorType(msg)
               else throw new java.lang.Error(msg)
             }
@@ -88,14 +96,20 @@ object desugar {
   }
 
   /** A type definition copied from `tdef` with a rhs typetree derived from it */
-  def derivedTypeParam(tdef: TypeDef) =
+  def derivedTypeParam(tdef: TypeDef, suffix: String = ""): TypeDef =
     cpy.TypeDef(tdef)(
-      rhs = new DerivedFromParamTree() withPos tdef.rhs.pos watching tdef)
+      name = tdef.name ++ suffix,
+      rhs = new DerivedFromParamTree(suffix).withPos(tdef.rhs.pos).watching(tdef)
+    )
+
+  /** A derived type definition watching `sym` */
+  def derivedTypeParam(sym: TypeSymbol)(implicit ctx: Context): TypeDef =
+    TypeDef(sym.name, new DerivedFromParamTree("").watching(sym)).withFlags(TypeParam)
 
   /** A value definition copied from `vdef` with a tpt typetree derived from it */
   def derivedTermParam(vdef: ValDef) =
     cpy.ValDef(vdef)(
-      tpt = new DerivedFromParamTree() withPos vdef.tpt.pos watching vdef)
+      tpt = new DerivedFromParamTree("") withPos vdef.tpt.pos watching vdef)
 
 // ----- Desugar methods -------------------------------------------------
 
@@ -317,8 +331,8 @@ object desugar {
     }
     def anyRef = ref(defn.AnyRefAlias.typeRef)
 
-    val derivedTparams = constrTparams map derivedTypeParam
-    val derivedVparamss = constrVparamss nestedMap derivedTermParam
+    val derivedTparams = constrTparams.map(derivedTypeParam(_))
+    val derivedVparamss = constrVparamss.nestedMap(derivedTermParam(_))
     val arity = constrVparamss.head.length
 
     val classTycon: Tree = new TypeRefTree // watching is set at end of method
@@ -419,9 +433,8 @@ object desugar {
     //      ev1: Eq[T1$1, T1$2], ..., evn: Eq[Tn$1, Tn$2]])
     //      : Eq[C[T1$1, ..., Tn$1], C[T1$2, ..., Tn$2]] = Eq
     def eqInstance = {
-      def append(tdef: TypeDef, str: String) = cpy.TypeDef(tdef)(name = tdef.name ++ str)
-      val leftParams = derivedTparams.map(append(_, "$1"))
-      val rightParams = derivedTparams.map(append(_, "$2"))
+      val leftParams = constrTparams.map(derivedTypeParam(_, "$1"))
+      val rightParams = constrTparams.map(derivedTypeParam(_, "$2"))
       val subInstances = (leftParams, rightParams).zipped.map((param1, param2) =>
         appliedRef(ref(defn.EqType), List(param1, param2)))
       DefDef(
@@ -456,19 +469,16 @@ object desugar {
     // For all other classes, the parent is AnyRef.
     val companions =
       if (isCaseClass) {
-        def extractType(t: Tree): Tree = t match {
-          case Apply(t1, _) => extractType(t1)
-          case TypeApply(t1, ts) => AppliedTypeTree(extractType(t1), ts)
-          case Select(t1, nme.CONSTRUCTOR) => extractType(t1)
-          case New(t1) => t1
-          case t1 => t1
-        }
         // The return type of the `apply` method
-        val applyResultTpt =
-          if (isEnumCase)
-            if (parents.isEmpty) enumClassTypeRef
-            else parents.map(extractType).reduceLeft(AndTypeTree)
-          else TypeTree()
+        val (applyResultTpt, widenDefs) =
+          if (!isEnumCase)
+            (TypeTree(), Nil)
+          else if (parents.isEmpty || enumClass.typeParams.isEmpty)
+            (enumClassTypeRef, Nil)
+          else {
+            val tparams = enumClass.typeParams.map(derivedTypeParam)
+            enumApplyResult(cdef, parents, tparams, appliedRef(enumClassRef, tparams))
+          }
 
         val parent =
           if (constrTparams.nonEmpty ||
@@ -479,11 +489,13 @@ object desugar {
             // todo: also use anyRef if constructor has a dependent method type (or rule that out)!
             (constrVparamss :\ (if (isEnumCase) applyResultTpt else classTypeRef)) (
               (vparams, restpe) => Function(vparams map (_.tpt), restpe))
+        def widenedCreatorExpr =
+          (creatorExpr /: widenDefs)((rhs, meth) => Apply(Ident(meth.name), rhs :: Nil))
         val applyMeths =
           if (mods is Abstract) Nil
           else
-            DefDef(nme.apply, derivedTparams, derivedVparamss, applyResultTpt, creatorExpr)
-              .withFlags(Synthetic | (constr1.mods.flags & DefaultParameterized)) :: Nil
+            DefDef(nme.apply, derivedTparams, derivedVparamss, applyResultTpt, widenedCreatorExpr)
+              .withFlags(Synthetic | (constr1.mods.flags & DefaultParameterized)) :: widenDefs
         val unapplyMeth = {
           val unapplyParam = makeSyntheticParameter(tpt = classTypeRef)
           val unapplyRHS = if (arity == 0) Literal(Constant(true)) else Ident(unapplyParam.name)

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

@@ -120,6 +120,52 @@ object DesugarEnums {
         TypeTree(), creator)
   }
 
+  /** The return type of an enum case apply method and any widening methods in which
+   *  the apply's right hand side will be wrapped. For parents of the form
+   *
+   *      extends E(args) with T1(args1) with ... TN(argsN)
+   *
+   *  and type parameters `tparams` the generated widen method is
+   *
+   *      def C$to$E[tparams](x$1: E[tparams] with T1 with ... TN) = x$1
+   *
+   *  @param cdef            The case definition
+   *  @param parents         The declared parents of the enum case
+   *  @param tparams         The type parameters of the enum case
+   *  @param appliedEnumRef  The enum class applied to `tparams`.
+   */
+  def enumApplyResult(
+      cdef: TypeDef,
+      parents: List[Tree],
+      tparams: List[TypeDef],
+      appliedEnumRef: Tree)(implicit ctx: Context): (Tree, List[DefDef]) = {
+
+    def extractType(t: Tree): Tree = t match {
+      case Apply(t1, _) => extractType(t1)
+      case TypeApply(t1, ts) => AppliedTypeTree(extractType(t1), ts)
+      case Select(t1, nme.CONSTRUCTOR) => extractType(t1)
+      case New(t1) => t1
+      case t1 => t1
+    }
+
+    val parentTypes = parents.map(extractType)
+    parentTypes.head match {
+      case parent: RefTree if parent.name == enumClass.name =>
+        // need a widen method to compute correct type parameters for enum base class
+        val widenParamType = (appliedEnumRef /: parentTypes.tail)(AndTypeTree)
+        val widenParam = makeSyntheticParameter(tpt = widenParamType)
+        val widenDef = DefDef(
+          name = s"${cdef.name}$$to$$${enumClass.name}".toTermName,
+          tparams = tparams,
+          vparamss = (widenParam :: Nil) :: Nil,
+          tpt = TypeTree(),
+          rhs = Ident(widenParam.name))
+        (TypeTree(), widenDef :: Nil)
+      case _ =>
+        (parentTypes.reduceLeft(AndTypeTree), Nil)
+    }
+  }
+
   /** A pair consisting of
    *   - the next enum tag
    *   - scaffolding containing the necessary definitions for singleton enum cases

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

@@ -227,6 +227,12 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
       this
     }
 
+    /** Install the derived type tree as a dependency on `sym` */
+    def watching(sym: Symbol): this.type = {
+      pushAttachment(OriginalSymbol, sym)
+      this
+    }
+
     /** A hook to ensure that all necessary symbols are completed so that
      *  OriginalSymbol attachments are propagated to this tree
      */
@@ -240,7 +246,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
    *  from the symbol in this type. These type trees have marker trees
    *  TypeRefOfSym or InfoOfSym as their originals.
    */
-  val References = new Property.Key[List[Tree]]
+  val References = new Property.Key[List[DerivedTypeTree]]
 
   /** Property key for TypeTrees marked with TypeRefOfSym or InfoOfSym
    *  which contains the symbol of the original tree from which this

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -228,11 +228,7 @@ class Namer { typer: Typer =>
 
   /** Record `sym` as the symbol defined by `tree` */
   def recordSym(sym: Symbol, tree: Tree)(implicit ctx: Context): Symbol = {
-    val refs = tree.attachmentOrElse(References, Nil)
-    if (refs.nonEmpty) {
-      tree.removeAttachment(References)
-      refs foreach (_.pushAttachment(OriginalSymbol, sym))
-    }
+    for (refs <- tree.removeAttachment(References); ref <- refs) ref.watching(sym)
     tree.pushAttachment(SymOfTree, sym)
     sym
   }

tests/pos/i2663.scala

@@ -0,0 +1,30 @@
+trait Tr
+enum Foo[T](x: T) {
+  case Bar[T](y: T) extends Foo(y)
+  case Bas[T](y: Int) extends Foo(y)
+  case Bam[T](y: String) extends Foo(y) with Tr
+  case Baz[S, T](y: String) extends Foo(y) with Tr
+}
+object Test {
+  import Foo._
+  val bar: Foo[Boolean] = Bar(true)
+  val bas: Foo[Int] = Bas(1)
+  val bam: Foo[String] & Tr = Bam("")
+  val baz: Foo[String] & Tr = Baz("")
+}
+
+enum Foo2[S <: T, T](x1: S, x2: T) {
+  case Bar[T](y: T) extends Foo2(y, y)
+  case Bas[T](y: Int) extends Foo2(y, y)
+  case Bam[T](y: String) extends Foo2(y, y) with Tr
+  case Baz[S, T](y: String) extends Foo2(y, y) with Tr
+}
+object Test2 {
+  import Foo2._
+  val bar: Foo2[Boolean, Boolean] = Bar(true)
+  val bas: Foo2[Int, Int] = Bas(1)
+  val bam: Foo2[String, String] & Tr = Bam("")
+  val baz: Foo2[String, String] & Tr = Baz("")
+}
+
+