Decouple ImplicitFunctionN from FunctionN.

This removes an illegal method override mentioned in #2000.

Author: nicolasstucki

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

@@ -104,7 +104,7 @@ class Definitions {
  *
  * ImplicitFunctionN traits follow this template:
  *
- * trait ImplicitFunctionN[T0,...,T{N-1}, R] extends Object with FunctionN[T0,...,T{N-1}, R] {
+ * trait ImplicitFunctionN[T0,...,T{N-1}, R] extends Object {
  * def apply(implicit $x0: T0, ..., $x{N_1}: T{N-1}): R
  * }
  */
@@ -118,22 +118,12 @@ class Definitions {
  for (i <- List.range(0, arity)) yield
  enterTypeParam(cls, name ++ "$T" ++ i.toString, Contravariant, decls)
  val resParam = enterTypeParam(cls, name ++ "$R", Covariant, decls)
- val (methodType, parentTraits) =
- if (name.startsWith(tpnme.ImplicitFunction)) {
- val superTrait =
- FunctionType(arity).appliedTo(argParams.map(_.typeRef) ::: resParam.typeRef :: Nil)
- (ImplicitMethodType, ctx.normalizeToClassRefs(superTrait :: Nil, cls, decls))
- }
- else (MethodType, Nil)
- val applyMeth =
- decls.enter(
- newMethod(cls, nme.apply,
- methodType(argParams.map(_.typeRef), resParam.typeRef), Deferred))
- denot.info =
- ClassInfo(ScalaPackageClass.thisType, cls, ObjectType :: parentTraits, decls)
+ val methodType = if (name.isImplicitFunction) ImplicitMethodType else MethodType
+ decls.enter(newMethod(cls, nme.apply, methodType(argParams.map(_.typeRef), resParam.typeRef), Deferred))
+ denot.info = ClassInfo(ScalaPackageClass.thisType, cls, ObjectType :: Nil, decls)
  }
  }
- newClassSymbol(ScalaPackageClass, name, Trait | NoInits, completer)
+ newClassSymbol(ScalaPackageClass, name, NoInitsTrait, completer)
  }
 
  private def newMethod(cls: ClassSymbol, name: TermName, info: Type, flags: FlagSet = EmptyFlags): TermSymbol =
@@ -822,7 +812,7 @@ class Definitions {
  * trait gets screwed up. Therefore, it is mandatory that FunctionXXL
  * is treated as a NoInit trait.
  */
- lazy val NoInitClasses = PhantomClasses + FunctionXXLClass
+ def isNoInitClass(cls: Symbol) = PhantomClasses.contains(cls) || (cls eq FunctionXXLClass) || isFunctionClass(cls)
 
  def isPolymorphicAfterErasure(sym: Symbol) =
  (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf)

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

@@ -175,7 +175,7 @@ class Mixin extends MiniPhaseTransform with SymTransformer { thisTransform =>
  case Some(call) =>
  if (defn.PhantomClasses.contains(baseCls)) Nil else call :: Nil
  case None =>
- if (baseCls.is(NoInitsTrait) || defn.NoInitClasses.contains(baseCls)) Nil
+ if (baseCls.is(NoInitsTrait) || defn.isNoInitClass(baseCls)) Nil
  else {
  //println(i"synth super call ${baseCls.primaryConstructor}: ${baseCls.primaryConstructor.info}")
  transformFollowingDeep(superRef(baseCls.primaryConstructor).appliedToNone) :: Nil

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

@@ -2003,20 +2003,29 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
  // local adaptation makes sure every adapted tree conforms to its pt
  // so will take the code path that decides on inlining
  return tpd.Block(adapt(tree, WildcardType) :: Nil, Literal(Constant(())))
- // convert function literal to SAM closure
  tree match {
- case Closure(Nil, id @ Ident(nme.ANON_FUN), _)
- if defn.isFunctionType(wtp) && !defn.isFunctionType(pt) =>
- pt match {
- case SAMType(meth)
- if wtp <:< meth.info.toFunctionType() =>
- // was ... && isFullyDefined(pt, ForceDegree.noBottom)
- // but this prevents case blocks from implementing polymorphic partial functions,
- // since we do not know the result parameter a priori. Have to wait until the
- // body is typechecked.
- return cpy.Closure(tree)(Nil, id, TypeTree(pt)).withType(pt)
- case _ =>
- }
+ case Closure(Nil, id @ Ident(nme.ANON_FUN), _) =>
+ val adaptToPrototype =
+ if (defn.isFunctionType(pt)) {
+ // convert implicit function to function
+ !defn.isImplicitFunctionType(pt) && defn.isImplicitFunctionType(wtp)
+ } else {
+ // convert function literal to SAM closure
+ defn.isFunctionType(wtp) && {
+ pt match {
+ case SAMType(meth)
+ if wtp <:< meth.info.toFunctionType() =>
+ // was ... && isFullyDefined(pt, ForceDegree.noBottom)
+ // but this prevents case blocks from implementing polymorphic partial functions,
+ // since we do not know the result parameter a priori. Have to wait until the
+ // body is typechecked.
+ true
+ case _ => false
+ }
+ }
+ }
+ if (adaptToPrototype)
+ return cpy.Closure(tree)(Nil, id, TypeTree(pt)).withType(pt)
  case _ =>
  }
  // try an implicit conversion

tests/run/implicitFunctionImpl.check

@@ -0,0 +1 @@
+42

tests/run/implicitFunctionImpl.scala

@@ -0,0 +1,11 @@
+
+object Test {
+ def main(args: Array[String]): Unit = {
+ println(new Fun().apply(42))
+
+ }
+}
+
+class Fun extends ImplicitFunction1[Int, Int] {
+ def apply(implicit v1: Int): Int = v1
+}