Make sure mixin accessors are not private.

Logic moved from RefChecks to Mixin; implementation
is now by name expansion instead of setting NotJavaPrivate
flag.

Author: odersky

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

@@ -72,7 +72,7 @@ class Mixin extends MiniPhaseTransform with SymTransformer { thisTransform =>
 
   override def transformSym(sym: SymDenotation)(implicit ctx: Context): SymDenotation =
     if (sym.is(Accessor, butNot = Deferred) && sym.owner.is(Trait))
-      sym.copySymDenotation(initFlags = sym.flags | Deferred)
+      sym.copySymDenotation(initFlags = sym.flags | Deferred).ensureNotPrivate
     else
       sym
 

src/dotty/tools/dotc/typer/RefChecks.scala

@@ -741,11 +741,9 @@ class RefChecks extends MiniPhase with SymTransformer { thisTransformer =>
    */
   override def transformSym(d: SymDenotation)(implicit ctx: Context) = {
     def mustBePublicInValueClass = d.isPrimaryConstructor || d.is(ParamAccessor)
-    def mustBePublicInTrait = !d.is(Method) || d.isSetter || d.is(ParamAccessor)
     def mustBePublic = {
       val cls = d.owner
-      (isDerivedValueClass(cls) && mustBePublicInValueClass ||
-      cls.is(Trait) && mustBePublicInTrait)
+      (isDerivedValueClass(cls) && mustBePublicInValueClass
     }
     if ((d is PrivateTerm) && mustBePublic) notPrivate(d) else d
   }