Move needsForwarder logic from ResolveSuper to MixinOps.

We'd like to make it reusable for a phase that treats Scala2 traits.

Author: odersky

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

@@ -31,6 +31,17 @@ class MixinOps(cls: ClassSymbol, thisTransform: DenotTransformer)(implicit ctx:
     //sup.select(target)
   }
 
+  def needsForwarder(meth: Symbol): Boolean = {
+    def needsDisambiguation = !meth.allOverriddenSymbols.forall(_ is Deferred)
+    def isOverridden = meth.overridingSymbol(cls).is(Method, butNot = Deferred)
+    meth.is(Method, butNot = PrivateOrAccessorOrDeferred) &&
+    !isOverridden &&
+    !meth.isConstructor &&
+    (needsDisambiguation/* || meth.owner.is(Scala2x)*/)
+  }
+
+  final val PrivateOrAccessorOrDeferred = Private | Accessor | Deferred
+
   def forwarder(target: Symbol) = (targs: List[Type]) => (vrefss: List[List[Tree]]) =>
     superRef(target).appliedToTypes(targs).appliedToArgss(vrefss)
 }

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

@@ -80,15 +80,9 @@ class ResolveSuper extends MiniPhaseTransform with IdentityDenotTransformer { th
       for (superAcc <- mixin.info.decls.filter(_ is SuperAccessor).toList)
         yield polyDefDef(implementation(superAcc.asTerm), forwarder(rebindSuper(cls, superAcc)))
 
-    def methodOverrides(mixin: ClassSymbol): List[Tree] = {
-      def isOverridden(meth: Symbol) = meth.overridingSymbol(cls).is(Method, butNot = Deferred)
-      def needsDisambiguation(meth: Symbol): Boolean =
-        meth.is(Method, butNot = PrivateOrAccessorOrDeferred) &&
-          !isOverridden(meth) &&
-          !meth.allOverriddenSymbols.forall(_ is Deferred)
-      for (meth <- mixin.info.decls.toList if needsDisambiguation(meth))
+    def methodOverrides(mixin: ClassSymbol): List[Tree] =
+      for (meth <- mixin.info.decls.toList if needsForwarder(meth))
         yield polyDefDef(implementation(meth.asTerm), forwarder(meth))
-    }
 
     val overrides = mixins.flatMap(mixin => superAccessors(mixin) ::: methodOverrides(mixin))