Merge pull request #764 from dotty-staging/mixin/forwarders

Mixin: class defined abstract members take precedence over interface defined.

Author: odersky

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

@@ -38,10 +38,12 @@ class MixinOps(cls: ClassSymbol, thisTransform: DenotTransformer)(implicit ctx:
   def isCurrent(sym: Symbol) = cls.info.member(sym.name).hasAltWith(_.symbol == sym)
 
   def needsForwarder(meth: Symbol): Boolean = {
-    def needsDisambiguation = !meth.allOverriddenSymbols.forall(_ is Deferred)
+    lazy val overridenSymbols = meth.allOverriddenSymbols
+    def needsDisambiguation = !overridenSymbols.forall(_ is Deferred)
+    def hasNonInterfaceDefinition = overridenSymbols.forall(!_.owner.is(Trait))
     meth.is(Method, butNot = PrivateOrAccessorOrDeferred) &&
     isCurrent(meth) &&
-    (needsDisambiguation || meth.owner.is(Scala2x))
+    (needsDisambiguation || hasNonInterfaceDefinition || meth.owner.is(Scala2x))
   }
 
   final val PrivateOrAccessorOrDeferred = Private | Accessor | Deferred

tests/run/i764.scala

@@ -0,0 +1,14 @@
+abstract class A {
+ def foo: Int
+}
+
+trait B {
+ def foo = 2
+}
+
+object Test extends A with B {
+  
+  def main(args: Array[String]): Unit = {
+    this.foo
+  }
+}