Fix problem with avoid.

When determining what to refine we should not rely only on signatures
but we need full denotation matching.

Author: odersky

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

@@ -62,9 +62,10 @@ trait TypeAssigner {
             case info: ClassInfo if variance > 0 =>
               val parentType = info.instantiatedParents.reduceLeft(ctx.typeComparer.andType(_, _))
               def addRefinement(parent: Type, decl: Symbol) = {
-                val inherited = parentType.findMember(decl.name, info.cls.thisType, Private)
-                val inheritedInfo = inherited.atSignature(decl.info.signature).info
-                    // @smarter atSignature probably wrong now; we are now missing out on types that refine the result type
+                val inherited =
+                  parentType.findMember(decl.name, info.cls.thisType, Private)
+                    .suchThat(decl.matches(_))
+                val inheritedInfo = inherited.info
                 if (inheritedInfo.exists && decl.info <:< inheritedInfo && !(inheritedInfo <:< decl.info))
                   typr.echo(
                     i"add ref $parent $decl --> ",