Merge pull request #361 from dotty-staging/fix/testLifted

Fix to testLifted

Author: DarkDimius

src/dotty/tools/dotc/core/TypeApplications.scala

@@ -509,7 +509,7 @@ class TypeApplications(val self: Type) extends AnyVal {
    *               { type $hkArg$0 = T1; ...; type $hkArg$n = Tn }
    *
    *  satisfies predicate `p`. Try base types in the order of their occurrence in `baseClasses`.
-   *  A type parameter matches a varianve V if it has V as its variance or if V == 0.
+   *  A type parameter matches a variance V if it has V as its variance or if V == 0.
    */
   def testLifted(tparams: List[Symbol], p: Type => Boolean)(implicit ctx: Context): Boolean = {
     def tryLift(bcs: List[ClassSymbol]): Boolean = bcs match {
@@ -534,7 +534,7 @@ class TypeApplications(val self: Type) extends AnyVal {
         false
     }
     if (tparams.isEmpty) false
-    else if (typeParams.nonEmpty) p(EtaExpand)
+    else if (typeParams.nonEmpty) p(EtaExpand) || tryLift(self.baseClasses)
     else tryLift(self.baseClasses)
   }
 }

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

@@ -28,9 +28,18 @@ trait TypeAssigner {
     }
   }
 
-  def avoid(tp: Type, syms: => List[Symbol])(implicit ctx: Context): Type = {
+  /** An upper approximation of the given type `tp` that does not refer to any symbol in `symsToAvoid`.
+   *  Approximation steps are:
+   *  
+   *   - follow aliases if the original refers to a forbidden symbol
+   *   - widen termrefs that refer to a forbidden symbol
+   *   - replace ClassInfos of forbidden classes by the intersection of their parents, refined by all 
+   *     non-private fields, methods, and type members.
+   *   - drop refinements referring to a forbidden symbol.
+   */
+  def avoid(tp: Type, symsToAvoid: => List[Symbol])(implicit ctx: Context): Type = {
     val widenMap = new TypeMap {
-      lazy val forbidden = syms.toSet
+      lazy val forbidden = symsToAvoid.toSet
       def toAvoid(tp: Type): Boolean = tp match {
         case tp: TermRef =>
           val sym = tp.symbol