private[scala] def unlifted[A, B](f: _root_.scala.Function1[A, Option[B]]): PartialFunction[A,B] = f match {
  case (lf @ (_: Lifted[A, B])) => lf.pf
  case (ff @ _) => new Unlifted(ff)
}

        else {
          tvars = tpparams map freshVar
          tp    = pattp.instantiateTypeParams(tpparams, tvars)

          debuglog("free type params (2) = " + ptparams)

          val ptvars = ptparams map freshVar
          val pt1    = pt.instantiateTypeParams(ptparams, ptvars)

          // See ticket #2486 for an example of code which would incorrectly
          // fail if we didn't allow for pattpMatchesPt.
          if (isPopulated(tp, pt1) && isInstantiatable(tvars ++ ptvars) || pattpMatchesPt)
             ptvars foreach instantiateTypeVar
          else {
            PatternTypeIncompatibleWithPtError1(tree0, pattp, pt)
            return ErrorType
          }
....
  /** Is intersection of given types populated? That is,
   *  for all types tp1, tp2 in intersection
   *    for all common base classes bc of tp1 and tp2
   *      let bt1, bt2 be the base types of tp1, tp2 relative to class bc
   *      Then:
   *        bt1 and bt2 have the same prefix, and
   *        any corresponding non-variant type arguments of bt1 and bt2 are the same
   */
  def isPopulated(tp1: Type, tp2: Type): Boolean = {
    def isConsistent(tp1: Type, tp2: Type): Boolean = (tp1.dealias, tp2.dealias) match {
      case (TypeRef(pre1, sym1, args1), TypeRef(pre2, sym2, args2)) =>
        assert(sym1 == sym2, (sym1, sym2))
        (    pre1 =:= pre2
          && forall3(args1, args2, sym1.typeParams) { (arg1, arg2, tparam) =>
               // if left-hand argument is a typevar, make it compatible with variance
               // this is for more precise pattern matching
               // todo: work this in the spec of this method
               // also: think what happens if there are embedded typevars?
               if (tparam.variance.isInvariant)
                 arg1 =:= arg2
               else !arg1.isInstanceOf[TypeVar] || {
                 if (tparam.variance.isContravariant) arg1 <:< arg2
                 else arg2 <:< arg1
               }
             }
        )
      case (et: ExistentialType, _) =>
        et.withTypeVars(isConsistent(_, tp2))
      case (_, et: ExistentialType) =>
        et.withTypeVars(isConsistent(tp1, _))
      case (_, _) =>
        throw new MatchError((tp1, tp2))
    }

    def check(tp1: Type, tp2: Type) = (
      if (tp1.typeSymbol.isClass && tp1.typeSymbol.hasFlag(FINAL))
        tp1 <:< tp2 || isNumericValueClass(tp1.typeSymbol) && isNumericValueClass(tp2.typeSymbol)
      else tp1.baseClasses forall (bc =>
        tp2.baseTypeIndex(bc) < 0 || isConsistent(tp1.baseType(bc), tp2.baseType(bc)))
    )

    check(tp1, tp2) && check(tp2, tp1)
  }