Fix pruning when adding a constraint

The variance in the code was exactly the opposite of what was claimed
in the comment. The reasoning in the comment was right.

Author: odersky

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -413,7 +413,7 @@ trait ConstraintHandling[AbstractContext] {
       def pruneLambdaParams(tp: Type) =
         if (comparedTypeLambdas.nonEmpty) {
           val approx = new ApproximatingTypeMap {
-            if (fromBelow) variance = -1
+            if (!fromBelow) variance = -1
             def apply(t: Type): Type = t match {
               case t @ TypeParamRef(tl: TypeLambda, n) if comparedTypeLambdas contains tl =>
                 val bounds = tl.paramInfos(n)

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -194,7 +194,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       case OrType(tp1, tp2) =>
         return toTextInfixType(tpnme.raw.BAR, tp1, tp2) { toText(tpnme.raw.BAR) }
 
-      case EtaExpansion(tycon) =>
+      case EtaExpansion(tycon) if !ctx.settings.YprintDebug.value =>
         return toText(tycon)
       case tp: RefinedType if defn.isFunctionType(tp) =>
         return toTextDependentFunction(tp.refinedInfo.asInstanceOf[MethodType])

tests/run/implicit-functors.check

@@ -7,19 +7,19 @@ import Utils._
 
 class Instances[F[_[_]], T[_]]
 
-trait Functor[F[_]]
+class Functor[F[_]](val kind: String)
 
 object Functor {
-  implicit val functorId: Functor[Id] = { println("functorId"); null }
-  implicit def functorGen[F[_]](implicit inst: Instances[Functor, F]): Functor[F] = { println("funcorGen"); null }
-  implicit def functorConst[T]: Functor[Const[T]] =  { println("funcorConst"); null }
+  implicit val functorId: Functor[Id] = new Functor[Id]("id")
+  implicit def functorGen[F[_]](implicit inst: Instances[Functor, F]): Functor[F] = new Functor[F]("gen")
+  implicit def functorConst[T]: Functor[Const[T]] = new Functor[Const[T]]("const")
 }
 
 case class Sm[A](value: A)
 object Sm {
-  implicit def smInstances[F[_[_]]]: Instances[F, Sm] = { println("smInstances"); null }
+  implicit def smInstances[F[_[_]]]: Instances[F, Sm] = null
 }
 
 object Test extends App {
-  implicitly[Functor[Sm]]
+  assert(implicitly[Functor[Sm]].kind == "gen")
 }