More targeted eta-lifting

Eta-lifting picked some arbitrary base type. It turned out that i94-nada failed once we add
a product trait to case classes (in the next commit) because Eta-Kifting picked Product
as the base type, even though the target type was bounded by Monad. We now change the scheme
so that the target type is included in the lifting, in order to avoid that we lift to
useless types.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/typer/VarianceChecker.scala b/src/dotty/tools/dotc/typer/VarianceChecker.scala
index 9ce3ca0b7..5865f0133 100644
--- a/src/dotty/tools/dotc/typer/VarianceChecker.scala
+++ b/src/dotty/tools/dotc/typer/VarianceChecker.scala
@@ -6,6 +6,7 @@ import core._
 import Types._, Contexts._, Flags._, Symbols._, Annotations._, Trees._, NameOps._
 import Decorators._
 import Variances._
+import config.Printers.variances
 
 /** Provides `check` method to check that all top-level definitions
  *  in tree are variance correct. Does not recurse inside methods.
@@ -77,7 +78,7 @@ class VarianceChecker()(implicit ctx: Context) {
      *  explicitly (their TypeDefs will be passed here.) For MethodTypes, the
      *  same is true of the parameters (ValDefs).
      */
-    def apply(status: Option[VarianceError], tp: Type): Option[VarianceError] = ctx.traceIndented(s"variance checking $tp of $base at $variance") {
+    def apply(status: Option[VarianceError], tp: Type): Option[VarianceError] = ctx.traceIndented(s"variance checking $tp of $base at $variance", variances) {
       if (status.isDefined) status
       else tp match {
         case tp: TypeRef =>