Bounds of type lambdas compare contravariantly

Enable checking of bounds when comparing type lambdas. This invalidates
a pattern used in t2994 and potentially other code, where a bound [X] -> Any
is used as a template that is a legal supertype of all other bounds. The old
behavior is still available under language:Scala2.

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/neg/hk-bounds.scala b/tests/neg/hk-bounds.scala
index 80c8cfaa8..db6712d72 100644
--- a/tests/neg/hk-bounds.scala
+++ b/tests/neg/hk-bounds.scala
@@ -21,3 +21,11 @@ object Test1 {
   baz[Foo] // error: Type argument [X0] -> Foo[X0] does not conform to lower bound [X0] -> Baz[X0]
 
 }
+object Test2 {
+  type Alias[F[X] <: Foo[X]] = F[Int]
+
+  def foo[M[_[_]], A[_]]: M[A] = null.asInstanceOf[M[A]]
+
+  val x = foo[Alias, Bar] // error: Type argument Test2.Alias does not conform to upper bound [X0 <: [X0] -> Any] -> Any
+
+}