Add test case

Author: odersky

tests/pos/i2989.scala

@@ -0,0 +1,12 @@
+class Foo[+X[_]] {
+  // OK
+  def foo1[Y[_]](right: Foo[Y]): Foo[Y] = right
+  // OK
+  def foo2[Y[_]](right: Foo[[T] => Y[T]]): Foo[Y] = right
+  // OK
+  def foo3[Y[_]](right: Foo[[T] => Y[T]]): Foo[[T] => Y[T]] = right
+  // Error:
+  //   found:    Foo[Y](right)
+  //   required: Foo[Y]
+  def foo4[Y[_]](right: Foo[Y]): Foo[[T] => Y[T]] = right
+}