Add test case for issue fixed in previous commit

Fixes #2981 which was a duplicate of #3213

Author: smarter

tests/pos/i2981.scala

@@ -0,0 +1,16 @@
+trait HList
+trait HNil extends HList
+
+trait FromTraversable[Out <: HList]
+object FromTraversable {
+  implicit def hnilFromTraversable[T]: FromTraversable[HNil] =
+    new FromTraversable[HNil]{}
+}
+
+object Filter {
+  def apply[A <: HList, O <: HList]()(implicit ftA: FromTraversable[A],
+                                      ftO: FromTraversable[O]): Unit = ()
+}
+object Main {
+  def main = Filter[HNil, HNil]()
+}