Add regression test for scala#6505

Fixes scala#6505

Author: odersky

compiler/test/dotc/pos-test-pickling.blacklist

@@ -40,6 +40,7 @@ i9999.scala
 9890.scala
 13491.scala
 7512.scala
+i6505.scala
 
 # Opaque type
 i5720.scala

tests/pos/i6505.scala

@@ -0,0 +1,45 @@
+class Foo {
+
+  type E[X]
+
+  def i: Int = ???
+  def e: E[Int] = ???
+
+  // Transforms `(T1, ... Tn)` into `(E[T1], ..., E[Tn])`
+  type F[T <: Tuple] <: Tuple = T match {
+    case EmptyTuple => EmptyTuple
+    case h *: t => E[h] *: F[t]
+  }
+
+  def foo1[Args <: Tuple](args: Args, args2: F[Args]): Unit = ()
+
+  foo1((i, i), (e, e)) // fails
+  foo1((i, i), (e, e): F[(Int, Int)]) // fails
+
+}
+
+class Foo2 {
+
+  type E[X]
+
+  def i: Int = ???
+  def e: E[Int] = ???
+
+  // Transforms `(T1, ... Tn)` into `(E[T1], ..., E[Tn])`
+  type F[T <: Tuple] <: Tuple = T match {
+    case EmptyTuple => EmptyTuple
+    case h *: t => E[h] *: F[t]
+  }
+
+  def foo2[Args <: Tuple, Args2 >: F[Args] <: F[Args]](args: Args, args2: Args2): Unit = ()
+
+  foo2((i, i), (e, e)) // fails
+
+  // all these work
+  foo2[(Int, Int), F[(Int, Int)]]((i, i), (e, e))
+  foo2[(Int, Int), F[(Int, Int)]]((i, i), (e, e))
+  foo2[(Int, Int), F[Int *: Int *: EmptyTuple]]((i, i), (e, e))
+  foo2[(Int, Int), (E[Int], E[Int])]((i, i), (e, e))
+  foo2[(Int, Int), E[Int] *: E[Int] *: EmptyTuple]((i, i), (e, e))
+
+}