New scheme for subtyping refined types.

- Instead of rebasing, use the DeBrujn level of a RefiendThis.
- Make sure lower type is a singleton by skolemizing it if necessary.
- Do the correct rebinding of the upper type's RefinedThis.

Remarks:

 - The new scheme discovered quite a lot of errors which are mostly fixded in
other commits of this branch. i0268 (GADT matching) still does not work, moved to pending.

 - Some optimizations are currently missing:
   (1) fast path refined subtyping
   (2) faster operations for substituting refined thistypes which
       explot the fact that RefinedThis is relatively rare.

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/pending/pos/i0268.scala b/tests/pending/pos/i0268.scala
new file mode 100644
index 000000000..6ac0c5c90
--- /dev/null
+++ b/tests/pending/pos/i0268.scala
@@ -0,0 +1,15 @@
+package typespatmat
+
+sealed trait Box2[T]
+final case class Int2(x: Int) extends Box2[Int]
+final case class Str2(x: String)
+                              extends Box2[String]
+final case class Gen[T](x: T) extends Box2[T]
+
+object Box2 {
+  def double2[T](x: Box2[T]): T = x match {
+    case Int2(i) => i * 2
+    case Str2(s) => s + s
+    case Gen(x) => x
+  }
+}