Fixed #264 - failure to typecheck GADTs

The previous scheme derived the right bounds, but then failed to use them
because a TypeRef already has a set info (its bounds). Changing the bounds in
the symbol by a side effect does not affect that. This is good! But it showed
that the previous scheme was too fragile because it used a sneaky side effect
when updating the symbol info which failed to propgate into the cached
info in TypeRef.

We now keep GADT computed bounds separate form the symbol info
in a map `gadt` in the current context.

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/pos/i0268.scala b/tests/pos/i0268.scala
new file mode 100644
index 000000000..6ac0c5c90
--- /dev/null
+++ b/tests/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
+  }
+}