SI-6680 unsoundness in gadt typing.

Introduces -Xstrict-inference to deal with the significant
gap between soundness and what presently compiles. I'm hopeful
that it's TOO strict, because it finds e.g. 75 errors compiling
immutable/IntMap.scala, but it might be that bad.

2 files changed, 30 insertions, 1 deletions

diff --git a/test/files/pos/gadts2.scala b/test/files/pos/gadts2.scala
index fc2a7e4333..d77c8a7ba4 100644
--- a/test/files/pos/gadts2.scala
+++ b/test/files/pos/gadts2.scala
@@ -4,7 +4,7 @@ object Test {
   case class MyInt(n: Int) extends Number
   case class MyDouble(d: Double) extends Number
 
-  trait Term[+a]
+  trait Term[a]
   case class Cell[a](var x: a) extends Term[a]
   final case class NumTerm(val n: Number) extends Term[Number]
 
diff --git a/test/files/pos/pattern-typing.scala b/test/files/pos/pattern-typing.scala
new file mode 100644
index 0000000000..7286cc38af
--- /dev/null
+++ b/test/files/pos/pattern-typing.scala
@@ -0,0 +1,29 @@
+import scala.language.higherKinds
+
+trait Bound[B]
+
+package p1 {
+  case class Sub[B <: Bound[B]](p: B)
+  object Test {
+    def g[A](x: Bound[A]) = ()
+    def f(x: Any) = x match { case Sub(p) => g(p) }
+  }
+}
+
+package p2 {
+  trait Traversable[+A] { def head: A = ??? }
+  trait Seq[+A] extends Traversable[A] { def length: Int = ??? }
+
+  case class SubHK[B <: Bound[B], CC[X] <: Traversable[X]](xs: CC[B])
+  class MyBound extends Bound[MyBound]
+  class MySeq extends Seq[MyBound]
+
+  object Test {
+    def g[B](x: Bound[B]) = ()
+
+    def f1(x: Any) = x match { case SubHK(xs) => xs }
+    def f2[B <: Bound[B], CC[X] <: Traversable[X]](sub: SubHK[B, CC]): CC[B] = sub match { case SubHK(xs) => xs }
+    def f3 = g(f1(SubHK(new MySeq)).head)
+    def f4 = g(f2(SubHK(new MySeq)).head)
+  }
+}