Improves exhaustiveness analysis to not warn ab...

Improves exhaustiveness analysis to not warn about types which cannot
match due to nonconformant type parameters. Also, look at the different
warnings emitted in the test case based on the presence of a constraint.
Nifty! Closes #3683, no review.

1 files changed, 20 insertions, 0 deletions

diff --git a/test/files/neg/bug3683a.scala b/test/files/neg/bug3683a.scala
new file mode 100644
index 0000000000..6d1915213a
--- /dev/null
+++ b/test/files/neg/bug3683a.scala
@@ -0,0 +1,20 @@
+sealed trait Foo
+sealed trait Bar extends Foo
+sealed trait W[T >: Bar <: Foo]
+case class X() extends W[Foo]
+case class XX() extends W[Bar]
+case class Y() extends W[Bar]
+case class Z[T >: Bar <: Foo](
+  z1: W[T]
+) extends W[T]
+
+object Main {
+  // should warn for not including XX()
+  def f1(w: W[Bar]): Int = {
+    w match {
+      // case XX() => 2
+      case Y() => 1
+      case Z(z) => f1(z)
+    }
+  }
+}
\ No newline at end of file