SI-7290 Discard duplicates in switchable alternative patterns.

The pattern matcher must not allow duplicates to hit the
backend when generating switches. It already eliminates then
if they appear on different cases (with an unreachability warning.)

This commit does the same for duplicated literal patterns in an
alternative pattern: discard and warn.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/files/run/t7290.scala b/test/files/run/t7290.scala
new file mode 100644
index 0000000000..01f7e8f68e
--- /dev/null
+++ b/test/files/run/t7290.scala
@@ -0,0 +1,9 @@
+object Test extends App {
+  val y = (0: Int) match {
+    case 1 => 1
+    case 0 | 0 => 0
+    case 2 | 2 | 2 | 3 | 2 | 3 => 0
+    case _ => -1
+  }
+  assert(y == 0, y)
+}