SI-7984 Issue unchecked warning for type aliases

 - Dealias pattern types before launching the CheckabilityChecker
 - Sharpen the error messages to explain that the dealiased type
   is the expansion of the alias.

1 files changed, 7 insertions, 0 deletions

diff --git a/test/files/neg/t7984.scala b/test/files/neg/t7984.scala
new file mode 100644
index 0000000000..ca09a89fc7
--- /dev/null
+++ b/test/files/neg/t7984.scala
@@ -0,0 +1,7 @@
+class Test {
+  type ListInt = List[Int]
+  List[Any]("") match {
+    case is: ListInt => is.head
+    case _ =>
+  }
+}