Closes #4431. Review by extempore.

2 files changed, 23 insertions, 0 deletions

diff --git a/test/files/neg/t4431.check b/test/files/neg/t4431.check
new file mode 100644
index 0000000000..7896ec1a62
--- /dev/null
+++ b/test/files/neg/t4431.check
@@ -0,0 +1,7 @@
+t4431.scala:5: error: class BB needs to be abstract, since there is a deferred declaration of method f which is not implemented in a subclass
+  class BB extends B { def f (): Unit }
+        ^
+t4431.scala:8: error: trait cannot redefine final method from class AnyRef
+  trait C { def wait (): Unit }
+                ^
+two errors found
diff --git a/test/files/neg/t4431.scala b/test/files/neg/t4431.scala
new file mode 100644
index 0000000000..5fbb239e04
--- /dev/null
+++ b/test/files/neg/t4431.scala
@@ -0,0 +1,16 @@
+object Test {
+  // this works.
+  class B { final def f(): Unit = () }
+  trait A extends B { def f (): Unit }
+  class BB extends B { def f (): Unit }
+
+  // this earns a VerifyError.
+  trait C { def wait (): Unit }
+  class D { }
+
+  def main(args: Array[String]): Unit = {
+    new B with A { }
+    new BB
+//    new D with C { }
+  }
+}