Make errors are not swept under the carpet

Typer#ensureReported's comment outlines an example where errors
could go unreported, resulting in error trees after typer without
any reported error messages. This commit makes sure that at least
one error is reported if a tree node has an error type.

Fixes #1802.

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/neg/i1802.scala b/tests/neg/i1802.scala
new file mode 100644
index 000000000..56da672a8
--- /dev/null
+++ b/tests/neg/i1802.scala
@@ -0,0 +1,21 @@
+import scala.collection.immutable.List
+import scala.reflect.{ ClassTag, classTag }
+import scala.language.implicitConversions
+
+object Exception {
+  type Catcher[+T] = PartialFunction[Throwable, T]
+
+  def mkCatcher[Ex <: Throwable: ClassTag, T](isDef: Ex => Boolean, f: Ex => T) = new Catcher[T] {
+    private def downcast(x: Throwable): Option[Ex] =
+      if (classTag[Ex].runtimeClass.isAssignableFrom(x.getClass)) Some(x.asInstanceOf[Ex])
+      else None
+
+    def isDefinedAt(x: Throwable) = downcast(x) exists isDef
+    def apply(x: Throwable): T = f(downcast(x).get)
+  }
+
+  def mkThrowableCatcher[T](isDef: Throwable => Boolean, f: Throwable => T) = mkCatcher(isDef, f)
+
+  implicit def throwableSubtypeToCatcher[Ex <: Throwable: ClassTag, T](pf: PartialFunction[Ex, T]) = // error: cyclic reference
+    mkCatcher(pf.isDefinedAt _, pf.apply _)
+}