SI-6318 fixes ClassTag.unapply for primitives

ClassTag.unapply now has overloads for primitive value classes
so that it can preserve boxiness when performing subtyping tests.

First I wanted to annotate ClassTag.unapply with a ClassTag itself,
i.e. to transform its signature from "def unapply(x: Any): Option[T]"
to "def unapply[U: ClassTag](x: U): Option[T]".

But then virtpatmat_typetag.scala exhibited a nasty problem.
When pattern matching with this unapply, patmat first infers U as something
and then tries to pattern match against this inferred type. And if U gets
inferred as an abstract type itself, bad things happen:
warning: The outer reference in this type test cannot be checked at run time.

That's why I decided to drop the ClassTag idea and go with 9 extra overloads.
Not very beautiful, but definitely robust.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/run/t6318_derived.scala b/test/files/run/t6318_derived.scala
new file mode 100644
index 0000000000..ccdc18daee
--- /dev/null
+++ b/test/files/run/t6318_derived.scala
@@ -0,0 +1,15 @@
+import scala.reflect.{ClassTag, classTag}
+
+object Test extends App {
+  def test[T: ClassTag](x: T) {
+    println(classTag[T].runtimeClass.isAssignableFrom(x.getClass))
+    println(classTag[T].unapply(x))
+  }
+
+  class X(val x: Int) extends AnyVal { override def toString = "X" }
+  val x = new X(1)
+  // the commented line crashes because of SI-6326
+  //println(classTag[X].runtimeClass.isAssignableFrom(x.getClass))
+  println(classTag[X].unapply(x))
+  test(x)
+}
\ No newline at end of file