codifies the state of the art wrt SI-8104

As it was discovered in SI-8104, whiteboxity doesn’t apply equally to
type parameters and type members of materialized type classes.

During implicit search and subsequent type inference, whitebox type parameters
are consistently erased to wildcards, whereas whitebox type members sometimes
remain as is and get in the way of signature conformance checks.

2 files changed, 27 insertions, 0 deletions

diff --git a/test/files/run/t8104/Macros_1.scala b/test/files/run/t8104/Macros_1.scala
new file mode 100644
index 0000000000..21d81a3687
--- /dev/null
+++ b/test/files/run/t8104/Macros_1.scala
@@ -0,0 +1,11 @@
+import scala.reflect.macros.WhiteboxContext
+
+object Macros {
+  def impl[T](c: WhiteboxContext)(implicit T: c.WeakTypeTag[T]) = {
+    import c.universe._
+    import definitions._
+    val fields = T.tpe.declarations.toList.collect{ case x: TermSymbol if x.isVal && x.isCaseAccessor => x }
+    val Repr = appliedType(TupleClass(fields.length).asType.toType, fields.map(_.typeSignature))
+    q"new Generic[$T]{ type Repr = $Repr }"
+  }
+}
\ No newline at end of file
diff --git a/test/files/run/t8104/Test_2.scala b/test/files/run/t8104/Test_2.scala
new file mode 100644
index 0000000000..630176f175
--- /dev/null
+++ b/test/files/run/t8104/Test_2.scala
@@ -0,0 +1,16 @@
+trait Generic[T] { type Repr }
+object Generic {
+  type Aux[T, Repr0] = Generic[T] { type Repr = Repr0 }
+  import scala.language.experimental.macros
+  implicit def materializeGeneric[T, Repr]: Generic.Aux[T, Repr] = macro Macros.impl[T]
+}
+
+object Test extends App {
+  case class C(x: Int, y: Int)
+
+  import scala.reflect.runtime.universe._
+  def reprify[T, Repr](x: T)(implicit generic: Generic.Aux[T, Repr], tag: TypeTag[Repr]) = println(tag)
+  reprify(C(40, 2))
+
+  implicitly[Generic.Aux[C, (Int, Int)]]
+}