Merge pull request #3311 from xeno-by/topic/fine-points-of-whiteboxity-master

(master) codifies the state of the art wrt SI-8104

6 files changed, 64 insertions, 0 deletions

diff --git a/test/files/neg/t8104.check b/test/files/neg/t8104.check
new file mode 100644
index 0000000000..69b3461bd5
--- /dev/null
+++ b/test/files/neg/t8104.check
@@ -0,0 +1,4 @@
+Test_2.scala:20: error: could not find implicit value for parameter e: Generic.Aux[Test.C,(Int, Int)]
+  implicitly[Generic.Aux[C, (Int, Int)]]
+            ^
+one error found
diff --git a/test/files/neg/t8104/Macros_1.scala b/test/files/neg/t8104/Macros_1.scala
new file mode 100644
index 0000000000..21d81a3687
--- /dev/null
+++ b/test/files/neg/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/neg/t8104/Test_2.scala b/test/files/neg/t8104/Test_2.scala
new file mode 100644
index 0000000000..585f76c00f
--- /dev/null
+++ b/test/files/neg/t8104/Test_2.scala
@@ -0,0 +1,21 @@
+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]: Generic[T] = 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))
+
+  // this is a compilation error at the moment as explained in SI-8104
+  // because matchesPt in implicit search says that depoly(<type of materializeGeneric>) isn't a subtype of Generic.Aux[C, (Int, Int)]
+  // which is rightfully so, because depoly only replaces type parameters, not type members with wildcard types
+  // however in the future we might want to relax the matchesPt check, so this might start compiling
+  // therefore, if you've broken this test, then you should be happy, because most likely you've just enabled an interesting use case!
+  implicitly[Generic.Aux[C, (Int, Int)]]
+}
diff --git a/test/files/run/t8104.check b/test/files/run/t8104.check
new file mode 100644
index 0000000000..c2593eb199
--- /dev/null
+++ b/test/files/run/t8104.check
@@ -0,0 +1 @@
+TypeTag[(Int, Int)]
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)]]
+}