Merge pull request #5284 from milessabin/topic/si-7046

SI-7046 reflection doesn't see all knownDirectSubclasses

This appears to do the right thing in the most typical scenarios in which `knownDirectSubclasses` would be used. The missing 5% is that subclasses defined in local scopes might not be seen by `knownDirectSubclasses` (see `Local` and `Riddle` in the test below). In mitigation, though, it is almost certain that a local subclass would represent an error in any scenario where `knownDirectSubclasses` might be used.

Errors for such situations are reported by recording (via a symbol attachment) that `knownDirectSubclasses` has been called and reporting an error if any additional children are added subsequently.

Despite these limitations and caveats, I believe that this represents a huge improvement over the status quo, and would eliminate 100% of the failures that I've seen in practice with people using shapeless for type class derivation.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/run/t7046-1/Macros_1.scala b/test/files/run/t7046-1/Macros_1.scala
new file mode 100644
index 0000000000..2a5bf82f62
--- /dev/null
+++ b/test/files/run/t7046-1/Macros_1.scala
@@ -0,0 +1,15 @@
+import scala.language.experimental.macros
+import scala.reflect.macros.blackbox.Context
+
+object Macros {
+  def impl[T](c: Context)(implicit ttag: c.WeakTypeTag[T]): c.Expr[List[String]] = {
+    import c.universe._;
+    val ttpe = ttag.tpe
+    val tsym = ttpe.typeSymbol.asClass
+    val subclasses = tsym.knownDirectSubclasses.toList.map(_.name.toString)
+
+    c.Expr[List[String]](q"$subclasses")
+  }
+
+  def knownDirectSubclasses[T]: List[String] = macro impl[T]
+}