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, 14 insertions, 0 deletions

diff --git a/test/files/pos/t7046-2/Macros_1.scala b/test/files/pos/t7046-2/Macros_1.scala
new file mode 100644
index 0000000000..07c0c61281
--- /dev/null
+++ b/test/files/pos/t7046-2/Macros_1.scala
@@ -0,0 +1,14 @@
+package p1
+
+import scala.reflect.macros.blackbox._
+import language.experimental._
+
+object Macro {
+  def impl(c: Context): c.Tree = {
+    import c.universe._
+    val tsym = rootMirror.staticClass("p1.Base")
+    val subclasses = tsym.knownDirectSubclasses.toList.map(_.name.toString)
+    q"$subclasses"
+  }
+  def p1_Base_knownDirectSubclasses: List[String] = macro impl
+}