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, 13 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index 9c9be4eb4d..464fa1ad18 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -185,6 +185,19 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
     }
   }
 
+  private var propCnt = 0
+  @inline final def withPropagateCyclicReferences[T](t: => T): T = {
+    try {
+      propCnt = propCnt+1
+      t
+    } finally {
+      propCnt = propCnt-1
+      assert(propCnt >= 0)
+    }
+  }
+
+  def propagateCyclicReferences: Boolean = propCnt > 0
+
   /** Representing ASTs as graphs */
   object treeBrowsers extends {
     val global: Global.this.type = Global.this