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, 5 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index dc35053835..fa5a1a25ad 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -313,6 +313,11 @@ trait Types
     /** If this is a lazy type, assign a new type to `sym`. */
     def complete(sym: Symbol) {}
 
+    /** If this is a lazy type corresponding to a subclass add it to its
+     *  parents children
+     */
+    def forceDirectSuperclasses: Unit = ()
+
     /** The term symbol associated with the type
       * Note that the symbol of the normalized type is returned (@see normalize)
       */