Merge pull request scala#6029 from milessabin/topic/si-10454

Force superclasses through non-lazy module types.

Author: retronym

src/reflect/scala/reflect/internal/Types.scala

@@ -1890,6 +1890,10 @@ trait Types
       super.invalidateTypeRefCaches()
       narrowedCache = null
     }
+    override def forceDirectSuperclasses: Unit =
+      sym0.rawInfo.decls.foreach { decl =>
+        if(decl.isModule || !decl.isTerm) decl.rawInfo.forceDirectSuperclasses
+      }
     override protected def finishPrefix(rest: String) = objectPrefix + rest
     override def directObjectString = super.safeToString
     override def toLongString = toString

test/files/run/t10454-1/Macros_1.scala

@@ -0,0 +1,20 @@
+import scala.language.experimental.macros
+
+import scala.reflect.macros.blackbox.Context
+
+class TC[T](val subclasses: List[String])
+
+object TC {
+  implicit def instance[T]: TC[T] = macro instanceImpl[T]
+
+  def instanceImpl[T](c: Context)(implicit tT: c.WeakTypeTag[T]): c.Tree = {
+    import c.universe._
+
+    val subclasses =
+      if (tT.tpe.typeSymbol.isClass)
+        tT.tpe.typeSymbol.asClass.knownDirectSubclasses.map(_.toString).toList
+      else Nil
+
+    q"""new TC[$tT]($subclasses)"""
+  }
+}

test/files/run/t10454-1/Test_2.scala

@@ -0,0 +1,9 @@
+object Test extends App {
+  def callMacro[T: TC]: List[String] = implicitly[TC[T]].subclasses
+  assert(callMacro[ADT] == List("class ADTConstructor"))
+}
+
+sealed trait ADT
+object ADT {
+  final case class ADTConstructor() extends ADT
+}

test/files/run/t10454-2/Macros_1.scala

@@ -0,0 +1,20 @@
+import scala.language.experimental.macros
+
+import scala.reflect.macros.blackbox.Context
+
+class TC[T](val subclasses: List[String])
+
+object TC {
+  implicit def instance[T]: TC[T] = macro instanceImpl[T]
+
+  def instanceImpl[T](c: Context)(implicit tT: c.WeakTypeTag[T]): c.Tree = {
+    import c.universe._
+
+    val subclasses =
+      if (tT.tpe.typeSymbol.isClass)
+        tT.tpe.typeSymbol.asClass.knownDirectSubclasses.map(_.toString).toList
+      else Nil
+
+    q"""new TC[$tT]($subclasses)"""
+  }
+}

test/files/run/t10454-2/Test_2.scala

@@ -0,0 +1,16 @@
+object Test extends App {
+  def callMacro[T: TC]: List[String] = implicitly[TC[T]].subclasses
+  assert(callMacro[ADT] == List("class ADTConstructor"))
+  assert(ADT.instance.subclasses == List("class ADTConstructor"))
+  assert(ADT.ADTConstructor.ctorInstance.subclasses == Nil)
+}
+
+sealed trait ADT
+object ADT {
+  final val instance = implicitly[TC[ADT]]
+
+  final case class ADTConstructor() extends ADT
+  object ADTConstructor {
+    final val ctorInstance = implicitly[TC[ADTConstructor]]
+  }
+}