Partial fix for SI-7046

4 files changed, 28 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/internal/StdAttachments.scala b/src/reflect/scala/reflect/internal/StdAttachments.scala
index cca33253be..3df31b538c 100644
--- a/src/reflect/scala/reflect/internal/StdAttachments.scala
+++ b/src/reflect/scala/reflect/internal/StdAttachments.scala
@@ -52,4 +52,10 @@ trait StdAttachments {
 
   /** Untyped list of subpatterns attached to selector dummy. */
   case class SubpatternsAttachment(patterns: List[Tree])
+
+  /** Attached to a class symbol to indicate that its children have been observed
+    * via knownDirectSubclasses. Children added subsequently will trigger an
+    * error to indicate that the earlier observation was incomplete.
+    */
+  case object KnownDirectSubclassesCalled extends PlainAttachment
 }
diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index 3b9ee9048a..6116952c70 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -110,6 +110,16 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     def knownDirectSubclasses = {
       // See `getFlag` to learn more about the `isThreadsafe` call in the body of this method.
       if (!isCompilerUniverse && !isThreadsafe(purpose = AllOps)) initialize
+
+      enclosingPackage.info.decls.foreach { sym =>
+        if(sourceFile == sym.sourceFile) {
+          sym.rawInfo.forceDirectSuperclasses
+        }
+      }
+
+      if(!isPastTyper)
+        updateAttachment(KnownDirectSubclassesCalled)
+
       children
     }
 
@@ -3351,7 +3361,12 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
 
     private[this] var childSet: Set[Symbol] = Set()
     override def children = childSet
-    override def addChild(sym: Symbol) { childSet = childSet + sym }
+    override def addChild(sym: Symbol) {
+      if(!isPastTyper && hasAttachment[KnownDirectSubclassesCalled.type] && !childSet.contains(sym))
+        globalError(s"knownDirectSubclasses of ${this.name} observed before subclass ${sym.name} registered")
+
+      childSet = childSet + sym
+    }
 
     def anonOrRefinementString = {
       if (hasCompleteInfo) {
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index 9697e16da7..3a645616eb 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -310,6 +310,11 @@ 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)
       */
diff --git a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
index 7725e4a2f0..8481cd8996 100644
--- a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
+++ b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
@@ -41,6 +41,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     this.ForAttachment
     this.SyntheticUnitAttachment
     this.SubpatternsAttachment
+    this.KnownDirectSubclassesCalled
     this.noPrint
     this.typeDebug
     this.Range