Annotate the type of HiddenKey values

* Makes it easy to check which ones can contain objects or not.

Author: eregon

src/main/java/org/truffleruby/Layouts.java

@@ -98,13 +98,13 @@ public abstract class Layouts {
     // These must appear before the generated layout list so the identifiers have been initialized by the time
     // the layout singletons are created.
 
-    public static final HiddenKey OBJECT_ID_IDENTIFIER = new HiddenKey("object_id");
-    public static final HiddenKey TAINTED_IDENTIFIER = new HiddenKey("tainted?");
-    public static final HiddenKey FROZEN_IDENTIFIER = new HiddenKey("frozen?");
-    public static final HiddenKey ASSOCIATED_IDENTIFIER = new HiddenKey("associated");
-    public static final HiddenKey FINALIZER_REF_IDENTIFIER = new HiddenKey("finalizerRef");
-    public static final HiddenKey MARKED_OBJECTS_IDENTIFIER = new HiddenKey("marked_objects");
-    public static final HiddenKey VALUE_WRAPPER_IDENTIFIER = new HiddenKey("value_wrapper");
+    public static final HiddenKey OBJECT_ID_IDENTIFIER = new HiddenKey("object_id"); // long
+    public static final HiddenKey TAINTED_IDENTIFIER = new HiddenKey("tainted?"); // boolean
+    public static final HiddenKey FROZEN_IDENTIFIER = new HiddenKey("frozen?"); // boolean
+    public static final HiddenKey ASSOCIATED_IDENTIFIER = new HiddenKey("associated"); // Pointer[]
+    public static final HiddenKey FINALIZER_REF_IDENTIFIER = new HiddenKey("finalizerRef"); // FinalizerReference
+    public static final HiddenKey MARKED_OBJECTS_IDENTIFIER = new HiddenKey("marked_objects"); // Object[]
+    public static final HiddenKey VALUE_WRAPPER_IDENTIFIER = new HiddenKey("value_wrapper"); // ValueWrapper
 
     // Generated layouts
 

src/main/java/org/truffleruby/core/format/unpack/UnpackRootNode.java

@@ -44,7 +44,7 @@ public Object execute(VirtualFrame frame) {
         frame.setInt(FormatFrameDescriptor.SOURCE_LENGTH_SLOT, (int) arguments[1]);
         frame.setInt(FormatFrameDescriptor.SOURCE_POSITION_SLOT, 0);
         frame.setBoolean(FormatFrameDescriptor.SOURCE_TAINTED_SLOT, (boolean) arguments[2]);
-        frame.setObject(FormatFrameDescriptor.SOURCE_ASSOCIATED_SLOT, frame.getArguments()[3]);
+        frame.setObject(FormatFrameDescriptor.SOURCE_ASSOCIATED_SLOT, arguments[3]);
         frame.setObject(FormatFrameDescriptor.OUTPUT_SLOT, new Object[expectedLength]);
         frame.setInt(FormatFrameDescriptor.OUTPUT_POSITION_SLOT, 0);
         frame.setBoolean(FormatFrameDescriptor.TAINT_SLOT, false);