Barrier the pointer stores of a cppia field set by name

src/hx/cppia/CppiaVars.cpp

@@ -227,7 +227,12 @@ Dynamic CppiaVar::setValue(hx::Object *inThis, Dynamic inValue)
       case fsInt: *(int *)(base) = inValue; return inValue;
       case fsBool: *(bool *)(base) = inValue; return inValue;
       case fsFloat: *(Float *)(base) = inValue; return inValue;
-      case fsString: *(String *)(base) = inValue; return inValue;
+      case fsString:
+         *(String *)(base) = inValue;
+         #ifdef HXCPP_GC_GENERATIONAL
+         HX_OBJ_WB_GET(inThis, hx::PointerOf(*(String *)(base)));
+         #endif
+         return inValue;
       case fsObject:
             switch(type->arrayType)
             {
@@ -259,6 +264,10 @@ Dynamic CppiaVar::setValue(hx::Object *inThis, Dynamic inValue)
                   *(Array<Dynamic> *)(base) = inValue;
                   break;
             }
+            // Every case above stores one object pointer at base.
+            #ifdef HXCPP_GC_GENERATIONAL
+            HX_OBJ_WB_GET(inThis, *(hx::Object **)(base));
+            #endif
             return inValue;
       case fsUnknown:
          break;

test/cppia/Client.hx

@@ -14,6 +14,13 @@ class ClientFoo implements IFoo {
    }
 }
 
+class ClientHolder {
+
+   public var values:Array<Int>;
+
+   public function new() {}
+}
+
 class Client
 {
    public static var clientBool0 = true;

test/cppia/cases/TestCommon.hx

@@ -1,6 +1,8 @@
 package cases;
 
 import cpp.cppia.Host;
+import cpp.vm.Gc;
+import cpp.vm.WeakRef;
 import utest.Test;
 import utest.Assert;
 
@@ -59,6 +61,27 @@ class TestCommon extends Test {
         Assert.equals(2, Common.callbackSet, 'Bad cppia closure');
     }
 
+    @:depends(testStatus)
+    function testSetFieldOfOldObject() {
+        final holder = Type.createInstance(Type.resolveClass('ClientHolder'), []);
+
+        // Full collections make the holder old: a generational collection no longer traverses it.
+        for (_ in 0...3) {
+            Gc.run(true);
+        }
+        final values = setValues(holder);
+        Gc.run(false);
+
+        Assert.notNull(values.get(), 'Freed a value set by name on an old object');
+    }
+
+    // Only a weak reference to the value leaves this frame, so that the stack does not keep it.
+    static function setValues(holder:Dynamic):WeakRef<Array<Int>> {
+        final values = [42];
+        Reflect.setField(holder, 'values', values);
+        return new WeakRef(values);
+    }
+
     @:depends(testStatus)
     function testInterfaceCalling() {
         final obj : IFoo = Type.createInstance(Type.resolveClass('ClientFoo'), []);

test/cppia/compile-host.hxml

@@ -1,6 +1,7 @@
 -m CppiaHost
 HostExtendedRoot
 -D scriptable
+-D HXCPP_GC_GENERATIONAL
 -D dll_export=host_classes.info
 -L utest
 --dce no