fix: Fix index getters / setters that return variants

Index getters / setters that return variants were crashing because of a bad attempt to cast the object held in the Variant to an Object.

This may be a bigger issue but it is fixed for arrays.

refs: #26

src/cpp/dart_bindings.cpp

@@ -791,9 +791,9 @@ void gd_object_to_dart_object(Dart_NativeArguments args) {
   }
 
   GDEWrapper *gde = GDEWrapper::instance();
-  // Defaults for non-engine classes
+
+  // Default for non-engine classes
   void *token = gde->get_library_ptr();
-  const GDExtensionInstanceBindingCallbacks *bindings_callbacks = &DartGodotInstanceBinding::engine_binding_callbacks;
 
   Dart_Handle bindings_token = Dart_GetNativeArgument(args, 2);
   if (!Dart_IsNull(bindings_token)) {
@@ -805,12 +805,11 @@ void gd_object_to_dart_object(Dart_NativeArguments args) {
     }
     uint64_t token_int = 0;
     Dart_IntegerToUint64(address, &token_int);
-    token = (void *)token_int;
-    bindings_callbacks = &DartGodotInstanceBinding::engine_binding_callbacks;
+    token = (void *)token_int;    
   }
 
   DartGodotInstanceBinding *binding = (DartGodotInstanceBinding *)gde_object_get_instance_binding(
-      reinterpret_cast<GDExtensionObjectPtr>(object_ptr), token, bindings_callbacks);
+      reinterpret_cast<GDExtensionObjectPtr>(object_ptr), token, &DartGodotInstanceBinding::engine_binding_callbacks);
   if (binding == nullptr) {
     Dart_SetReturnValue(args, Dart_Null());
   } else {

src/dart/godot_dart/lib/src/variant/variant.dart

@@ -172,6 +172,9 @@ class Variant implements Finalizable {
   Variant([Object? obj]) {
     if (obj == null) {
       gde.ffiBindings.gde_variant_new_nil(nativePtr.cast());
+    } else if (obj is Variant) {
+      throw ArgumentError.value(
+          obj, 'obj', 'Do not construct Variants with Variants.');
     } else {
       _initFromObject(obj);
     }
@@ -355,9 +358,11 @@ Object? convertFromVariantPtr(
         Pointer<GDExtensionObjectPtr> ptr =
             arena.allocate(sizeOf<GDExtensionObjectPtr>());
         c!(ptr.cast(), variantPtr);
+        final token =
+            typeInfo?.bindingToken ?? GodotObject.sTypeInfo.bindingToken;
         ret = gde.dartBindings.gdObjectToDartObject(
           ptr.value,
-          typeInfo?.bindingToken,
+          token,
         );
         break;
 

tools/binding_generator/lib/src/generators/builtin_type_generator.dart

@@ -306,17 +306,29 @@ void _writeMethods(CodeSink o, BuiltinClass builtin) {
   // TODO: This can be made more efficient for PackedXArray, but for now we're going
   // to just use Variant's indexed getter / setters
   if (builtin.indexingReturnType != null && builtin.name != 'Dictionary') {
+    final returnTypeCategory =
+        GodotApiInfo.instance().getTypeCategory(builtin.indexingReturnType!);
     var dartReturnType = godotTypeToDartType(builtin.indexingReturnType);
     o.b('$dartReturnType operator [](int index) {', () {
       o.p('final self = Variant(this);');
       o.p('final ret = gde.variantGetIndexed(self, index);');
-      o.p('return convertFromVariant(ret, null) as $dartReturnType;');
+      if (dartReturnType == 'Variant') {
+        o.p('return ret;');
+      } else if (returnTypeCategory == TypeCategory.engineClass) {
+        o.p('return convertFromVariant(ret, $dartReturnType.sTypeInfo) as $dartReturnType;');
+      } else {
+        o.p('return convertFromVariant(ret, null) as $dartReturnType;');
+      }
     }, '}');
     o.nl();
     o.b('void operator []=(int index, $dartReturnType value) {', () {
       o.p('final self = Variant(this);');
-      o.p('final variantValue = Variant(value);');
-      o.p('gde.variantSetIndexed(self, index, variantValue);');
+      if (dartReturnType == 'Variant') {
+        o.p('gde.variantSetIndexed(self, index, value);');
+      } else {
+        o.p('final variantValue = Variant(value);');
+        o.p('gde.variantSetIndexed(self, index, variantValue);');
+      }
     }, '}');
     o.nl();
   }