Implement missing Node & Resource placeholders

Implemented by request of @neikeq to advance in the GDExtension version of Mono.

* If a Resource type is missing upon load, it will be remembered together with its data (Unless manually overriden).
* If a Node type is missing upon load, it will be also be remembered together with its data (unless deleted).

This feature makes working with GDExtension much easier, as it ensures that missing types no longer cause data loss.

1 files changed, 63 insertions, 0 deletions

diff --git a/scene/main/missing_node.h b/scene/main/missing_node.h
new file mode 100644
index 0000000000..b0f9492456
--- /dev/null
+++ b/scene/main/missing_node.h
@@ -0,0 +1,63 @@
+/*************************************************************************/
+/*  missing_node.h                                                       */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef MISSING_NODE_H
+#define MISSING_NODE_H
+
+#include "core/io/missing_resource.h"
+#include "scene/main/node.h"
+
+class MissingNode : public Node {
+	GDCLASS(MissingNode, Node)
+	OrderedHashMap<StringName, Variant> properties;
+
+	String original_class;
+	bool recording_properties = false;
+
+protected:
+	bool _set(const StringName &p_name, const Variant &p_value);
+	bool _get(const StringName &p_name, Variant &r_ret) const;
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+	static void _bind_methods();
+
+public:
+	void set_original_class(const String &p_class);
+	String get_original_class() const;
+
+	void set_recording_properties(bool p_enable);
+	bool is_recording_properties() const;
+
+	virtual TypedArray<String> get_configuration_warnings() const override;
+
+	MissingNode();
+};
+
+#endif // MISSING_NODE_H