Merge pull request #50786 from reduz/implement-resource-uids

Implement Resource UIDs

14 files changed, 540 insertions, 94 deletions

diff --git a/core/io/resource.h b/core/io/resource.h
index 0f88738f76..e864b371ad 100644
--- a/core/io/resource.h
+++ b/core/io/resource.h
@@ -31,6 +31,7 @@
 #ifndef RESOURCE_H
 #define RESOURCE_H
 
+#include "core/io/resource_uid.h"
 #include "core/object/class_db.h"
 #include "core/object/ref_counted.h"
 #include "core/templates/safe_refcount.h"
diff --git a/core/io/resource_format_binary.cpp b/core/io/resource_format_binary.cpp
index a8eeaa6602..81ba5cc68d 100644
--- a/core/io/resource_format_binary.cpp
+++ b/core/io/resource_format_binary.cpp
@@ -816,13 +816,18 @@ String ResourceLoaderBinary::get_unicode_string() {
 }
 
 void ResourceLoaderBinary::get_dependencies(FileAccess *p_f, List<String> *p_dependencies, bool p_add_types) {
-	open(p_f);
+	open(p_f, false, true);
 	if (error) {
 		return;
 	}
 
 	for (int i = 0; i < external_resources.size(); i++) {
-		String dep = external_resources[i].path;
+		String dep;
+		if (external_resources[i].uid != ResourceUID::INVALID_ID) {
+			dep = ResourceUID::get_singleton()->id_to_text(external_resources[i].uid);
+		} else {
+			dep = external_resources[i].path;
+		}
 
 		if (p_add_types && external_resources[i].type != String()) {
 			dep += "::" + external_resources[i].type;
@@ -832,7 +837,7 @@ void ResourceLoaderBinary::get_dependencies(FileAccess *p_f, List<String> *p_dep
 	}
 }
 
-void ResourceLoaderBinary::open(FileAccess *p_f) {
+void ResourceLoaderBinary::open(FileAccess *p_f, bool p_no_resources, bool p_keep_uuid_paths) {
 	error = OK;
 
 	f = p_f;
@@ -891,10 +896,24 @@ void ResourceLoaderBinary::open(FileAccess *p_f) {
 	if (flags & ResourceFormatSaverBinaryInstance::FORMAT_FLAG_NAMED_SCENE_IDS) {
 		using_named_scene_ids = true;
 	}
-	for (int i = 0; i < 13; i++) {
+	if (flags & ResourceFormatSaverBinaryInstance::FORMAT_FLAG_UIDS) {
+		using_uids = true;
+	}
+
+	if (using_uids) {
+		uid = f->get_64();
+	} else {
+		uid = ResourceUID::INVALID_ID;
+	}
+
+	for (int i = 0; i < 5; i++) {
 		f->get_32(); //skip a few reserved fields
 	}
 
+	if (p_no_resources) {
+		return;
+	}
+
 	uint32_t string_table_size = f->get_32();
 	string_map.resize(string_table_size);
 	for (uint32_t i = 0; i < string_table_size; i++) {
@@ -908,8 +927,18 @@ void ResourceLoaderBinary::open(FileAccess *p_f) {
 	for (uint32_t i = 0; i < ext_resources_size; i++) {
 		ExtResource er;
 		er.type = get_unicode_string();
-
 		er.path = get_unicode_string();
+		if (using_uids) {
+			er.uid = f->get_64();
+			if (!p_keep_uuid_paths && er.uid != ResourceUID::INVALID_ID) {
+				if (ResourceUID::get_singleton()->has_id(er.uid)) {
+					// If a UID is found and the path is valid, it will be used, otherwise, it falls back to the path.
+					er.path = ResourceUID::get_singleton()->get_id_path(er.uid);
+				} else {
+					WARN_PRINT(String(res_path + ": In external resouce #" + itos(i) + ", invalid UUID: " + ResourceUID::get_singleton()->id_to_text(er.uid) + " - using text path instead: " + er.path).utf8().get_data());
+				}
+			}
+		}
 
 		external_resources.push_back(er);
 	}
@@ -1173,8 +1202,15 @@ Error ResourceFormatLoaderBinary::rename_dependencies(const String &p_path, cons
 	uint64_t importmd_ofs = f->get_64();
 	fw->store_64(0); //metadata offset
 
-	for (int i = 0; i < 14; i++) {
-		fw->store_32(0);
+	uint32_t flags = f->get_32();
+	bool using_uids = (flags & ResourceFormatSaverBinaryInstance::FORMAT_FLAG_UIDS);
+	uint64_t uid_data = f->get_64();
+
+	fw->store_32(flags);
+	fw->store_64(uid_data);
+
+	for (int i = 0; i < 5; i++) {
+		f->store_32(0); // reserved
 		f->get_32();
 	}
 
@@ -1195,6 +1231,16 @@ Error ResourceFormatLoaderBinary::rename_dependencies(const String &p_path, cons
 		String type = get_ustring(f);
 		String path = get_ustring(f);
 
+		if (using_uids) {
+			ResourceUID::ID uid = f->get_64();
+			if (uid != ResourceUID::INVALID_ID) {
+				if (ResourceUID::get_singleton()->has_id(uid)) {
+					// If a UID is found and the path is valid, it will be used, otherwise, it falls back to the path.
+					path = ResourceUID::get_singleton()->get_id_path(uid);
+				}
+			}
+		}
+
 		bool relative = false;
 		if (!path.begins_with("res://")) {
 			path = local_path.plus_file(path).simplify_path();
@@ -1206,6 +1252,8 @@ Error ResourceFormatLoaderBinary::rename_dependencies(const String &p_path, cons
 			path = np;
 		}
 
+		String full_path = path;
+
 		if (relative) {
 			//restore relative
 			path = local_path.path_to_file(path);
@@ -1213,6 +1261,11 @@ Error ResourceFormatLoaderBinary::rename_dependencies(const String &p_path, cons
 
 		save_ustring(fw, type);
 		save_ustring(fw, path);
+
+		if (using_uids) {
+			ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(full_path);
+			f->store_64(uid);
+		}
 	}
 
 	int64_t size_diff = (int64_t)fw->get_position() - (int64_t)f->get_position();
@@ -1268,6 +1321,28 @@ String ResourceFormatLoaderBinary::get_resource_type(const String &p_path) const
 	return ClassDB::get_compatibility_remapped_class(r);
 }
 
+ResourceUID::ID ResourceFormatLoaderBinary::get_resource_uid(const String &p_path) const {
+	String ext = p_path.get_extension().to_lower();
+	if (!ClassDB::is_resource_extension(ext)) {
+		return ResourceUID::INVALID_ID;
+	}
+
+	FileAccess *f = FileAccess::open(p_path, FileAccess::READ);
+	if (!f) {
+		return ResourceUID::INVALID_ID; //could not read
+	}
+
+	ResourceLoaderBinary loader;
+	loader.local_path = ProjectSettings::get_singleton()->localize_path(p_path);
+	loader.res_path = loader.local_path;
+	//loader.set_local_path( Globals::get_singleton()->localize_path(p_path) );
+	loader.open(f, true);
+	if (loader.error != OK) {
+		return ResourceUID::INVALID_ID; //could not read
+	}
+	return loader.uid;
+}
+
 ///////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////
@@ -1824,8 +1899,10 @@ Error ResourceFormatSaverBinaryInstance::save(const String &p_path, const RES &p
 
 	save_unicode_string(f, p_resource->get_class());
 	f->store_64(0); //offset to import metadata
-	f->store_32(FORMAT_FLAG_NAMED_SCENE_IDS);
-	for (int i = 0; i < 13; i++) {
+	f->store_32(FORMAT_FLAG_NAMED_SCENE_IDS | FORMAT_FLAG_UIDS);
+	ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(p_path, true);
+	f->store_64(uid);
+	for (int i = 0; i < 5; i++) {
 		f->store_32(0); // reserved
 	}
 
@@ -1891,6 +1968,8 @@ Error ResourceFormatSaverBinaryInstance::save(const String &p_path, const RES &p
 		String path = save_order[i]->get_path();
 		path = relative_paths ? local_path.path_to_file(path) : path;
 		save_unicode_string(f, path);
+		ResourceUID::ID ruid = ResourceSaver::get_resource_id_for_path(save_order[i]->get_path(), false);
+		f->store_64(ruid);
 	}
 	// save internal resource table
 	f->store_32(saved_resources.size()); //amount of internal resources
diff --git a/core/io/resource_format_binary.h b/core/io/resource_format_binary.h
index e3dcf44492..ac964d2053 100644
--- a/core/io/resource_format_binary.h
+++ b/core/io/resource_format_binary.h
@@ -47,6 +47,8 @@ class ResourceLoaderBinary {
 
 	uint64_t importmd_ofs = 0;
 
+	ResourceUID::ID uid = ResourceUID::INVALID_ID;
+
 	Vector<char> str_buf;
 	List<RES> resource_cache;
 
@@ -57,10 +59,12 @@ class ResourceLoaderBinary {
 	struct ExtResource {
 		String path;
 		String type;
+		ResourceUID::ID uid = ResourceUID::INVALID_ID;
 		RES cache;
 	};
 
 	bool using_named_scene_ids = false;
+	bool using_uids = false;
 	bool use_sub_threads = false;
 	float *progress = nullptr;
 	Vector<ExtResource> external_resources;
@@ -94,7 +98,7 @@ public:
 	void set_translation_remapped(bool p_remapped);
 
 	void set_remaps(const Map<String, String> &p_remaps) { remaps = p_remaps; }
-	void open(FileAccess *p_f);
+	void open(FileAccess *p_f, bool p_no_resources = false, bool p_keep_uuid_paths = false);
 	String recognize(FileAccess *p_f);
 	void get_dependencies(FileAccess *p_f, List<String> *p_dependencies, bool p_add_types);
 
@@ -109,6 +113,7 @@ public:
 	virtual void get_recognized_extensions(List<String> *p_extensions) const;
 	virtual bool handles_type(const String &p_type) const;
 	virtual String get_resource_type(const String &p_path) const;
+	virtual ResourceUID::ID get_resource_uid(const String &p_path) const;
 	virtual void get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types = false);
 	virtual Error rename_dependencies(const String &p_path, const Map<String, String> &p_map);
 };
@@ -157,7 +162,8 @@ class ResourceFormatSaverBinaryInstance {
 
 public:
 	enum {
-		FORMAT_FLAG_NAMED_SCENE_IDS = 1
+		FORMAT_FLAG_NAMED_SCENE_IDS = 1,
+		FORMAT_FLAG_UIDS = 2,
 	};
 	Error save(const String &p_path, const RES &p_resource, uint32_t p_flags = 0);
 	static void write_variant(FileAccess *f, const Variant &p_property, Map<RES, int> &resource_map, Map<RES, int> &external_resources, Map<StringName, int> &string_map, const PropertyInfo &p_hint = PropertyInfo());
diff --git a/core/io/resource_importer.cpp b/core/io/resource_importer.cpp
index 511c145f2b..e7c0176e5a 100644
--- a/core/io/resource_importer.cpp
+++ b/core/io/resource_importer.cpp
@@ -93,6 +93,8 @@ Error ResourceFormatImporter::_get_path_and_type(const String &p_path, PathAndTy
 				r_path_and_type.type = ClassDB::get_compatibility_remapped_class(value);
 			} else if (assign == "importer") {
 				r_path_and_type.importer = value;
+			} else if (assign == "uid") {
+				r_path_and_type.uid = ResourceUID::get_singleton()->text_to_id(value);
 			} else if (assign == "group_file") {
 				r_path_and_type.group_file = value;
 			} else if (assign == "metadata") {
@@ -336,6 +338,17 @@ String ResourceFormatImporter::get_resource_type(const String &p_path) const {
 	return pat.type;
 }
 
+ResourceUID::ID ResourceFormatImporter::get_resource_uid(const String &p_path) const {
+	PathAndType pat;
+	Error err = _get_path_and_type(p_path, pat);
+
+	if (err != OK) {
+		return ResourceUID::INVALID_ID;
+	}
+
+	return pat.uid;
+}
+
 Variant ResourceFormatImporter::get_resource_metadata(const String &p_path) const {
 	PathAndType pat;
 	Error err = _get_path_and_type(p_path, pat);
diff --git a/core/io/resource_importer.h b/core/io/resource_importer.h
index 62cb608a42..a1cacbd306 100644
--- a/core/io/resource_importer.h
+++ b/core/io/resource_importer.h
@@ -42,6 +42,7 @@ class ResourceFormatImporter : public ResourceFormatLoader {
 		String importer;
 		String group_file;
 		Variant metadata;
+		uint64_t uid = ResourceUID::INVALID_ID;
 	};
 
 	Error _get_path_and_type(const String &p_path, PathAndType &r_path_and_type, bool *r_valid = nullptr) const;
@@ -63,6 +64,8 @@ public:
 	virtual bool recognize_path(const String &p_path, const String &p_for_type = String()) const;
 	virtual bool handles_type(const String &p_type) const;
 	virtual String get_resource_type(const String &p_path) const;
+	virtual ResourceUID::ID get_resource_uid(const String &p_path) const;
+
 	virtual Variant get_resource_metadata(const String &p_path) const;
 	virtual bool is_import_valid(const String &p_path) const;
 	virtual void get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types = false);
diff --git a/core/io/resource_loader.cpp b/core/io/resource_loader.cpp
index 0c825a62bb..7e69b2ecab 100644
--- a/core/io/resource_loader.cpp
+++ b/core/io/resource_loader.cpp
@@ -84,6 +84,14 @@ String ResourceFormatLoader::get_resource_type(const String &p_path) const {
 	return "";
 }
 
+ResourceUID::ID ResourceFormatLoader::get_resource_uid(const String &p_path) const {
+	if (get_script_instance() && get_script_instance()->has_method("_get_resource_uid")) {
+		return get_script_instance()->call("_get_resource_uid", p_path);
+	}
+
+	return ResourceUID::INVALID_ID;
+}
+
 void ResourceFormatLoader::get_recognized_extensions_for_type(const String &p_type, List<String> *p_extensions) const {
 	if (p_type == "" || handles_type(p_type)) {
 		get_recognized_extensions(p_extensions);
@@ -270,13 +278,18 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
 	thread_load_mutex->unlock();
 }
 
-Error ResourceLoader::load_threaded_request(const String &p_path, const String &p_type_hint, bool p_use_sub_threads, ResourceFormatLoader::CacheMode p_cache_mode, const String &p_source_resource) {
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
+static String _validate_local_path(const String &p_path) {
+	ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(p_path);
+	if (uid != ResourceUID::INVALID_ID) {
+		return ResourceUID::get_singleton()->get_id_path(uid);
+	} else if (p_path.is_rel_path()) {
+		return "res://" + p_path;
 	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
+		return ProjectSettings::get_singleton()->localize_path(p_path);
 	}
+}
+Error ResourceLoader::load_threaded_request(const String &p_path, const String &p_type_hint, bool p_use_sub_threads, ResourceFormatLoader::CacheMode p_cache_mode, const String &p_source_resource) {
+	String local_path = _validate_local_path(p_path);
 
 	thread_load_mutex->lock();
 
@@ -399,12 +412,7 @@ float ResourceLoader::_dependency_get_progress(const String &p_path) {
 }
 
 ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const String &p_path, float *r_progress) {
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
-	}
+	String local_path = _validate_local_path(p_path);
 
 	thread_load_mutex->lock();
 	if (!thread_load_tasks.has(local_path)) {
@@ -424,12 +432,7 @@ ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const
 }
 
 RES ResourceLoader::load_threaded_get(const String &p_path, Error *r_error) {
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
-	}
+	String local_path = _validate_local_path(p_path);
 
 	thread_load_mutex->lock();
 	if (!thread_load_tasks.has(local_path)) {
@@ -510,12 +513,7 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, Resour
 		*r_error = ERR_CANT_OPEN;
 	}
 
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
-	}
+	String local_path = _validate_local_path(p_path);
 
 	if (p_cache_mode != ResourceFormatLoader::CACHE_MODE_IGNORE) {
 		thread_load_mutex->lock();
@@ -612,12 +610,7 @@ RES ResourceLoader::load(const String &p_path, const String &p_type_hint, Resour
 }
 
 bool ResourceLoader::exists(const String &p_path, const String &p_type_hint) {
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
-	}
+	String local_path = _validate_local_path(p_path);
 
 	if (ResourceCache::has(local_path)) {
 		return true; // If cached, it probably exists
@@ -677,14 +670,7 @@ void ResourceLoader::remove_resource_format_loader(Ref<ResourceFormatLoader> p_f
 }
 
 int ResourceLoader::get_import_order(const String &p_path) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -702,14 +688,7 @@ int ResourceLoader::get_import_order(const String &p_path) {
 }
 
 String ResourceLoader::get_import_group_file(const String &p_path) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -727,14 +706,7 @@ String ResourceLoader::get_import_group_file(const String &p_path) {
 }
 
 bool ResourceLoader::is_import_valid(const String &p_path) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -752,14 +724,7 @@ bool ResourceLoader::is_import_valid(const String &p_path) {
 }
 
 bool ResourceLoader::is_imported(const String &p_path) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -777,14 +742,7 @@ bool ResourceLoader::is_imported(const String &p_path) {
 }
 
 void ResourceLoader::get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -800,14 +758,7 @@ void ResourceLoader::get_dependencies(const String &p_path, List<String> *p_depe
 }
 
 Error ResourceLoader::rename_dependencies(const String &p_path, const Map<String, String> &p_map) {
-	String path = _path_remap(p_path);
-
-	String local_path;
-	if (path.is_rel_path()) {
-		local_path = "res://" + path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(path);
-	}
+	String local_path = _path_remap(_validate_local_path(p_path));
 
 	for (int i = 0; i < loader_count; i++) {
 		if (!loader[i]->recognize_path(local_path)) {
@@ -825,12 +776,7 @@ Error ResourceLoader::rename_dependencies(const String &p_path, const Map<String
 }
 
 String ResourceLoader::get_resource_type(const String &p_path) {
-	String local_path;
-	if (p_path.is_rel_path()) {
-		local_path = "res://" + p_path;
-	} else {
-		local_path = ProjectSettings::get_singleton()->localize_path(p_path);
-	}
+	String local_path = _validate_local_path(p_path);
 
 	for (int i = 0; i < loader_count; i++) {
 		String result = loader[i]->get_resource_type(local_path);
@@ -842,6 +788,19 @@ String ResourceLoader::get_resource_type(const String &p_path) {
 	return "";
 }
 
+ResourceUID::ID ResourceLoader::get_resource_uid(const String &p_path) {
+	String local_path = _validate_local_path(p_path);
+
+	for (int i = 0; i < loader_count; i++) {
+		ResourceUID::ID id = loader[i]->get_resource_uid(local_path);
+		if (id != ResourceUID::INVALID_ID) {
+			return id;
+		}
+	}
+
+	return ResourceUID::INVALID_ID;
+}
+
 String ResourceLoader::_path_remap(const String &p_path, bool *r_translation_remapped) {
 	String new_path = p_path;
 
diff --git a/core/io/resource_loader.h b/core/io/resource_loader.h
index c656b9a69c..b9e234fdd2 100644
--- a/core/io/resource_loader.h
+++ b/core/io/resource_loader.h
@@ -56,6 +56,7 @@ public:
 	virtual bool recognize_path(const String &p_path, const String &p_for_type = String()) const;
 	virtual bool handles_type(const String &p_type) const;
 	virtual String get_resource_type(const String &p_path) const;
+	virtual ResourceUID::ID get_resource_uid(const String &p_path) const;
 	virtual void get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types = false);
 	virtual Error rename_dependencies(const String &p_path, const Map<String, String> &p_map);
 	virtual bool is_import_valid(const String &p_path) const { return true; }
@@ -157,6 +158,7 @@ public:
 	static void add_resource_format_loader(Ref<ResourceFormatLoader> p_format_loader, bool p_at_front = false);
 	static void remove_resource_format_loader(Ref<ResourceFormatLoader> p_format_loader);
 	static String get_resource_type(const String &p_path);
+	static ResourceUID::ID get_resource_uid(const String &p_path);
 	static void get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types = false);
 	static Error rename_dependencies(const String &p_path, const Map<String, String> &p_map);
 	static bool is_import_valid(const String &p_path);
diff --git a/core/io/resource_saver.cpp b/core/io/resource_saver.cpp
index e1bd4ed7fe..6158f421d1 100644
--- a/core/io/resource_saver.cpp
+++ b/core/io/resource_saver.cpp
@@ -39,6 +39,7 @@ Ref<ResourceFormatSaver> ResourceSaver::saver[MAX_SAVERS];
 int ResourceSaver::saver_count = 0;
 bool ResourceSaver::timestamp_on_save = false;
 ResourceSavedCallback ResourceSaver::save_callback = nullptr;
+ResourceSaverGetResourceIDForPath ResourceSaver::save_get_id_for_path = nullptr;
 
 Error ResourceFormatSaver::save(const String &p_path, const RES &p_resource, uint32_t p_flags) {
 	if (get_script_instance() && get_script_instance()->has_method("_save")) {
@@ -258,3 +259,14 @@ void ResourceSaver::remove_custom_savers() {
 		remove_resource_format_saver(custom_savers[i]);
 	}
 }
+
+ResourceUID::ID ResourceSaver::get_resource_id_for_path(const String &p_path, bool p_generate) {
+	if (save_get_id_for_path) {
+		return save_get_id_for_path(p_path, p_generate);
+	}
+	return ResourceUID::INVALID_ID;
+}
+
+void ResourceSaver::set_get_resource_id_for_path(ResourceSaverGetResourceIDForPath p_callback) {
+	save_get_id_for_path = p_callback;
+}
diff --git a/core/io/resource_saver.h b/core/io/resource_saver.h
index 07154aac4d..2fc8d32126 100644
--- a/core/io/resource_saver.h
+++ b/core/io/resource_saver.h
@@ -48,6 +48,7 @@ public:
 };
 
 typedef void (*ResourceSavedCallback)(Ref<Resource> p_resource, const String &p_path);
+typedef ResourceUID::ID (*ResourceSaverGetResourceIDForPath)(const String &p_path, bool p_generate);
 
 class ResourceSaver {
 	enum {
@@ -58,6 +59,7 @@ class ResourceSaver {
 	static int saver_count;
 	static bool timestamp_on_save;
 	static ResourceSavedCallback save_callback;
+	static ResourceSaverGetResourceIDForPath save_get_id_for_path;
 
 	static Ref<ResourceFormatSaver> _find_custom_resource_format_saver(String path);
 
@@ -80,7 +82,10 @@ public:
 	static void set_timestamp_on_save(bool p_timestamp) { timestamp_on_save = p_timestamp; }
 	static bool get_timestamp_on_save() { return timestamp_on_save; }
 
+	static ResourceUID::ID get_resource_id_for_path(const String &p_path, bool p_generate = false);
+
 	static void set_save_callback(ResourceSavedCallback p_callback);
+	static void set_get_resource_id_for_path(ResourceSaverGetResourceIDForPath p_callback);
 
 	static bool add_custom_resource_format_saver(String script_path);
 	static void remove_custom_resource_format_saver(String script_path);
diff --git a/core/io/resource_uid.cpp b/core/io/resource_uid.cpp
new file mode 100644
index 0000000000..d4e8fcb6b0
--- /dev/null
+++ b/core/io/resource_uid.cpp
@@ -0,0 +1,262 @@
+/*************************************************************************/
+/*  resource_uid.cpp                                                     */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 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.                */
+/*************************************************************************/
+
+#include "resource_uid.h"
+#include "core/crypto/crypto.h"
+#include "core/io/dir_access.h"
+#include "core/io/file_access.h"
+
+static constexpr uint32_t char_count = ('z' - 'a');
+static constexpr uint32_t base = char_count + ('9' - '0');
+
+const char *ResourceUID::CACHE_FILE = "res://.godot/uid_cache.bin";
+
+String ResourceUID::id_to_text(ID p_id) const {
+	if (p_id < 0) {
+		return "uid://<invalid>";
+	}
+	String txt;
+
+	while (p_id) {
+		uint32_t c = p_id % base;
+		if (c < char_count) {
+			txt = String::chr('a' + c) + txt;
+		} else {
+			txt = String::chr('0' + (c - char_count)) + txt;
+		}
+		p_id /= base;
+	}
+
+	return "uid://" + txt;
+}
+
+ResourceUID::ID ResourceUID::text_to_id(const String &p_text) const {
+	if (!p_text.begins_with("uid://") || p_text == "uid://<invalid>") {
+		return INVALID_ID;
+	}
+
+	uint32_t l = p_text.length();
+	uint64_t uid = 0;
+	for (uint32_t i = 6; i < l; i++) {
+		uid *= base;
+		uint32_t c = p_text[i];
+		if (c >= 'a' && c <= 'z') {
+			uid += c - 'a';
+		} else if (c >= '0' && c <= '9') {
+			uid += c - '0' + char_count;
+		} else {
+			return INVALID_ID;
+		}
+	}
+	return ID(uid & 0x7FFFFFFFFFFFFFFF);
+}
+
+ResourceUID::ID ResourceUID::create_id() const {
+	mutex.lock();
+	if (crypto.is_null()) {
+		crypto = Ref<Crypto>(Crypto::create());
+	}
+	mutex.unlock();
+	while (true) {
+		PackedByteArray bytes = crypto->generate_random_bytes(8);
+		ERR_FAIL_COND_V(bytes.size() != 8, INVALID_ID);
+		const uint64_t *ptr64 = (const uint64_t *)bytes.ptr();
+		ID id = int64_t((*ptr64) & 0x7FFFFFFFFFFFFFFF);
+		mutex.lock();
+		bool exists = unique_ids.has(id);
+		mutex.unlock();
+		if (!exists) {
+			return id;
+		}
+	}
+}
+
+bool ResourceUID::has_id(ID p_id) const {
+	MutexLock l(mutex);
+	return unique_ids.has(p_id);
+}
+void ResourceUID::add_id(ID p_id, const String &p_path) {
+	MutexLock l(mutex);
+	ERR_FAIL_COND(unique_ids.has(p_id));
+	Cache c;
+	c.cs = p_path.utf8();
+	unique_ids[p_id] = c;
+	changed = true;
+}
+
+void ResourceUID::set_id(ID p_id, const String &p_path) {
+	MutexLock l(mutex);
+	ERR_FAIL_COND(!unique_ids.has(p_id));
+	CharString cs = p_path.utf8();
+	if (strcmp(cs.ptr(), unique_ids[p_id].cs.ptr()) != 0) {
+		unique_ids[p_id].cs = cs;
+		unique_ids[p_id].saved_to_cache = false; //changed
+		changed = true;
+	}
+}
+
+String ResourceUID::get_id_path(ID p_id) const {
+	MutexLock l(mutex);
+	ERR_FAIL_COND_V(!unique_ids.has(p_id), String());
+	const CharString &cs = unique_ids[p_id].cs;
+	String s(cs.ptr());
+	return s;
+}
+void ResourceUID::remove_id(ID p_id) {
+	MutexLock l(mutex);
+	ERR_FAIL_COND(!unique_ids.has(p_id));
+	unique_ids.erase(p_id);
+}
+
+Error ResourceUID::save_to_cache() {
+	if (!FileAccess::exists(CACHE_FILE)) {
+		DirAccessRef d = DirAccess::create(DirAccess::ACCESS_RESOURCES);
+		d->make_dir_recursive(String(CACHE_FILE).get_base_dir()); //ensure base dir exists
+	}
+
+	FileAccessRef f = FileAccess::open(CACHE_FILE, FileAccess::WRITE);
+	if (!f) {
+		return ERR_CANT_OPEN;
+	}
+
+	MutexLock l(mutex);
+	f->store_32(unique_ids.size());
+
+	cache_entries = 0;
+
+	for (OrderedHashMap<ID, Cache>::Element E = unique_ids.front(); E; E = E.next()) {
+		f->store_64(E.key());
+		uint32_t s = E.get().cs.length();
+		f->store_32(s);
+		f->store_buffer((const uint8_t *)E.get().cs.ptr(), s);
+		E.get().saved_to_cache = true;
+		cache_entries++;
+	}
+
+	changed = false;
+	return OK;
+}
+
+Error ResourceUID::load_from_cache() {
+	FileAccessRef f = FileAccess::open(CACHE_FILE, FileAccess::READ);
+	if (!f) {
+		return ERR_CANT_OPEN;
+	}
+
+	MutexLock l(mutex);
+	unique_ids.clear();
+
+	uint32_t entry_count = f->get_32();
+	for (uint32_t i = 0; i < entry_count; i++) {
+		int64_t id = f->get_64();
+		int32_t len = f->get_32();
+		Cache c;
+		c.cs.resize(len + 1);
+		ERR_FAIL_COND_V(c.cs.size() != len + 1, ERR_FILE_CORRUPT); // out of memory
+		c.cs[len] = 0;
+		int32_t rl = f->get_buffer((uint8_t *)c.cs.ptrw(), len);
+		ERR_FAIL_COND_V(rl != len, ERR_FILE_CORRUPT);
+
+		c.saved_to_cache = true;
+		unique_ids[id] = c;
+	}
+
+	cache_entries = entry_count;
+	changed = false;
+	return OK;
+}
+
+Error ResourceUID::update_cache() {
+	if (!changed) {
+		return OK;
+	}
+
+	if (cache_entries == 0) {
+		return save_to_cache();
+	}
+	MutexLock l(mutex);
+
+	FileAccess *f = nullptr;
+	for (OrderedHashMap<ID, Cache>::Element E = unique_ids.front(); E; E = E.next()) {
+		if (!E.get().saved_to_cache) {
+			if (f == nullptr) {
+				f = FileAccess::open(CACHE_FILE, FileAccess::READ_WRITE); //append
+				if (!f) {
+					return ERR_CANT_OPEN;
+				}
+				f->seek_end();
+			}
+			f->store_64(E.key());
+			uint32_t s = E.get().cs.length();
+			f->store_32(s);
+			f->store_buffer((const uint8_t *)E.get().cs.ptr(), s);
+			E.get().saved_to_cache = true;
+			cache_entries++;
+		}
+	}
+
+	if (f != nullptr) {
+		f->seek(0);
+		f->store_32(cache_entries); //update amount of entries
+		f->close();
+		memdelete(f);
+	}
+
+	changed = false;
+
+	return OK;
+}
+
+void ResourceUID::clear() {
+	cache_entries = 0;
+	unique_ids.clear();
+	changed = false;
+}
+void ResourceUID::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("id_to_text", "id"), &ResourceUID::id_to_text);
+	ClassDB::bind_method(D_METHOD("text_to_id", "text_id"), &ResourceUID::text_to_id);
+
+	ClassDB::bind_method(D_METHOD("create_id"), &ResourceUID::create_id);
+
+	ClassDB::bind_method(D_METHOD("has_id", "id"), &ResourceUID::has_id);
+	ClassDB::bind_method(D_METHOD("add_id", "id", "path"), &ResourceUID::add_id);
+	ClassDB::bind_method(D_METHOD("set_id", "id", "path"), &ResourceUID::set_id);
+	ClassDB::bind_method(D_METHOD("get_id_path", "id"), &ResourceUID::get_id_path);
+	ClassDB::bind_method(D_METHOD("remove_id", "id", "path"), &ResourceUID::remove_id);
+
+	BIND_CONSTANT(INVALID_ID)
+}
+ResourceUID *ResourceUID::singleton = nullptr;
+ResourceUID::ResourceUID() {
+	ERR_FAIL_COND(singleton != nullptr);
+	singleton = this;
+}
+ResourceUID::~ResourceUID() {
+}
diff --git a/core/io/resource_uid.h b/core/io/resource_uid.h
new file mode 100644
index 0000000000..b12138425a
--- /dev/null
+++ b/core/io/resource_uid.h
@@ -0,0 +1,89 @@
+/*************************************************************************/
+/*  resource_uid.h                                                       */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 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 RESOURCE_UUID_H
+#define RESOURCE_UUID_H
+
+#include "core/object/ref_counted.h"
+#include "core/string/string_name.h"
+#include "core/templates/ordered_hash_map.h"
+
+class Crypto;
+class ResourceUID : public Object {
+	GDCLASS(ResourceUID, Object)
+public:
+	typedef int64_t ID;
+	enum {
+		INVALID_ID = -1
+	};
+
+	static const char *CACHE_FILE;
+
+private:
+	mutable Ref<Crypto> crypto;
+	Mutex mutex;
+	struct Cache {
+		CharString cs;
+		bool saved_to_cache = false;
+	};
+
+	OrderedHashMap<ID, Cache> unique_ids; //unique IDs and utf8 paths (less memory used)
+	static ResourceUID *singleton;
+
+	uint32_t cache_entries = 0;
+	bool changed = false;
+
+protected:
+	static void _bind_methods();
+
+public:
+	String id_to_text(ID p_id) const;
+	ID text_to_id(const String &p_text) const;
+
+	ID create_id() const;
+	bool has_id(ID p_id) const;
+	void add_id(ID p_id, const String &p_path);
+	void set_id(ID p_id, const String &p_path);
+	String get_id_path(ID p_id) const;
+	void remove_id(ID p_id);
+
+	Error load_from_cache();
+	Error save_to_cache();
+	Error update_cache();
+
+	void clear();
+
+	static ResourceUID *get_singleton() { return singleton; }
+
+	ResourceUID();
+	~ResourceUID();
+};
+
+#endif // RESOURCEUUID_H
diff --git a/core/object/class_db.cpp b/core/object/class_db.cpp
index a0ed5db70a..57495a4fbd 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -1495,6 +1495,10 @@ void ClassDB::get_resource_base_extensions(List<String> *p_extensions) {
 	}
 }
 
+bool ClassDB::is_resource_extension(const StringName &p_extension) {
+	return resource_base_extensions.has(p_extension);
+}
+
 void ClassDB::get_extensions_for_type(const StringName &p_class, List<String> *p_extensions) {
 	const StringName *K = nullptr;
 
diff --git a/core/object/class_db.h b/core/object/class_db.h
index fd574fd2d8..3a84e9ab38 100644
--- a/core/object/class_db.h
+++ b/core/object/class_db.h
@@ -396,6 +396,7 @@ public:
 	static void add_resource_base_extension(const StringName &p_extension, const StringName &p_class);
 	static void get_resource_base_extensions(List<String> *p_extensions);
 	static void get_extensions_for_type(const StringName &p_class, List<String> *p_extensions);
+	static bool is_resource_extension(const StringName &p_extension);
 
 	static void add_compatibility_class(const StringName &p_class, const StringName &p_fallback);
 
diff --git a/core/register_core_types.cpp b/core/register_core_types.cpp
index eb37267546..c088390cf0 100644
--- a/core/register_core_types.cpp
+++ b/core/register_core_types.cpp
@@ -56,6 +56,7 @@
 #include "core/io/pck_packer.h"
 #include "core/io/resource_format_binary.h"
 #include "core/io/resource_importer.h"
+#include "core/io/resource_uid.h"
 #include "core/io/stream_peer_ssl.h"
 #include "core/io/tcp_server.h"
 #include "core/io/translation_loader_po.h"
@@ -102,6 +103,8 @@ static NativeExtensionManager *native_extension_manager = nullptr;
 extern void register_global_constants();
 extern void unregister_global_constants();
 
+static ResourceUID *resource_uid = nullptr;
+
 void register_core_types() {
 	//consistency check
 	static_assert(sizeof(Callable) <= 16);
@@ -225,6 +228,10 @@ void register_core_types() {
 
 	GDREGISTER_VIRTUAL_CLASS(NativeExtensionManager);
 
+	GDREGISTER_VIRTUAL_CLASS(ResourceUID);
+
+	resource_uid = memnew(ResourceUID);
+
 	native_extension_manager = memnew(NativeExtensionManager);
 
 	ip = IP::create();
@@ -286,6 +293,7 @@ void register_core_singletons() {
 	Engine::get_singleton()->add_singleton(Engine::Singleton("EngineDebugger", _EngineDebugger::get_singleton()));
 	Engine::get_singleton()->add_singleton(Engine::Singleton("Time", Time::get_singleton()));
 	Engine::get_singleton()->add_singleton(Engine::Singleton("NativeExtensionManager", NativeExtensionManager::get_singleton()));
+	Engine::get_singleton()->add_singleton(Engine::Singleton("ResourceUID", ResourceUID::get_singleton()));
 }
 
 void register_core_extensions() {
@@ -304,6 +312,8 @@ void unregister_core_types() {
 	native_extension_manager->deinitialize_extensions(NativeExtension::INITIALIZATION_LEVEL_CORE);
 
 	memdelete(native_extension_manager);
+
+	memdelete(resource_uid);
 	memdelete(_resource_loader);
 	memdelete(_resource_saver);
 	memdelete(_os);