Implement Resource UIDs

* Most resource types now have unique identifiers.
* Applies to text, binary and imported resources.
* File formats reference both by text and UID (when available). UID always has priority.
* Resource UIDs are 64 bits for better compatibility with the engine.
* Can be represented and used textually, example `uuid://dapwmgsmnl28u`.
* A special binary cache file is used and exported, containing the mappings.

Example of how it looks:

```GDScript
[gd_scene load_steps=2 format=3 uid="uid://dw86wq31afig2"]

[ext_resource type="PackedScene" uid="uid://bt36ojelx8q6c" path="res://subscene.scn" id="1_t56hs"]
```

GDScript, shaders and other special resource files can't currently provide UIDs, but this should be doable with special keywords on the files.
This will be reserved for future PRs.

25 files changed, 901 insertions, 127 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 e889586afc..38ad541a40 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 f612b84404..6819511eb9 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 c5dfe1f2b0..b685f973e8 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 80cb85fba3..bdfc7538a0 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")) {
@@ -259,3 +260,14 @@ 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 e2db5918e3..f871dd464a 100644
--- a/core/object/class_db.cpp
+++ b/core/object/class_db.cpp
@@ -1496,6 +1496,10 @@ 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);
diff --git a/doc/classes/@GlobalScope.xml b/doc/classes/@GlobalScope.xml
index d0bd517050..c0e8b76969 100644
--- a/doc/classes/@GlobalScope.xml
+++ b/doc/classes/@GlobalScope.xml
@@ -1259,6 +1259,8 @@
 		<member name="ResourceSaver" type="ResourceSaver" setter="" getter="">
 			The [ResourceSaver] singleton.
 		</member>
+		<member name="ResourceUID" type="ResourceUID" setter="" getter="">
+		</member>
 		<member name="TextServerManager" type="TextServerManager" setter="" getter="">
 			The [TextServerManager] singleton.
 		</member>
diff --git a/doc/classes/ResourceUID.xml b/doc/classes/ResourceUID.xml
new file mode 100644
index 0000000000..407aed72b2
--- /dev/null
+++ b/doc/classes/ResourceUID.xml
@@ -0,0 +1,73 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="ResourceUID" inherits="Object" version="4.0">
+	<brief_description>
+	</brief_description>
+	<description>
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="add_id">
+			<return type="void">
+			</return>
+			<argument index="0" name="id" type="int">
+			</argument>
+			<argument index="1" name="path" type="String">
+			</argument>
+			<description>
+			</description>
+		</method>
+		<method name="create_id" qualifiers="const">
+			<return type="int">
+			</return>
+			<description>
+			</description>
+		</method>
+		<method name="get_id_path" qualifiers="const">
+			<return type="String">
+			</return>
+			<argument index="0" name="id" type="int">
+			</argument>
+			<description>
+			</description>
+		</method>
+		<method name="has_id" qualifiers="const">
+			<return type="bool">
+			</return>
+			<argument index="0" name="id" type="int">
+			</argument>
+			<description>
+			</description>
+		</method>
+		<method name="id_to_text" qualifiers="const">
+			<return type="String">
+			</return>
+			<argument index="0" name="id" type="int">
+			</argument>
+			<description>
+			</description>
+		</method>
+		<method name="set_id">
+			<return type="void">
+			</return>
+			<argument index="0" name="id" type="int">
+			</argument>
+			<argument index="1" name="path" type="String">
+			</argument>
+			<description>
+			</description>
+		</method>
+		<method name="text_to_id" qualifiers="const">
+			<return type="int">
+			</return>
+			<argument index="0" name="text_id" type="String">
+			</argument>
+			<description>
+			</description>
+		</method>
+	</methods>
+	<constants>
+		<constant name="INVALID_ID" value="-1">
+		</constant>
+	</constants>
+</class>
diff --git a/drivers/unix/file_access_unix.cpp b/drivers/unix/file_access_unix.cpp
index 6ea55219bb..f07c654bd6 100644
--- a/drivers/unix/file_access_unix.cpp
+++ b/drivers/unix/file_access_unix.cpp
@@ -111,7 +111,7 @@ Error FileAccessUnix::_open(const String &p_path, int p_mode_flags) {
 		}
 	}
 
-	if (is_backup_save_enabled() && (p_mode_flags & WRITE) && !(p_mode_flags & READ)) {
+	if (is_backup_save_enabled() && (p_mode_flags == WRITE)) {
 		save_path = path;
 		path = path + ".tmp";
 	}
diff --git a/drivers/windows/file_access_windows.cpp b/drivers/windows/file_access_windows.cpp
index d6deda7b5d..f504bad60d 100644
--- a/drivers/windows/file_access_windows.cpp
+++ b/drivers/windows/file_access_windows.cpp
@@ -108,7 +108,7 @@ Error FileAccessWindows::_open(const String &p_path, int p_mode_flags) {
 	}
 #endif
 
-	if (is_backup_save_enabled() && p_mode_flags & WRITE && !(p_mode_flags & READ)) {
+	if (is_backup_save_enabled() && p_mode_flags == WRITE) {
 		save_path = path;
 		path = path + ".tmp";
 	}
diff --git a/editor/dependency_editor.cpp b/editor/dependency_editor.cpp
index c18b8743cd..9824397076 100644
--- a/editor/dependency_editor.cpp
+++ b/editor/dependency_editor.cpp
@@ -180,6 +180,15 @@ void DependencyEditor::_update_list() {
 			path = n;
 			type = "Resource";
 		}
+
+		ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(path);
+		if (uid != ResourceUID::INVALID_ID) {
+			// dependency is in uid format, obtain proper path
+			ERR_CONTINUE(!ResourceUID::get_singleton()->has_id(uid));
+
+			path = ResourceUID::get_singleton()->get_id_path(uid);
+		}
+
 		String name = path.get_file();
 
 		Ref<Texture2D> icon = EditorNode::get_singleton()->get_class_icon(type);
diff --git a/editor/editor_export.cpp b/editor/editor_export.cpp
index fc483b46b7..3866d866d6 100644
--- a/editor/editor_export.cpp
+++ b/editor/editor_export.cpp
@@ -1050,6 +1050,13 @@ Error EditorExportPlatform::export_project_files(const Ref<EditorExportPreset> &
 			return err;
 		}
 	}
+	if (FileAccess::exists(ResourceUID::CACHE_FILE)) {
+		Vector<uint8_t> array = FileAccess::get_file_as_array(ResourceUID::CACHE_FILE);
+		err = p_func(p_udata, ResourceUID::CACHE_FILE, array, idx, total, enc_in_filters, enc_ex_filters, key);
+		if (err != OK) {
+			return err;
+		}
+	}
 
 	// Store text server data if it is supported.
 	if (TS->has_feature(TextServer::FEATURE_USE_SUPPORT_DATA)) {
diff --git a/editor/editor_file_system.cpp b/editor/editor_file_system.cpp
index 82a71c0e0c..8d7096e9f0 100644
--- a/editor/editor_file_system.cpp
+++ b/editor/editor_file_system.cpp
@@ -43,7 +43,7 @@
 
 EditorFileSystem *EditorFileSystem::singleton = nullptr;
 //the name is the version, to keep compatibility with different versions of Godot
-#define CACHE_FILE_NAME "filesystem_cache6"
+#define CACHE_FILE_NAME "filesystem_cache7"
 
 void EditorFileSystemDirectory::sort_files() {
 	files.sort_custom<FileInfoSort>();
@@ -116,7 +116,26 @@ String EditorFileSystemDirectory::get_file_path(int p_idx) const {
 
 Vector<String> EditorFileSystemDirectory::get_file_deps(int p_idx) const {
 	ERR_FAIL_INDEX_V(p_idx, files.size(), Vector<String>());
-	return files[p_idx]->deps;
+	Vector<String> deps;
+
+	for (int i = 0; i < files[p_idx]->deps.size(); i++) {
+		String dep = files[p_idx]->deps[i];
+		int sep_idx = dep.find("::"); //may contain type information, unwanted
+		if (sep_idx != -1) {
+			dep = dep.substr(0, sep_idx);
+		}
+		ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(dep);
+		if (uid != ResourceUID::INVALID_ID) {
+			//return proper dependency resoure from uid
+			if (ResourceUID::get_singleton()->has_id(uid)) {
+				dep = ResourceUID::get_singleton()->get_id_path(uid);
+			} else {
+				continue;
+			}
+		}
+		deps.push_back(dep);
+	}
+	return deps;
 }
 
 bool EditorFileSystemDirectory::get_file_import_is_valid(int p_idx) const {
@@ -234,7 +253,7 @@ void EditorFileSystem::_scan_filesystem() {
 
 			} else {
 				Vector<String> split = l.split("::");
-				ERR_CONTINUE(split.size() != 8);
+				ERR_CONTINUE(split.size() != 9);
 				String name = split[0];
 				String file;
 
@@ -243,15 +262,16 @@ void EditorFileSystem::_scan_filesystem() {
 
 				FileCache fc;
 				fc.type = split[1];
-				fc.modification_time = split[2].to_int();
-				fc.import_modification_time = split[3].to_int();
-				fc.import_valid = split[4].to_int() != 0;
-				fc.import_group_file = split[5].strip_edges();
-				fc.script_class_name = split[6].get_slice("<>", 0);
-				fc.script_class_extends = split[6].get_slice("<>", 1);
-				fc.script_class_icon_path = split[6].get_slice("<>", 2);
-
-				String deps = split[7].strip_edges();
+				fc.uid = split[2].to_int();
+				fc.modification_time = split[3].to_int();
+				fc.import_modification_time = split[4].to_int();
+				fc.import_valid = split[5].to_int() != 0;
+				fc.import_group_file = split[6].strip_edges();
+				fc.script_class_name = split[7].get_slice("<>", 0);
+				fc.script_class_extends = split[7].get_slice("<>", 1);
+				fc.script_class_icon_path = split[7].get_slice("<>", 2);
+
+				String deps = split[8].strip_edges();
 				if (deps.length()) {
 					Vector<String> dp = deps.split("<>");
 					for (int i = 0; i < dp.size(); i++) {
@@ -368,6 +388,7 @@ bool EditorFileSystem::_test_for_reimport(const String &p_path, bool p_only_impo
 	Vector<String> dest_files;
 	String dest_md5 = "";
 	int version = 0;
+	bool found_uid = false;
 
 	while (true) {
 		assign = Variant();
@@ -395,6 +416,8 @@ bool EditorFileSystem::_test_for_reimport(const String &p_path, bool p_only_impo
 				version = value;
 			} else if (assign == "importer") {
 				importer_name = value;
+			} else if (assign == "uid") {
+				found_uid = true;
 			} else if (!p_only_imported_files) {
 				if (assign == "source_file") {
 					source_file = value;
@@ -414,6 +437,10 @@ bool EditorFileSystem::_test_for_reimport(const String &p_path, bool p_only_impo
 		return false; //keep mode, do not reimport
 	}
 
+	if (!found_uid) {
+		return true; //UUID not found, old format, reimport.
+	}
+
 	Ref<ResourceImporter> importer = ResourceFormatImporter::get_singleton()->get_importer_by_name(importer_name);
 
 	if (importer->get_format_version() > version) {
@@ -582,6 +609,9 @@ bool EditorFileSystem::_update_scan_actions() {
 
 	if (reimports.size()) {
 		reimport_files(reimports);
+	} else {
+		//reimport files will update the uid cache file so if nothing was reimported, update it manually
+		ResourceUID::get_singleton()->update_cache();
 	}
 
 	if (first_scan) {
@@ -756,6 +786,7 @@ void EditorFileSystem::_scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess
 
 			if (fc && fc->modification_time == mt && fc->import_modification_time == import_mt && !_test_for_reimport(path, true)) {
 				fi->type = fc->type;
+				fi->uid = fc->uid;
 				fi->deps = fc->deps;
 				fi->modified_time = fc->modification_time;
 				fi->import_modified_time = fc->import_modification_time;
@@ -781,8 +812,14 @@ void EditorFileSystem::_scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess
 					//note: I think this should not happen any longer..
 				}
 
+				if (fc->uid == ResourceUID::INVALID_ID) {
+					// imported files should always have a UUID, so attempt to fetch it.
+					fi->uid = ResourceLoader::get_resource_uid(path);
+				}
+
 			} else {
 				fi->type = ResourceFormatImporter::get_singleton()->get_resource_type(path);
+				fi->uid = ResourceFormatImporter::get_singleton()->get_resource_uid(path);
 				fi->import_group_file = ResourceFormatImporter::get_singleton()->get_import_group_file(path);
 				fi->script_class_name = _get_global_script_class(fi->type, path, &fi->script_class_extends, &fi->script_class_icon_path);
 				fi->modified_time = 0;
@@ -799,6 +836,7 @@ void EditorFileSystem::_scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess
 			if (fc && fc->modification_time == mt) {
 				//not imported, so just update type if changed
 				fi->type = fc->type;
+				fi->uid = fc->uid;
 				fi->modified_time = fc->modification_time;
 				fi->deps = fc->deps;
 				fi->import_modified_time = 0;
@@ -809,6 +847,7 @@ void EditorFileSystem::_scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess
 			} else {
 				//new or modified time
 				fi->type = ResourceLoader::get_resource_type(path);
+				fi->uid = ResourceLoader::get_resource_uid(path);
 				fi->script_class_name = _get_global_script_class(fi->type, path, &fi->script_class_extends, &fi->script_class_icon_path);
 				fi->deps = _get_dependencies(path);
 				fi->modified_time = mt;
@@ -817,6 +856,14 @@ void EditorFileSystem::_scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess
 			}
 		}
 
+		if (fi->uid != ResourceUID::INVALID_ID) {
+			if (ResourceUID::get_singleton()->has_id(fi->uid)) {
+				ResourceUID::get_singleton()->set_id(fi->uid, path);
+			} else {
+				ResourceUID::get_singleton()->add_id(fi->uid, path);
+			}
+		}
+
 		for (int i = 0; i < ScriptServer::get_language_count(); i++) {
 			ScriptLanguage *lang = ScriptServer::get_language(i);
 			if (lang->supports_documentation() && fi->type == lang->get_type()) {
@@ -1181,7 +1228,7 @@ void EditorFileSystem::_save_filesystem_cache(EditorFileSystemDirectory *p_dir,
 		if (p_dir->files[i]->import_group_file != String()) {
 			group_file_cache.insert(p_dir->files[i]->import_group_file);
 		}
-		String s = p_dir->files[i]->file + "::" + p_dir->files[i]->type + "::" + itos(p_dir->files[i]->modified_time) + "::" + itos(p_dir->files[i]->import_modified_time) + "::" + itos(p_dir->files[i]->import_valid) + "::" + p_dir->files[i]->import_group_file + "::" + p_dir->files[i]->script_class_name + "<>" + p_dir->files[i]->script_class_extends + "<>" + p_dir->files[i]->script_class_icon_path;
+		String s = p_dir->files[i]->file + "::" + p_dir->files[i]->type + "::" + itos(p_dir->files[i]->uid) + "::" + itos(p_dir->files[i]->modified_time) + "::" + itos(p_dir->files[i]->import_modified_time) + "::" + itos(p_dir->files[i]->import_valid) + "::" + p_dir->files[i]->import_group_file + "::" + p_dir->files[i]->script_class_name + "<>" + p_dir->files[i]->script_class_extends + "<>" + p_dir->files[i]->script_class_icon_path;
 		s += "::";
 		for (int j = 0; j < p_dir->files[i]->deps.size(); j++) {
 			if (j > 0) {
@@ -1462,6 +1509,11 @@ void EditorFileSystem::update_file(const String &p_file) {
 		//was removed
 		_delete_internal_files(p_file);
 		if (cpos != -1) { // Might've never been part of the editor file system (*.* files deleted in Open dialog).
+			if (fs->files[cpos]->uid != ResourceUID::INVALID_ID) {
+				if (ResourceUID::get_singleton()->has_id(fs->files[cpos]->uid)) {
+					ResourceUID::get_singleton()->remove_id(fs->files[cpos]->uid);
+				}
+			}
 			memdelete(fs->files[cpos]);
 			fs->files.remove(cpos);
 		}
@@ -1472,6 +1524,7 @@ void EditorFileSystem::update_file(const String &p_file) {
 	}
 
 	String type = ResourceLoader::get_resource_type(p_file);
+	ResourceUID::ID uid = ResourceLoader::get_resource_uid(p_file);
 
 	if (cpos == -1) {
 		// The file did not exist, it was added.
@@ -1504,12 +1557,22 @@ void EditorFileSystem::update_file(const String &p_file) {
 	}
 
 	fs->files[cpos]->type = type;
+	fs->files[cpos]->uid = uid;
 	fs->files[cpos]->script_class_name = _get_global_script_class(type, p_file, &fs->files[cpos]->script_class_extends, &fs->files[cpos]->script_class_icon_path);
 	fs->files[cpos]->import_group_file = ResourceLoader::get_import_group_file(p_file);
 	fs->files[cpos]->modified_time = FileAccess::get_modified_time(p_file);
 	fs->files[cpos]->deps = _get_dependencies(p_file);
 	fs->files[cpos]->import_valid = ResourceLoader::is_import_valid(p_file);
 
+	if (uid != ResourceUID::INVALID_ID) {
+		if (ResourceUID::get_singleton()->has_id(uid)) {
+			ResourceUID::get_singleton()->set_id(uid, p_file);
+		} else {
+			ResourceUID::get_singleton()->add_id(uid, p_file);
+		}
+
+		ResourceUID::get_singleton()->update_cache();
+	}
 	// Update preview
 	EditorResourcePreview::get_singleton()->check_for_invalidation(p_file);
 
@@ -1532,7 +1595,6 @@ Error EditorFileSystem::_reimport_group(const String &p_group_file, const Vector
 		ERR_CONTINUE(file_importer_name == String());
 
 		if (importer_name != String() && importer_name != file_importer_name) {
-			print_line("one importer '" + importer_name + "' the other '" + file_importer_name + "'.");
 			EditorNode::get_singleton()->show_warning(vformat(TTR("There are multiple importers for different types pointing to file %s, import aborted"), p_group_file));
 			ERR_FAIL_V(ERR_FILE_CORRUPT);
 		}
@@ -1702,6 +1764,8 @@ void EditorFileSystem::_reimport_file(const String &p_file, const Map<StringName
 		params = *p_custom_options;
 	}
 
+	ResourceUID::ID uid = ResourceUID::INVALID_ID;
+
 	if (FileAccess::exists(p_file + ".import")) {
 		//use existing
 		if (p_custom_options == nullptr) {
@@ -1716,8 +1780,16 @@ void EditorFileSystem::_reimport_file(const String &p_file, const Map<StringName
 						params[E->get()] = cf->get_value("params", E->get());
 					}
 				}
-				if (p_custom_importer == String() && cf->has_section("remap")) {
-					importer_name = cf->get_value("remap", "importer");
+
+				if (cf->has_section("remap")) {
+					if (p_custom_importer == String()) {
+						importer_name = cf->get_value("remap", "importer");
+					}
+
+					if (cf->has_section_key("remap", "uid")) {
+						String uidt = cf->get_value("remap", "uid");
+						uid = ResourceUID::get_singleton()->text_to_id(uidt);
+					}
 				}
 			}
 		}
@@ -1800,6 +1872,12 @@ void EditorFileSystem::_reimport_file(const String &p_file, const Map<StringName
 		f->store_line("type=\"" + importer->get_resource_type() + "\"");
 	}
 
+	if (uid == ResourceUID::INVALID_ID) {
+		uid = ResourceUID::get_singleton()->create_id();
+	}
+
+	f->store_line("uid=\"" + ResourceUID::get_singleton()->id_to_text(uid) + "\""); //store in readable format
+
 	Vector<String> dest_paths;
 
 	if (err == OK) {
@@ -1885,8 +1963,15 @@ void EditorFileSystem::_reimport_file(const String &p_file, const Map<StringName
 	fs->files[cpos]->import_modified_time = FileAccess::get_modified_time(p_file + ".import");
 	fs->files[cpos]->deps = _get_dependencies(p_file);
 	fs->files[cpos]->type = importer->get_resource_type();
+	fs->files[cpos]->uid = uid;
 	fs->files[cpos]->import_valid = ResourceLoader::is_import_valid(p_file);
 
+	if (ResourceUID::get_singleton()->has_id(uid)) {
+		ResourceUID::get_singleton()->set_id(uid, p_file);
+	} else {
+		ResourceUID::get_singleton()->add_id(uid, p_file);
+	}
+
 	//if file is currently up, maybe the source it was loaded from changed, so import math must be updated for it
 	//to reload properly
 	if (ResourceCache::has(p_file)) {
@@ -1937,11 +2022,18 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 	Set<String> groups_to_reimport;
 
 	for (int i = 0; i < p_files.size(); i++) {
-		String group_file = ResourceFormatImporter::get_singleton()->get_import_group_file(p_files[i]);
+		String file = p_files[i];
+
+		ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(file);
+		if (uid != ResourceUID::INVALID_ID && ResourceUID::get_singleton()->has_id(uid)) {
+			file = ResourceUID::get_singleton()->get_id_path(uid);
+		}
+
+		String group_file = ResourceFormatImporter::get_singleton()->get_import_group_file(file);
 
-		if (group_file_cache.has(p_files[i])) {
+		if (group_file_cache.has(file)) {
 			//maybe the file itself is a group!
-			groups_to_reimport.insert(p_files[i]);
+			groups_to_reimport.insert(file);
 			//groups do not belong to grups
 			group_file = String();
 		} else if (group_file != String()) {
@@ -1950,15 +2042,15 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 		} else {
 			//it's a regular file
 			ImportFile ifile;
-			ifile.path = p_files[i];
-			ResourceFormatImporter::get_singleton()->get_import_order_threads_and_importer(p_files[i], ifile.order, ifile.threaded, ifile.importer);
+			ifile.path = file;
+			ResourceFormatImporter::get_singleton()->get_import_order_threads_and_importer(file, ifile.order, ifile.threaded, ifile.importer);
 			reimport_files.push_back(ifile);
 		}
 
 		//group may have changed, so also update group reference
 		EditorFileSystemDirectory *fs = nullptr;
 		int cpos = -1;
-		if (_find_file(p_files[i], &fs, cpos)) {
+		if (_find_file(file, &fs, cpos)) {
 			fs->files.write[cpos]->import_group_file = group_file;
 		}
 	}
@@ -2023,6 +2115,8 @@ void EditorFileSystem::reimport_files(const Vector<String> &p_files) {
 		}
 	}
 
+	ResourceUID::get_singleton()->update_cache(); //after reimporting, update the cache
+
 	_save_filesystem_cache();
 	importing = false;
 	if (!is_scanning()) {
@@ -2108,6 +2202,30 @@ void EditorFileSystem::move_group_file(const String &p_path, const String &p_new
 	}
 }
 
+ResourceUID::ID EditorFileSystem::_resource_saver_get_resource_id_for_path(const String &p_path, bool p_generate) {
+	if (!p_path.is_resource_file() || p_path.begins_with("res://.godot")) {
+		//saved externally (configuration file) or internal file, do not assign an ID.
+		return ResourceUID::INVALID_ID;
+	}
+
+	EditorFileSystemDirectory *fs = nullptr;
+	int cpos = -1;
+
+	if (!singleton->_find_file(p_path, &fs, cpos)) {
+		if (p_generate) {
+			return ResourceUID::get_singleton()->create_id(); //just create a new one, we will be notified of save anyway and fetch the right UUID at that time, to keep things simple.
+		} else {
+			return ResourceUID::INVALID_ID;
+		}
+	} else if (fs->files[cpos]->uid != ResourceUID::INVALID_ID) {
+		return fs->files[cpos]->uid;
+	} else if (p_generate) {
+		return ResourceUID::get_singleton()->create_id(); //just create a new one, we will be notified of save anyway and fetch the right UUID at that time, to keep things simple.
+	} else {
+		return ResourceUID::INVALID_ID;
+	}
+}
+
 void EditorFileSystem::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_filesystem"), &EditorFileSystem::get_filesystem);
 	ClassDB::bind_method(D_METHOD("is_scanning"), &EditorFileSystem::is_scanning);
@@ -2169,8 +2287,11 @@ EditorFileSystem::EditorFileSystem() {
 	scan_changes_pending = false;
 	revalidate_import_files = false;
 	import_threads.init();
+	ResourceUID::get_singleton()->clear(); //will be updated on scan
+	ResourceSaver::set_get_resource_id_for_path(_resource_saver_get_resource_id_for_path);
 }
 
 EditorFileSystem::~EditorFileSystem() {
 	import_threads.finish();
+	ResourceSaver::set_get_resource_id_for_path(nullptr);
 }
diff --git a/editor/editor_file_system.h b/editor/editor_file_system.h
index 37eee13c16..9dce29d09c 100644
--- a/editor/editor_file_system.h
+++ b/editor/editor_file_system.h
@@ -55,6 +55,7 @@ class EditorFileSystemDirectory : public Object {
 	struct FileInfo {
 		String file;
 		StringName type;
+		ResourceUID::ID uid = ResourceUID::INVALID_ID;
 		uint64_t modified_time = 0;
 		uint64_t import_modified_time = 0;
 		bool import_valid = false;
@@ -159,6 +160,7 @@ class EditorFileSystem : public Node {
 	/* Used for reading the filesystem cache file */
 	struct FileCache {
 		String type;
+		ResourceUID::ID uid = ResourceUID::INVALID_ID;
 		uint64_t modification_time = 0;
 		uint64_t import_modification_time = 0;
 		Vector<String> deps;
@@ -251,6 +253,8 @@ class EditorFileSystem : public Node {
 
 	void _reimport_thread(uint32_t p_index, ImportThreadData *p_import_data);
 
+	static ResourceUID::ID _resource_saver_get_resource_id_for_path(const String &p_path, bool p_generate);
+
 protected:
 	void _notification(int p_what);
 	static void _bind_methods();
diff --git a/main/main.cpp b/main/main.cpp
index b7f67e8f6c..0a8c814d51 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -1089,6 +1089,8 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	// Initialize user data dir.
 	OS::get_singleton()->ensure_user_data_dir();
 
+	ResourceUID::get_singleton()->load_from_cache(); // load UUIDs from cache.
+
 	GLOBAL_DEF("memory/limits/multithreaded_server/rid_pool_prealloc", 60);
 	ProjectSettings::get_singleton()->set_custom_property_info("memory/limits/multithreaded_server/rid_pool_prealloc",
 			PropertyInfo(Variant::INT,
diff --git a/scene/resources/resource_format_text.cpp b/scene/resources/resource_format_text.cpp
index 5cf107e8ea..a0a8ad08d5 100644
--- a/scene/resources/resource_format_text.cpp
+++ b/scene/resources/resource_format_text.cpp
@@ -413,6 +413,17 @@ Error ResourceLoaderText::load() {
 		String type = next_tag.fields["type"];
 		String id = next_tag.fields["id"];
 
+		if (next_tag.fields.has("uid")) {
+			String uidt = next_tag.fields["uid"];
+			ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(uidt);
+			if (uid != ResourceUID::INVALID_ID && 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);
+			} else {
+				WARN_PRINT(String(res_path + ":" + itos(lines) + " - ext_resource, invalid UUID: " + uidt + " - using text path instead: " + path).utf8().get_data());
+			}
+		}
+
 		if (path.find("://") == -1 && path.is_rel_path()) {
 			// path is relative to file being loaded, so convert to a resource path
 			path = ProjectSettings::get_singleton()->localize_path(local_path.get_base_dir().plus_file(path));
@@ -746,7 +757,18 @@ void ResourceLoaderText::get_dependencies(FileAccess *p_f, List<String> *p_depen
 		String path = next_tag.fields["path"];
 		String type = next_tag.fields["type"];
 
-		if (path.find("://") == -1 && path.is_rel_path()) {
+		bool using_uid = false;
+		if (next_tag.fields.has("uid")) {
+			//if uid exists, return uid in text format, not the path
+			String uidt = next_tag.fields["uid"];
+			ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(uidt);
+			if (uid != ResourceUID::INVALID_ID) {
+				path = ResourceUID::get_singleton()->id_to_text(uid);
+				using_uid = true;
+			}
+		}
+
+		if (!using_uid && path.find("://") == -1 && path.is_rel_path()) {
 			// path is relative to file being loaded, so convert to a resource path
 			path = ProjectSettings::get_singleton()->localize_path(local_path.get_base_dir().plus_file(path));
 		}
@@ -819,6 +841,14 @@ Error ResourceLoaderText::rename_dependencies(FileAccess *p_f, const String &p_p
 			String id = next_tag.fields["id"];
 			String type = next_tag.fields["type"];
 
+			if (next_tag.fields.has("uid")) {
+				String uidt = next_tag.fields["uid"];
+				ResourceUID::ID uid = ResourceUID::get_singleton()->text_to_id(uidt);
+				if (uid != ResourceUID::INVALID_ID && 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 = base_path.plus_file(path).simplify_path();
@@ -835,7 +865,14 @@ Error ResourceLoaderText::rename_dependencies(FileAccess *p_f, const String &p_p
 				path = base_path.path_to_file(path);
 			}
 
-			fw->store_line("[ext_resource path=\"" + path + "\" type=\"" + type + "\" id=\"" + id + "\"]");
+			String s = "[ext_resource type=\"" + type + "\"";
+
+			ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(path);
+			if (uid != ResourceUID::INVALID_ID) {
+				s += " uid=\"" + ResourceUID::get_singleton()->id_to_text(uid) + "\"";
+			}
+			s += " path=\"" + path + "\" id=\"" + id + "\"]";
+			fw->store_line(s); // Bundled.
 
 			tag_end = f->get_position();
 		}
@@ -921,6 +958,12 @@ void ResourceLoaderText::open(FileAccess *p_f, bool p_skip_first_tag) {
 		return;
 	}
 
+	if (tag.fields.has("uid")) {
+		res_uid = ResourceUID::get_singleton()->text_to_id(tag.fields["uid"]);
+	} else {
+		res_uid = ResourceUID::INVALID_ID;
+	}
+
 	if (tag.fields.has("load_steps")) {
 		resources_total = tag.fields["load_steps"];
 	} else {
@@ -976,7 +1019,12 @@ Error ResourceLoaderText::save_as_binary(FileAccess *p_f, const String &p_path)
 
 	bs_save_unicode_string(wf.f, is_scene ? "PackedScene" : resource_type);
 	wf->store_64(0); //offset to import metadata, this is no longer used
-	for (int i = 0; i < 14; i++) {
+
+	f->store_32(ResourceFormatSaverBinaryInstance::FORMAT_FLAG_NAMED_SCENE_IDS | ResourceFormatSaverBinaryInstance::FORMAT_FLAG_UIDS);
+
+	f->store_64(res_uid);
+
+	for (int i = 0; i < 5; i++) {
 		wf->store_32(0); // reserved
 	}
 
@@ -1018,9 +1066,15 @@ Error ResourceLoaderText::save_as_binary(FileAccess *p_f, const String &p_path)
 		String path = next_tag.fields["path"];
 		String type = next_tag.fields["type"];
 		String id = next_tag.fields["id"];
+		ResourceUID::ID uid = ResourceUID::INVALID_ID;
+		if (next_tag.fields.has("uid")) {
+			String uidt = next_tag.fields["uid"];
+			uid = ResourceUID::get_singleton()->text_to_id(uidt);
+		}
 
 		bs_save_unicode_string(wf.f, type);
 		bs_save_unicode_string(wf.f, path);
+		wf.f->store_64(uid);
 
 		int lindex = dummy_read.external_resources.size();
 		Ref<DummyResource> dr;
@@ -1257,6 +1311,32 @@ String ResourceLoaderText::recognize(FileAccess *p_f) {
 	return tag.fields["type"];
 }
 
+ResourceUID::ID ResourceLoaderText::get_uid(FileAccess *p_f) {
+	error = OK;
+
+	lines = 1;
+	f = p_f;
+
+	stream.f = f;
+
+	ignore_resource_parsing = true;
+
+	VariantParser::Tag tag;
+	Error err = VariantParser::parse_tag(&stream, lines, error_text, tag);
+
+	if (err) {
+		_printerr();
+		return ResourceUID::INVALID_ID;
+	}
+
+	if (tag.fields.has("uid")) { //field is optional
+		String uidt = tag.fields["uid"];
+		return ResourceUID::get_singleton()->text_to_id(uidt);
+	}
+
+	return ResourceUID::INVALID_ID;
+}
+
 /////////////////////
 
 RES ResourceFormatLoaderText::load(const String &p_path, const String &p_original_path, Error *r_error, bool p_use_sub_threads, float *r_progress, CacheMode p_cache_mode) {
@@ -1277,7 +1357,6 @@ RES ResourceFormatLoaderText::load(const String &p_path, const String &p_origina
 	loader.local_path = ProjectSettings::get_singleton()->localize_path(path);
 	loader.progress = r_progress;
 	loader.res_path = loader.local_path;
-	//loader.set_local_path( ProjectSettings::get_singleton()->localize_path(p_path) );
 	loader.open(f);
 	err = loader.load();
 	if (r_error) {
@@ -1330,11 +1409,28 @@ String ResourceFormatLoaderText::get_resource_type(const String &p_path) const {
 	ResourceLoaderText loader;
 	loader.local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 	loader.res_path = loader.local_path;
-	//loader.set_local_path( ProjectSettings::get_singleton()->localize_path(p_path) );
 	String r = loader.recognize(f);
 	return ClassDB::get_compatibility_remapped_class(r);
 }
 
+ResourceUID::ID ResourceFormatLoaderText::get_resource_uid(const String &p_path) const {
+	String ext = p_path.get_extension().to_lower();
+
+	if (ext != "tscn" && ext != "tres") {
+		return ResourceUID::INVALID_ID;
+	}
+
+	FileAccess *f = FileAccess::open(p_path, FileAccess::READ);
+	if (!f) {
+		return ResourceUID::INVALID_ID; //could not read
+	}
+
+	ResourceLoaderText loader;
+	loader.local_path = ProjectSettings::get_singleton()->localize_path(p_path);
+	loader.res_path = loader.local_path;
+	return loader.get_uid(f);
+}
+
 void ResourceFormatLoaderText::get_dependencies(const String &p_path, List<String> *p_dependencies, bool p_add_types) {
 	FileAccess *f = FileAccess::open(p_path, FileAccess::READ);
 	if (!f) {
@@ -1344,7 +1440,6 @@ void ResourceFormatLoaderText::get_dependencies(const String &p_path, List<Strin
 	ResourceLoaderText loader;
 	loader.local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 	loader.res_path = loader.local_path;
-	//loader.set_local_path( ProjectSettings::get_singleton()->localize_path(p_path) );
 	loader.get_dependencies(f, p_dependencies, p_add_types);
 }
 
@@ -1357,7 +1452,6 @@ Error ResourceFormatLoaderText::rename_dependencies(const String &p_path, const
 	ResourceLoaderText loader;
 	loader.local_path = ProjectSettings::get_singleton()->localize_path(p_path);
 	loader.res_path = loader.local_path;
-	//loader.set_local_path( ProjectSettings::get_singleton()->localize_path(p_path) );
 	return loader.rename_dependencies(f, p_path, p_map);
 }
 
@@ -1373,7 +1467,6 @@ Error ResourceFormatLoaderText::convert_file_to_binary(const String &p_src_path,
 	const String &path = p_src_path;
 	loader.local_path = ProjectSettings::get_singleton()->localize_path(path);
 	loader.res_path = loader.local_path;
-	//loader.set_local_path( ProjectSettings::get_singleton()->localize_path(p_path) );
 	loader.open(f);
 	return loader.save_as_binary(f, p_dst_path);
 }
@@ -1548,6 +1641,12 @@ Error ResourceFormatSaverTextInstance::save(const String &p_path, const RES &p_r
 		}
 		title += "format=" + itos(FORMAT_VERSION) + "";
 
+		ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(local_path, true);
+
+		if (uid != ResourceUID::INVALID_ID) {
+			title += " uid=\"" + ResourceUID::get_singleton()->id_to_text(uid) + "\"";
+		}
+
 		f->store_string(title);
 		f->store_line("]\n"); // One empty line.
 	}
@@ -1612,7 +1711,14 @@ Error ResourceFormatSaverTextInstance::save(const String &p_path, const RES &p_r
 	for (int i = 0; i < sorted_er.size(); i++) {
 		String p = sorted_er[i].resource->get_path();
 
-		f->store_string("[ext_resource path=\"" + p + "\" type=\"" + sorted_er[i].resource->get_save_class() + "\" id=\"" + sorted_er[i].id + "\"]\n"); // Bundled.
+		String s = "[ext_resource type=\"" + sorted_er[i].resource->get_save_class() + "\"";
+
+		ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(p, false);
+		if (uid != ResourceUID::INVALID_ID) {
+			s += " uid=\"" + ResourceUID::get_singleton()->id_to_text(uid) + "\"";
+		}
+		s += " path=\"" + p + "\" id=\"" + sorted_er[i].id + "\"]\n";
+		f->store_string(s); // Bundled.
 	}
 
 	if (external_resources.size()) {
diff --git a/scene/resources/resource_format_text.h b/scene/resources/resource_format_text.h
index 5173619a17..373e71b2c4 100644
--- a/scene/resources/resource_format_text.h
+++ b/scene/resources/resource_format_text.h
@@ -74,6 +74,8 @@ class ResourceLoaderText {
 
 	mutable int lines = 0;
 
+	ResourceUID::ID res_uid = ResourceUID::INVALID_ID;
+
 	Map<String, String> remaps;
 
 	static Error _parse_sub_resources(void *p_self, VariantParser::Stream *p_stream, Ref<Resource> &r_res, int &line, String &r_err_str) { return reinterpret_cast<ResourceLoaderText *>(p_self)->_parse_sub_resource(p_stream, r_res, line, r_err_str); }
@@ -120,6 +122,7 @@ public:
 
 	void open(FileAccess *p_f, bool p_skip_first_tag = false);
 	String recognize(FileAccess *p_f);
+	ResourceUID::ID get_uid(FileAccess *p_f);
 	void get_dependencies(FileAccess *p_f, List<String> *p_dependencies, bool p_add_types);
 	Error rename_dependencies(FileAccess *p_f, const String &p_path, const Map<String, String> &p_map);
 
@@ -136,6 +139,7 @@ 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);