Make internal unique scene resource ID deterministic

Changes the Resource::generate_scene_unique_id() to be deterministic and
seedable.

Fixes #97110

4 files changed, 27 insertions, 11 deletions

diff --git a/core/io/resource.cpp b/core/io/resource.cpp
index 5f8a4b85a4..0ff4fbe490 100644
--- a/core/io/resource.cpp
+++ b/core/io/resource.cpp
@@ -99,31 +99,42 @@ void Resource::set_path_cache(const String &p_path) {
 	GDVIRTUAL_CALL(_set_path_cache, p_path);
 }
 
+static thread_local RandomPCG unique_id_gen(0, RandomPCG::DEFAULT_INC);
+
+void Resource::seed_scene_unique_id(uint32_t p_seed) {
+	unique_id_gen.seed(p_seed);
+}
+
 String Resource::generate_scene_unique_id() {
 	// Generate a unique enough hash, but still user-readable.
 	// If it's not unique it does not matter because the saver will try again.
-	OS::DateTime dt = OS::get_singleton()->get_datetime();
-	uint32_t hash = hash_murmur3_one_32(OS::get_singleton()->get_ticks_usec());
-	hash = hash_murmur3_one_32(dt.year, hash);
-	hash = hash_murmur3_one_32(dt.month, hash);
-	hash = hash_murmur3_one_32(dt.day, hash);
-	hash = hash_murmur3_one_32(dt.hour, hash);
-	hash = hash_murmur3_one_32(dt.minute, hash);
-	hash = hash_murmur3_one_32(dt.second, hash);
-	hash = hash_murmur3_one_32(Math::rand(), hash);
+	if (unique_id_gen.get_seed() == 0) {
+		OS::DateTime dt = OS::get_singleton()->get_datetime();
+		uint32_t hash = hash_murmur3_one_32(OS::get_singleton()->get_ticks_usec());
+		hash = hash_murmur3_one_32(dt.year, hash);
+		hash = hash_murmur3_one_32(dt.month, hash);
+		hash = hash_murmur3_one_32(dt.day, hash);
+		hash = hash_murmur3_one_32(dt.hour, hash);
+		hash = hash_murmur3_one_32(dt.minute, hash);
+		hash = hash_murmur3_one_32(dt.second, hash);
+		hash = hash_murmur3_one_32(Math::rand(), hash);
+		unique_id_gen.seed(hash);
+	}
+
+	uint32_t random_num = unique_id_gen.rand();
 
 	static constexpr uint32_t characters = 5;
 	static constexpr uint32_t char_count = ('z' - 'a');
 	static constexpr uint32_t base = char_count + ('9' - '0');
 	String id;
 	for (uint32_t i = 0; i < characters; i++) {
-		uint32_t c = hash % base;
+		uint32_t c = random_num % base;
 		if (c < char_count) {
 			id += String::chr('a' + c);
 		} else {
 			id += String::chr('0' + (c - char_count));
 		}
-		hash /= base;
+		random_num /= base;
 	}
 
 	return id;
diff --git a/core/io/resource.h b/core/io/resource.h
index 8966c0233c..015f7ad197 100644
--- a/core/io/resource.h
+++ b/core/io/resource.h
@@ -114,6 +114,7 @@ public:
 	virtual void set_path_cache(const String &p_path); // Set raw path without involving resource cache.
 	_FORCE_INLINE_ bool is_built_in() const { return path_cache.is_empty() || path_cache.contains("::") || path_cache.begins_with("local://"); }
 
+	static void seed_scene_unique_id(uint32_t p_seed);
 	static String generate_scene_unique_id();
 	void set_scene_unique_id(const String &p_id);
 	String get_scene_unique_id() const;
diff --git a/core/io/resource_format_binary.cpp b/core/io/resource_format_binary.cpp
index b4826c356e..3bfa022382 100644
--- a/core/io/resource_format_binary.cpp
+++ b/core/io/resource_format_binary.cpp
@@ -2136,6 +2136,8 @@ static String _resource_get_class(Ref<Resource> p_resource) {
 }
 
 Error ResourceFormatSaverBinaryInstance::save(const String &p_path, const Ref<Resource> &p_resource, uint32_t p_flags) {
+	Resource::seed_scene_unique_id(p_path.hash());
+
 	Error err;
 	Ref<FileAccess> f;
 	if (p_flags & ResourceSaver::FLAG_COMPRESS) {
diff --git a/scene/resources/resource_format_text.cpp b/scene/resources/resource_format_text.cpp
index d531eea311..5aa6bf718c 100644
--- a/scene/resources/resource_format_text.cpp
+++ b/scene/resources/resource_format_text.cpp
@@ -1708,6 +1708,8 @@ static String _resource_get_class(Ref<Resource> p_resource) {
 }
 
 Error ResourceFormatSaverTextInstance::save(const String &p_path, const Ref<Resource> &p_resource, uint32_t p_flags) {
+	Resource::seed_scene_unique_id(p_path.hash()); // Seeding for save path should make it deterministic for importers.
+
 	if (p_path.ends_with(".tscn")) {
 		packed_scene = p_resource;
 	}