game_list: Fix ISO cache bypass in is_from_yml branch for multi-game ISOs (#18683)

Fixes regression from #18546 and #18679.

## Problem
The is_from_yml ISO branch constructed iso_archive unconditionally,
bypassing the cache check inside add_game, making the cache write-only
for yml-sourced ISOs.

## Fix
Added a lightweight index cache entry (iso_path + "//index") storing the
subdir list + mtime. On hit, skips archive construction entirely. On
miss, walks as before and writes the index

rpcs3/Loader/iso_cache.cpp

@@ -19,17 +19,23 @@ namespace
 		return dir;
 	}
 
-	// FNV-64 hash of the ISO path used as the cache filename stem.
+	// FNV-64 hash of the given key used as the cache filename stem.
-	std::string get_cache_stem(const std::string& iso_path)
+	std::string get_cache_stem(std::string_view key)
 	{
 		usz hash = rpcs3::fnv_seed;
-		for (const char c : iso_path)
+		for (const char c : key)
 		{
 			hash ^= static_cast<u8>(c);
 			hash *= rpcs3::fnv_prime;
 		}
 		return fmt::format("%016llx", hash);
 	}
+
+	// Separate stem for the per-ISO subdir index entry.
+	std::string get_index_stem(const std::string& iso_path)
+	{
+		return get_cache_stem(iso_path + "//index");
+	}
 }
 
 namespace iso_cache
@@ -134,15 +140,96 @@ namespace iso_cache
 		}
 	}
 
+	bool load_index(const std::string& iso_path, std::vector<std::string>& out_subdirs)
+	{
+		fs::stat_t iso_stat{};
+		if (!fs::get_stat(iso_path, iso_stat) || iso_stat.is_directory)
+		{
+			return false;
+		}
+
+		const std::string dir      = get_cache_dir();
+		const std::string yml_path = dir + get_index_stem(iso_path) + ".yml";
+
+		const fs::file yml_file(yml_path);
+		if (!yml_file)
+		{
+			return false;
+		}
+
+		const auto [node, error] = yaml_load(yml_file.to_string());
+		if (!error.empty())
+		{
+			iso_cache_log.warning("Failed to parse index YAML for '%s': %s", iso_path, error);
+			return false;
+		}
+
+		const s64 cached_mtime = node["mtime"].as<s64>(0);
+		if (cached_mtime != iso_stat.mtime)
+		{
+			return false;
+		}
+
+		const YAML::Node subdirs_node = node["subdirs"];
+		if (!subdirs_node || !subdirs_node.IsSequence())
+		{
+			return false;
+		}
+
+		for (const auto& entry : subdirs_node)
+		{
+			std::string name = entry.as<std::string>("");
+			if (!name.empty())
+			{
+				out_subdirs.push_back(std::move(name));
+			}
+		}
+
+		return !out_subdirs.empty();
+	}
+
+	void save_index(const std::string& iso_path, const std::vector<std::string>& subdirs)
+	{
+		fs::stat_t iso_stat{};
+		if (!fs::get_stat(iso_path, iso_stat))
+		{
+			return;
+		}
+		const std::string dir      = get_cache_dir();
+		const std::string yml_path = dir + get_index_stem(iso_path) + ".yml";
+
+		YAML::Emitter out;
+		out << YAML::BeginMap;
+		out << YAML::Key << "mtime"   << YAML::Value << static_cast<long long>(iso_stat.mtime);
+		out << YAML::Key << "subdirs" << YAML::Value << YAML::BeginSeq;
+		for (const std::string& s : subdirs)
+		{
+			out << s;
+		}
+		out << YAML::EndSeq;
+		out << YAML::EndMap;
+
+		if (fs::pending_file yml_file(yml_path); yml_file.file)
+		{
+			yml_file.file.write(out.c_str(), out.size());
+			yml_file.commit();
+		}
+		else
+		{
+			iso_cache_log.warning("Failed to write index YAML for '%s'", iso_path);
+		}
+	}
+
 	void cleanup(const std::unordered_set<std::string>& valid_iso_paths)
 	{
 		const std::string dir = get_cache_dir();
 
-		// Build a set of stems that should exist.
+		// Build a set of stems that should exist, including index entries.
 		std::unordered_set<std::string> valid_stems;
 		for (const std::string& path : valid_iso_paths)
 		{
 			valid_stems.insert(get_cache_stem(path));
+			valid_stems.insert(get_index_stem(path));
 		}
 
 		// Delete any cache files whose stem is not in the valid set.

rpcs3/Loader/iso_cache.h

@@ -17,6 +17,7 @@ struct iso_metadata_cache_entry
 	std::vector<u8> icon_data{};
 	std::string movie_path{};
 	std::string audio_path{};
+	std::vector<std::string> subdirs{};
 };
 
 namespace iso_cache
@@ -27,6 +28,9 @@ namespace iso_cache
 	// Persists a populated cache entry to disk.
 	void save(const std::string& iso_path, const std::string& cache_key, const iso_metadata_cache_entry& entry);
 
+	bool load_index(const std::string& iso_path, std::vector<std::string>& out_subdirs);
+	void save_index(const std::string& iso_path, const std::vector<std::string>& subdirs);
+
 	// Remove cache entries for ISOs that are no longer in the scanned set.
 	void cleanup(const std::unordered_set<std::string>& valid_iso_paths);
 }

rpcs3/rpcs3qt/game_list_frame.cpp

@@ -861,10 +861,22 @@ void game_list_frame::OnParsingFinished()
 		{
 			if (is_iso_file(entry.path))
 			{
+				std::vector<std::string> subdirs;
+
+				if (iso_cache::load_index(entry.path, subdirs))
+				{
+					for (const std::string& name : subdirs)
+					{
+						if (m_refresh_watcher.isCanceled()) break;
+						add_game(entry.path, name);
+					}
+
+					return;
+				}
+
 				iso_archive archive(entry.path);
 				const iso_fs_node& root = archive.root();
 				const std::regex ps3_gm_regex("^PS3_GM[[:digit:]]{2}$");
-				bool found = false;
 
 				for (const auto& child : root.children)
 				{
@@ -872,24 +884,26 @@ void game_list_frame::OnParsingFinished()
 					{
 						break;
 					}
-
 					if (!child->metadata.is_directory)
 					{
 						continue;
 					}
 
 					const std::string& name = child->metadata.name;
-
 					if (name == "PS3_GAME" || std::regex_match(name, ps3_gm_regex))
 					{
+						subdirs.push_back(name);
 						add_game(entry.path, name);
-						found = true;
 					}
 				}
-
+				if (subdirs.empty())
-				if (!found)
 				{
 					add_game(entry.path);
+					subdirs.push_back("PS3_GAME");
+				}
+				if (!m_refresh_watcher.isCanceled())
+				{
+					iso_cache::save_index(entry.path, subdirs);
 				}
 
 				return;