feat(filesystem): add custom save path support per game

- Add custom_save_paths map to Settings::Values
- Implement ReadCustomSavePathValues and SaveCustomSavePathValues in Config
- Update CreateSaveDataFactory to check for custom save paths
- Support per-game title ID save path overrides

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/common/settings.h

@@ -683,6 +683,9 @@ struct Values {
     // Cheats
     // Key: build_id (hex string), Value: set of disabled cheat names
     std::map<std::string, std::set<std::string>> disabled_cheats;
+
+    // Custom Save Paths
+    std::map<u64, std::string> custom_save_paths;
 };
 
 extern Values values;

src/core/hle/service/filesystem/filesystem.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <utility>
@@ -419,8 +420,22 @@ std::shared_ptr<FileSys::SaveDataFactory> FileSystemController::CreateSaveDataFa
     ProgramId program_id) {
     using CitronPath = Common::FS::CitronPath;
     const auto rw_mode = FileSys::OpenMode::ReadWrite;
-
     auto vfs = system.GetFilesystem();
+
+    // Check for a custom save path for the current game.
+    if (Settings::values.custom_save_paths.count(program_id)) {
+        const std::string& custom_path_str = Settings::values.custom_save_paths.at(program_id);
+        const std::filesystem::path custom_path = custom_path_str;
+
+        // If the custom path is valid and points to a directory, use it.
+        if (!custom_path_str.empty() && Common::FS::IsDir(custom_path)) {
+            LOG_INFO(Service_FS, "Using custom save path for program_id={:016X}: {}", program_id, custom_path_str);
+            auto custom_save_directory = vfs->OpenDirectory(custom_path_str, rw_mode);
+            return std::make_shared<FileSys::SaveDataFactory>(system, program_id, std::move(custom_save_directory));
+        }
+    }
+
+    // If no valid custom path was found, use the default NAND directory.
     const auto nand_directory =
         vfs->OpenDirectory(Common::FS::GetCitronPathString(CitronPath::NANDDir), rw_mode);
     return std::make_shared<FileSys::SaveDataFactory>(system, program_id,

src/frontend_common/config.cpp

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: 2023 yuzu Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <algorithm>
@@ -299,6 +300,24 @@ void Config::ReadDebuggingValues() {
     EndGroup();
 }
 
+void Config::ReadCustomSavePathValues() {
+    BeginGroup(std::string("CustomSavePaths"));
+
+    const int size = BeginArray(std::string(""));
+    for (int i = 0; i < size; ++i) {
+        SetArrayIndex(i);
+        const auto title_id = ReadUnsignedIntegerSetting(std::string("title_id"), 0);
+        const auto path = ReadStringSetting(std::string("path"), std::string(""));
+
+        if (title_id != 0 && !path.empty()) {
+            Settings::values.custom_save_paths.insert_or_assign(title_id, path);
+        }
+    }
+    EndArray();
+
+    EndGroup();
+}
+
 #ifdef __unix__
 void Config::ReadLinuxValues() {
     BeginGroup(Settings::TranslateCategory(Settings::Category::Linux));
@@ -438,6 +457,7 @@ void Config::ReadValues() {
     if (global) {
         ReadDataStorageValues();
         ReadDebuggingValues();
+        ReadCustomSavePathValues();
         ReadDisabledAddOnValues();
         ReadDisabledCheatValues();
         ReadNetworkValues();
@@ -542,6 +562,7 @@ void Config::SaveValues() {
         LOG_DEBUG(Config, "Saving global generic configuration values");
         SaveDataStorageValues();
         SaveDebuggingValues();
+        SaveCustomSavePathValues();
         SaveDisabledAddOnValues();
         SaveDisabledCheatValues();
         SaveNetworkValues();
@@ -631,6 +652,22 @@ void Config::SaveDebuggingValues() {
     EndGroup();
 }
 
+void Config::SaveCustomSavePathValues() {
+    BeginGroup(std::string("CustomSavePaths"));
+
+    int i = 0;
+    BeginArray(std::string(""));
+    for (const auto& elem : Settings::values.custom_save_paths) {
+        SetArrayIndex(i);
+        WriteIntegerSetting(std::string("title_id"), elem.first, std::make_optional(static_cast<u64>(0)));
+        WriteStringSetting(std::string("path"), elem.second, std::make_optional(std::string("")));
+        ++i;
+    }
+    EndArray();
+
+    EndGroup();
+}
+
 #ifdef __unix__
 void Config::SaveLinuxValues() {
     BeginGroup(Settings::TranslateCategory(Settings::Category::Linux));

src/frontend_common/config.h

@@ -1,4 +1,5 @@
 // SPDX-FileCopyrightText: 2023 yuzu Emulator Project
+// SPDX-FileCopyrightText: 2025 citron Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #pragma once
@@ -76,6 +77,7 @@ protected:
     void ReadCoreValues();
     void ReadDataStorageValues();
     void ReadDebuggingValues();
+    void ReadCustomSavePathValues();
 #ifdef __unix__
     void ReadLinuxValues();
 #endif
@@ -112,6 +114,7 @@ protected:
     void SaveCoreValues();
     void SaveDataStorageValues();
     void SaveDebuggingValues();
+    void SaveCustomSavePathValues();
 #ifdef __unix__
     void SaveLinuxValues();
 #endif