Had to rename sfml to sfmlbackend because on Windows the filesystem is case insensitive so include <SFML/*> was accidentally including _my_ <sfml/config.hpp> file.

include/sfmlbackend/config.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include <nlohmann/json.hpp>
+#include <fstream>
+#include <codecvt>
+
+struct Config {
+  nlohmann::json $config;
+  std::string $src_path;
+
+  Config(const std::string src_path);
+
+  Config(nlohmann::json config, std::string src_path)
+    : $config(config), $src_path(src_path) {}
+
+  nlohmann::json &operator[](const std::string &key);
+  nlohmann::json &json() { return $config; };
+  std::wstring wstring(const std::string main_key, const std::string sub_key);
+  std::vector<std::string> keys();
+};