Override more methods in agi::fs::path

operator<< is used in logging, among other places, and generic_string()
needs to be forced to use UTF-8 just like string()

Fixes #261.

libaegisub/include/libaegisub/fs.h

@@ -54,6 +54,11 @@ class path : public std::filesystem::path {
 		return std::string(reinterpret_cast<const char *>(result.c_str()), result.size());
 	}
 
+	inline std::string generic_string() const {
+		const auto result = std::filesystem::path::generic_u8string();
+		return std::string(reinterpret_cast<const char *>(result.c_str()), result.size());
+	}
+
 	// We do not override wstring() here: While the conversion method for this is technically unspecified here,
 	// it seems to always return UTF-16 in practice. If this ever changes, wstring() can be overwritten or deleted here.
 
@@ -63,6 +68,15 @@ class path : public std::filesystem::path {
 		return path(lhs_ / rhs_);
 	}
 
+	// This will only work if C is char, but for other calls we will get a compiler error, which
+	// is what we want. If operator<< for wostreams is ever needed, the compiler will complain and
+	// an implementation can be added.
+	template <typename C, typename T>
+	inline friend std::basic_ostream<C, T>& operator<<(std::basic_ostream<C, T> &ostr, path const& rhs) {
+		ostr << std::quoted(rhs.string());
+		return ostr;
+	}
+
 #define WRAP_SFP(name) \
 	inline path name() const { \
 		return path(std::filesystem::path::name()); \