diff --git a/3rd/filesystem.h b/3rd/filesystem.h
index 53f4ad4e..86a63928 100644
--- a/3rd/filesystem.h
+++ b/3rd/filesystem.h
@@ -25,23 +25,6 @@
 // SOFTWARE.
 //
 //---------------------------------------------------------------------------------------
-//
-// To dynamically select std::filesystem where available on most platforms,
-// you could use:
-//
-// #if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || (defined(__cplusplus) && __cplusplus >= 201703L)) && defined(__has_include)
-// #if __has_include(<filesystem>) && (!defined(__MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 101500)
-// #define GHC_USE_STD_FS
-// #include <filesystem>
-// namespace fs = std::filesystem;
-// #endif
-// #endif
-// #ifndef GHC_USE_STD_FS
-// #include <ghc/filesystem.hpp>
-// namespace fs = ghc::filesystem;
-// #endif
-//
-//---------------------------------------------------------------------------------------
 #ifndef GHC_FILESYSTEM_H
 #define GHC_FILESYSTEM_H
 
@@ -53,7 +36,7 @@
 
 #ifndef GHC_OS_DETECTED
 #if defined(__APPLE__) && defined(__MACH__)
-#define GHC_OS_MACOS
+#define GHC_OS_APPLE
 #elif defined(__linux__)
 #define GHC_OS_LINUX
 #if defined(__ANDROID__)
@@ -181,7 +164,7 @@
 #include <langinfo.h>
 #endif
 #endif
-#ifdef GHC_OS_MACOS
+#ifdef GHC_OS_APPLE
 #include <Availability.h>
 #endif
 
@@ -308,7 +291,7 @@
 //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
 // ghc::filesystem version in decimal (major * 10000 + minor * 100 + patch)
-#define GHC_FILESYSTEM_VERSION 10514L
+#define GHC_FILESYSTEM_VERSION 10515L
 
 #if !defined(GHC_WITH_EXCEPTIONS) && (defined(__EXCEPTIONS) || defined(__cpp_exceptions) || defined(_CPPUNWIND))
 #define GHC_WITH_EXCEPTIONS
@@ -1159,6 +1142,10 @@ GHC_FS_API void create_hard_link(const path& to, const path& new_hard_link, std:
 GHC_FS_API uintmax_t hard_link_count(const path& p, std::error_code& ec) noexcept;
 #endif
 
+#if defined(GHC_OS_WINDOWS) && (!defined(__GLIBCXX__) || (defined(_GLIBCXX_HAVE__WFOPEN) && defined(_GLIBCXX_USE_WCHAR_T)))
+#define GHC_HAS_FSTREAM_OPEN_WITH_WCHAR
+#endif
+
 // Non-C++17 add-on std::fstream wrappers with path
 template <class charT, class traits = std::char_traits<charT>>
 class basic_filebuf : public std::basic_filebuf<charT, traits>
@@ -1170,7 +1157,7 @@ class basic_filebuf : public std::basic_filebuf<charT, traits>
     const basic_filebuf& operator=(const basic_filebuf&) = delete;
     basic_filebuf<charT, traits>* open(const path& p, std::ios_base::openmode mode)
     {
-#if defined(GHC_OS_WINDOWS) && !defined(__GLIBCXX__)
+#ifdef GHC_HAS_FSTREAM_OPEN_WITH_WCHAR
         return std::basic_filebuf<charT, traits>::open(p.wstring().c_str(), mode) ? this : 0;
 #else
         return std::basic_filebuf<charT, traits>::open(p.string().c_str(), mode) ? this : 0;
@@ -1183,7 +1170,7 @@ class basic_ifstream : public std::basic_ifstream<charT, traits>
 {
 public:
     basic_ifstream() {}
-#if defined(GHC_OS_WINDOWS) && !defined(__GLIBCXX__)
+#ifdef GHC_HAS_FSTREAM_OPEN_WITH_WCHAR
     explicit basic_ifstream(const path& p, std::ios_base::openmode mode = std::ios_base::in)
         : std::basic_ifstream<charT, traits>(p.wstring().c_str(), mode)
     {
@@ -1206,7 +1193,7 @@ class basic_ofstream : public std::basic_ofstream<charT, traits>
 {
 public:
     basic_ofstream() {}
-#if defined(GHC_OS_WINDOWS) && !defined(__GLIBCXX__)
+#ifdef GHC_HAS_FSTREAM_OPEN_WITH_WCHAR
     explicit basic_ofstream(const path& p, std::ios_base::openmode mode = std::ios_base::out)
         : std::basic_ofstream<charT, traits>(p.wstring().c_str(), mode)
     {
@@ -1229,7 +1216,7 @@ class basic_fstream : public std::basic_fstream<charT, traits>
 {
 public:
     basic_fstream() {}
-#if defined(GHC_OS_WINDOWS) && !defined(__GLIBCXX__)
+#ifdef GHC_HAS_FSTREAM_OPEN_WITH_WCHAR
     explicit basic_fstream(const path& p, std::ios_base::openmode mode = std::ios_base::in | std::ios_base::out)
         : std::basic_fstream<charT, traits>(p.wstring().c_str(), mode)
     {
@@ -3170,7 +3157,7 @@ GHC_INLINE path path::extension() const
         auto iter = end();
         const auto& fn = *--iter;
         impl_string_type::size_type pos = fn._path.rfind('.');
-        if (pos != std::string::npos && pos > 0) {
+        if (pos != std::string::npos && pos > 0 && fn._path != "..") {
             return path(fn._path.substr(pos), native_format);
         }
     }
@@ -4650,9 +4637,11 @@ GHC_INLINE void last_write_time(const path& p, file_time_type new_time, std::err
     if (!::SetFileTime(file.get(), 0, 0, &ft)) {
         ec = detail::make_system_error();
     }
-#elif defined(GHC_OS_MACOS) && \
-    (__MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_13) || (__IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_11_0) || \
-    (__TV_OS_VERSION_MIN_REQUIRED < __TVOS_11_0) || (__WATCH_OS_VERSION_MIN_REQUIRED < __WATCHOS_4_0)
+#elif defined(GHC_OS_APPLE) && \
+    (__MAC_OS_X_VERSION_MIN_REQUIRED && __MAC_OS_X_VERSION_MIN_REQUIRED < 101300 \
+     || __IPHONE_OS_VERSION_MIN_REQUIRED && __IPHONE_OS_VERSION_MIN_REQUIRED < 110000 \
+     || __TV_OS_VERSION_MIN_REQUIRED && __TVOS_VERSION_MIN_REQUIRED < 110000 \
+     || __WATCH_OS_VERSION_MIN_REQUIRED && __WATCHOS_VERSION_MIN_REQUIRED < 40000)
     struct ::stat fs;
     if (::stat(p.c_str(), &fs) == 0) {
         struct ::timeval tv[2];