path: root/gcc-filesystem.patch

From eda88e06651c9293012212b665ca592c85bef645 Mon Sep 17 00:00:00 2001
From: Liu Hao <lh_mouse@126.com>
Date: Sat, 26 Jan 2019 15:14:38 +0800
Subject: [PATCH] Backport patches for std::filesystem from master.

This is done by running the following commands on `gcc-8-branch`:

  git cherry-pick 861db1097d3f 2fd48392d0a4 70fea18e0bbb d4fd5c4964cf
  git checkout master -- libstdc++-v3/src/filesystem/  \
    libstdc++-v3/include/bits/fs_\* libstdc++-v3/include/std/filesystem

Testsuites and change logs were discarded to reduce the amount of
modification.

Signed-off-by: Liu Hao <lh_mouse@126.com>
---
 libstdc++-v3/config.h.in                      |  12 +
 libstdc++-v3/config/io/basic_file_stdio.cc    |  33 ++
 libstdc++-v3/config/io/basic_file_stdio.h     |   5 +
 libstdc++-v3/configure                        |  35 ++
 libstdc++-v3/configure.ac                     |   2 +
 libstdc++-v3/crossconfig.m4                   |   1 +
 libstdc++-v3/include/bits/fs_dir.h            |  14 +-
 libstdc++-v3/include/bits/fs_path.h           | 250 +++++++-------
 libstdc++-v3/include/bits/fstream.tcc         |  36 ++
 .../include/experimental/bits/fs_path.h       |  74 ++--
 libstdc++-v3/include/std/fstream              | 119 +++++++
 libstdc++-v3/src/filesystem/dir-common.h      |  56 ++-
 libstdc++-v3/src/filesystem/dir.cc            |   5 +-
 libstdc++-v3/src/filesystem/ops-common.h      | 105 +++++-
 libstdc++-v3/src/filesystem/ops.cc            | 186 +++++-----
 libstdc++-v3/src/filesystem/path.cc           |  24 +-
 libstdc++-v3/src/filesystem/std-dir.cc        |   5 +-
 libstdc++-v3/src/filesystem/std-ops.cc        | 318 ++++++++++--------
 libstdc++-v3/src/filesystem/std-path.cc       | 123 ++++---
 19 files changed, 942 insertions(+), 461 deletions(-)

diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index 765cedc6edf..3fb685ce9aa 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -264,6 +264,9 @@
 /* Only used in build directory testsuite_hooks.h. */
 #undef HAVE_LIMIT_VMEM
 
+/* Define to 1 if you have the `link' function. */
+#undef HAVE_LINK
+
 /* Define if futex syscall is available. */
 #undef HAVE_LINUX_FUTEX
 
@@ -339,6 +342,9 @@
 /* Define to 1 if you have the `quick_exit' function. */
 #undef HAVE_QUICK_EXIT
 
+/* Define to 1 if you have the `readlink' function. */
+#undef HAVE_READLINK
+
 /* Define to 1 if you have the `setenv' function. */
 #undef HAVE_SETENV
 
@@ -408,6 +414,9 @@
 /* Define if strxfrm_l is available in <string.h>. */
 #undef HAVE_STRXFRM_L
 
+/* Define to 1 if you have the `symlink' function. */
+#undef HAVE_SYMLINK
+
 /* Define to 1 if the target runtime linker supports binding the same symbol
    to different versions. */
 #undef HAVE_SYMVER_SYMBOL_RENAMING_RUNTIME_SUPPORT
@@ -706,6 +715,9 @@
 /* Define to 1 if you have the `_tanl' function. */
 #undef HAVE__TANL
 
+/* Define to 1 if you have the `_wfopen' function. */
+#undef HAVE__WFOPEN
+
 /* Define to 1 if you have the `__cxa_thread_atexit' function. */
 #undef HAVE___CXA_THREAD_ATEXIT
 
diff --git a/libstdc++-v3/config/io/basic_file_stdio.cc b/libstdc++-v3/config/io/basic_file_stdio.cc
index a46814802cd..09ccd6a4788 100644
--- a/libstdc++-v3/config/io/basic_file_stdio.cc
+++ b/libstdc++-v3/config/io/basic_file_stdio.cc
@@ -249,6 +249,39 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     return __ret;
   }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+  __basic_file<char>*
+  __basic_file<char>::open(const wchar_t* __name, ios_base::openmode __mode)
+  {
+    __basic_file* __ret = NULL;
+    const char* __c_mode = fopen_mode(__mode);
+    if (__c_mode && !this->is_open())
+      {
+	wchar_t __wc_mode[4] = { };
+	int __i = 0;
+	do
+	  {
+	    switch(__c_mode[__i]) {
+	    case 'a': __wc_mode[__i] = L'a'; break;
+	    case 'b': __wc_mode[__i] = L'b'; break;
+	    case 'r': __wc_mode[__i] = L'r'; break;
+	    case 'w': __wc_mode[__i] = L'w'; break;
+	    case '+': __wc_mode[__i] = L'+'; break;
+	    default: return __ret;
+	    }
+	  }
+	while (__c_mode[++__i]);
+
+	if ((_M_cfile = _wfopen(__name, __wc_mode)))
+	  {
+	    _M_cfile_created = true;
+	    __ret = this;
+	  }
+      }
+    return __ret;
+  }
+#endif
+
   bool
   __basic_file<char>::is_open() const throw ()
   { return _M_cfile != 0; }
diff --git a/libstdc++-v3/config/io/basic_file_stdio.h b/libstdc++-v3/config/io/basic_file_stdio.h
index 58f24f670f6..3c857272c57 100644
--- a/libstdc++-v3/config/io/basic_file_stdio.h
+++ b/libstdc++-v3/config/io/basic_file_stdio.h
@@ -84,6 +84,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __basic_file*
       open(const char* __name, ios_base::openmode __mode, int __prot = 0664);
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      __basic_file*
+      open(const wchar_t* __name, ios_base::openmode __mode);
+#endif
+
       __basic_file*
       sys_open(__c_file* __file, ios_base::openmode);
 
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 5535bfa2b5a..b9883d413f6 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -28127,6 +28127,17 @@ eval as_val=\$$as_ac_var
 #define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
 _ACEOF
 
+fi
+done
+
+  for ac_func in _wfopen
+do :
+  ac_fn_c_check_func "$LINENO" "_wfopen" "ac_cv_func__wfopen"
+if test "x$ac_cv_func__wfopen" = x""yes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE__WFOPEN 1
+_ACEOF
+
 fi
 done
 
@@ -66122,6 +66133,17 @@ eval as_val=\$$as_ac_var
 #define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
 _ACEOF
 
+fi
+done
+
+    for ac_func in _wfopen
+do :
+  ac_fn_c_check_func "$LINENO" "_wfopen" "ac_cv_func__wfopen"
+if test "x$ac_cv_func__wfopen" = x""yes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE__WFOPEN 1
+_ACEOF
+
 fi
 done
 
@@ -80025,6 +80047,19 @@ _ACEOF
 
 fi
 
+done
+
+for ac_func in link readlink symlink
+do :
+  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
+ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
+eval as_val=\$$as_ac_var
+   if test "x$as_val" = x""yes; then :
+  cat >>confdefs.h <<_ACEOF
+#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
+_ACEOF
+
+fi
 done
 
 
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index 0ef96270c9c..dde1c4da944 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -263,6 +263,7 @@ if $GLIBCXX_IS_NATIVE; then
 
   AC_CHECK_FUNCS(__cxa_thread_atexit_impl __cxa_thread_atexit)
   AC_CHECK_FUNCS(aligned_alloc posix_memalign memalign _aligned_malloc)
+  AC_CHECK_FUNCS(_wfopen)
 
   # For iconv support.
   AM_ICONV
@@ -419,6 +420,7 @@ GLIBCXX_CHECK_GTHREADS
 
 # For Filesystem TS.
 AC_CHECK_HEADERS([fcntl.h dirent.h sys/statvfs.h utime.h])
+AC_CHECK_FUNCS(link readlink symlink)
 GLIBCXX_ENABLE_FILESYSTEM_TS
 GLIBCXX_CHECK_FILESYSTEM_DEPS
 
diff --git a/libstdc++-v3/crossconfig.m4 b/libstdc++-v3/crossconfig.m4
index cb6e3afff3d..669d87f7602 100644
--- a/libstdc++-v3/crossconfig.m4
+++ b/libstdc++-v3/crossconfig.m4
@@ -199,6 +199,7 @@ case "${host}" in
     GLIBCXX_CHECK_MATH_SUPPORT
     GLIBCXX_CHECK_STDLIB_SUPPORT
     AC_CHECK_FUNCS(aligned_alloc posix_memalign memalign _aligned_malloc)
+    AC_CHECK_FUNCS(_wfopen)
     ;;
   *-netbsd*)
     SECTION_FLAGS='-ffunction-sections -fdata-sections'
diff --git a/libstdc++-v3/include/bits/fs_dir.h b/libstdc++-v3/include/bits/fs_dir.h
index 9ee1cb66b61..6b332e171cf 100644
--- a/libstdc++-v3/include/bits/fs_dir.h
+++ b/libstdc++-v3/include/bits/fs_dir.h
@@ -138,13 +138,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       refresh(__ec);
     }
 
-    void
-    refresh()
-    { _M_type = symlink_status().type(); }
-
-    void
-    refresh(error_code& __ec) noexcept
-    { _M_type = symlink_status(__ec).type(); }
+    void refresh() { _M_type = symlink_status().type(); }
+    void refresh(error_code& __ec) { _M_type = symlink_status(__ec).type(); }
 
     // observers
     const filesystem::path& path() const noexcept { return _M_path; }
@@ -318,10 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     _M_file_type(error_code& __ec) const noexcept
     {
       if (_M_type != file_type::none && _M_type != file_type::symlink)
-	{
-	  __ec.clear();
-	  return _M_type;
-	}
+	return _M_type;
       return status(__ec).type();
     }
 
diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index fb85d489fd8..e3938d06d59 100644
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -37,11 +37,11 @@
 #include <vector>
 #include <locale>
 #include <iosfwd>
+#include <iomanip>
 #include <codecvt>
 #include <string_view>
 #include <system_error>
 #include <bits/stl_algobase.h>
-#include <bits/quoted_string.h>
 #include <bits/locale_conv.h>
 
 #if defined(_WIN32) && !defined(__CYGWIN__)
@@ -65,8 +65,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   /// A filesystem path.
   class path
   {
-    template<typename _CharT>
-      struct __is_encoded_char : std::false_type { };
+    template<typename _CharT, typename _Ch = remove_const_t<_CharT>>
+      using __is_encoded_char
+	= __or_<is_same<_Ch, char>, is_same<_Ch, wchar_t>,
+		is_same<_Ch, char16_t>, is_same<_Ch, char32_t>>;
 
     template<typename _Iter,
 	     typename _Iter_traits = std::iterator_traits<_Iter>>
@@ -106,8 +108,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _Tp1, typename _Tp2 = void>
       using _Path = typename
-	std::enable_if<__and_<__not_<is_same<remove_cv_t<_Tp1>, path>>,
-			      __not_<is_void<_Tp1>>,
+	std::enable_if<__and_<__not_<is_same<_Tp1, path>>,
 			      __constructible_from<_Tp1, _Tp2>>::value,
 		       path>::type;
 
@@ -145,7 +146,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	     typename _Iter = decltype(_S_range_begin(std::declval<_Tp>())),
 	     typename _Val = typename std::iterator_traits<_Iter>::value_type>
       using __value_type_is_char
-	= typename std::enable_if<std::is_same<_Val, char>::value>::type;
+	= std::enable_if_t<std::is_same_v<std::remove_const_t<_Val>, char>>;
 
   public:
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
@@ -231,37 +232,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     // appends
 
-    path& operator/=(const path& __p)
-    {
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-      if (__p.is_absolute()
-	  || (__p.has_root_name() && __p.root_name() != root_name()))
-	operator=(__p);
-      else
-	{
-	  string_type __pathname;
-	  if (__p.has_root_directory())
-	    __pathname = root_name().native();
-	  else if (has_filename() || (!has_root_directory() && is_absolute()))
-	    __pathname = _M_pathname + preferred_separator;
-	  __pathname += __p.relative_path().native(); // XXX is this right?
-	  _M_pathname.swap(__pathname);
-	  _M_split_cmpts();
-	}
-#else
-      // Much simpler, as any path with root-name or root-dir is absolute.
-      if (__p.is_absolute())
-	operator=(__p);
-      else
-	{
-	  if (has_filename() || (_M_type == _Type::_Root_name))
-	    _M_pathname += preferred_separator;
-	  _M_pathname += __p.native();
-	  _M_split_cmpts();
-	}
-#endif
-      return *this;
-    }
+    path& operator/=(const path& __p);
 
     template <class _Source>
       _Path<_Source>&
@@ -377,7 +348,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     bool has_filename() const;
     bool has_stem() const;
     bool has_extension() const;
-    bool is_absolute() const { return has_root_directory(); }
+    bool is_absolute() const;
     bool is_relative() const { return !is_absolute(); }
 
     // generation
@@ -392,6 +363,40 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     iterator begin() const;
     iterator end() const;
 
+    /// Write a path to a stream
+    template<typename _CharT, typename _Traits>
+      friend std::basic_ostream<_CharT, _Traits>&
+      operator<<(std::basic_ostream<_CharT, _Traits>& __os, const path& __p)
+      {
+	__os << std::quoted(__p.string<_CharT, _Traits>());
+	return __os;
+      }
+
+    /// Read a path from a stream
+    template<typename _CharT, typename _Traits>
+      friend std::basic_istream<_CharT, _Traits>&
+      operator>>(std::basic_istream<_CharT, _Traits>& __is, path& __p)
+      {
+	std::basic_string<_CharT, _Traits> __tmp;
+	if (__is >> std::quoted(__tmp))
+	  __p = std::move(__tmp);
+	return __is;
+      }
+
+    // Create a basic_string by reading until a null character.
+    template<typename _InputIterator,
+	     typename _Traits = std::iterator_traits<_InputIterator>,
+	     typename _CharT
+	       = typename std::remove_cv_t<typename _Traits::value_type>>
+      static std::basic_string<_CharT>
+      _S_string_from_iter(_InputIterator __source)
+      {
+	std::basic_string<_CharT> __str;
+	for (_CharT __ch = *__source; __ch != _CharT(); __ch = *++__source)
+	  __str.push_back(__ch);
+	return __str;
+      }
+
   private:
     enum class _Type : unsigned char {
 	_Multi, _Root_name, _Root_dir, _Filename
@@ -404,19 +409,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     enum class _Split { _Stem, _Extension };
 
-    path&
-    _M_append(path __p)
-    {
-      if (__p.is_absolute())
-	operator=(std::move(__p));
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-      else if (__p.has_root_name() && __p.root_name() != root_name())
-	operator=(std::move(__p));
-#endif
-      else
-	operator/=(const_cast<const path&>(__p));
-      return *this;
-    }
+    path& _M_append(path __p);
 
     pair<const string_type*, size_t> _M_find_extension() const;
 
@@ -444,11 +437,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       static string_type
       _S_convert(_InputIterator __src, __null_terminated)
       {
-	using _Tp = typename std::iterator_traits<_InputIterator>::value_type;
-	std::basic_string<typename remove_cv<_Tp>::type> __tmp;
-	for (; *__src != _Tp{}; ++__src)
-	  __tmp.push_back(*__src);
-	return _S_convert(__tmp.c_str(), __tmp.c_str() + __tmp.size());
+	auto __s = _S_string_from_iter(__src);
+	return _S_convert(__s.c_str(), __s.c_str() + __s.size());
       }
 
     static string_type
@@ -468,10 +458,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _S_convert_loc(_InputIterator __src, __null_terminated,
 		     const std::locale& __loc)
       {
-	std::string __tmp;
-	while (*__src != '\0')
-	  __tmp.push_back(*__src++);
-	return _S_convert_loc(__tmp.data(), __tmp.data()+__tmp.size(), __loc);
+	std::string __s = _S_string_from_iter(__src);
+	return _S_convert_loc(__s.data(), __s.data() + __s.size(), __loc);
       }
 
     template<typename _CharT, typename _Traits, typename _Allocator>
@@ -501,25 +489,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     _Type _M_type = _Type::_Filename;
   };
 
-  template<>
-    struct path::__is_encoded_char<char> : std::true_type
-    { using value_type = char; };
-
-  template<>
-    struct path::__is_encoded_char<wchar_t> : std::true_type
-    { using value_type = wchar_t; };
-
-  template<>
-    struct path::__is_encoded_char<char16_t> : std::true_type
-    { using value_type = char16_t; };
-
-  template<>
-    struct path::__is_encoded_char<char32_t> : std::true_type
-    { using value_type = char32_t; };
-
-  template<typename _Tp>
-    struct path::__is_encoded_char<const _Tp> : __is_encoded_char<_Tp> { };
-
   inline void swap(path& __lhs, path& __rhs) noexcept { __lhs.swap(__rhs); }
 
   size_t hash_value(const path& __p) noexcept;
@@ -556,58 +525,50 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     return __result;
   }
 
-  /// Write a path to a stream
-  template<typename _CharT, typename _Traits>
-    basic_ostream<_CharT, _Traits>&
-    operator<<(basic_ostream<_CharT, _Traits>& __os, const path& __p)
-    {
-      auto __tmp = __p.string<_CharT, _Traits>();
-      using __quoted_string
-	= std::__detail::_Quoted_string<decltype(__tmp)&, _CharT>;
-      __os << __quoted_string{__tmp, '"', '\\'};
-      return __os;
-    }
-
-  /// Read a path from a stream
-  template<typename _CharT, typename _Traits>
-    basic_istream<_CharT, _Traits>&
-    operator>>(basic_istream<_CharT, _Traits>& __is, path& __p)
-    {
-      basic_string<_CharT, _Traits> __tmp;
-      using __quoted_string
-	= std::__detail::_Quoted_string<decltype(__tmp)&, _CharT>;
-      if (__is >> __quoted_string{ __tmp, '"', '\\' })
-	__p = std::move(__tmp);
-      return __is;
-    }
-
-  template<typename _Source>
+  template<typename _InputIterator>
     inline auto
-    u8path(const _Source& __source)
-    -> decltype(filesystem::path(__source, std::locale::classic()))
+    u8path(_InputIterator __first, _InputIterator __last)
+    -> decltype(filesystem::path(__first, __last, std::locale::classic()))
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-      const std::string __u8str{__source};
-      return std::filesystem::u8path(__u8str.begin(), __u8str.end());
+      codecvt_utf8<path::value_type> __cvt;
+      path::string_type __tmp;
+      if constexpr (is_pointer_v<_InputIterator>)
+	{
+	  if (__str_codecvt_in(__first, __last, __tmp, __cvt))
+	    return path{ __tmp };
+	}
+      else
+	{
+	  const std::string __u8str{__first, __last};
+	  const char* const __ptr = __u8str.data();
+	  if (__str_codecvt_in(__ptr, __ptr + __u8str.size(), __tmp, __cvt))
+	    return path{ __tmp };
+	}
+      return {};
 #else
-      return path{ __source };
+      return path{ __first, __last };
 #endif
     }
 
-  template<typename _InputIterator>
+  template<typename _Source>
     inline auto
-    u8path(_InputIterator __first, _InputIterator __last)
-    -> decltype(filesystem::path(__first, __last, std::locale::classic()))
+    u8path(const _Source& __source)
+    -> decltype(filesystem::path(__source, std::locale::classic()))
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-      codecvt_utf8<value_type> __cvt;
-      string_type __tmp;
-      if (__str_codecvt_in(__first, __last, __tmp, __cvt))
-	return path{ __tmp };
+      if constexpr (is_convertible_v<const _Source&, std::string_view>)
+	{
+	  const std::string_view __s = __source;
+	  return filesystem::u8path(__s.data(), __s.data() + __s.size());
+	}
       else
-	return {};
+	{
+	  std::string __s = path::_S_string_from_iter(__source);
+	  return filesystem::u8path(__s.data(), __s.data() + __s.size());
+	}
 #else
-      return path{ __first, __last };
+      return path{ __source };
 #endif
     }
 
@@ -916,11 +877,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path::string(const _Allocator& __a) const
     {
       if constexpr (is_same_v<_CharT, value_type>)
+	{
 #if _GLIBCXX_USE_CXX11_ABI
-	return { _M_pathname, __a };
+	  return { _M_pathname, __a };
 #else
-	return { _M_pathname, string_type::size_type(0), __a };
+	  if constexpr (is_same_v<_Allocator, string_type::allocator_type>)
+	    return _M_pathname;
+	  else
+	    return { _M_pathname, string_type::size_type(0), __a };
 #endif
+	}
       else
 	return _S_str_convert<_CharT, _Traits>(_M_pathname, __a);
     }
@@ -1072,6 +1038,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     return ext.first && ext.second != string_type::npos;
   }
 
+  inline bool
+  path::is_absolute() const
+  {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+    return has_root_name() && has_root_directory();
+#else
+    return has_root_directory();
+#endif
+  }
+
   inline path::iterator
   path::begin() const
   {
@@ -1088,6 +1064,38 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     return iterator(this, true);
   }
 
+#ifndef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  inline path& path::operator/=(const path& __p)
+  {
+    // Much simpler than the specification in the standard,
+    // as any path with root-name or root-dir is absolute.
+    if (__p.is_absolute())
+      operator=(__p);
+    else
+      {
+	if (has_filename() || (_M_type == _Type::_Root_name))
+	  _M_pathname += preferred_separator;
+	_M_pathname += __p.native();
+	_M_split_cmpts();
+      }
+    return *this;
+  }
+#endif
+
+  inline path&
+  path::_M_append(path __p)
+  {
+    if (__p.is_absolute())
+      operator=(std::move(__p));
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+    else if (__p.has_root_name() && __p.root_name() != root_name())
+      operator=(std::move(__p));
+#endif
+    else
+      operator/=(const_cast<const path&>(__p));
+    return *this;
+  }
+
   inline path::iterator&
   path::iterator::operator++()
   {
diff --git a/libstdc++-v3/include/bits/fstream.tcc b/libstdc++-v3/include/bits/fstream.tcc
index f23ff7af4eb..d9eff00823a 100644
--- a/libstdc++-v3/include/bits/fstream.tcc
+++ b/libstdc++-v3/include/bits/fstream.tcc
@@ -207,6 +207,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return __ret;
     }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+  template<typename _CharT, typename _Traits>
+    basic_filebuf<_CharT, _Traits>*
+    basic_filebuf<_CharT, _Traits>::
+    open(const wchar_t* __s, ios_base::openmode __mode)
+    {
+      __filebuf_type *__ret = 0;
+      if (!this->is_open())
+	{
+	  _M_file.open(__s, __mode);
+	  if (this->is_open())
+	    {
+	      _M_allocate_internal_buffer();
+	      _M_mode = __mode;
+
+	      // Setup initial buffer to 'uncommitted' mode.
+	      _M_reading = false;
+	      _M_writing = false;
+	      _M_set_buffer(-1);
+
+	      // Reset to initial state.
+	      _M_state_last = _M_state_cur = _M_state_beg;
+
+	      // 27.8.1.3,4
+	      if ((__mode & ios_base::ate)
+		  && this->seekoff(0, ios_base::end, __mode)
+		  == pos_type(off_type(-1)))
+		this->close();
+	      else
+		__ret = this;
+	    }
+	}
+      return __ret;
+    }
+#endif // HAVE__WFOPEN && USE_WCHAR_T
+
   template<typename _CharT, typename _Traits>
     typename basic_filebuf<_CharT, _Traits>::__filebuf_type*
     basic_filebuf<_CharT, _Traits>::
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 088d62f8f43..340cc59d541 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -79,8 +79,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   /// A filesystem path.
   class path
   {
-    template<typename _CharT>
-      struct __is_encoded_char : std::false_type { };
+    template<typename _CharT,
+	     typename _Ch = typename remove_const<_CharT>::type>
+      using __is_encoded_char
+	= __or_<is_same<_Ch, char>, is_same<_Ch, wchar_t>,
+		is_same<_Ch, char16_t>, is_same<_Ch, char32_t>>;
 
     template<typename _Iter,
 	     typename _Iter_traits = std::iterator_traits<_Iter>>
@@ -163,8 +166,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     template<typename _Tp,
 	     typename _Iter = decltype(_S_range_begin(std::declval<_Tp>())),
 	     typename _Val = typename std::iterator_traits<_Iter>::value_type>
-      using __value_type_is_char
-	= typename std::enable_if<std::is_same<_Val, char>::value>::type;
+      using __value_type_is_char = typename std::enable_if<
+	std::is_same<typename std::remove_const<_Val>::type, char>::value
+	>::type;
 
   public:
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
@@ -370,7 +374,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     bool has_filename() const;
     bool has_stem() const;
     bool has_extension() const;
-    bool is_absolute() const { return has_root_directory(); }
+    bool is_absolute() const;
     bool is_relative() const { return !is_absolute(); }
 
     // iterators
@@ -380,6 +384,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     iterator begin() const;
     iterator end() const;
 
+    // Create a basic_string by reading until a null character.
+    template<typename _InputIterator,
+	     typename _Traits = std::iterator_traits<_InputIterator>,
+	     typename _CharT
+	       = typename std::remove_cv<typename _Traits::value_type>::type>
+      static std::basic_string<_CharT>
+      _S_string_from_iter(_InputIterator __source)
+      {
+	std::basic_string<_CharT> __str;
+	for (_CharT __ch = *__source; __ch != _CharT(); __ch = *++__source)
+	  __str.push_back(__ch);
+	return __str;
+      }
+
   private:
     enum class _Type : unsigned char {
 	_Multi, _Root_name, _Root_dir, _Filename
@@ -429,11 +447,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       static string_type
       _S_convert(_InputIterator __src, __null_terminated)
       {
-	using _Tp = typename std::iterator_traits<_InputIterator>::value_type;
-	std::basic_string<typename remove_cv<_Tp>::type> __tmp;
-	for (; *__src != _Tp{}; ++__src)
-	  __tmp.push_back(*__src);
-	return _S_convert(__tmp.c_str(), __tmp.c_str() + __tmp.size());
+	auto __s = _S_string_from_iter(__src);
+	return _S_convert(__s.c_str(), __s.c_str() + __s.size());
       }
 
     static string_type
@@ -453,10 +468,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _S_convert_loc(_InputIterator __src, __null_terminated,
 		     const std::locale& __loc)
       {
-	std::string __tmp;
-	while (*__src != '\0')
-	  __tmp.push_back(*__src++);
-	return _S_convert_loc(__tmp.data(), __tmp.data()+__tmp.size(), __loc);
+	std::string __s = _S_string_from_iter(__src);
+	return _S_convert_loc(__s.data(), __s.data() + __s.size(), __loc);
       }
 
     bool _S_is_dir_sep(value_type __ch)
@@ -526,7 +539,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       auto __tmp = __p.string<_CharT, _Traits>();
       using __quoted_string
 	= std::__detail::_Quoted_string<decltype(__tmp)&, _CharT>;
-      __os << __quoted_string{__tmp, '"', '\\'};
+      __os << __quoted_string{__tmp, _CharT('"'), _CharT('\\')};
       return __os;
     }
 
@@ -538,7 +551,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       basic_string<_CharT, _Traits> __tmp;
       using __quoted_string
 	= std::__detail::_Quoted_string<decltype(__tmp)&, _CharT>;
-      if (__is >> __quoted_string{ __tmp, '"', '\\' })
+      if (__is >> __quoted_string{ __tmp, _CharT('"'), _CharT('\\') })
 	__p = std::move(__tmp);
       return __is;
     }
@@ -596,25 +609,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     std::string _M_what = _M_gen_what();
   };
 
-  template<>
-    struct path::__is_encoded_char<char> : std::true_type
-    { using value_type = char; };
-
-  template<>
-    struct path::__is_encoded_char<wchar_t> : std::true_type
-    { using value_type = wchar_t; };
-
-  template<>
-    struct path::__is_encoded_char<char16_t> : std::true_type
-    { using value_type = char16_t; };
-
-  template<>
-    struct path::__is_encoded_char<char32_t> : std::true_type
-    { using value_type = char32_t; };
-
-  template<typename _Tp>
-    struct path::__is_encoded_char<const _Tp> : __is_encoded_char<_Tp> { };
-
   struct path::_Cmpt : path
   {
     _Cmpt(string_type __s, _Type __t, size_t __pos)
@@ -1001,6 +995,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     return ext.first && ext.second != string_type::npos;
   }
 
+  inline bool
+  path::is_absolute() const
+  {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+    return has_root_name() && has_root_directory();
+#else
+    return has_root_directory();
+#endif
+  }
+
   inline path::iterator
   path::begin() const
   {
diff --git a/libstdc++-v3/include/std/fstream b/libstdc++-v3/include/std/fstream
index 3a5895d68b0..740d12d3bb6 100644
--- a/libstdc++-v3/include/std/fstream
+++ b/libstdc++-v3/include/std/fstream
@@ -304,6 +304,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __filebuf_type*
       open(const char* __s, ios_base::openmode __mode);
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @brief  Opens an external file.
+       *  @param  __s  The name of the file, as a wide character string.
+       *  @param  __mode  The open mode flags.
+       *  @return  @c this on success, NULL on failure
+       */
+      __filebuf_type*
+      open(const wchar_t* __s, ios_base::openmode __mode);
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Opens an external file.
@@ -517,6 +528,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	this->open(__s, __mode);
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @param  Create an input file stream.
+       *  @param  __s  Wide string specifying the filename.
+       *  @param  __mode  Open file in specified mode (see std::ios_base).
+       *
+       *  @c ios_base::in is automatically included in @a __mode.
+       */
+      basic_ifstream(const wchar_t* __s,
+		     ios_base::openmode __mode = ios_base::in)
+      : __istream_type(), _M_filebuf()
+      {
+	this->init(&_M_filebuf);
+	this->open(__s, __mode);
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Create an input file stream.
@@ -632,6 +660,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  this->clear();
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @brief  Opens an external file.
+       *  @param  __s  The name of the file, as a wide character string.
+       *  @param  __mode  The open mode flags.
+       *
+       *  Calls @c std::basic_filebuf::open(__s,__mode|in).  If that function
+       *  fails, @c failbit is set in the stream's error state.
+       */
+      void
+      open(const wchar_t* __s, ios_base::openmode __mode = ios_base::in)
+      {
+	if (!_M_filebuf.open(__s, __mode | ios_base::in))
+	  this->setstate(ios_base::failbit);
+	else
+	  this->clear();
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Opens an external file.
@@ -743,6 +790,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	this->open(__s, __mode);
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @param  Create an output file stream.
+       *  @param  __s  Wide string specifying the filename.
+       *  @param  __mode  Open file in specified mode (see std::ios_base).
+       *
+       *  @c ios_base::out | @c ios_base::trunc is automatically included in
+       *  @a __mode.
+       */
+      basic_ofstream(const wchar_t* __s,
+		     ios_base::openmode __mode = ios_base::out|ios_base::trunc)
+      : __ostream_type(), _M_filebuf()
+      {
+	this->init(&_M_filebuf);
+	this->open(__s, __mode);
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Create an output file stream.
@@ -858,6 +923,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  this->clear();
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @brief  Opens an external file.
+       *  @param  __s  The name of the file.
+       *  @param  __mode  The open mode flags.
+       *
+       *  Calls @c std::basic_filebuf::open(__s,__mode|out).  If that
+       *  function fails, @c failbit is set in the stream's error state.
+       */
+      void
+      open(const wchar_t* __s, ios_base::openmode __mode = ios_base::out)
+      {
+	if (!_M_filebuf.open(__s, __mode | ios_base::out))
+	  this->setstate(ios_base::failbit);
+	else
+	  this->clear();
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Opens an external file.
@@ -969,6 +1053,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	this->open(__s, __mode);
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @param  Create an input/output file stream.
+       *  @param  __s  Wide string specifying the filename.
+       *  @param  __mode  Open file in specified mode (see std::ios_base).
+       */
+      basic_fstream(const wchar_t* __s,
+		    ios_base::openmode __mode = ios_base::in | ios_base::out)
+      : __iostream_type(0), _M_filebuf()
+      {
+	this->init(&_M_filebuf);
+	this->open(__s, __mode);
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Create an input/output file stream.
@@ -1081,6 +1180,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  this->clear();
       }
 
+#if _GLIBCXX_HAVE__WFOPEN && _GLIBCXX_USE_WCHAR_T
+      /**
+       *  @brief  Opens an external file.
+       *  @param  __s  The name of the file.
+       *  @param  __mode  The open mode flags.
+       *
+       *  Calls @c std::basic_filebuf::open(__s,__mode).  If that
+       *  function fails, @c failbit is set in the stream's error state.
+       */
+      void
+      open(const wchar_t* __s,
+	   ios_base::openmode __mode = ios_base::in | ios_base::out)
+      {
+	if (!_M_filebuf.open(__s, __mode))
+	  this->setstate(ios_base::failbit);
+	else
+	  this->clear();
+      }
+#endif
+
 #if __cplusplus >= 201103L
       /**
        *  @brief  Opens an external file.
diff --git a/libstdc++-v3/src/filesystem/dir-common.h b/libstdc++-v3/src/filesystem/dir-common.h
index 21ba01ca970..03875819d04 100644
--- a/libstdc++-v3/src/filesystem/dir-common.h
+++ b/libstdc++-v3/src/filesystem/dir-common.h
@@ -26,6 +26,9 @@
 #define _GLIBCXX_DIR_COMMON_H 1
 
 #include <string.h>  // strcmp
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+#include <wchar.h>  // wcscmp
+#endif
 #ifdef _GLIBCXX_HAVE_DIRENT_H
 # ifdef _GLIBCXX_HAVE_SYS_TYPES_H
 #  include <sys/types.h>
@@ -35,26 +38,42 @@
 # error "the <dirent.h> header is needed to build the Filesystem TS"
 #endif
 
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-# undef opendir
-# define opendir _wopendir
-#endif
-
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 namespace filesystem
 {
+namespace __gnu_posix
+{
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+// Adapt the Windows _wxxx functions to look like POSIX xxx, but for wchar_t*.
+using char_type = wchar_t;
+using DIR = ::_WDIR;
+using dirent = _wdirent;
+inline DIR* opendir(const wchar_t* path) { return ::_wopendir(path); }
+inline dirent* readdir(DIR* dir) { return ::_wreaddir(dir); }
+inline int closedir(DIR* dir) { return ::_wclosedir(dir); }
+#else
+using char_type = char;
+using DIR = ::DIR;
+typedef struct ::dirent dirent;
+using ::opendir;
+using ::readdir;
+using ::closedir;
+#endif
+} // namespace __gnu_posix
+
+namespace posix = __gnu_posix;
 
 struct _Dir_base
 {
-  _Dir_base(DIR* dirp = nullptr) : dirp(dirp) { }
+  _Dir_base(posix::DIR* dirp = nullptr) : dirp(dirp) { }
 
   // If no error occurs then dirp is non-null,
   // otherwise null (whether error ignored or not).
-  _Dir_base(const char* p, bool skip_permission_denied,
+  _Dir_base(const posix::char_type* pathname, bool skip_permission_denied,
 	    error_code& ec) noexcept
-  : dirp(::opendir(p))
+  : dirp(posix::opendir(pathname))
   {
     if (dirp)
       ec.clear();
@@ -72,22 +91,22 @@ struct _Dir_base
 
   _Dir_base& operator=(_Dir_base&&) = delete;
 
-  ~_Dir_base() { if (dirp) ::closedir(dirp); }
+  ~_Dir_base() { if (dirp) posix::closedir(dirp); }
 
-  const struct ::dirent*
+  const posix::dirent*
   advance(bool skip_permission_denied, error_code& ec) noexcept
   {
     ec.clear();
 
     int err = std::exchange(errno, 0);
-    const struct ::dirent* entp = readdir(dirp);
+    const posix::dirent* entp = posix::readdir(dirp);
     // std::swap cannot be used with Bionic's errno
     err = std::exchange(errno, err);
 
     if (entp)
       {
 	// skip past dot and dot-dot
-	if (!strcmp(entp->d_name, ".") || !strcmp(entp->d_name, ".."))
+	if (is_dot_or_dotdot(entp->d_name))
 	  return advance(skip_permission_denied, ec);
 	return entp;
       }
@@ -105,15 +124,24 @@ struct _Dir_base
       }
   }
 
-  DIR*	dirp;
+  static bool is_dot_or_dotdot(const char* s) noexcept
+  { return !strcmp(s, ".") || !strcmp(s, ".."); }
+
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  static bool is_dot_or_dotdot(const wchar_t* s) noexcept
+  { return !wcscmp(s, L".") || !wcscmp(s, L".."); }
+#endif
+
+  posix::DIR*	dirp;
 };
 
 } // namespace filesystem
 
 // BEGIN/END macros must be defined before including this file.
 _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
+
 inline file_type
-get_file_type(const ::dirent& d __attribute__((__unused__)))
+get_file_type(const std::filesystem::__gnu_posix::dirent& d [[gnu::unused]])
 {
 #ifdef _GLIBCXX_HAVE_STRUCT_DIRENT_D_TYPE
   switch (d.d_type)
diff --git a/libstdc++-v3/src/filesystem/dir.cc b/libstdc++-v3/src/filesystem/dir.cc
index 7e712c553c3..01c3decaba6 100644
--- a/libstdc++-v3/src/filesystem/dir.cc
+++ b/libstdc++-v3/src/filesystem/dir.cc
@@ -37,6 +37,7 @@
 #include "dir-common.h"
 
 namespace fs = std::experimental::filesystem;
+namespace posix = std::filesystem::__gnu_posix;
 
 struct fs::_Dir : std::filesystem::_Dir_base
 {
@@ -47,7 +48,7 @@ struct fs::_Dir : std::filesystem::_Dir_base
       path = p;
   }
 
-  _Dir(DIR* dirp, const path& p) : _Dir_base(dirp), path(p) { }
+  _Dir(posix::DIR* dirp, const path& p) : _Dir_base(dirp), path(p) { }
 
   _Dir(_Dir&&) = default;
 
@@ -185,7 +186,7 @@ recursive_directory_iterator(const path& p, directory_options options,
 {
   if (ec)
     ec->clear();
-  if (DIR* dirp = ::opendir(p.c_str()))
+  if (posix::DIR* dirp = posix::opendir(p.c_str()))
     {
       auto sp = std::make_shared<_Dir_stack>();
       sp->push(_Dir{ dirp, p });
diff --git a/libstdc++-v3/src/filesystem/ops-common.h b/libstdc++-v3/src/filesystem/ops-common.h
index bc186836bd4..c1b817189a9 100644
--- a/libstdc++-v3/src/filesystem/ops-common.h
+++ b/libstdc++-v3/src/filesystem/ops-common.h
@@ -34,12 +34,103 @@
 #  include <sys/stat.h>
 # endif
 #endif
+#if !_GLIBCXX_USE_UTIMENSAT && _GLIBCXX_HAVE_UTIME_H
+# include <utime.h> // utime
+#endif
+
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+# include <wchar.h>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 namespace filesystem
 {
+namespace __gnu_posix
+{
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+// Adapt the Windows _wxxx functions to look like POSIX xxx, but for wchar_t*.
+  inline int open(const wchar_t* path, int flags)
+  { return ::_wopen(path, flags); }
+
+  inline int open(const wchar_t* path, int flags, int mode)
+  { return ::_wopen(path, flags, mode); }
+
+  inline int close(int fd)
+  { return ::_close(fd); }
+
+  typedef struct ::_stat stat_type;
+
+  inline int stat(const wchar_t* path, stat_type* buffer)
+  { return ::_wstat(path, buffer); }
+
+  inline lstat(const wchar_t* path, stat_type* buffer)
+  {
+    // TODO symlinks not currently supported
+    return stat(path, buffer);
+  }
+
+  using ::mode_t;
+
+  inline int chmod(const wchar_t* path, mode_t mode)
+  { return ::_wchmod(path, mode); }
+
+  inline int mkdir(const wchar_t* path, mode_t)
+  { return ::_wmkdir(path); }
+
+  inline wchar_t* getcwd(wchar_t* buf, size_t size)
+  { return ::_wgetcwd(buf, size > (size_t)INT_MAX ? INT_MAX : (int)size); }
+
+  inline int chdir(const wchar_t* path)
+  { return ::_wchdir(path); }
+
+#if !_GLIBCXX_USE_UTIMENSAT && _GLIBCXX_HAVE_UTIME_H
+  using utimbuf = _utimbuf;
+
+  inline int utime(const wchar_t* path, utimbuf* times)
+  { return ::_wutime(path, times); }
+#endif
+
+  inline int rename(const wchar_t* oldname, const wchar_t* newname)
+  { return _wrename(oldname, newname); }
+
+  inline int truncate(const wchar_t* path, _off64_t length)
+  {
+    const int fd = ::_wopen(path, _O_BINARY|_O_RDWR);
+    if (fd == -1)
+      return fd;
+    const int ret = ::ftruncate64(fd, length);
+    int err;
+    ::_get_errno(&err);
+    ::_close(fd);
+    ::_set_errno(err);
+    return ret;
+  }
+  using char_type = wchar_t;
+#else // _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  using ::open;
+  using ::close;
+#ifdef _GLIBCXX_HAVE_SYS_STAT_H
+  typedef struct ::stat stat_type;
+  using ::stat;
+  using ::lstat;
+#endif
+  using ::mode_t;
+  using ::chmod;
+  using ::mkdir;
+  using ::getcwd;
+  using ::chdir;
+#if !_GLIBCXX_USE_UTIMENSAT && _GLIBCXX_HAVE_UTIME_H
+  using ::utimbuf;
+  using ::utime;
+#endif
+  using ::rename;
+  using ::truncate;
+  using char_type = char;
+#endif // _GLIBCXX_FILESYSTEM_IS_WINDOWS
+} // namespace __gnu_posix
+
   template<typename Bitmask>
     inline bool is_set(Bitmask obj, Bitmask bits)
     {
@@ -53,7 +144,7 @@ namespace filesystem
   }
 
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-  typedef struct ::stat stat_type;
+  using __gnu_posix::stat_type;
 
   inline std::chrono::system_clock::time_point
   file_time(const stat_type& st, std::error_code& ec) noexcept
@@ -82,11 +173,17 @@ namespace filesystem
   };
 
   bool
-  do_copy_file(const char* from, const char* to,
+  do_copy_file(const __gnu_posix::char_type* from,
+	       const __gnu_posix::char_type* to,
 	       copy_options_existing_file options,
 	       stat_type* from_st, stat_type* to_st,
 	       std::error_code& ec) noexcept;
 
+  void
+  do_space(const __gnu_posix::char_type* pathname,
+	   uintmax_t& capacity, uintmax_t& free, uintmax_t& available,
+	   std::error_code&);
+
 #endif // _GLIBCXX_HAVE_SYS_STAT_H
 
 } // namespace filesystem
@@ -95,7 +192,7 @@ namespace filesystem
 _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
 
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-  typedef struct ::stat stat_type;
+  using std::filesystem::__gnu_posix::stat_type;
 
   inline file_type
   make_file_type(const stat_type& st) noexcept
@@ -111,8 +208,10 @@ _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
       return file_type::block;
     else if (S_ISFIFO(st.st_mode))
       return file_type::fifo;
+#ifdef S_ISLNK // not present in mingw
     else if (S_ISLNK(st.st_mode))
       return file_type::symlink;
+#endif
 #ifdef S_ISSOCK // not present until POSIX:2001
     else if (S_ISSOCK(st.st_mode))
       return file_type::socket;
diff --git a/libstdc++-v3/src/filesystem/ops.cc b/libstdc++-v3/src/filesystem/ops.cc
index de290625e54..40cadbf6270 100644
--- a/libstdc++-v3/src/filesystem/ops.cc
+++ b/libstdc++-v3/src/filesystem/ops.cc
@@ -47,20 +47,17 @@
 #if !_GLIBCXX_USE_UTIMENSAT && _GLIBCXX_HAVE_UTIME_H
 # include <utime.h> // utime
 #endif
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+# include <windows.h>
+#endif
 
 #define _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM \
   namespace experimental { namespace filesystem {
 #define _GLIBCXX_END_NAMESPACE_FILESYSTEM } }
 #include "ops-common.h"
 
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-# undef utime
-# define utime _wutime
-# undef chmod
-# define chmod _wchmod
-#endif
-
 namespace fs = std::experimental::filesystem;
+namespace posix = std::filesystem::__gnu_posix;
 
 fs::path
 fs::absolute(const path& p, const path& base)
@@ -109,7 +106,7 @@ namespace
     void operator()(void* p) const { ::free(p); }
   };
 
-  using char_ptr = std::unique_ptr<char[], free_as_in_malloc>;
+  using char_ptr = std::unique_ptr<fs::path::value_type[], free_as_in_malloc>;
 }
 
 fs::path
@@ -122,7 +119,8 @@ fs::canonical(const path& p, const path& base, error_code& ec)
   char_ptr buf{ nullptr };
 # if _XOPEN_VERSION < 700
   // Not safe to call realpath(path, NULL)
-  buf.reset( (char*)::malloc(PATH_MAX) );
+  using char_type = fs::path::value_type;
+  buf.reset( (char_type*)::malloc(PATH_MAX * sizeof(char_type)) );
 # endif
   if (char* rp = ::realpath(pa.c_str(), buf.get()))
     {
@@ -241,12 +239,13 @@ namespace
   using std::filesystem::is_set;
 
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-  typedef struct ::stat stat_type;
+  using posix::stat_type;
 
   using std::filesystem::is_not_found_errno;
   using std::filesystem::file_time;
   using std::filesystem::do_copy_file;
 #endif // _GLIBCXX_HAVE_SYS_STAT_H
+
 } // namespace
 
 void
@@ -263,15 +262,15 @@ fs::copy(const path& from, const path& to, copy_options options,
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2681. filesystem::copy() cannot copy symlinks
   if (use_lstat || copy_symlinks
-      ? ::lstat(from.c_str(), &from_st)
-      : ::stat(from.c_str(), &from_st))
+      ? posix::lstat(from.c_str(), &from_st)
+      : posix::stat(from.c_str(), &from_st))
     {
       ec.assign(errno, std::generic_category());
       return;
     }
   if (use_lstat
-      ? ::lstat(to.c_str(), &to_st)
-      : ::stat(to.c_str(), &to_st))
+      ? posix::lstat(to.c_str(), &to_st)
+      : posix::stat(to.c_str(), &to_st))
     {
       if (!is_not_found_errno(errno))
 	{
@@ -424,19 +423,6 @@ fs::create_directories(const path& p, error_code& ec) noexcept
       ec = std::make_error_code(errc::invalid_argument);
       return false;
     }
-
-  file_status st = symlink_status(p, ec);
-  if (is_directory(st))
-    return false;
-  else if (ec && !status_known(st))
-    return false;
-  else if (exists(st))
-    {
-      if (!ec)
-	ec = std::make_error_code(std::errc::not_a_directory);
-      return false;
-    }
-
   std::stack<path> missing;
   path pp = p;
 
@@ -445,29 +431,24 @@ fs::create_directories(const path& p, error_code& ec) noexcept
       ec.clear();
       const auto& filename = pp.filename();
       if (!is_dot(filename) && !is_dotdot(filename))
-	{
-	  missing.push(std::move(pp));
-	  pp = missing.top().parent_path();
-	}
-      else
-	pp = pp.parent_path();
+	missing.push(pp);
+      pp.remove_filename();
     }
 
   if (ec || missing.empty())
     return false;
 
-  bool created;
   do
     {
       const path& top = missing.top();
-      created = create_directory(top, ec);
-      if (ec)
-	return false;
+      create_directory(top, ec);
+      if (ec && is_directory(top))
+	ec.clear();
       missing.pop();
     }
-  while (!missing.empty());
+  while (!missing.empty() && !ec);
 
-  return created;
+  return missing.empty();
 }
 
 namespace
@@ -477,8 +458,8 @@ namespace
   {
     bool created = false;
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-    ::mode_t mode = static_cast<std::underlying_type_t<fs::perms>>(perm);
-    if (::mkdir(p.c_str(), mode))
+    posix::mode_t mode = static_cast<std::underlying_type_t<fs::perms>>(perm);
+    if (posix::mkdir(p.c_str(), mode))
       {
 	const int err = errno;
 	if (err != EEXIST || !is_directory(p, ec))
@@ -531,7 +512,7 @@ fs::create_directory(const path& p, const path& attributes,
 {
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
   stat_type st;
-  if (::stat(attributes.c_str(), &st))
+  if (posix::stat(attributes.c_str(), &st))
     {
       ec.assign(errno, std::generic_category());
       return false;
@@ -580,11 +561,16 @@ void
 fs::create_hard_link(const path& to, const path& new_hard_link,
 		     error_code& ec) noexcept
 {
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#ifdef _GLIBCXX_HAVE_LINK
   if (::link(to.c_str(), new_hard_link.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
+#elif defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (CreateHardLinkW(new_hard_link.c_str(), to.c_str(), NULL))
+    ec.clear();
+  else
+    ec.assign((int)GetLastError(), generic_category());
 #else
   ec = std::make_error_code(std::errc::not_supported);
 #endif
@@ -604,7 +590,7 @@ void
 fs::create_symlink(const path& to, const path& new_symlink,
 		   error_code& ec) noexcept
 {
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#ifdef _GLIBCXX_HAVE_SYMLINK
   if (::symlink(to.c_str(), new_symlink.c_str()))
     ec.assign(errno, std::generic_category());
   else
@@ -614,7 +600,6 @@ fs::create_symlink(const path& to, const path& new_symlink,
 #endif
 }
 
-
 fs::path
 fs::current_path()
 {
@@ -630,8 +615,8 @@ fs::current_path(error_code& ec)
 {
   path p;
 #ifdef _GLIBCXX_HAVE_UNISTD_H
-#ifdef __GLIBC__
-  if (char_ptr cwd = char_ptr{::getcwd(nullptr, 0)})
+#if defined __GLIBC__ || defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (char_ptr cwd = char_ptr{posix::getcwd(nullptr, 0)})
     {
       p.assign(cwd.get());
       ec.clear();
@@ -639,6 +624,7 @@ fs::current_path(error_code& ec)
   else
     ec.assign(errno, std::generic_category());
 #else
+#ifdef _PC_PATH_MAX
   long path_max = pathconf(".", _PC_PATH_MAX);
   size_t size;
   if (path_max == -1)
@@ -647,9 +633,15 @@ fs::current_path(error_code& ec)
       size = 10240;
   else
       size = path_max;
+#elif defined(PATH_MAX)
+  size_t size = PATH_MAX;
+#else
+  size_t size = 1024;
+#endif
   for (char_ptr buf; p.empty(); size *= 2)
     {
-      buf.reset((char*)malloc(size));
+      using char_type = fs::path::value_type;
+      buf.reset((char_type*)malloc(size * sizeof(char_type)));
       if (buf)
 	{
 	  if (getcwd(buf.get(), size))
@@ -689,7 +681,7 @@ void
 fs::current_path(const path& p, error_code& ec) noexcept
 {
 #ifdef _GLIBCXX_HAVE_UNISTD_H
-  if (::chdir(p.c_str()))
+  if (posix::chdir(p.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -716,14 +708,14 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
   int err = 0;
   file_status s1, s2;
   stat_type st1, st2;
-  if (::stat(p1.c_str(), &st1) == 0)
+  if (posix::stat(p1.c_str(), &st1) == 0)
     s1 = make_file_status(st1);
   else if (is_not_found_errno(errno))
     s1.type(file_type::not_found);
   else
     err = errno;
 
-  if (::stat(p2.c_str(), &st2) == 0)
+  if (posix::stat(p2.c_str(), &st2) == 0)
     s2 = make_file_status(st2);
   else if (is_not_found_errno(errno))
     s2.type(file_type::not_found);
@@ -773,7 +765,7 @@ namespace
     {
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
       stat_type st;
-      if (::stat(p.c_str(), &st))
+      if (posix::stat(p.c_str(), &st))
 	{
 	  ec.assign(errno, std::generic_category());
 	  return deflt;
@@ -823,7 +815,7 @@ fs::hard_link_count(const path& p)
 std::uintmax_t
 fs::hard_link_count(const path& p, error_code& ec) noexcept
 {
-  return do_stat(p, ec, std::mem_fn(&stat::st_nlink),
+  return do_stat(p, ec, std::mem_fn(&stat_type::st_nlink),
 		 static_cast<uintmax_t>(-1));
 }
 
@@ -899,11 +891,11 @@ fs::last_write_time(const path& p __attribute__((__unused__)),
   else
     ec.clear();
 #elif _GLIBCXX_HAVE_UTIME_H
-  ::utimbuf times;
+  posix::utimbuf times;
   times.modtime = s.count();
   times.actime = do_stat(p, ec, [](const auto& st) { return st.st_atime; },
 			 times.modtime);
-  if (::utime(p.c_str(), &times))
+  if (posix::utime(p.c_str(), &times))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -956,7 +948,7 @@ fs::permissions(const path& p, perms prms, error_code& ec) noexcept
 #else
   if (nofollow && is_symlink(st))
     ec = std::make_error_code(std::errc::operation_not_supported);
-  else if (::chmod(p.c_str(), static_cast<mode_t>(prms)))
+  else if (posix::chmod(p.c_str(), static_cast<mode_t>(prms)))
     err = errno;
 #endif
 
@@ -976,10 +968,10 @@ fs::read_symlink(const path& p)
   return tgt;
 }
 
-fs::path fs::read_symlink(const path& p, error_code& ec)
+fs::path fs::read_symlink(const path& p [[gnu::unused]], error_code& ec)
 {
   path result;
-#ifdef _GLIBCXX_HAVE_SYS_STAT_H
+#if defined(_GLIBCXX_HAVE_READLINK) && defined(_GLIBCXX_HAVE_SYS_STAT_H)
   stat_type st;
   if (::lstat(p.c_str(), &st))
     {
@@ -1033,6 +1025,19 @@ fs::remove(const path& p)
 bool
 fs::remove(const path& p, error_code& ec) noexcept
 {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (exists(symlink_status(p, ec)))
+    {
+      if ((is_directory(p, ec) && RemoveDirectoryW(p.c_str()))
+	  || DeleteFileW(p.c_str()))
+	{
+	  ec.clear();
+	  return true;
+	}
+      else if (!ec)
+	ec.assign((int)GetLastError(), generic_category());
+    }
+#else
   if (::remove(p.c_str()) == 0)
     {
       ec.clear();
@@ -1042,6 +1047,7 @@ fs::remove(const path& p, error_code& ec) noexcept
     ec.clear();
   else
     ec.assign(errno, std::generic_category());
+#endif
   return false;
 }
 
@@ -1095,7 +1101,7 @@ fs::rename(const path& from, const path& to)
 void
 fs::rename(const path& from, const path& to, error_code& ec) noexcept
 {
-  if (::rename(from.c_str(), to.c_str()))
+  if (posix::rename(from.c_str(), to.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -1116,7 +1122,7 @@ fs::resize_file(const path& p, uintmax_t size, error_code& ec) noexcept
 #ifdef _GLIBCXX_HAVE_UNISTD_H
   if (size > static_cast<uintmax_t>(std::numeric_limits<off_t>::max()))
     ec.assign(EINVAL, std::generic_category());
-  else if (::truncate(p.c_str(), size))
+  else if (posix::truncate(p.c_str(), size))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -1144,23 +1150,14 @@ fs::space(const path& p, error_code& ec) noexcept
     static_cast<uintmax_t>(-1),
     static_cast<uintmax_t>(-1)
   };
-#ifdef _GLIBCXX_HAVE_SYS_STATVFS_H
-  struct ::statvfs f;
-  if (::statvfs(p.c_str(), &f))
-      ec.assign(errno, std::generic_category());
-  else
-    {
-      uintmax_t fragment_size = f.f_frsize;
-      info = space_info{
-	f.f_blocks * fragment_size,
-	f.f_bfree * fragment_size,
-	f.f_bavail * fragment_size
-      };
-      ec.clear();
-    }
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  path dir = absolute(p);
+  dir.remove_filename();
+  auto str = dir.c_str();
 #else
-  ec = std::make_error_code(std::errc::not_supported);
+  auto str = p.c_str();
 #endif
+  std::filesystem::do_space(str, info.capacity, info.free, info.available, ec);
   return info;
 }
 
@@ -1170,7 +1167,7 @@ fs::status(const fs::path& p, error_code& ec) noexcept
 {
   file_status status;
   stat_type st;
-  if (::stat(p.c_str(), &st))
+  if (posix::stat(p.c_str(), &st))
     {
       int err = errno;
       ec.assign(err, std::generic_category());
@@ -1194,7 +1191,7 @@ fs::symlink_status(const fs::path& p, std::error_code& ec) noexcept
 {
   file_status status;
   stat_type st;
-  if (::lstat(p.c_str(), &st))
+  if (posix::lstat(p.c_str(), &st))
     {
       int err = errno;
       ec.assign(err, std::generic_category());
@@ -1269,27 +1266,38 @@ fs::path fs::temp_directory_path()
 
 fs::path fs::temp_directory_path(error_code& ec)
 {
+  path p;
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-  ec = std::make_error_code(std::errc::not_supported);
-  return {}; // TODO
+  unsigned len = 1024;
+  std::wstring buf;
+  do
+    {
+      buf.resize(len);
+      len = GetTempPathW(buf.size(), buf.data());
+    } while (len > buf.size());
+
+  if (len == 0)
+    {
+      ec.assign((int)GetLastError(), std::system_category());
+      return p;
+    }
+  buf.resize(len);
+  p = std::move(buf);
 #else
   const char* tmpdir = nullptr;
   const char* env[] = { "TMPDIR", "TMP", "TEMP", "TEMPDIR", nullptr };
   for (auto e = env; tmpdir == nullptr && *e != nullptr; ++e)
     tmpdir = ::getenv(*e);
-  path p = tmpdir ? tmpdir : "/tmp";
+  p = tmpdir ? tmpdir : "/tmp";
   auto st = status(p, ec);
-  if (!ec)
+  if (ec)
+    p.clear();
+  else if (!is_directory(st))
     {
-      if (is_directory(st))
-	{
-	  ec.clear();
-	  return p;
-	}
-      else
-	ec = std::make_error_code(std::errc::not_a_directory);
+      p.clear();
+      ec = std::make_error_code(std::errc::not_a_directory);
     }
-  return {};
 #endif
+  return p;
 }
 
diff --git a/libstdc++-v3/src/filesystem/path.cc b/libstdc++-v3/src/filesystem/path.cc
index 899d94e0067..fb70d30fdca 100644
--- a/libstdc++-v3/src/filesystem/path.cc
+++ b/libstdc++-v3/src/filesystem/path.cc
@@ -61,6 +61,12 @@ path::replace_filename(const path& replacement)
   return *this;
 }
 
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+const fs::path::value_type dot = L'.';
+#else
+const fs::path::value_type dot = '.';
+#endif
+
 path&
 path::replace_extension(const path& replacement)
 {
@@ -78,8 +84,8 @@ path::replace_extension(const path& replacement)
 	  _M_pathname.erase(back._M_pos + ext.second);
 	}
     }
-  if (!replacement.empty() && replacement.native()[0] != '.')
-    _M_pathname += '.';
+  if (!replacement.empty() && replacement.native()[0] != dot)
+    _M_pathname += dot;
   _M_pathname += replacement.native();
   _M_split_cmpts();
   return *this;
@@ -297,7 +303,7 @@ path::has_filename() const
 std::pair<const path::string_type*, std::size_t>
 path::_M_find_extension() const
 {
-  const std::string* s = nullptr;
+  const string_type* s = nullptr;
 
   if (_M_type != _Type::_Multi)
     s = &_M_pathname;
@@ -312,14 +318,14 @@ path::_M_find_extension() const
     {
       if (auto sz = s->size())
 	{
-	  if (sz <= 2 && (*s)[0] == '.')
+	  if (sz <= 2 && (*s)[0] == dot)
 	    {
-	      if (sz == 1 || (*s)[1] == '.')  // filename is "." or ".."
+	      if (sz == 1 || (*s)[1] == dot)  // filename is "." or ".."
 		return { s, string_type::npos };
 	      else
 		return { s, 0 };  // filename is like ".?"
 	    }
-	  return { s, s->rfind('.') };
+	  return { s, s->rfind(dot) };
 	}
     }
   return {};
@@ -405,7 +411,7 @@ path::_M_split_cmpts()
 	{
 	  const auto& last = _M_cmpts.back();
 	  pos = last._M_pos + last._M_pathname.size();
-	  _M_cmpts.emplace_back(string_type(1, '.'), _Type::_Filename, pos);
+	  _M_cmpts.emplace_back(string_type(1, dot), _Type::_Filename, pos);
 	}
     }
 
@@ -495,8 +501,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   std::string filesystem_error::_M_gen_what()
   {
     using std::filesystem::fs_err_concat;
-    return fs_err_concat(system_error::what(), _M_path1.native(),
-			 _M_path2.native());
+    return fs_err_concat(system_error::what(), _M_path1.u8string(),
+			 _M_path2.u8string());
   }
 
 _GLIBCXX_END_NAMESPACE_CXX11
diff --git a/libstdc++-v3/src/filesystem/std-dir.cc b/libstdc++-v3/src/filesystem/std-dir.cc
index 98eb22ab920..4c9a287ad80 100644
--- a/libstdc++-v3/src/filesystem/std-dir.cc
+++ b/libstdc++-v3/src/filesystem/std-dir.cc
@@ -37,6 +37,7 @@
 #include "dir-common.h"
 
 namespace fs = std::filesystem;
+namespace posix = std::filesystem::__gnu_posix;
 
 struct fs::_Dir : _Dir_base
 {
@@ -47,7 +48,7 @@ struct fs::_Dir : _Dir_base
       path = p;
   }
 
-  _Dir(DIR* dirp, const path& p) : _Dir_base(dirp), path(p) { }
+  _Dir(posix::DIR* dirp, const path& p) : _Dir_base(dirp), path(p) { }
 
   _Dir(_Dir&&) = default;
 
@@ -180,7 +181,7 @@ recursive_directory_iterator(const path& p, directory_options options,
                              error_code* ecptr)
 : _M_options(options), _M_pending(true)
 {
-  if (DIR* dirp = ::opendir(p.c_str()))
+  if (posix::DIR* dirp = posix::opendir(p.c_str()))
     {
       if (ecptr)
 	ecptr->clear();
diff --git a/libstdc++-v3/src/filesystem/std-ops.cc b/libstdc++-v3/src/filesystem/std-ops.cc
index c0742d73b5c..e266fa6d3f8 100644
--- a/libstdc++-v3/src/filesystem/std-ops.cc
+++ b/libstdc++-v3/src/filesystem/std-ops.cc
@@ -25,6 +25,7 @@
 #ifndef _GLIBCXX_USE_CXX11_ABI
 # define _GLIBCXX_USE_CXX11_ABI 1
 # define NEED_DO_COPY_FILE
+# define NEED_DO_SPACE
 #endif
 
 #include <filesystem>
@@ -52,19 +53,16 @@
 #if !_GLIBCXX_USE_UTIMENSAT && _GLIBCXX_HAVE_UTIME_H
 # include <utime.h> // utime
 #endif
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+# include <windows.h>
+#endif
 
 #define _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM namespace filesystem {
 #define _GLIBCXX_END_NAMESPACE_FILESYSTEM }
 #include "ops-common.h"
 
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-# undef utime
-# define utime _wutime
-# undef chmod
-# define chmod _wchmod
-#endif
-
 namespace fs = std::filesystem;
+namespace posix = std::filesystem::__gnu_posix;
 
 fs::path
 fs::absolute(const path& p)
@@ -74,7 +72,7 @@ fs::absolute(const path& p)
   path ret = absolute(p, ec);
   if (ec)
     _GLIBCXX_THROW_OR_ABORT(filesystem_error("cannot make absolute path", p,
-	std::make_error_code(errc::not_supported)));
+					     ec));
   return ret;
 #else
   return current_path() / p;
@@ -90,17 +88,28 @@ fs::absolute(const path& p, error_code& ec)
       ec = make_error_code(std::errc::no_such_file_or_directory);
       return ret;
     }
-  if (p.is_absolute())
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  const wstring& s = p.native();
+  uint32_t len = 1024;
+  wstring buf;
+  do
     {
-      ec.clear();
-      ret = p;
-      return ret;
+      buf.resize(len);
+      len = GetFullPathNameW(s.c_str(), len, buf.data(), nullptr);
     }
+  while (len > buf.size());
 
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-  ec = std::make_error_code(errc::not_supported);
+  if (len == 0)
+    ec.assign((int)GetLastError(), std::system_category());
+  else
+    {
+      ec.clear();
+      buf.resize(len);
+      ret = std::move(buf);
+    }
 #else
-  ret = current_path(ec);
+  ec.clear();
+  ret = current_path();
   ret /= p;
 #endif
   return ret;
@@ -131,7 +140,7 @@ namespace
     void operator()(void* p) const { ::free(p); }
   };
 
-  using char_ptr = std::unique_ptr<char[], free_as_in_malloc>;
+  using char_ptr = std::unique_ptr<fs::path::value_type[], free_as_in_malloc>;
 }
 
 fs::path
@@ -146,7 +155,8 @@ fs::canonical(const path& p, error_code& ec)
   char_ptr buf{ nullptr };
 # if _XOPEN_VERSION < 700
   // Not safe to call realpath(path, NULL)
-  buf.reset( (char*)::malloc(PATH_MAX) );
+  using char_type = fs::path::value_type;
+  buf.reset( (char_type*)::malloc(PATH_MAX * sizeof(char_type)) );
 # endif
   if (char* rp = ::realpath(pa.c_str(), buf.get()))
     {
@@ -267,7 +277,7 @@ namespace std::filesystem
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
 #ifdef NEED_DO_COPY_FILE
 bool
-fs::do_copy_file(const char* from, const char* to,
+fs::do_copy_file(const path::value_type* from, const path::value_type* to,
 		 copy_options_existing_file options,
 		 stat_type* from_st, stat_type* to_st,
 		 std::error_code& ec) noexcept
@@ -277,7 +287,7 @@ fs::do_copy_file(const char* from, const char* to,
 
   if (to_st == nullptr)
     {
-      if (::stat(to, &st1))
+      if (posix::stat(to, &st1))
 	{
 	  const int err = errno;
 	  if (!is_not_found_errno(err))
@@ -299,7 +309,7 @@ fs::do_copy_file(const char* from, const char* to,
 
   if (from_st == nullptr)
     {
-      if (::stat(from, &st2))
+      if (posix::stat(from, &st2))
 	{
 	  ec.assign(errno, std::generic_category());
 	  return false;
@@ -357,12 +367,12 @@ fs::do_copy_file(const char* from, const char* to,
     }
 
   struct CloseFD {
-    ~CloseFD() { if (fd != -1) ::close(fd); }
-    bool close() { return ::close(std::exchange(fd, -1)) == 0; }
+    ~CloseFD() { if (fd != -1) posix::close(fd); }
+    bool close() { return posix::close(std::exchange(fd, -1)) == 0; }
     int fd;
   };
 
-  CloseFD in = { ::open(from, O_RDONLY) };
+  CloseFD in = { posix::open(from, O_RDONLY) };
   if (in.fd == -1)
     {
       ec.assign(errno, std::generic_category());
@@ -373,7 +383,7 @@ fs::do_copy_file(const char* from, const char* to,
     oflag |= O_TRUNC;
   else
     oflag |= O_EXCL;
-  CloseFD out = { ::open(to, oflag, S_IWUSR) };
+  CloseFD out = { posix::open(to, oflag, S_IWUSR) };
   if (out.fd == -1)
     {
       if (errno == EEXIST && options.skip)
@@ -383,12 +393,12 @@ fs::do_copy_file(const char* from, const char* to,
       return false;
     }
 
-#ifdef _GLIBCXX_USE_FCHMOD
+#if defined _GLIBCXX_USE_FCHMOD && ! defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
   if (::fchmod(out.fd, from_st->st_mode))
-#elif defined _GLIBCXX_USE_FCHMODAT
+#elif defined _GLIBCXX_USE_FCHMODAT && ! defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
   if (::fchmodat(AT_FDCWD, to, from_st->st_mode, 0))
 #else
-  if (::chmod(to, from_st->st_mode))
+  if (posix::chmod(to, from_st->st_mode))
 #endif
     {
       ec.assign(errno, std::generic_category());
@@ -396,7 +406,7 @@ fs::do_copy_file(const char* from, const char* to,
     }
 
   size_t count = from_st->st_size;
-#ifdef _GLIBCXX_USE_SENDFILE
+#if defined _GLIBCXX_USE_SENDFILE && ! defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
   off_t offset = 0;
   ssize_t n = ::sendfile(out.fd, in.fd, &offset, count);
   if (n < 0 && errno != ENOSYS && errno != EINVAL)
@@ -475,15 +485,15 @@ fs::copy(const path& from, const path& to, copy_options options,
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2681. filesystem::copy() cannot copy symlinks
   if (use_lstat || copy_symlinks
-      ? ::lstat(from.c_str(), &from_st)
-      : ::stat(from.c_str(), &from_st))
+      ? posix::lstat(from.c_str(), &from_st)
+      : posix::stat(from.c_str(), &from_st))
     {
       ec.assign(errno, std::generic_category());
       return;
     }
   if (use_lstat
-      ? ::lstat(to.c_str(), &to_st)
-      : ::stat(to.c_str(), &to_st))
+      ? posix::lstat(to.c_str(), &to_st)
+      : posix::stat(to.c_str(), &to_st))
     {
       if (!is_not_found_errno(errno))
 	{
@@ -636,74 +646,38 @@ fs::create_directories(const path& p, error_code& ec)
       ec = std::make_error_code(errc::invalid_argument);
       return false;
     }
-
-  file_status st = symlink_status(p, ec);
-  if (is_directory(st))
-    return false;
-  else if (ec && !status_known(st))
-    return false;
-  else if (exists(st))
-    {
-      if (!ec)
-	ec = std::make_error_code(std::errc::not_a_directory);
-      return false;
-    }
-
   std::stack<path> missing;
   path pp = p;
 
-  // Strip any trailing slash
-  if (pp.has_relative_path() && !pp.has_filename())
-    pp = pp.parent_path();
-
-  do
+  while (pp.has_filename() && status(pp, ec).type() == file_type::not_found)
     {
+      ec.clear();
       const auto& filename = pp.filename();
-      if (is_dot(filename) || is_dotdot(filename))
-	pp = pp.parent_path();
-      else
-	{
-	  missing.push(std::move(pp));
-	  if (missing.size() > 1000) // sanity check
-	    {
-	      ec = std::make_error_code(std::errc::filename_too_long);
-	      return false;
-	    }
-	  pp = missing.top().parent_path();
-	}
+      if (!is_dot(filename) && !is_dotdot(filename))
+	missing.push(pp);
+      pp = pp.parent_path();
 
-      if (pp.empty())
-	break;
-
-      st = status(pp, ec);
-      if (exists(st))
+      if (missing.size() > 1000) // sanity check
 	{
-	  if (ec)
-	    return false;
-	  if (!is_directory(st))
-	    {
-	      ec = std::make_error_code(std::errc::not_a_directory);
-	      return false;
-	    }
+	  ec = std::make_error_code(std::errc::filename_too_long);
+	  return false;
 	}
-
-      if (ec && exists(st))
-	return false;
     }
-  while (st.type() == file_type::not_found);
 
-  bool created;
+  if (ec || missing.empty())
+    return false;
+
   do
     {
       const path& top = missing.top();
-      created = create_directory(top, ec);
-      if (ec)
-	return false;
+      create_directory(top, ec);
+      if (ec && is_directory(top))
+	ec.clear();
       missing.pop();
     }
-  while (!missing.empty());
+  while (!missing.empty() && !ec);
 
-  return created;
+  return missing.empty();
 }
 
 namespace
@@ -713,8 +687,9 @@ namespace
   {
     bool created = false;
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-    ::mode_t mode = static_cast<std::underlying_type_t<fs::perms>>(perm);
-    if (::mkdir(p.c_str(), mode))
+    posix::mode_t mode
+      = static_cast<std::underlying_type_t<fs::perms>>(perm);
+    if (posix::mkdir(p.c_str(), mode))
       {
 	const int err = errno;
 	if (err != EEXIST || !is_directory(p, ec))
@@ -767,7 +742,7 @@ fs::create_directory(const path& p, const path& attributes,
 {
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
   stat_type st;
-  if (::stat(attributes.c_str(), &st))
+  if (posix::stat(attributes.c_str(), &st))
     {
       ec.assign(errno, std::generic_category());
       return false;
@@ -809,18 +784,23 @@ fs::create_hard_link(const path& to, const path& new_hard_link)
   create_hard_link(to, new_hard_link, ec);
   if (ec)
     _GLIBCXX_THROW_OR_ABORT(filesystem_error("cannot create hard link",
-	  to, new_hard_link, ec));
+					     to, new_hard_link, ec));
 }
 
 void
 fs::create_hard_link(const path& to, const path& new_hard_link,
 		     error_code& ec) noexcept
 {
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#ifdef _GLIBCXX_HAVE_LINK
   if (::link(to.c_str(), new_hard_link.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
+#elif defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (CreateHardLinkW(new_hard_link.c_str(), to.c_str(), NULL))
+    ec.clear();
+  else
+    ec.assign((int)GetLastError(), generic_category());
 #else
   ec = std::make_error_code(std::errc::not_supported);
 #endif
@@ -840,7 +820,7 @@ void
 fs::create_symlink(const path& to, const path& new_symlink,
 		   error_code& ec) noexcept
 {
-#ifdef _GLIBCXX_HAVE_UNISTD_H
+#ifdef _GLIBCXX_HAVE_SYMLINK
   if (::symlink(to.c_str(), new_symlink.c_str()))
     ec.assign(errno, std::generic_category());
   else
@@ -866,8 +846,8 @@ fs::current_path(error_code& ec)
 {
   path p;
 #ifdef _GLIBCXX_HAVE_UNISTD_H
-#ifdef __GLIBC__
-  if (char_ptr cwd = char_ptr{::getcwd(nullptr, 0)})
+#if defined __GLIBC__ || defined _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (char_ptr cwd = char_ptr{posix::getcwd(nullptr, 0)})
     {
       p.assign(cwd.get());
       ec.clear();
@@ -875,6 +855,7 @@ fs::current_path(error_code& ec)
   else
     ec.assign(errno, std::generic_category());
 #else
+#ifdef _PC_PATH_MAX
   long path_max = pathconf(".", _PC_PATH_MAX);
   size_t size;
   if (path_max == -1)
@@ -883,9 +864,15 @@ fs::current_path(error_code& ec)
       size = 10240;
   else
       size = path_max;
+#elif defined(PATH_MAX)
+  size_t size = PATH_MAX;
+#else
+  size_t size = 1024;
+#endif
   for (char_ptr buf; p.empty(); size *= 2)
     {
-      buf.reset((char*)malloc(size));
+      using char_type = fs::path::value_type;
+      buf.reset((char_type*)malloc(size * sizeof(char_type)));
       if (buf)
 	{
 	  if (getcwd(buf.get(), size))
@@ -925,7 +912,7 @@ void
 fs::current_path(const path& p, error_code& ec) noexcept
 {
 #ifdef _GLIBCXX_HAVE_UNISTD_H
-  if (::chdir(p.c_str()))
+  if (posix::chdir(p.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -952,14 +939,14 @@ fs::equivalent(const path& p1, const path& p2, error_code& ec) noexcept
   int err = 0;
   file_status s1, s2;
   stat_type st1, st2;
-  if (::stat(p1.c_str(), &st1) == 0)
+  if (posix::stat(p1.c_str(), &st1) == 0)
     s1 = make_file_status(st1);
   else if (is_not_found_errno(errno))
     s1.type(file_type::not_found);
   else
     err = errno;
 
-  if (::stat(p2.c_str(), &st2) == 0)
+  if (posix::stat(p2.c_str(), &st2) == 0)
     s2 = make_file_status(st2);
   else if (is_not_found_errno(errno))
     s2.type(file_type::not_found);
@@ -1008,8 +995,8 @@ namespace
     do_stat(const fs::path& p, std::error_code& ec, Accessor f, T deflt)
     {
 #ifdef _GLIBCXX_HAVE_SYS_STAT_H
-      fs::stat_type st;
-      if (::stat(p.c_str(), &st))
+      posix::stat_type st;
+      if (posix::stat(p.c_str(), &st))
 	{
 	  ec.assign(errno, std::generic_category());
 	  return deflt;
@@ -1059,7 +1046,7 @@ fs::hard_link_count(const path& p)
 std::uintmax_t
 fs::hard_link_count(const path& p, error_code& ec) noexcept
 {
-  return do_stat(p, ec, std::mem_fn(&stat::st_nlink),
+  return do_stat(p, ec, std::mem_fn(&stat_type::st_nlink),
 		 static_cast<uintmax_t>(-1));
 }
 
@@ -1135,11 +1122,11 @@ fs::last_write_time(const path& p __attribute__((__unused__)),
   else
     ec.clear();
 #elif _GLIBCXX_HAVE_UTIME_H
-  ::utimbuf times;
+  posix::utimbuf times;
   times.modtime = s.count();
   times.actime = do_stat(p, ec, [](const auto& st) { return st.st_atime; },
 			 times.modtime);
-  if (::utime(p.c_str(), &times))
+  if (posix::utime(p.c_str(), &times))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -1194,7 +1181,7 @@ fs::permissions(const path& p, perms prms, perm_options opts,
 #else
   if (nofollow && is_symlink(st))
     ec = std::make_error_code(std::errc::operation_not_supported);
-  else if (::chmod(p.c_str(), static_cast<mode_t>(prms)))
+  else if (posix::chmod(p.c_str(), static_cast<mode_t>(prms)))
     err = errno;
 #endif
 
@@ -1234,10 +1221,10 @@ fs::read_symlink(const path& p)
   return tgt;
 }
 
-fs::path fs::read_symlink(const path& p, error_code& ec)
+fs::path fs::read_symlink(const path& p [[gnu::unused]], error_code& ec)
 {
   path result;
-#ifdef _GLIBCXX_HAVE_SYS_STAT_H
+#if defined(_GLIBCXX_HAVE_READLINK) && defined(_GLIBCXX_HAVE_SYS_STAT_H)
   stat_type st;
   if (::lstat(p.c_str(), &st))
     {
@@ -1310,6 +1297,19 @@ fs::remove(const path& p)
 bool
 fs::remove(const path& p, error_code& ec) noexcept
 {
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  if (exists(symlink_status(p, ec)))
+    {
+      if ((is_directory(p, ec) && RemoveDirectoryW(p.c_str()))
+	  || DeleteFileW(p.c_str()))
+	{
+	  ec.clear();
+	  return true;
+	}
+      else if (!ec)
+	ec.assign((int)GetLastError(), generic_category());
+    }
+#else
   if (::remove(p.c_str()) == 0)
     {
       ec.clear();
@@ -1319,6 +1319,7 @@ fs::remove(const path& p, error_code& ec) noexcept
     ec.clear();
   else
     ec.assign(errno, std::generic_category());
+#endif
   return false;
 }
 
@@ -1372,7 +1373,7 @@ fs::rename(const path& from, const path& to)
 void
 fs::rename(const path& from, const path& to, error_code& ec) noexcept
 {
-  if (::rename(from.c_str(), to.c_str()))
+  if (posix::rename(from.c_str(), to.c_str()))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -1393,7 +1394,7 @@ fs::resize_file(const path& p, uintmax_t size, error_code& ec) noexcept
 #ifdef _GLIBCXX_HAVE_UNISTD_H
   if (size > static_cast<uintmax_t>(std::numeric_limits<off_t>::max()))
     ec.assign(EINVAL, std::generic_category());
-  else if (::truncate(p.c_str(), size))
+  else if (posix::truncate(p.c_str(), size))
     ec.assign(errno, std::generic_category());
   else
     ec.clear();
@@ -1413,31 +1414,67 @@ fs::space(const path& p)
   return s;
 }
 
-fs::space_info
-fs::space(const path& p, error_code& ec) noexcept
+#ifdef NEED_DO_SPACE
+void
+fs::do_space(const __gnu_posix::char_type* pathname,
+	 uintmax_t& capacity, uintmax_t& free, uintmax_t& available,
+	 std::error_code& ec)
 {
-  space_info info = {
-    static_cast<uintmax_t>(-1),
-    static_cast<uintmax_t>(-1),
-    static_cast<uintmax_t>(-1)
-  };
 #ifdef _GLIBCXX_HAVE_SYS_STATVFS_H
   struct ::statvfs f;
-  if (::statvfs(p.c_str(), &f))
+  if (::statvfs(pathname, &f))
       ec.assign(errno, std::generic_category());
   else
     {
-      uintmax_t fragment_size = f.f_frsize;
-      info = space_info{
-	f.f_blocks * fragment_size,
-	f.f_bfree * fragment_size,
-	f.f_bavail * fragment_size
-      };
+      if (f.f_frsize != (unsigned long)-1)
+	{
+	  const uintmax_t fragment_size = f.f_frsize;
+	  const fsblkcnt_t unknown = -1;
+	  if (f.f_blocks != unknown)
+	    capacity = f.f_blocks * fragment_size;
+	  if (f.f_bfree != unknown)
+	    free = f.f_bfree * fragment_size;
+	  if (f.f_bavail != unknown)
+	    available = f.f_bavail * fragment_size;
+	}
       ec.clear();
     }
+#elif _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  ULARGE_INTEGER bytes_avail = {}, bytes_total = {}, bytes_free = {};
+  if (GetDiskFreeSpaceExW(pathname, &bytes_avail, &bytes_total, &bytes_free))
+    {
+      if (bytes_total.QuadPart != 0)
+	capacity = bytes_total.QuadPart;
+      if (bytes_free.QuadPart != 0)
+	free = bytes_free.QuadPart;
+      if (bytes_avail.QuadPart != 0)
+	available = bytes_avail.QuadPart;
+      ec.clear();
+    }
+  else
+    ec.assign((int)GetLastError(), std::system_category());
 #else
   ec = std::make_error_code(std::errc::not_supported);
 #endif
+}
+#endif // NEED_DO_SPACE
+
+fs::space_info
+fs::space(const path& p, error_code& ec) noexcept
+{
+  space_info info = {
+    static_cast<uintmax_t>(-1),
+    static_cast<uintmax_t>(-1),
+    static_cast<uintmax_t>(-1)
+  };
+#if _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  path dir = absolute(p);
+  dir.remove_filename();
+  auto str = dir.c_str();
+#else
+  auto str = p.c_str();
+#endif
+  do_space(str, info.capacity, info.free, info.available, ec);
   return info;
 }
 
@@ -1447,7 +1484,7 @@ fs::status(const fs::path& p, error_code& ec) noexcept
 {
   file_status status;
   stat_type st;
-  if (::stat(p.c_str(), &st))
+  if (posix::stat(p.c_str(), &st))
     {
       int err = errno;
       ec.assign(err, std::generic_category());
@@ -1471,7 +1508,7 @@ fs::symlink_status(const fs::path& p, std::error_code& ec) noexcept
 {
   file_status status;
   stat_type st;
-  if (::lstat(p.c_str(), &st))
+  if (posix::lstat(p.c_str(), &st))
     {
       int err = errno;
       ec.assign(err, std::generic_category());
@@ -1518,28 +1555,39 @@ fs::path fs::temp_directory_path()
 
 fs::path fs::temp_directory_path(error_code& ec)
 {
+  path p;
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-  ec = std::make_error_code(std::errc::not_supported);
-  return {}; // TODO
+  unsigned len = 1024;
+  std::wstring buf;
+  do
+    {
+      buf.resize(len);
+      len = GetTempPathW(buf.size(), buf.data());
+    } while (len > buf.size());
+
+  if (len == 0)
+    {
+      ec.assign((int)GetLastError(), std::system_category());
+      return p;
+    }
+  buf.resize(len);
+  p = std::move(buf);
 #else
   const char* tmpdir = nullptr;
   const char* env[] = { "TMPDIR", "TMP", "TEMP", "TEMPDIR", nullptr };
   for (auto e = env; tmpdir == nullptr && *e != nullptr; ++e)
     tmpdir = ::getenv(*e);
-  path p = tmpdir ? tmpdir : "/tmp";
+  p = tmpdir ? tmpdir : "/tmp";
+#endif
   auto st = status(p, ec);
-  if (!ec)
+  if (ec)
+    p.clear();
+  else if (!is_directory(st))
     {
-      if (is_directory(st))
-	{
-	  ec.clear();
-	  return p;
-	}
-      else
-	ec = std::make_error_code(std::errc::not_a_directory);
+      p.clear();
+      ec = std::make_error_code(std::errc::not_a_directory);
     }
-  return {};
-#endif
+  return p;
 }
 
 fs::path
diff --git a/libstdc++-v3/src/filesystem/std-path.cc b/libstdc++-v3/src/filesystem/std-path.cc
index c5bf8099036..f6c0b8bb0f6 100644
--- a/libstdc++-v3/src/filesystem/std-path.cc
+++ b/libstdc++-v3/src/filesystem/std-path.cc
@@ -38,6 +38,66 @@ fs::filesystem_error::~filesystem_error() = default;
 
 constexpr path::value_type path::preferred_separator;
 
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+path&
+path::operator/=(const path& __p)
+{
+  if (__p.is_absolute()
+      || (__p.has_root_name() && __p.root_name() != root_name()))
+    return operator=(__p);
+
+  basic_string_view<value_type> __lhs = _M_pathname;
+  bool __add_sep = false;
+
+  if (__p.has_root_directory())
+    {
+      // Remove any root directory and relative path
+      if (_M_type != _Type::_Root_name)
+	{
+	  if (!_M_cmpts.empty()
+	      && _M_cmpts.front()._M_type == _Type::_Root_name)
+	    __lhs = _M_cmpts.front()._M_pathname;
+	  else
+	    __lhs = {};
+	}
+    }
+  else if (has_filename() || (!has_root_directory() && is_absolute()))
+    __add_sep = true;
+
+  basic_string_view<value_type> __rhs = __p._M_pathname;
+  // Omit any root-name from the generic format pathname:
+  if (__p._M_type == _Type::_Root_name)
+    __rhs = {};
+  else if (!__p._M_cmpts.empty()
+      && __p._M_cmpts.front()._M_type == _Type::_Root_name)
+    __rhs.remove_prefix(__p._M_cmpts.front()._M_pathname.size());
+
+  const size_t __len = __lhs.size() + (int)__add_sep + __rhs.size();
+  const size_t __maxcmpts = _M_cmpts.size() + __p._M_cmpts.size();
+  if (_M_pathname.capacity() < __len || _M_cmpts.capacity() < __maxcmpts)
+    {
+      // Construct new path and swap (strong exception-safety guarantee).
+      string_type __tmp;
+      __tmp.reserve(__len);
+      __tmp = __lhs;
+      if (__add_sep)
+	__tmp += preferred_separator;
+      __tmp += __rhs;
+      path __newp = std::move(__tmp);
+      swap(__newp);
+    }
+  else
+    {
+      _M_pathname = __lhs;
+      if (__add_sep)
+	_M_pathname += preferred_separator;
+      _M_pathname += __rhs;
+      _M_split_cmpts();
+    }
+  return *this;
+}
+#endif
+
 path&
 path::remove_filename()
 {
@@ -74,6 +134,12 @@ path::replace_filename(const path& replacement)
   return *this;
 }
 
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+const fs::path::value_type dot = L'.';
+#else
+const fs::path::value_type dot = '.';
+#endif
+
 path&
 path::replace_extension(const path& replacement)
 {
@@ -85,18 +151,17 @@ path::replace_extension(const path& replacement)
 	_M_pathname.erase(ext.second);
       else
 	{
-	  auto& back = _M_cmpts.back();
+	  const auto& back = _M_cmpts.back();
 	  if (ext.first != &back._M_pathname)
 	    _GLIBCXX_THROW_OR_ABORT(
 		std::logic_error("path::replace_extension failed"));
-	  back._M_pathname.erase(ext.second);
 	  _M_pathname.erase(back._M_pos + ext.second);
 	}
     }
    // If replacement is not empty and does not begin with a dot character,
    // a dot character is appended
-  if (!replacement.empty() && replacement.native()[0] != '.')
-    _M_pathname += '.';
+  if (!replacement.empty() && replacement.native()[0] != dot)
+    _M_pathname += dot;
   operator+=(replacement);
   return *this;
 }
@@ -333,11 +398,7 @@ path::has_filename() const
 
 namespace
 {
-#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-  inline bool is_dot(wchar_t c) { return c == L'.'; }
-#else
-  inline bool is_dot(char c) { return c == '.'; }
-#endif
+  inline bool is_dot(fs::path::value_type c) { return c == dot; }
 
   inline bool is_dot(const fs::path& path)
   {
@@ -377,7 +438,7 @@ path::lexically_normal() const
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
       // Replace each slash character in the root-name
-      if (p._M_type == _Type::_Root_name || p._M_type == _Type::_Root_dir)
+      if (p._M_type == _Type::_Root_name)
 	{
 	  string_type s = p.native();
 	  std::replace(s.begin(), s.end(), L'/', L'\\');
@@ -397,8 +458,7 @@ path::lexically_normal() const
 	    }
 	  else if (!ret.has_relative_path())
 	    {
-	      // remove a dot-dot filename immediately after root-directory
-	      if (!ret.has_root_directory())
+	      if (!ret.is_absolute())
 		ret /= p;
 	    }
 	  else
@@ -406,30 +466,15 @@ path::lexically_normal() const
 	      // Got a path with a relative path (i.e. at least one non-root
 	      // element) and no filename at the end (i.e. empty last element),
 	      // so must have a trailing slash. See what is before it.
-	      auto elem = ret._M_cmpts.end() - 2;
+	      auto elem = std::prev(ret.end(), 2);
 	      if (elem->has_filename() && !is_dotdot(*elem))
 		{
 		  // Remove the filename before the trailing slash
 		  // (equiv. to ret = ret.parent_path().remove_filename())
-
-		  if (elem == ret._M_cmpts.begin())
-		    ret.clear();
-		  else
-		    {
-		      ret._M_pathname.erase(elem->_M_pos);
-		      // Remove empty filename at the end:
-		      ret._M_cmpts.pop_back();
-		      // If we still have a trailing non-root dir separator
-		      // then leave an empty filename at the end:
-		      if (std::prev(elem)->_M_type == _Type::_Filename)
-			elem->clear();
-		      else // remove the component completely:
-			ret._M_cmpts.pop_back();
-		    }
+		  ret._M_pathname.erase(elem._M_cur->_M_pos);
+		  ret._M_cmpts.erase(elem._M_cur, ret._M_cmpts.end());
 		}
-	      else
-		// Append the ".." to something ending in "../" which happens
-		// when normalising paths like ".././.." and "../a/../.."
+	      else // ???
 		ret /= p;
 	    }
 	}
@@ -475,12 +520,10 @@ path::lexically_relative(const path& base) const
       const path& p = *b;
       if (is_dotdot(p))
 	--n;
-      else if (!p.empty() && !is_dot(p))
+      else if (!is_dot(p))
 	++n;
     }
-    if (n == 0 && (a == end() || a->empty()))
-      ret = ".";
-    else if (n >= 0)
+    if (n >= 0)
     {
       const path dotdot("..");
       while (n--)
@@ -504,7 +547,7 @@ path::lexically_proximate(const path& base) const
 std::pair<const path::string_type*, std::size_t>
 path::_M_find_extension() const
 {
-  const std::string* s = nullptr;
+  const string_type* s = nullptr;
 
   if (_M_type == _Type::_Filename)
     s = &_M_pathname;
@@ -519,9 +562,9 @@ path::_M_find_extension() const
     {
       if (auto sz = s->size())
 	{
-	  if (sz <= 2 && (*s)[0] == '.')
+	  if (sz <= 2 && (*s)[0] == dot)
 	    return { s, string_type::npos };
-	  const auto pos = s->rfind('.');
+	  const auto pos = s->rfind(dot);
 	  return { s, pos ? pos : string_type::npos };
 	}
     }
@@ -722,8 +765,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
   std::string filesystem_error::_M_gen_what()
   {
-    return fs_err_concat(system_error::what(), _M_path1.native(),
-			 _M_path2.native());
+    return fs_err_concat(system_error::what(), _M_path1.u8string(),
+			 _M_path2.u8string());
   }
 
 _GLIBCXX_END_NAMESPACE_CXX11
-- 
2.20.1