[PATCH 1/4]: C++ P1423R3 char8_t remediation: Decouple constraints for u8path from path constructors

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[PATCH 1/4]: C++ P1423R3 char8_t remediation: Decouple constraints for u8path from path constructors

Tom Honermann
This patch moves helper classes and functions for std::filesystem::path
out of the class definition to a detail namespace so that they are
available to the implementations of std::filesystem::u8path.  Prior to
this patch, the SFINAE constraints for those implementations were
specified via delegation to the overloads of path constructors with a
std::locale parameter; it just so happened that those overloads had the
same constraints.  As of P1423R3, u8path and those overloads no longer
have the same constraints, so this dependency must be broken.

This patch also updates the experimental implementation of the
filesystem TS to add SFINAE constraints to its implementations of
u8path.  These functions were previously unconstrained and marked with a
TODO comment.

This patch does not provide any intentional behavioral changes other
than the added constraints to the experimental filesystem TS
implementation of u8path.

I recommend applying the patch and viewing the diff with white space
ignored when reviewing; there will be many fewer differences this way.

Alternatives to this refactoring would have been to make the u8path
overloads friends of class path, or to make the helpers public members.
Both of those approaches struck me as less desirable than this approach,
though this approach does require more code changes and will affect
implementation detail portions of mangled names for path constructors
and inline member functions (mostly function template specializations).

libstdc++-v3/ChangeLog:

2019-09-15  Tom Honermann  <[hidden email]>

      * include/bits/fs_path.h: Moved helper utilities out of
        std::filesystem::path into a detail namespace to make them
        available for use by u8path.
      * include/experimental/bits/fs_path.h: Moved helper utilities out
        of std::experimental::filesystem::v1::path into a detail
        namespace to make them available for use by u8path.

Tom.

diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index e1083acf30f..71354515403 100644
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -59,103 +59,114 @@ namespace filesystem
 {
 _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
-  /** @addtogroup filesystem
+  class path;
+
+namespace __detail
+{
+  /** @addtogroup filesystem-detail
    *  @{
    */
 
-  /// A filesystem path.
-  class path
-  {
-    template<typename _CharT>
-      using __is_encoded_char = __is_one_of<remove_const_t<_CharT>,
-    char,
+  template<typename _CharT>
+    using __is_encoded_char = __is_one_of<remove_const_t<_CharT>,
+  char,
 #ifdef _GLIBCXX_USE_CHAR8_T
-    char8_t,
+  char8_t,
 #endif
 #if _GLIBCXX_USE_WCHAR_T
-    wchar_t,
+  wchar_t,
 #endif
-    char16_t, char32_t>;
+  char16_t, char32_t>;
 
-    template<typename _Iter,
-     typename _Iter_traits = std::iterator_traits<_Iter>>
-      using __is_path_iter_src
- = __and_<__is_encoded_char<typename _Iter_traits::value_type>,
- std::is_base_of<std::input_iterator_tag,
- typename _Iter_traits::iterator_category>>;
+  template<typename _Iter,
+   typename _Iter_traits = std::iterator_traits<_Iter>>
+    using __is_path_iter_src
+      = __and_<__is_encoded_char<typename _Iter_traits::value_type>,
+       std::is_base_of<std::input_iterator_tag,
+       typename _Iter_traits::iterator_category>>;
 
-    template<typename _Iter>
-      static __is_path_iter_src<_Iter>
-      __is_path_src(_Iter, int);
-
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static __is_encoded_char<_CharT>
-      __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
-
-    template<typename _CharT, typename _Traits>
-      static __is_encoded_char<_CharT>
-      __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
+  template<typename _Iter>
+    static __is_path_iter_src<_Iter>
+    __is_path_src(_Iter, int);
 
-    template<typename _Unknown>
-      static std::false_type
-      __is_path_src(const _Unknown&, ...);
-
-    template<typename _Tp1, typename _Tp2>
-      struct __constructible_from;
-
-    template<typename _Iter>
-      struct __constructible_from<_Iter, _Iter>
-      : __is_path_iter_src<_Iter>
-      { };
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static __is_encoded_char<_CharT>
+    __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
 
-    template<typename _Source>
-      struct __constructible_from<_Source, void>
-      : decltype(__is_path_src(std::declval<_Source>(), 0))
-      { };
+  template<typename _CharT, typename _Traits>
+    static __is_encoded_char<_CharT>
+    __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
 
-    template<typename _Tp1, typename _Tp2 = void>
-      using _Path = typename
- std::enable_if<__and_<__not_<is_same<remove_cv_t<_Tp1>, path>>,
-      __not_<is_void<remove_pointer_t<_Tp1>>>,
-      __constructible_from<_Tp1, _Tp2>>::value,
-       path>::type;
+  template<typename _Unknown>
+    static std::false_type
+    __is_path_src(const _Unknown&, ...);
 
-    template<typename _Source>
-      static _Source
-      _S_range_begin(_Source __begin) { return __begin; }
+  template<typename _Tp1, typename _Tp2>
+    struct __constructible_from;
 
-    struct __null_terminated { };
+  template<typename _Iter>
+    struct __constructible_from<_Iter, _Iter>
+    : __is_path_iter_src<_Iter>
+    { };
 
-    template<typename _Source>
-      static __null_terminated
-      _S_range_end(_Source) { return {}; }
+  template<typename _Source>
+    struct __constructible_from<_Source, void>
+    : decltype(__is_path_src(std::declval<_Source>(), 0))
+    { };
 
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static const _CharT*
-      _S_range_begin(const basic_string<_CharT, _Traits, _Alloc>& __str)
-      { return __str.data(); }
+  template<typename _Tp1, typename _Tp2 = void>
+    using _Path = typename
+      std::enable_if<__and_<__not_<is_same<remove_cv_t<_Tp1>, path>>,
+    __not_<is_void<remove_pointer_t<_Tp1>>>,
+    __constructible_from<_Tp1, _Tp2>>::value,
+     path>::type;
 
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static const _CharT*
-      _S_range_end(const basic_string<_CharT, _Traits, _Alloc>& __str)
-      { return __str.data() + __str.size(); }
+  template<typename _Source>
+    static _Source
+    _S_range_begin(_Source __begin) { return __begin; }
 
-    template<typename _CharT, typename _Traits>
-      static const _CharT*
-      _S_range_begin(const basic_string_view<_CharT, _Traits>& __str)
-      { return __str.data(); }
+  struct __null_terminated { };
 
-    template<typename _CharT, typename _Traits>
-      static const _CharT*
-      _S_range_end(const basic_string_view<_CharT, _Traits>& __str)
-      { return __str.data() + __str.size(); }
+  template<typename _Source>
+    static __null_terminated
+    _S_range_end(_Source) { return {}; }
+
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static const _CharT*
+    _S_range_begin(const basic_string<_CharT, _Traits, _Alloc>& __str)
+    { return __str.data(); }
+
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static const _CharT*
+    _S_range_end(const basic_string<_CharT, _Traits, _Alloc>& __str)
+    { return __str.data() + __str.size(); }
+
+  template<typename _CharT, typename _Traits>
+    static const _CharT*
+    _S_range_begin(const basic_string_view<_CharT, _Traits>& __str)
+    { return __str.data(); }
+
+  template<typename _CharT, typename _Traits>
+    static const _CharT*
+    _S_range_end(const basic_string_view<_CharT, _Traits>& __str)
+    { return __str.data() + __str.size(); }
+
+  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
+      = std::enable_if_t<std::is_same_v<std::remove_const_t<_Val>, char>>;
+
+  // @} group filesystem-detail
+} // namespace __detail
 
-    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
- = std::enable_if_t<std::is_same_v<std::remove_const_t<_Val>, char>>;
+  /** @addtogroup filesystem
+   *  @{
+   */
 
+  /// A filesystem path.
+  class path
+  {
   public:
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
     using value_type = wchar_t;
@@ -193,29 +204,29 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     { _M_split_cmpts(); }
 
     template<typename _Source,
-     typename _Require = _Path<_Source>>
+     typename _Require = __detail::_Path<_Source>>
       path(_Source const& __source, format = auto_format)
-      : _M_pathname(_S_convert(_S_range_begin(__source),
-       _S_range_end(__source)))
+      : _M_pathname(_S_convert(__detail::_S_range_begin(__source),
+       __detail::_S_range_end(__source)))
       { _M_split_cmpts(); }
 
     template<typename _InputIterator,
-     typename _Require = _Path<_InputIterator, _InputIterator>>
+     typename _Require = __detail::_Path<_InputIterator, _InputIterator>>
       path(_InputIterator __first, _InputIterator __last, format = auto_format)
       : _M_pathname(_S_convert(__first, __last))
       { _M_split_cmpts(); }
 
     template<typename _Source,
-     typename _Require = _Path<_Source>,
-     typename _Require2 = __value_type_is_char<_Source>>
+     typename _Require = __detail::_Path<_Source>,
+     typename _Require2 = __detail::__value_type_is_char<_Source>>
       path(_Source const& __source, const locale& __loc, format = auto_format)
-      : _M_pathname(_S_convert_loc(_S_range_begin(__source),
-   _S_range_end(__source), __loc))
+      : _M_pathname(_S_convert_loc(__detail::_S_range_begin(__source),
+   __detail::_S_range_end(__source), __loc))
       { _M_split_cmpts(); }
 
     template<typename _InputIterator,
-     typename _Require = _Path<_InputIterator, _InputIterator>,
-     typename _Require2 = __value_type_is_char<_InputIterator>>
+     typename _Require = __detail::_Path<_InputIterator, _InputIterator>,
+     typename _Require2 = __detail::__value_type_is_char<_InputIterator>>
       path(_InputIterator __first, _InputIterator __last, const locale& __loc,
    format = auto_format)
       : _M_pathname(_S_convert_loc(__first, __last, __loc))
@@ -231,17 +242,17 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path& assign(string_type&& __source);
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator=(_Source const& __source)
       { return *this = path(__source); }
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       assign(_Source const& __source)
       { return *this = path(__source); }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       assign(_InputIterator __first, _InputIterator __last)
       { return *this = path(__first, __last); }
 
@@ -250,23 +261,25 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path& operator/=(const path& __p);
 
     template <class _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator/=(_Source const& __source)
       {
- _M_append(_S_convert(_S_range_begin(__source), _S_range_end(__source)));
+ _M_append(_S_convert(__detail::_S_range_begin(__source),
+                     __detail::_S_range_end(__source)));
  return *this;
       }
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       append(_Source const& __source)
       {
- _M_append(_S_convert(_S_range_begin(__source), _S_range_end(__source)));
+ _M_append(_S_convert(__detail::_S_range_begin(__source),
+                     __detail::_S_range_end(__source)));
  return *this;
       }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       append(_InputIterator __first, _InputIterator __last)
       {
  _M_append(_S_convert(__first, __last));
@@ -282,23 +295,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path& operator+=(basic_string_view<value_type> __x);
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator+=(_Source const& __x) { return concat(__x); }
 
     template<typename _CharT>
-      _Path<_CharT*, _CharT*>&
+      __detail::_Path<_CharT*, _CharT*>&
       operator+=(_CharT __x);
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       concat(_Source const& __x)
       {
- _M_concat(_S_convert(_S_range_begin(__x), _S_range_end(__x)));
+ _M_concat(_S_convert(__detail::_S_range_begin(__x),
+                     __detail::_S_range_end(__x)));
  return *this;
       }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       concat(_InputIterator __first, _InputIterator __last)
       {
  _M_concat(_S_convert(__first, __last));
@@ -496,11 +510,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       struct _Cvt;
 
     static basic_string_view<value_type>
-    _S_convert(value_type* __src, __null_terminated)
+    _S_convert(value_type* __src, __detail::__null_terminated)
     { return __src; }
 
     static basic_string_view<value_type>
-    _S_convert(const value_type* __src, __null_terminated)
+    _S_convert(const value_type* __src, __detail::__null_terminated)
     { return __src; }
 
     static basic_string_view<value_type>
@@ -522,7 +536,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _InputIterator>
       static string_type
-      _S_convert(_InputIterator __src, __null_terminated)
+      _S_convert(_InputIterator __src, __detail::__null_terminated)
       {
  // Read from iterator into basic_string until a null value is seen:
  auto __s = _S_string_from_iter(__src);
@@ -544,7 +558,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _InputIterator>
       static string_type
-      _S_convert_loc(_InputIterator __src, __null_terminated,
+      _S_convert_loc(_InputIterator __src, __detail::__null_terminated,
      const std::locale& __loc)
       {
  const std::string __s = _S_string_from_iter(__src);
@@ -623,10 +637,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   size_t hash_value(const path& __p) noexcept;
 
   /// Create a path from a UTF-8-encoded sequence of char
-  template<typename _InputIterator>
-    inline auto
+  template<typename _InputIterator,
+   typename _Require = __detail::_Path<_InputIterator, _InputIterator>,
+   typename _Require2 = __detail::__value_type_is_char<_InputIterator>>
+    inline path
     u8path(_InputIterator __first, _InputIterator __last)
-    -> decltype(filesystem::path(__first, __last, std::locale::classic()))
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
       // XXX This assumes native wide encoding is UTF-16.
@@ -654,10 +669,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     }
 
   /// Create a path from a UTF-8-encoded sequence of char
-  template<typename _Source>
-    inline auto
+  template<typename _Source,
+   typename _Require = __detail::_Path<_Source>,
+   typename _Require2 = __detail::__value_type_is_char<_Source>>
+    inline path
     u8path(const _Source& __source)
-    -> decltype(filesystem::path(__source, std::locale::classic()))
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
       if constexpr (is_convertible_v<const _Source&, std::string_view>)
@@ -944,7 +960,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   }
 
   template<typename _CharT>
-    inline path::_Path<_CharT*, _CharT*>&
+    inline __detail::_Path<_CharT*, _CharT*>&
     path::operator+=(_CharT __x)
     {
       auto* __addr = std::__addressof(__x);
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index a3655f616f2..3f9a69514a1 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -71,111 +71,120 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   using std::basic_string_view;
 #endif
 
-  /**
-   * @addtogroup filesystem-ts
-   * @{
+namespace __detail
+{
+  /** @addtogroup filesystem-ts-detail
+   *  @{
    */
 
-  /// A filesystem path.
-  class path
-  {
-    template<typename _CharT,
-     typename _Ch = typename remove_const<_CharT>::type>
-      using __is_encoded_char
- = __or_<is_same<_Ch, char>,
- is_same<_Ch, wchar_t>,
+  template<typename _CharT,
+   typename _Ch = typename remove_const<_CharT>::type>
+    using __is_encoded_char
+      = __or_<is_same<_Ch, char>,
+      is_same<_Ch, wchar_t>,
 #ifdef _GLIBCXX_USE_CHAR8_T
- is_same<_Ch, char8_t>,
+      is_same<_Ch, char8_t>,
 #endif
- is_same<_Ch, char16_t>,
- is_same<_Ch, char32_t>>;
+      is_same<_Ch, char16_t>,
+      is_same<_Ch, char32_t>>;
 
-    template<typename _Iter,
-     typename _Iter_traits = std::iterator_traits<_Iter>>
-      using __is_path_iter_src
- = __and_<__is_encoded_char<typename _Iter_traits::value_type>,
- std::is_base_of<std::input_iterator_tag,
- typename _Iter_traits::iterator_category>>;
+  template<typename _Iter,
+   typename _Iter_traits = std::iterator_traits<_Iter>>
+    using __is_path_iter_src
+      = __and_<__is_encoded_char<typename _Iter_traits::value_type>,
+       std::is_base_of<std::input_iterator_tag,
+       typename _Iter_traits::iterator_category>>;
 
-    template<typename _Iter>
-      static __is_path_iter_src<_Iter>
-      __is_path_src(_Iter, int);
+  template<typename _Iter>
+    static __is_path_iter_src<_Iter>
+    __is_path_src(_Iter, int);
 
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static __is_encoded_char<_CharT>
-      __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static __is_encoded_char<_CharT>
+    __is_path_src(const basic_string<_CharT, _Traits, _Alloc>&, int);
 
 #if __cplusplus >= 201402L
-    template<typename _CharT, typename _Traits>
-      static __is_encoded_char<_CharT>
-      __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
+  template<typename _CharT, typename _Traits>
+    static __is_encoded_char<_CharT>
+    __is_path_src(const basic_string_view<_CharT, _Traits>&, int);
 #endif
 
-    template<typename _Unknown>
-      static std::false_type
-      __is_path_src(const _Unknown&, ...);
+  template<typename _Unknown>
+    static std::false_type
+    __is_path_src(const _Unknown&, ...);
 
-    template<typename _Tp1, typename _Tp2>
-      struct __constructible_from;
+  template<typename _Tp1, typename _Tp2>
+    struct __constructible_from;
 
-    template<typename _Iter>
-      struct __constructible_from<_Iter, _Iter>
-      : __is_path_iter_src<_Iter>
-      { };
+  template<typename _Iter>
+    struct __constructible_from<_Iter, _Iter>
+    : __is_path_iter_src<_Iter>
+    { };
 
-    template<typename _Source>
-      struct __constructible_from<_Source, void>
-      : decltype(__is_path_src(std::declval<_Source>(), 0))
-      { };
-
-    template<typename _Tp1, typename _Tp2 = void,
-     typename _Tp1_nocv = typename remove_cv<_Tp1>::type,
-     typename _Tp1_noptr = typename remove_pointer<_Tp1>::type>
-      using _Path = typename
- std::enable_if<__and_<__not_<is_same<_Tp1_nocv, path>>,
-      __not_<is_void<_Tp1_noptr>>,
-      __constructible_from<_Tp1, _Tp2>>::value,
-       path>::type;
+  template<typename _Source>
+    struct __constructible_from<_Source, void>
+    : decltype(__is_path_src(std::declval<_Source>(), 0))
+    { };
+
+  template<typename _Tp1, typename _Tp2 = void,
+   typename _Tp1_nocv = typename remove_cv<_Tp1>::type,
+   typename _Tp1_noptr = typename remove_pointer<_Tp1>::type>
+    using _Path = typename
+      std::enable_if<__and_<__not_<is_same<_Tp1_nocv, path>>,
+    __not_<is_void<_Tp1_noptr>>,
+    __constructible_from<_Tp1, _Tp2>>::value,
+     path>::type;
 
-    template<typename _Source>
-      static _Source
-      _S_range_begin(_Source __begin) { return __begin; }
+  template<typename _Source>
+    static _Source
+    _S_range_begin(_Source __begin) { return __begin; }
 
-    struct __null_terminated { };
+  struct __null_terminated { };
 
-    template<typename _Source>
-      static __null_terminated
-      _S_range_end(_Source) { return {}; }
+  template<typename _Source>
+    static __null_terminated
+    _S_range_end(_Source) { return {}; }
 
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static const _CharT*
-      _S_range_begin(const basic_string<_CharT, _Traits, _Alloc>& __str)
-      { return __str.data(); }
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static const _CharT*
+    _S_range_begin(const basic_string<_CharT, _Traits, _Alloc>& __str)
+    { return __str.data(); }
 
-    template<typename _CharT, typename _Traits, typename _Alloc>
-      static const _CharT*
-      _S_range_end(const basic_string<_CharT, _Traits, _Alloc>& __str)
-      { return __str.data() + __str.size(); }
+  template<typename _CharT, typename _Traits, typename _Alloc>
+    static const _CharT*
+    _S_range_end(const basic_string<_CharT, _Traits, _Alloc>& __str)
+    { return __str.data() + __str.size(); }
 
 #if __cplusplus >= 201402L
-    template<typename _CharT, typename _Traits>
-      static const _CharT*
-      _S_range_begin(const basic_string_view<_CharT, _Traits>& __str)
-      { return __str.data(); }
-
-    template<typename _CharT, typename _Traits>
-      static const _CharT*
-      _S_range_end(const basic_string_view<_CharT, _Traits>& __str)
-      { return __str.data() + __str.size(); }
+  template<typename _CharT, typename _Traits>
+    static const _CharT*
+    _S_range_begin(const basic_string_view<_CharT, _Traits>& __str)
+    { return __str.data(); }
+
+  template<typename _CharT, typename _Traits>
+    static const _CharT*
+    _S_range_end(const basic_string_view<_CharT, _Traits>& __str)
+    { return __str.data() + __str.size(); }
 #endif
 
-    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<typename std::remove_const<_Val>::type, char>::value
- >::type;
+  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<typename std::remove_const<_Val>::type, char>::value
+      >::type;
+
+  // @} group filesystem-ts-detail
+} // namespace __detail
 
+  /**
+   * @addtogroup filesystem-ts
+   * @{
+   */
+
+  /// A filesystem path.
+  class path
+  {
   public:
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
     typedef wchar_t value_type;
@@ -205,29 +214,29 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     { _M_split_cmpts(); }
 
     template<typename _Source,
-     typename _Require = _Path<_Source>>
+     typename _Require = __detail::_Path<_Source>>
       path(_Source const& __source)
-      : _M_pathname(_S_convert(_S_range_begin(__source),
-       _S_range_end(__source)))
+      : _M_pathname(_S_convert(__detail::_S_range_begin(__source),
+       __detail::_S_range_end(__source)))
       { _M_split_cmpts(); }
 
     template<typename _InputIterator,
-     typename _Require = _Path<_InputIterator, _InputIterator>>
+     typename _Require = __detail::_Path<_InputIterator, _InputIterator>>
       path(_InputIterator __first, _InputIterator __last)
       : _M_pathname(_S_convert(__first, __last))
       { _M_split_cmpts(); }
 
     template<typename _Source,
-     typename _Require = _Path<_Source>,
-     typename _Require2 = __value_type_is_char<_Source>>
+     typename _Require = __detail::_Path<_Source>,
+     typename _Require2 = __detail::__value_type_is_char<_Source>>
       path(_Source const& __source, const locale& __loc)
-      : _M_pathname(_S_convert_loc(_S_range_begin(__source),
-   _S_range_end(__source), __loc))
+      : _M_pathname(_S_convert_loc(__detail::_S_range_begin(__source),
+   __detail::_S_range_end(__source), __loc))
       { _M_split_cmpts(); }
 
     template<typename _InputIterator,
-     typename _Require = _Path<_InputIterator, _InputIterator>,
-     typename _Require2 = __value_type_is_char<_InputIterator>>
+     typename _Require = __detail::_Path<_InputIterator, _InputIterator>,
+     typename _Require2 = __detail::__value_type_is_char<_InputIterator>>
       path(_InputIterator __first, _InputIterator __last, const locale& __loc)
       : _M_pathname(_S_convert_loc(__first, __last, __loc))
       { _M_split_cmpts(); }
@@ -242,17 +251,17 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path& assign(string_type&& __source);
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator=(_Source const& __source)
       { return *this = path(__source); }
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       assign(_Source const& __source)
       { return *this = path(__source); }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       assign(_InputIterator __first, _InputIterator __last)
       { return *this = path(__first, __last); }
 
@@ -261,20 +270,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path& operator/=(const path& __p) { return _M_append(__p._M_pathname); }
 
     template <class _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator/=(_Source const& __source)
       { return append(__source); }
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       append(_Source const& __source)
       {
- return _M_append(_S_convert(_S_range_begin(__source),
-    _S_range_end(__source)));
+ return _M_append(_S_convert(__detail::_S_range_begin(__source),
+    __detail::_S_range_end(__source)));
       }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       append(_InputIterator __first, _InputIterator __last)
       { return _M_append(_S_convert(__first, __last)); }
 
@@ -289,20 +298,23 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 #endif
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       operator+=(_Source const& __x) { return concat(__x); }
 
     template<typename _CharT>
-      _Path<_CharT*, _CharT*>&
+      __detail::_Path<_CharT*, _CharT*>&
       operator+=(_CharT __x);
 
     template<typename _Source>
-      _Path<_Source>&
+      __detail::_Path<_Source>&
       concat(_Source const& __x)
-      { return *this += _S_convert(_S_range_begin(__x), _S_range_end(__x)); }
+      {
+ return *this += _S_convert(__detail::_S_range_begin(__x),
+   __detail::_S_range_end(__x));
+      }
 
     template<typename _InputIterator>
-      _Path<_InputIterator, _InputIterator>&
+      __detail::_Path<_InputIterator, _InputIterator>&
       concat(_InputIterator __first, _InputIterator __last)
       { return *this += _S_convert(__first, __last); }
 
@@ -446,11 +458,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       struct _Cvt;
 
     static string_type
-    _S_convert(value_type* __src, __null_terminated)
+    _S_convert(value_type* __src, __detail::__null_terminated)
     { return string_type(__src); }
 
     static string_type
-    _S_convert(const value_type* __src, __null_terminated)
+    _S_convert(const value_type* __src, __detail::__null_terminated)
     { return string_type(__src); }
 
     template<typename _Iter>
@@ -464,7 +476,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _InputIterator>
       static string_type
-      _S_convert(_InputIterator __src, __null_terminated)
+      _S_convert(_InputIterator __src, __detail::__null_terminated)
       {
  auto __s = _S_string_from_iter(__src);
  return _S_convert(__s.c_str(), __s.c_str() + __s.size());
@@ -484,7 +496,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
     template<typename _InputIterator>
       static string_type
-      _S_convert_loc(_InputIterator __src, __null_terminated,
+      _S_convert_loc(_InputIterator __src, __detail::__null_terminated,
      const std::locale& __loc)
       {
  const std::string __s = _S_string_from_iter(__src);
@@ -580,8 +592,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     }
 
   /// Create a path from a UTF-8-encoded sequence of char
-  // TODO constrain with _Path<InputIterator, InputIterator> and __value_type_is_char
-  template<typename _InputIterator>
+  template<typename _InputIterator,
+   typename _Require = __detail::_Path<_InputIterator, _InputIterator>,
+   typename _Require2 = __detail::__value_type_is_char<_InputIterator>>
     inline path
     u8path(_InputIterator __first, _InputIterator __last)
     {
@@ -602,8 +615,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     }
 
   /// Create a path from a UTF-8-encoded sequence of char
-  // TODO constrain with _Path<Source> and __value_type_is_char
-  template<typename _Source>
+  template<typename _Source,
+   typename _Require = __detail::_Path<_Source>,
+   typename _Require2 = __detail::__value_type_is_char<_Source>>
     inline path
     u8path(const _Source& __source)
     {
@@ -872,7 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 #endif
 
   template<typename _CharT>
-    inline path::_Path<_CharT*, _CharT*>&
+    inline __detail::_Path<_CharT*, _CharT*>&
     path::operator+=(_CharT __x)
     {
       auto* __addr = std::__addressof(__x);