[libcxx-commits] [libcxx] [libcxx] proper guarding for locale usage in filesystem on Windows (PR #165470)

[A. Jiang via libcxx-commits]

================
@@ -24,28 +27,30 @@
 
 _LIBCPP_BEGIN_NAMESPACE_FILESYSTEM
 
+#  if !defined(_LIBCPP_WIN32API) || _LIBCPP_HAS_LOCALIZATION
----------------
frederick-vs-ja wrote:

I strongly think that it's unconforming to use the `_NullSentinel` parameter in the function of a standard name (`u8path`).

I think it's better to reform the code like this:

<details><summary>Collapse/Expand</summary>
<p>

```C++
_LIBCPP_BEGIN_NAMESPACE_FILESYSTEM

#  if defined(_LIBCPP_WIN32API) && _LIBCPP_HAS_LOCALIZATION
#    define _LIBCPP_FS_U8PATH_CONVERTS_ENCODING 1
#  else
#    define _LIBCPP_FS_U8PATH_CONVERTS_ENCODING 0
#  endif

#  if _LIBCPP_FS_U8PATH_CONVERTS_ENCODING
template <class _InputIt, class _Sentinel>
_LIBCPP_HIDE_FROM_ABI string __make_tmp_string_for_u8path(_InputIt __f, _Sentinel __l) {
  static_assert(__is_pathable<_InputIt>::value);
  static_assert(
#    if _LIBCPP_HAS_CHAR8_T
      is_same<typename __is_pathable<_InputIt>::__char_type, char8_t>::value ||
#    endif
      is_same<typename __is_pathable<_InputIt>::__char_type, char>::value);

  if constexpr (is_same_v<_InputIt, _NullSentinel>) {
    string __tmp;
    constexpr char __sentinel{};
    for (; *__f != __sentinel; ++__f)
      __tmp.push_back(*__f);
    return __tmp;
  } else {
    static_assert(is_same_v<_InputIt, _Sentinel>);
    return string(__f, __l);
  }
}
#  endif // _LIBCPP_FS_U8PATH_CONVERTS_ENCODING

template <class _InputIt, class _Sentinel>
_LIBCPP_HIDE_FROM_ABI path __u8path(_InputIt __f, _Sentinel __l) {
#  if _LIBCPP_FS_U8PATH_CONVERTS_ENCODING
  auto __tmp = std::filesystem::__make_tmp_string_for_u8path(__f, __l);
  using _CVT = __widen_from_utf8<sizeof(wchar_t) * __CHAR_BIT__>;
  std::wstring __w;
  __w.reserve(__tmp.size());
  _CVT()(back_inserter(__w), __tmp.data(), __tmp.data() + __tmp.size());
  return path(__w);
#  else
  return path(__f, __l);
#  endif // _LIBCPP_FS_U8PATH_CONVERTS_ENCODING
}

template <class _InputIt, __enable_if_t<__is_pathable<_InputIt>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_WITH_CHAR8_T path u8path(_InputIt __f, _InputIt __l) {
  static_assert(
#  if _LIBCPP_HAS_CHAR8_T
      is_same<typename __is_pathable<_InputIt>::__char_type, char8_t>::value ||
#  endif
          is_same<typename __is_pathable<_InputIt>::__char_type, char>::value,
      "u8path(Iter, Iter) requires Iter have a value_type of type 'char'"
      " or 'char8_t'");
  return std::filesystem::__u8path(__f, __l);
}

template <class _Source, __enable_if_t<__is_pathable<_Source>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_WITH_CHAR8_T path u8path(const _Source& __s) {
  static_assert(
#  if _LIBCPP_HAS_CHAR8_T
      is_same<typename __is_pathable<_Source>::__char_type, char8_t>::value ||
#  endif
          is_same<typename __is_pathable<_Source>::__char_type, char>::value,
      "u8path(Source const&) requires Source have a character type of type "
      "'char' or 'char8_t'");
#  if _LIBCPP_FS_U8PATH_CONVERTS_ENCODING
  using _Traits = __is_pathable<_Source>;
  return std::filesystem::__u8path(
      std::__unwrap_iter(_Traits::__range_begin(__s)), std::__unwrap_iter(_Traits::__range_end(__s)));
#  else
  return path(__s);
#  endif // _LIBCPP_FS_U8PATH_CONVERTS_ENCODING
}

#  undef _LIBCPP_FS_U8PATH_CONVERTS_ENCODING

_LIBCPP_END_NAMESPACE_FILESYSTEM
```

</p>
</details> 

https://github.com/llvm/llvm-project/pull/165470