commit cb232cf3d475d51fe5e550680bff64dfd32f57a5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 29 19:36:39 2019 +0000

    libstdc++: Fix experimental::filesystem::u8path(const Source&) for Windows
    
    This function failed to compile when called with a std::string.
    
    Also, constructing a path with a char8_t string did not correctly treat
    the string as already UTF-8 encoded.
    
            * include/bits/fs_path.h (u8path(InputIterator, InputIterator))
            (u8path(const Source&)) [_GLIBCXX_FILESYSTEM_IS_WINDOWS]: Simplify
            conditions.
            * include/experimental/bits/fs_path.h [_GLIBCXX_FILESYSTEM_IS_WINDOWS]
            (__u8path(const Source&, char)): Add overloads for std::string and
            types convertible to std::string.
            (_Cvt::_S_wconvert): Add a new overload for char8_t strings and use
            codecvt_utf8_utf16 to do the correct conversion.

diff --git a/libstdc++-v3/include/bits/fs_path.h b/libstdc++-v3/include/bits/fs_path.h
index b129372447b..20ec42da57d 100644
--- a/libstdc++-v3/include/bits/fs_path.h
+++ b/libstdc++-v3/include/bits/fs_path.h
@@ -691,14 +691,8 @@ namespace __detail
     u8path(_InputIterator __first, _InputIterator __last)
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-#ifdef _GLIBCXX_USE_CHAR8_T
-      if constexpr (is_same_v<_CharT, char8_t>)
+      if constexpr (is_same_v<_CharT, char>)
 	{
-	  return path{ __first, __last };
-	}
-      else
-	{
-#endif
 	  // XXX This assumes native wide encoding is UTF-16.
 	  std::codecvt_utf8_utf16<path::value_type> __cvt;
 	  path::string_type __tmp;
@@ -710,16 +704,16 @@ namespace __detail
 	  else
 	    {
 	      const std::string __u8str{__first, __last};
-	      const char* const __ptr = __u8str.data();
-	      if (__str_codecvt_in_all(__ptr, __ptr + __u8str.size(), __tmp, __cvt))
+	      const char* const __p = __u8str.data();
+	      if (__str_codecvt_in_all(__p, __p + __u8str.size(), __tmp, __cvt))
 		return path{ __tmp };
 	    }
 	  _GLIBCXX_THROW_OR_ABORT(filesystem_error(
 	      "Cannot convert character sequence",
 	      std::make_error_code(errc::illegal_byte_sequence)));
-#ifdef _GLIBCXX_USE_CHAR8_T
 	}
-#endif
+      else
+	return path{ __first, __last };
 #else
       // This assumes native normal encoding is UTF-8.
       return path{ __first, __last };
@@ -737,14 +731,8 @@ namespace __detail
     u8path(const _Source& __source)
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
-#ifdef _GLIBCXX_USE_CHAR8_T
-      if constexpr (is_same_v<_CharT, char8_t>)
+      if constexpr (is_same_v<_CharT, char>)
 	{
-	  return path{ __source };
-	}
-      else
-	{
-#endif
 	  if constexpr (is_convertible_v<const _Source&, std::string_view>)
 	    {
 	      const std::string_view __s = __source;
@@ -755,9 +743,9 @@ namespace __detail
 	      std::string __s = path::_S_string_from_iter(__source);
 	      return filesystem::u8path(__s.data(), __s.data() + __s.size());
 	    }
-#ifdef _GLIBCXX_USE_CHAR8_T
 	}
-#endif
+      else
+	return path{ __source };
 #else
       return path{ __source };
 #endif
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 91202e5b008..5ce012eec81 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -644,8 +644,22 @@ namespace __detail
 
   /// Create a path from a UTF-8-encoded sequence of char
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  inline path
+  __u8path(const string& __s, char)
+  {
+    return filesystem::u8path(__s.data(), __s.data() + __s.size());
+  }
+
   template<typename _Source>
-    inline path
+    inline __enable_if_t<is_convertible<const _Source&, string>::value, path>
+    __u8path(const _Source& __source, char)
+    {
+      std::string __s = __source;
+      return filesystem::u8path(__s.data(), __s.data() + __s.size());
+    }
+
+  template<typename _Source>
+    inline __enable_if_t<!is_convertible<const _Source&, string>::value, path>
     __u8path(const _Source& __source, char)
     {
       std::string __s = path::_S_string_from_iter(__source);
@@ -733,8 +747,21 @@ namespace __detail
     struct path::_Cvt
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+#ifdef _GLIBCXX_USE_CHAR8_T
       static string_type
-      _S_wconvert(const char* __f, const char* __l, true_type)
+      _S_wconvert(const char8_t* __f, const char8_t* __l, const char8_t*)
+      {
+	const char* __f2 = (const char*)__f;
+	const char* __l2 = (const char*)__l;
+	std::wstring __wstr;
+	std::codecvt_utf8_utf16<wchar_t> __wcvt;
+	if (__str_codecvt_in_all(__f2, __l2, __wstr, __wcvt))
+	  return __wstr;
+      }
+#endif
+
+      static string_type
+      _S_wconvert(const char* __f, const char* __l, const char*)
       {
 	using _Cvt = std::codecvt<wchar_t, char, mbstate_t>;
 	const auto& __cvt = std::use_facet<_Cvt>(std::locale{});
@@ -747,36 +774,29 @@ namespace __detail
       }
 
       static string_type
-      _S_wconvert(const _CharT* __f, const _CharT* __l, false_type)
+      _S_wconvert(const _CharT* __f, const _CharT* __l, const void*)
       {
-#ifdef _GLIBCXX_USE_CHAR8_T
-	if constexpr (is_same<_CharT, char8_t>::value)
-	  return _S_wconvert((const char*)__f, (const char*)__l, true_type());
-	else
-#endif
+	struct _UCvt : std::codecvt<_CharT, char, std::mbstate_t>
+	{ } __cvt;
+	std::string __str;
+	if (__str_codecvt_out_all(__f, __l, __str, __cvt))
 	  {
-	    struct _UCvt : std::codecvt<_CharT, char, std::mbstate_t>
-	    { } __cvt;
-	    std::string __str;
-	    if (__str_codecvt_out_all(__f, __l, __str, __cvt))
-	      {
-		const char* __f2 = __str.data();
-		const char* __l2 = __f2 + __str.size();
-		std::codecvt_utf8_utf16<wchar_t> __wcvt;
-		std::wstring __wstr;
-		if (__str_codecvt_in_all(__f2, __l2, __wstr, __wcvt))
-		  return __wstr;
-	      }
-	    _GLIBCXX_THROW_OR_ABORT(filesystem_error(
-		  "Cannot convert character sequence",
-		  std::make_error_code(errc::illegal_byte_sequence)));
+	    const char* __f2 = __str.data();
+	    const char* __l2 = __f2 + __str.size();
+	    std::codecvt_utf8_utf16<wchar_t> __wcvt;
+	    std::wstring __wstr;
+	    if (__str_codecvt_in_all(__f2, __l2, __wstr, __wcvt))
+	      return __wstr;
 	  }
+	_GLIBCXX_THROW_OR_ABORT(filesystem_error(
+	      "Cannot convert character sequence",
+	      std::make_error_code(errc::illegal_byte_sequence)));
       }
 
       static string_type
       _S_convert(const _CharT* __f, const _CharT* __l)
       {
-	return _S_wconvert(__f, __l, is_same<_CharT, char>{});
+	return _S_wconvert(__f, __l, (const _CharT*)nullptr);
       }
 #else
       static string_type
@@ -786,19 +806,17 @@ namespace __detail
 	if constexpr (is_same<_CharT, char8_t>::value)
 	  return string_type(__f, __l);
 	else
-	  {
 #endif
+	  {
 	    struct _UCvt : std::codecvt<_CharT, char, std::mbstate_t>
 	    { } __cvt;
 	    std::string __str;
 	    if (__str_codecvt_out_all(__f, __l, __str, __cvt))
 	      return __str;
-#ifdef _GLIBCXX_USE_CHAR8_T
+	    _GLIBCXX_THROW_OR_ABORT(filesystem_error(
+		  "Cannot convert character sequence",
+		  std::make_error_code(errc::illegal_byte_sequence)));
 	  }
-#endif
-	_GLIBCXX_THROW_OR_ABORT(filesystem_error(
-	      "Cannot convert character sequence",
-	      std::make_error_code(errc::illegal_byte_sequence)));
       }
 #endif