https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95048
--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:b331bf303bdc1edead41e2b3d11d1a7804b433cf commit r13-3909-gb331bf303bdc1edead41e2b3d11d1a7804b433cf Author: Jonathan Wakely <jwak...@redhat.com> Date: Fri Nov 11 15:22:02 2022 +0000 libstdc++: Fix wstring conversions in filesystem::path [PR95048] In commit r9-7381-g91756c4abc1757 I changed filesystem::path to use std::codecvt<CharT, char, mbstate_t> for conversions from all wide strings to UTF-8, instead of using std::codecvt_utf8<CharT>. This was done because for 16-bit wchar_t, std::codecvt_utf8<wchar_t> only supports UCS-2 and not UTF-16. The rationale for the change was sound, but the actual fix was not. It's OK to use std::codecvt for char16_t or char32_t, because the specializations for those types always use UTF-8 , but std::codecvt<wchar_t, char, mbstate_t> uses the current locale's encodings, and the narrow encoding is probably ASCII and can't support non-ASCII characters. The correct fix is to use std::codecvt only for char16_t and char32_t. For 32-bit wchar_t we could have continued using std::codecvt_utf8 because that uses UTF-32 which is fine, switching to std::codecvt broke non-Windows targets with 32-bit wchar_t. For 16-bit wchar_t we did need to change, but should have changed to std::codecvt_utf8_utf16<wchar_t> instead, as that always uses UTF-16 not UCS-2. I actually noted that in the commit message for r9-7381-g91756c4abc1757 but didn't use that option. Oops. This replaces the unconditional std::codecvt<CharT, char, mbstate_t> with a type defined via template specialization, so it can vary depending on the wide character type. The code is also simplified to remove some of the mess of #ifdef and if-constexpr conditions. libstdc++-v3/ChangeLog: PR libstdc++/95048 * include/bits/fs_path.h (path::_Codecvt): New class template that selects the kind of code conversion done. (path::_Codecvt<wchar_t>): Select based on sizeof(wchar_t). (_GLIBCXX_CONV_FROM_UTF8): New macro to allow the same code to be used for Windows and POSIX. (path::_S_convert(const EcharT*, const EcharT*)): Simplify by using _Codecvt and _GLIBCXX_CONV_FROM_UTF8 abstractions. (path::_S_str_convert(basic_string_view<value_type>, const A&)): Simplify nested conditions. * include/experimental/bits/fs_path.h (path::_Cvt): Define nested typedef controlling type of code conversion done. (path::_Cvt::_S_wconvert): Use new typedef. (path::string(const A&)): Likewise. * testsuite/27_io/filesystem/path/construct/95048.cc: New test. * testsuite/experimental/filesystem/path/construct/95048.cc: New test.
