Re: [PATCH v3] libstdc++: Fix handling of surrogate CP in codecvt [PR108976]

[Jonathan Wakely <jwakely@redhat.com>]

On Thu, 28 Sept 2023 at 20:39, Dimitrij Mijoski via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> This patch fixes the handling of surrogate code points in all standard
> facets for transcoding Unicode that are based on std::codecvt. Surrogate
> code points should always be treated as error. On the other hand
> surrogate code units can only appear in UTF-16 and only when they come
> in a proper pair.
>
> Additionally, it fixes a bug in std::codecvt_utf16::in() when odd number
> of bytes were given in the range [from, from_end), error was returned
> always. The last byte in such range does not form a full UTF-16 code
> unit and we can not make any decisions for error, instead partial should
> be returned.
>
> The testsuite for testing these facets was updated in the following
> order:
>
> 1. All functions that test codecvts that work with UTF-8 were refactored
>    and made more generic so they accept codecvt that works with the char
>    type char8_t.
> 2. The same functions were updated with new test cases for transcoding
>    errors and now additionally test for surrogates, overlong UTF-8
>    sequences, code points out of the Unicode range, and more tests for
>    missing leading and trailing code units.
> 3. New tests were added to test codecvt_utf16 in both of its variants,
>    UTF-16 <-> UTF-32/UCS-4 and UTF-16 <-> UCS-2.
>
> libstdc++-v3/ChangeLog:
>
>         * src/c++11/codecvt.cc (read_utf8_code_point): Fix handing of
>         surrogates in UTF-8.
>         (ucs4_out): Fix handling of surrogates in UCS-4 -> UTF-8.
>         (ucs4_in): Fix handling of range with odd number of bytes.
>         (ucs4_out): Fix handling of surrogates in UCS-4 -> UTF-16.
>         (ucs2_out): Fix handling of surrogates in UCS-2 -> UTF-16.
>         (ucs2_in): Fix handling of range with odd number of bytes.
>         (__codecvt_utf16_base<char16_t>::do_in): Likewise.
>         (__codecvt_utf16_base<char32_t>::do_in): Likewise.
>         (__codecvt_utf16_base<wchar_t>::do_in): Likewise.
>         * testsuite/22_locale/codecvt/codecvt_unicode.cc: Renames, add
>         tests for codecvt_utf16<char16_t> and codecvt_utf16<char32_t>.
>         * testsuite/22_locale/codecvt/codecvt_unicode.h: Refactor UTF-8
>         testing functions for char8_t, add more test cases for errors,
>         add testing functions for codecvt_utf16.
>         * testsuite/22_locale/codecvt/codecvt_unicode_wchar_t.cc:
>         Renames, add tests for codecvt_utf16<whchar_t>.
>         * testsuite/22_locale/codecvt/codecvt_utf16/79980.cc (test06):
>         Fix test.
>         * testsuite/22_locale/codecvt/codecvt_unicode_char8_t.cc: New test.

Thanks, your v2 patch was still on my TODO list. I've pushed this
version to trunk now.