Re: [PATCH v4 0/3] C++20 P0482R6 and C2X N2653: char8_t, mbrtoc8(), and c8rtomb()

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

> On 30 Jun 2022, at 09:52, Tom Honermann via Libc-alpha <libc-alpha@sourceware.org> wrote:
> 
> This series of patches provides the following:
> - A fix for BZ #25744 [1].
> - Implementations of the mbrtoc8 and c8rtomb functions adopted for
>  C++20 via WG21 P0482R6 [2] and for C2X via WG14 N2653 [3].
> - A char8_t typedef as adopted for C2X via WG14 N2653 [3].
> 
> The fix for BZ #25744 [1] is included in this patch series because the tests
> for mbrtoc8 and c8rtomb depend on it for exercising the special case where a
> pair of Unicode code points is converted to/from a single double byte sequence.
> Such conversion cases exist for Big5-HKSCS. 
> 
> N2653 was adopted by WG14 for C2X and wording is present in the N2912 revision
> of the C2X working draft [4].  This patch series enables the new declarations
> in C2X mode and when _GNU_SOURCE is defined. 
> 
> This patch series addresses feedback provided in response to the prior
> submission series starting at [5].  All feedback was addressed except as noted
> below:
> - I removed the previously proposed wcsmbs/test-char8-type.c test as redundant
>  per feedback. I prototyped extending the c++-types.data test as suggested,
>  but that would have introduced a C++20 dependency.  The test demonstrated that
>  the char16_t and char32_t types were mapped to 'Ds' and 'Di' as expected, but
>  char8_t got mapped to 'h' rather than 'Du'.  It might be worth extending this
>  test in the future if/when C++20 support becomes a minimal requirement.
> - I did not switch the iconvdata/tst-iconv-big5-hkscs-to-2ucs4.c test to use
>  TEST_COMPARE in favor of the existing custom error handling; the current
>  error messages are customized to provide a more detailed explanation of the
>  error, so removing that seemed like an arguable regression.  My changes retain
>  consistency with the existing code.  I think it is reasonable to switch to
>  TEST_COMPARE, but I think that should be done separately from this change and
>  separately motivated.
> - I did not change the c8rtomb() and mbrtoc8() implementations to use thread
>  local storage when PS is null; the implementations continue to use static
>  storage consistent with c16rtomb(), mbrtoc16(), c32rtomb(), and mbrtoc32().
>  I think it is reasonable to switch all of these functions to use thread
>  local storage, but I think such a change should be done consistently across
>  all of them and should be separately motivated.
> 
> Thank you to Joseph Myers, Carlos O'Donell, Adhemerval Zanella, and Florian
> Weimer for prior reviews of this patch series.
> 
> Tested on Linux x86_64.
> 
> [1]: Bug 25744
>     "mbrtowc with Big5-HKSCS returns 2 instead of 1 when consuming the
>     second byte of certain double byte characters"
>     https://sourceware.org/bugzilla/show_bug.cgi?id=25744
> 
> [2]: WG21 P0482R6
>     "char8_t: A type for UTF-8 characters and strings (Revision 6)"
>     https://wg21.link/p0482r6
> 
> [3]: WG14 N2653
>     "char8_t: A type for UTF-8 characters and strings (Revision 1)"
>     http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2653.htm
> 
> [4]: WG14 N2912
>     "Programming languages — C working draft — June 8, 2022"
>     https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2912.pdf
> 
> [5]: libc-alpha mailing list
>     "[PATCH 0/3]: C++20 P0482R6 and C2X N2653: support for char8_t, mbrtoc8(), and c8rtomb()."
>     https://sourceware.org/pipermail/libc-alpha/2022-February/136723.html

Hi Tom,

Patches look good in general, just some really minor style issues I
found in last review.  I have fixed them and if you are ok I can
install them, I have create a branch so you can check [1].

[1] https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/azanella/mbrtoc8-c8rtomb