On Sat, 8 Jan 2022 at 00:42, Tom Honermann via Libstdc++ < libstd...@gcc.gnu.org> wrote:
> This patch completes implementation of the C++20 proposal P0482R6 [1] by > adding declarations of std::c8rtomb() and std::mbrtoc8() in <cuchar> if > provided by the C library in <uchar.h>. > > This patch addresses feedback provided in response to a previous patch > submission [2]. > > Autoconf changes determine if the C library declares c8rtomb and mbrtoc8 > at global scope when uchar.h is included and compiled with either > -fchar8_t or -std=c++20. New _GLIBCXX_USE_UCHAR_C8RTOMB_MBRTOC8_FCHAR8_T > and _GLIBCXX_USE_UCHAR_C8RTOMB_MBRTOC8_CXX20 configuration macros > reflect the probe results. The <cuchar> header declares these functions > in the std namespace only if available and the _GLIBCXX_USE_CHAR8_T > configuration macro is defined (by default it is defined if the C++20 > __cpp_char8_t feature test macro is defined) > > Patches to glibc to implement c8rtomb and mbrtoc8 have been submitted [3]. > > New tests validate the presence of these declarations. The tests pass > trivially if the C library does not provide these functions. Otherwise > they ensure that the functions are declared when <cuchar> is included > and either -fchar8_t or -std=c++20 is enabled. > > Tested on Linux x86_64. > > libstdc++-v3/ChangeLog: > > 2022-01-07 Tom Honermann <t...@honermann.net> > > * acinclude.m4 Define config macros if uchar.h provides > c8rtomb() and mbrtoc8(). > * config.h.in: Re-generate. > * configure: Re-generate. > * include/c_compatibility/uchar.h: Declare ::c8rtomb and > ::mbrtoc8. > * include/c_global/cuchar: Declare std::c8rtomb and > std::mbrtoc8. > * include/c_std/cuchar: Declare std::c8rtomb and std::mbrtoc8. > * testsuite/21_strings/headers/cuchar/functions_std_cxx20.cc: > New test. > * testsuite/21_strings/headers/cuchar/functions_std_fchar8_t.cc: > New test. > Thanks, Tom, this looks good and I'll get it committed for GCC 12. My only concern is that the new tests depend on an internal macro: +#if _GLIBCXX_USE_UCHAR_C8RTOMB_MBRTOC8_CXX20 + using std::mbrtoc8; + using std::c8rtomb; I prefer if tests are written as "user code" when possible, and not using our internal macros. That isn't always possible, and in this case would require adding new effective-target keyword to testsuite/lib/libstdc++.exp just for use in these two tests. I don't think we should bother with that. I suppose strictly speaking we should not define __cpp_lib_char8_t unless these two functions are present in libc. But I'm not sure we want to change that now either.
