Jonathan Wakely 74b5101cc9 libstdc++: Handle encodings in localized chrono formatting [PR109162] ... This implements the C++23 paper P2419R2 (Clarify handling of encodings in localized formatting of chrono types). The requirement is that when the literal encoding is "a Unicode encoding form" and the formatting locale uses a different encoding, any locale-specific strings such as "août" for std::chrono::August should be converted to the literal encoding. Using the recently-added std::locale::encoding() function we can check the locale's encoding and then use iconv if a conversion is needed. Because nl_langinfo_l and iconv_open both allocate memory, a naive implementation would perform multiple allocations and deallocations for every snippet of locale-specific text that needs to be converted to UTF-8. To avoid that, a new internal locale::facet is defined to store the text_encoding and an iconv_t descriptor, which are then cached in the formatting locale. This requires access to the internals of a std::locale object in src/c++20/format.cc, so that new file needs to be compiled with -fno-access-control, as well as -std=gnu++26 in order to use std::text_encoding. Because the new std::text_encoding and std::locale::encoding() symbols are only in the libstdc++exp.a archive, we need to include src/c++26/text_encoding.cc in the main library, but not export its symbols yet. This means they can be used by the two new functions which are exported from the main library. The encoding conversions are done for C++20, treating it as a DR that resolves LWG 3656. With this change we can increase the value of the __cpp_lib_format macro for C++23. The value should be 202207 for P2419R2, but we already implement P2510R3 (Formatting pointers) so can use the value 202304. libstdc++-v3/ChangeLog: PR libstdc++/109162 * acinclude.m4 (libtool_VERSION): Update to 6:34:0. * config/abi/pre/gnu.ver: Disambiguate old patters. Add new GLIBCXX_3.4.34 symbol version and new exports. * configure: Regenerate. * include/bits/chrono_io.h (_ChronoSpec::_M_locale_specific): Add new accessor functions to use a reserved bit in _Spec. (__formatter_chrono::_M_parse): Use _M_locale_specific(true) when chrono-specs contains locale-dependent conversion specifiers. (__formatter_chrono::_M_format): Open iconv descriptor if conversion to UTF-8 will be needed. (__formatter_chrono::_M_write): New function to write a localized string with possible character conversion. (__formatter_chrono::_M_a_A, __formatter_chrono::_M_b_B) (__formatter_chrono::_M_p, __formatter_chrono::_M_r) (__formatter_chrono::_M_x, __formatter_chrono::_M_X) (__formatter_chrono::_M_locale_fmt): Use _M_write. * include/bits/version.def (format): Update value. * include/bits/version.h: Regenerate. * include/std/format (_GLIBCXX_P2518R3): Check feature test macro instead of __cplusplus. (basic_format_context): Declare __formatter_chrono as friend. * src/c++20/Makefile.am: Add new file. * src/c++20/Makefile.in: Regenerate. * src/c++20/format.cc: New file. * testsuite/std/time/format_localized.cc: New test. * testsuite/util/testsuite_abi.cc: Add new symbol version.		2024-07-31 17:07:10 +01:00
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pre	libstdc++: Handle encodings in localized chrono formatting [PR109162]	2024-07-31 17:07:10 +01:00
compatibility.h