https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113318
--- Comment #6 from GCC 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:df0a668b784556fe4317317d58961652d93d53de commit r14-8182-gdf0a668b784556fe4317317d58961652d93d53de Author: Jonathan Wakely <jwak...@redhat.com> Date: Mon Jan 15 15:42:50 2024 +0000 libstdc++: Implement C++26 std::text_encoding (P1885R12) [PR113318] This is another C++26 change, approved in Varna 2023. We require a new static array of data that is extracted from the IANA Character Sets database. A new Python script to generate a header from the IANA CSV file is added. The text_encoding class is basically just a pointer to an {ID,name} pair in the static array. The aliases view is also just the same pointer (or empty), and the view's iterator moves forwards and backwards in the array while the array elements have the same ID (or to one element further, for a past-the-end iterator). Because those iterators refer to a global array that never goes out of scope, there's no reason they should every produce undefined behaviour or indeterminate values. They should either have well-defined behaviour, or abort. The overhead of ensuring those properties is pretty low, so seems worth it. This means that an aliases_view iterator should never be able to access out-of-bounds. A non-value-initialized iterator always points to an element of the static array even when not dereferenceable (the array has unreachable entries at the start and end, which means that even a past-the-end iterator for the last encoding in the array still points to valid memory). Dereferencing an iterator can always return a valid array element, or "" for a non-dereferenceable iterator (but doing so will abort when assertions are enabled). In the language being proposed for C++26, dereferencing an invalid iterator erroneously returns "". Attempting to increment/decrement past the last/first element in the view is erroneously a no-op, so aborts when assertions are enabled, and doesn't change value otherwise. Similarly, constructing a std::text_encoding with an invalid id (one that doesn't have the value of an enumerator) erroneously behaves the same as constructing with id::unknown, or aborts with assertions enabled. libstdc++-v3/ChangeLog: PR libstdc++/113318 * acinclude.m4 (GLIBCXX_CONFIGURE): Add c++26 directory. (GLIBCXX_CHECK_TEXT_ENCODING): Define. * config.h.in: Regenerate. * configure: Regenerate. * configure.ac: Use GLIBCXX_CHECK_TEXT_ENCODING. * include/Makefile.am: Add new headers. * include/Makefile.in: Regenerate. * include/bits/locale_classes.h (locale::encoding): Declare new member function. * include/bits/unicode.h (__charset_alias_match): New function. * include/bits/text_encoding-data.h: New file. * include/bits/version.def (text_encoding): Define. * include/bits/version.h: Regenerate. * include/std/text_encoding: New file. * src/Makefile.am: Add new subdirectory. * src/Makefile.in: Regenerate. * src/c++26/Makefile.am: New file. * src/c++26/Makefile.in: New file. * src/c++26/text_encoding.cc: New file. * src/experimental/Makefile.am: Include c++26 convenience library. * src/experimental/Makefile.in: Regenerate. * python/libstdcxx/v6/printers.py (StdTextEncodingPrinter): New printer. * scripts/gen_text_encoding_data.py: New file. * testsuite/22_locale/locale/encoding.cc: New test. * testsuite/ext/unicode/charset_alias_match.cc: New test. * testsuite/std/text_encoding/cons.cc: New test. * testsuite/std/text_encoding/members.cc: New test. * testsuite/std/text_encoding/requirements.cc: New test. Reviewed-by: Ulrich Drepper <drepper....@gmail.com> Reviewed-by: Patrick Palka <ppa...@redhat.com>
