https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116657
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-13 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:5ceea2ac106d6dd1aa8175670b15a801316cf1c9 commit r13-9015-g5ceea2ac106d6dd1aa8175670b15a801316cf1c9 Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Apr 30 09:52:13 2024 +0100 libstdc++: Fix std::chrono::tzdb to work with vanguard format I found some issues in the std::chrono::tzdb parser by testing the tzdata "vanguard" format, which uses new features that aren't enabled in the "main" and "rearguard" data formats. Since 2024a the keyword "minimum" is no longer valid for the FROM and TO fields in a Rule line, which means that "m" is now a valid abbreviation for "maximum". Previously we expected either "mi" or "ma". For backwards compatibility, a FROM field beginning with "mi" is still supported and is treated as 1900. The "maximum" keyword is only allowed in TO now, because it makes no sense in FROM. To support these changes the minmax_year and minmax_year2 classes for parsing FROM and TO are replaced with a single years_from_to class that reads both fields. The vanguard format makes use of %z in Zone FORMAT fields, which caused an exception to be thrown from ZoneInfo::set_abbrev because no % or / characters were expected when a Zone doesn't use a named Rule. The ZoneInfo::to(sys_info&) function now uses format_abbrev_str to replace any %z with the current offset. Although format_abbrev_str also checks for %s and STD/DST formats, those only make sense when a named Rule is in effect, so won't occur when ZoneInfo::to(sys_info&) is used. Since making this change on trunk, the tzdata-2024b release started using %z in the main format, not just vanguard. This makes a backport to release branches necessary (see PR 116657). This change also implements a feature that has always been missing from time_zone::_M_get_sys_info: finding the Rule that is active before the specified time point, so that we can correctly handle %s in the FORMAT for the first new sys_info that gets created. This requires implementing a poorly documented feature of zic, to get the LETTERS field from a later transition, as described at https://mm.icann.org/pipermail/tz/2024-April/058891.html In order for this to work we need to be able to distinguish an empty letters field (as used by CE%sT where the variable part is either empty or "S") from "the letters field is not known for this transition". The tzdata file uses "-" for an empty letters field, which libstdc++ was previously replacing with "" when the Rule was parsed. Instead, we now preserve the "-" in the Rule object, so that "" can be used for the case where we don't know the letters (and so need to decide it). libstdc++-v3/ChangeLog: * src/c++20/tzdb.cc (minmax_year, minmax_year2): Remove. (years_from_to): New class replacing minmax_year and minmax_year2. (format_abbrev_str, select_std_or_dst_abbrev): Move earlier in the file. Handle "-" for letters. (ZoneInfo::to): Use format_abbrev_str to expand %z. (ZoneInfo::set_abbrev): Remove exception. Change parameter from reference to value. (operator>>(istream&, Rule&)): Do not clear letters when it contains "-". (time_zone::_M_get_sys_info): Add missing logic to find the Rule in effect before the time point. * testsuite/std/time/tzdb/1.cc: Adjust for vanguard format using "GMT" as the Zone name, not as a Link to "Etc/GMT". * testsuite/std/time/time_zone/sys_info_abbrev.cc: New test. (cherry picked from commit 0ca8d56f2085715f27ee536c6c344bc47af49cdd)
