On Mon, Apr 27, 2026 at 1:51 AM Álvaro Begué <[email protected]> wrote:
> When a Zone line specifies a numeric value as its RULES field (the > constant DST save value for that zone line, e.g. Africa/Gaborone's > "2 1 CAST" line), the parser stored the standard offset alone in > ZoneInfo::m_offset. ZoneInfo::to() then returned that as > sys_info::offset, dropping the numeric save and reporting a total > offset that was wrong by the save amount. > > This was inconsistent with the two ZoneInfo constructors that take a > sys_info, which previously stored the *total* offset (stdoff + save) in > m_offset. As a result m_offset's semantics depended on which code path > created the ZoneInfo, and only the parser path's lines with non-zero > numeric save were observably broken. > > Fix by giving m_offset a single semantics: always the standard offset > only. The two sys_info-taking constructors now subtract the save before > storing, and to() adds it back when reconstructing the sys_info. > > The remaining .offset() callers inside _M_get_sys_info already expect > the standard offset (they are computing rule firing times, where the > save component is added separately from the active rule's save value), > so no other call sites need adjustment. > > libstdc++-v3/ChangeLog: > > PR libstdc++/124851 > * src/c++20/tzdb.cc (ZoneInfo::ZoneInfo(sys_info&&)): Store > stdoff only in m_offset (subtract info.save). > (ZoneInfo::ZoneInfo(const pair<sys_info, string_view>&)): > Likewise. > (ZoneInfo::offset()): Document new semantics. > (ZoneInfo::to(sys_info&)): Add m_save back to offset() when > populating sys_info::offset. > * testsuite/std/time/time_zone/numeric_save.cc: New test. > It seems that all tabs at the begining of the line were removed by your mail program, this made it very curbersome to apply the patch, but I reproduced it locally. The changes LGTM. I will push it to trunk after it gets approved. > > Signed-off-by: Álvaro Begué <[email protected]> > --- > libstdc++-v3/src/c++20/tzdb.cc | 9 +-- > .../std/time/time_zone/numeric_save.cc | 58 +++++++++++++++++++ > 2 files changed, 63 insertions(+), 4 deletions(-) > create mode 100644 > libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc > > diff --git a/libstdc++-v3/src/c++20/tzdb.cc > b/libstdc++-v3/src/c++20/tzdb.cc > index b0fbfc46a..1e49bb749 100644 > --- a/libstdc++-v3/src/c++20/tzdb.cc > +++ b/libstdc++-v3/src/c++20/tzdb.cc > @@ -478,11 +478,12 @@ namespace std::chrono > > ZoneInfo(sys_info&& info) > : m_buf(std::move(info.abbrev)), m_expanded(true), > m_save(info.save), > - m_offset(info.offset), m_until(info.end) > + m_offset(info.offset - seconds(info.save)), m_until(info.end) > { } > > ZoneInfo(const pair<sys_info, string_view>& info) > - : m_expanded(true), m_save(info.first.save), > m_offset(info.first.offset), > + : m_expanded(true), m_save(info.first.save), > + m_offset(info.first.offset - seconds(info.first.save)), > m_until(info.first.end) > { > if (info.second.size()) > @@ -494,7 +495,7 @@ namespace std::chrono > m_buf += info.first.abbrev; > } > > - // STDOFF: Seconds from UTC during standard time. > + // STDOFF: Seconds from UTC during standard time (without any save). > seconds > offset() const noexcept { return m_offset; } > > @@ -539,7 +540,7 @@ namespace std::chrono > return false; > > info.end = until(); > - info.offset = offset(); > + info.offset = offset() + seconds(m_save); > info.save = minutes(m_save); > info.abbrev = format(); > format_abbrev_str(info); // expand %z > diff --git a/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc > b/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc > new file mode 100644 > index 000000000..1b5b22263 > --- /dev/null > +++ b/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc > @@ -0,0 +1,58 @@ > +// { dg-do run { target c++20 } } > +// { dg-require-effective-target tzdb } > +// { dg-require-effective-target cxx11_abi } > +// { dg-xfail-run-if "no weak override on AIX" { powerpc-ibm-aix* } } > + > +// When a Zone line specifies a numeric value as its RULES field, that > +// value is the constant DST save value for that zone line. Per > +// [time.zone.info.sys] sys_info::offset is the total UTC offset > +// (stdoff + save). > + > +#include <chrono> > +#include <fstream> > +#include <testsuite_hooks.h> > + > +static bool override_used = false; > + > +namespace __gnu_cxx > +{ > + const char* zoneinfo_dir_override() { > + override_used = true; > + return "./"; > + } > +} > + > +int > +main() > +{ > + using namespace std::chrono; > + > + std::ofstream("tzdata.zi") << R"(# version test_numeric_save > +Z Test/Gaborone 2 - CAT 1943 Sep 19 2 > + 2 1 CAST 1944 Mar 19 2 > + 2 - CAT > +)"; > + > + const auto& db = reload_tzdb(); > + VERIFY( override_used ); > + VERIFY( db.version == "test_numeric_save" ); > + > + auto* tz = locate_zone("Test/Gaborone"); > + > + // Sample well inside the CAST (numeric-save) zone line. > + auto info = tz->get_info(sys_days(1943y/December/15)); > + VERIFY( info.offset == 3h ); // stdoff +2h + save +1h > + VERIFY( info.save == 60min ); > + VERIFY( info.abbrev == "CAST" ); > + > + // Bordering zone lines should report the standard offset with save 0. > + auto before = tz->get_info(sys_days(1943y/September/1)); > + VERIFY( before.offset == 2h ); > + VERIFY( before.save == 0min ); > + VERIFY( before.abbrev == "CAT" ); > + > + auto after = tz->get_info(sys_days(1944y/April/15)); > + VERIFY( after.offset == 2h ); > + VERIFY( after.save == 0min ); > + VERIFY( after.abbrev == "CAT" ); > +} > -- > 2.34.1 > >
