[PATCH v2] libstdc++: Support ON-format DAY in Zone UNTIL field [PR124852]
Tomasz Kamiński
tkaminsk@redhat.com
Tue May 12 09:35:49 GMT 2026
From: Álvaro Begué <alvaro.begue@gmail.com>
The Zone-line UNTIL parser only accepted a plain day-of-month integer
for the DAY field, while the tzdata.zi grammar accepts the same ON-style
forms as Rule lines: lastSun, Sun>=8, Sat<=20, etc. Real zones use these
forms in their UNTIL DAY: Europe/Simferopol's `3 - MSK 1997 Mar lastSu
1u`, for instance, became `Mar 1` (silently misparsed) instead of `Mar
30`, leaving Simferopol an extra 29 days in MSK.
The previous parser's `int d = 1; in >> m >> d >> t;` chain silently
left d == 1 when the day token wasn't a digit, then went on to parse the
remainder as the TIME field.
Renames on_day to on_month_day, and factor out the day-component parser
parser from operator>>(istream&, on_month_day&) as operator>> for newly
added on_day_t tag type, and reuse it for the UNTIL DAY field. It
handles all three on_day forms (DayOfMonth, LastWeekday, LessEq /
GreaterEq). The MONTH-only and YEAR-only short forms are still accepted
because the DAY/TIME fields are optional and default to day 1, time 00:00.
The on_day struct's pin() method handles the year/month-relative
resolution.
The DAY field is unambiguously distinguishable from a TIME field that
could otherwise follow the MONTH directly: per zic's grammar, MONTH
must be followed by DAY before any TIME is allowed. So we always
attempt to parse a DAY if any non-whitespace remains after the MONTH.
libstdc++-v3/ChangeLog:
PR libstdc++/124852
* src/c++20/tzdb.cc (on_day): Rename to...
(on_day_month): Rename from on_day.
(on_day_month::on_day_t, on_day_month::on_day): Define.
(operator>>(istream&, on_day_t&&)): Factored out of
operator>>(istream&, on_day&).
(operator>>(istream&, on_day&)): Use on_day_t parser.
(operator>>(istream&, ZoneInfo&)): Replace the integer DAY
parser with on_day_t for the UNTIL field.
* testsuite/std/time/time_zone/until_day_on.cc: New test.
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Co-authored-by: Tomasz Kamiński <tkaminsk@redhat.com>
Signed-off-by: Álvaro Begué <alvaro.begue@gmail.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
---
v2 changes:
- rename on_day to on_month_day for clarity
- introduce on_day_t/on_day helpers and replace parse_day_spec
with operator>> for on_day_t
- adds comment on VERIFY( override_used ) checks
I think on_month_day is better name (it is always day of month),
also store reference in on_day_t helper, so I do not need to wonder
about nulls.
Testing on x86_64-linux. The *tzdb* passed.
OK for trunk when all test passes?
libstdc++-v3/src/c++20/tzdb.cc | 74 +++++---
.../std/time/time_zone/until_day_on.cc | 170 ++++++++++++++++++
2 files changed, 218 insertions(+), 26 deletions(-)
create mode 100644 libstdc++-v3/testsuite/std/time/time_zone/until_day_on.cc
diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index e9ce120622c..96c6b462d18 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -214,7 +214,7 @@ namespace std::chrono
constinit atomic<tzdb_list::_Node*> tzdb_list::_Node::_S_head_cache{nullptr};
#endif
- // The data structures defined in this file (Rule, on_day, at_time etc.)
+ // The data structures defined in this file (Rule, on_month_day, at_time etc.)
// are used to represent the information parsed from the tzdata.zi file
// described at https://man7.org/linux/man-pages/man8/zic.8.html#FILES
@@ -303,7 +303,7 @@ namespace std::chrono
};
// The IN and ON fields of a RULE record, e.g. "March lastSunday".
- struct on_day
+ struct on_month_day
{
using rep = uint_least16_t;
// Equivalent to Kind, chrono::month, chrono::day, chrono::weekday,
@@ -367,7 +367,15 @@ namespace std::chrono
return ymd;
}
- friend istream& operator>>(istream&, on_day&);
+ struct on_day_t // tag type for reading ON and DAY fields only
+ {
+ on_month_day& parent;
+ friend istream& operator>>(istream&, on_day_t&&);
+ };
+
+ on_day_t on_day() { return on_day_t{*this}; }
+
+ friend istream& operator>>(istream&, on_month_day&);
};
// Wrapper for two chrono::year values, which reads the FROM and TO
@@ -590,9 +598,9 @@ namespace std::chrono
// A RULE record from the tzdata.zi timezone info file.
struct Rule
{
- // This allows on_day to reuse padding of at_time.
+ // This allows on_month_day to reuse padding of at_time.
// This keeps the size to 8 bytes and the alignment to 4 bytes.
- struct datetime : at_time { on_day day; };
+ struct datetime : at_time { on_month_day day; };
// TODO combining name+letters into a single string (like in ZoneInfo)
// would save sizeof(string) and make Rule fit in a single cacheline.
@@ -654,17 +662,17 @@ namespace std::chrono
<< ' ' << r.when.day.get_month() << ' ';
switch (r.when.day.kind)
{
- case on_day::DayOfMonth:
+ case on_month_day::DayOfMonth:
out << (unsigned)r.when.day.get_day();
break;
- case on_day::LastWeekday:
+ case on_month_day::LastWeekday:
out << "last" << weekday(r.when.day.day_of_week);
break;
- case on_day::LessEq:
+ case on_month_day::LessEq:
out << weekday(r.when.day.day_of_week) << " <= "
<< r.when.day.day_of_month;
break;
- case on_day::GreaterEq:
+ case on_month_day::GreaterEq:
out << weekday(r.when.day.day_of_week) << " >= "
<< r.when.day.day_of_month;
break;
@@ -2200,22 +2208,23 @@ namespace std::chrono
}
};
- istream& operator>>(istream& in, on_day& to)
+ // Read the day-component of an on_month_day expression (everything after
+ // the month). Three forms are accepted: a plain day-of-month number,
+ // "lastXxx" where Xxx is a weekday name (LastWeekday), or "Xxx<=N" or
+ // "Xxx>=N" (LessEq / GreaterEq). On failure the function sets failbit
+ // and leaves `to.parent` unchanged.
+ istream& operator>>(istream& in, on_month_day::on_day_t&& to)
{
- on_day on{};
- abbrev_month m{};
- in >> m;
- on.month = static_cast<unsigned>(m.m);
+ on_month_day& on = to.parent;
int c = ws(in).peek();
if ('0' <= c && c <= '9')
{
- on.kind = on_day::DayOfMonth;
unsigned d;
in >> d;
if (d <= 31) [[likely]]
{
+ on.kind = on_month_day::DayOfMonth;
on.day_of_month = d;
- to = on;
return in;
}
}
@@ -2224,9 +2233,8 @@ namespace std::chrono
in.ignore(4);
if (abbrev_weekday w{}; in >> w) [[likely]]
{
- on.kind = on_day::LastWeekday;
+ on.kind = on_month_day::LastWeekday;
on.day_of_week = w.wd.c_encoding();
- to = on;
return in;
}
}
@@ -2238,14 +2246,13 @@ namespace std::chrono
{
if (in.get() == '=')
{
- on.kind = c == '<' ? on_day::LessEq : on_day::GreaterEq;
- on.day_of_week = w.wd.c_encoding();
unsigned d;
in >> d;
if (d <= 31) [[likely]]
{
+ on.kind = c == '<' ? on_month_day::LessEq : on_month_day::GreaterEq;
+ on.day_of_week = w.wd.c_encoding();
on.day_of_month = d;
- to = on;
return in;
}
}
@@ -2255,6 +2262,17 @@ namespace std::chrono
return in;
}
+ istream& operator>>(istream& in, on_month_day& to)
+ {
+ on_month_day md{};
+ abbrev_month m{};
+ in >> m;
+ md.month = static_cast<unsigned>(m.m);
+ if (in >> md.on_day())
+ to = md;
+ return in;
+ }
+
istream& operator>>(istream& in, at_time& at)
{
int sign = 1;
@@ -2357,12 +2375,16 @@ namespace std::chrono
in.exceptions(ios::goodbit); // Don't throw ios::failure if YEAR absent.
if (int y = int(year::max()); in >> y)
{
- abbrev_month m{January};
- int d = 1;
+ on_month_day on{.kind = on_month_day::DayOfMonth, .month = 1, .day_of_month = 1};
at_time t{};
- // XXX DAY should support ON format, e.g. lastSun or Sun>=8
- in >> m >> d >> t;
- inf.m_until = sys_days(year(y)/m.m/day(d)) + seconds(t.time);
+ if (abbrev_month m{January}; in >> m)
+ {
+ on.month = static_cast<unsigned>(m.m);
+ if (!ws(in).eof())
+ in >> on.on_day() >> t;
+ }
+ year_month_day ymd = on.pin(year(y));
+ inf.m_until = sys_days(ymd) + seconds(t.time);
if (t.indicator != at_time::Universal)
{ // UNTIL uses "the rules in effect just before the transition"
// adjust by STDOFF
diff --git a/libstdc++-v3/testsuite/std/time/time_zone/until_day_on.cc b/libstdc++-v3/testsuite/std/time/time_zone/until_day_on.cc
new file mode 100644
index 00000000000..70879b40e34
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/time/time_zone/until_day_on.cc
@@ -0,0 +1,170 @@
+// { 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* } }
+
+// The DAY portion of a Zone line's UNTIL field accepts not only a
+// numeric day-of-month but also "lastXxx" (last weekday in the month)
+// and "Xxx<=N" / "Xxx>=N" forms, just like the ON field of a Rule line.
+//
+// Real-world example: Europe/Simferopol has
+// 3 - MSK 1997 Mar lastSu 1u
+// which places the boundary on 1997-03-30 (the last Sunday of March).
+
+#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 "./";
+ }
+}
+
+void
+test_lastsu()
+{
+ using namespace std::chrono;
+
+ std::ofstream("tzdata.zi") << R"(# version test_lastsu
+Z Test/LastSu 3 - MSK 1997 Mar lastSu 1u
+ 3 - X
+)";
+
+ const auto& db = reload_tzdb();
+ VERIFY( override_used ); // If this fails then XFAIL for the target.
+ VERIFY( db.version == "test_lastsu" );
+
+ auto* tz = locate_zone("Test/LastSu");
+
+ // True boundary: 1997-03-30 01:00 UTC (lastSu of March 1997 is Mar 30,
+ // and the indicator is 'u' = Universal so no offset adjustment).
+ sys_seconds boundary = sys_days{1997y/March/30} + 1h;
+
+ // Just before: still in the MSK line.
+ auto before = tz->get_info(boundary - 1s);
+ VERIFY( before.abbrev == "MSK" );
+ VERIFY( before.offset == 3h );
+
+ // At/after the boundary: in the X line.
+ auto at = tz->get_info(boundary);
+ VERIFY( at.abbrev == "X" );
+
+ // Check that the lastSu day is parsed correctly, and not defaulted
+ // to the 1st: a March 15 query must still be in the MSK line.
+ auto mid_march = tz->get_info(sys_days{1997y/March/15});
+ VERIFY( mid_march.abbrev == "MSK" );
+ VERIFY( mid_march.offset == 3h );
+}
+
+void
+test_sun_ge_n()
+{
+ using namespace std::chrono;
+
+ std::ofstream("tzdata.zi") << R"(# version test_sun_ge_n
+Z Test/SunGE 0 - A 1990 Jun Sun>=8 0u
+ 0 - B
+)";
+
+ const auto& db = reload_tzdb();
+ VERIFY( override_used ); // If this fails then XFAIL for the target.
+ VERIFY( db.version == "test_sun_ge_n" );
+
+ auto* tz = locate_zone("Test/SunGE");
+
+ // First Sunday >= June 8 1990 = June 10 (June 8 1990 was a Friday).
+ sys_seconds boundary = sys_days{1990y/June/10};
+
+ auto before = tz->get_info(boundary - 1s);
+ VERIFY( before.abbrev == "A" );
+ auto at = tz->get_info(boundary);
+ VERIFY( at.abbrev == "B" );
+
+ // Check that Sun>=8 is parsed correctly, and not defaulted to the 1st.
+ auto early = tz->get_info(sys_days{1990y/June/1});
+ VERIFY( early.abbrev == "A" );
+}
+
+void
+test_sun_le_n()
+{
+ using namespace std::chrono;
+
+ std::ofstream("tzdata.zi") << R"(# version test_sun_le_n
+Z Test/SunLE 0 - A 1990 Jun Sun<=15 0u
+ 0 - B
+)";
+
+ const auto& db = reload_tzdb();
+ VERIFY( override_used ); // If this fails then XFAIL for the target.
+ VERIFY( db.version == "test_sun_le_n" );
+
+ auto* tz = locate_zone("Test/SunLE");
+
+ // Last Sunday <= June 15 1990 = June 10.
+ sys_seconds boundary = sys_days{1990y/June/10};
+
+ auto before = tz->get_info(boundary - 1s);
+ VERIFY( before.abbrev == "A" );
+ auto at = tz->get_info(boundary);
+ VERIFY( at.abbrev == "B" );
+}
+
+void
+test_year_only()
+{
+ using namespace std::chrono;
+
+ // MONTH, DAY and TIME default to January 1st 00:00 if not specified.
+ std::ofstream("tzdata.zi") << R"(# version test_year_only
+Z Test/YearOnly 0 - A 1990
+ 0 - B
+)";
+
+ const auto& db = reload_tzdb();
+ VERIFY( override_used ); // If this fails then XFAIL for the target.
+ VERIFY( db.version == "test_year_only" );
+
+ auto* tz = locate_zone("Test/YearOnly");
+ auto before = tz->get_info(sys_days{1989y/December/31} + 23h);
+ VERIFY( before.abbrev == "A" );
+ auto at = tz->get_info(sys_days{1990y/January/1});
+ VERIFY( at.abbrev == "B" );
+}
+
+void
+test_year_month_only()
+{
+ using namespace std::chrono;
+
+ // DAY and TIME default to the 1st 00:00 if not specified.
+ std::ofstream("tzdata.zi") << R"(# version test_year_month_only
+Z Test/YearMonth 0 - A 1990 Jul
+ 0 - B
+)";
+
+ const auto& db = reload_tzdb();
+ VERIFY( override_used ); // If this fails then XFAIL for the target.
+ VERIFY( db.version == "test_year_month_only" );
+
+ auto* tz = locate_zone("Test/YearMonth");
+ auto before = tz->get_info(sys_days{1990y/June/30} + 23h);
+ VERIFY( before.abbrev == "A" );
+ auto at = tz->get_info(sys_days{1990y/July/1});
+ VERIFY( at.abbrev == "B" );
+}
+
+int
+main()
+{
+ test_lastsu();
+ test_sun_ge_n();
+ test_sun_le_n();
+ test_year_only();
+ test_year_month_only();
+}
--
2.54.0
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