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LibJS+LibUnicode: Support ambiguous time zone transitions
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Browse source 
For example, time zone transitions can result in repeated or skipped
wall times. Temporal wants us to handle these transitions.
This commit is contained in:
Timothy Flynn 2025-06-02 11:04:29 -04:00 • committed by Shannon Booth
commit 8145572180
Notes: github-actions[bot] 2025-06-02 21:10:26 +00:00
4 changed files with 92 additions and 12 deletions
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53
Libraries/LibUnicode/TimeZone.cpp
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@ -10,6 +10,7 @@
#include <LibUnicode/ICU.h>
#include <LibUnicode/TimeZone.h>
#include <unicode/basictz.h>
#include <unicode/timezone.h>
#include <unicode/ucal.h>
@ -139,6 +140,15 @@ Optional<String> resolve_primary_time_zone(StringView time_zone)
return icu_string_to_string(iana_id);
}
static UDate to_icu_time(UnixDateTime time)
{
// We must clamp the time we provide to ICU such that the result of converting milliseconds to days fits in an i32.
// Further, that conversion must still be valid after applying DST offsets to the time we provide.
static constexpr auto min_time = (static_cast<UDate>(AK::NumericLimits<i32>::min()) + U_MILLIS_PER_DAY) * U_MILLIS_PER_DAY;
static constexpr auto max_time = (static_cast<UDate>(AK::NumericLimits<i32>::max()) - U_MILLIS_PER_DAY) * U_MILLIS_PER_DAY;
return clamp(static_cast<UDate>(time.milliseconds_since_epoch()), min_time, max_time);
}
Optional<TimeZoneOffset> time_zone_offset(StringView time_zone, UnixDateTime time)
{
UErrorCode status = U_ZERO_ERROR;
@ -150,11 +160,7 @@ Optional<TimeZoneOffset> time_zone_offset(StringView time_zone, UnixDateTime tim
i32 raw_offset = 0;
i32 dst_offset = 0;
// We must clamp the time we provide to ICU such that the result of converting milliseconds to days fits in an i32.
// Further, that conversion must still be valid after applying DST offsets to the time we provide.
static constexpr auto min_time = (static_cast<UDate>(AK::NumericLimits<i32>::min()) + U_MILLIS_PER_DAY) * U_MILLIS_PER_DAY;
static constexpr auto max_time = (static_cast<UDate>(AK::NumericLimits<i32>::max()) - U_MILLIS_PER_DAY) * U_MILLIS_PER_DAY;
auto icu_time = clamp(static_cast<UDate>(time.milliseconds_since_epoch()), min_time, max_time);
auto icu_time = to_icu_time(time);
time_zone_data->time_zone().getOffset(icu_time, 0, raw_offset, dst_offset, status);
if (icu_failure(status))
@ -166,4 +172,41 @@ Optional<TimeZoneOffset> time_zone_offset(StringView time_zone, UnixDateTime tim
};
}
Vector<TimeZoneOffset> disambiguated_time_zone_offsets(StringView time_zone, UnixDateTime time)
{
UErrorCode status = U_ZERO_ERROR;
auto time_zone_data = TimeZoneData::for_time_zone(time_zone);
if (!time_zone_data.has_value())
return {};
auto& basic_time_zone = as<icu::BasicTimeZone>(time_zone_data->time_zone());
auto icu_time = to_icu_time(time);
auto get_offset = [&](auto disambiguation_option) -> Optional<TimeZoneOffset> {
i32 raw_offset = 0;
i32 dst_offset = 0;
basic_time_zone.getOffsetFromLocal(icu_time, disambiguation_option, disambiguation_option, raw_offset, dst_offset, status);
if (icu_failure(status))
return {};
return TimeZoneOffset {
.offset = AK::Duration::from_milliseconds(raw_offset + dst_offset),
.in_dst = dst_offset == 0 ? TimeZoneOffset::InDST::No : TimeZoneOffset::InDST::Yes,
};
};
auto former = get_offset(UCAL_TZ_LOCAL_FORMER);
auto latter = get_offset(UCAL_TZ_LOCAL_LATTER);
Vector<TimeZoneOffset> offsets;
if (former.has_value())
offsets.append(*former);
if (latter.has_value() && latter->offset != former->offset)
offsets.append(*latter);
return offsets;
}
}