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LibUnicode: Fall back to GMT offset when a time zone name is unavailable

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The following table in TR-35 includes a web of fall back rules when the
requested time zone style is unavailable:
https://unicode.org/reports/tr35/tr35-dates.html#dfst-zone

Conveniently, the subset of styles supported by ECMA-402 (and therefore
LibUnicode) all either fall back to GMT offset or to a style that is
unsupported but itself falls back to GMT offset.
This commit is contained in:
Timothy Flynn 2022-01-11 12:06:26 -05:00 • committed by Linus Groh
parent 8d35563f28
commit d50f5e14f8
2 changed files with 26 additions and 8 deletions
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15
Tests/LibUnicode/TestUnicodeDateTimeFormat.cpp
View file

@ -35,31 +35,32 @@ TEST_CASE(time_zone_name)
TestData { "en"sv, Unicode::CalendarPatternStyle::Short, "America/Los_Angeles"sv, "PDT"sv },
TestData { "ar"sv, Unicode::CalendarPatternStyle::Long, "America/Los_Angeles"sv, "توقيت المحيط الهادي الصيفي"sv },
// The "ar" locale does not have a short name for PDT. LibUnicode will need to fall back to GMT offset when we have that data.
TestData { "ar"sv, Unicode::CalendarPatternStyle::Short, "America/Los_Angeles"sv, "غرينتش-٨"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Long, "America/Vancouver"sv, "Pacific Daylight Time"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Short, "America/Vancouver"sv, "PDT"sv },
TestData { "ar"sv, Unicode::CalendarPatternStyle::Long, "America/Vancouver"sv, "توقيت المحيط الهادي الصيفي"sv },
// The "ar" locale does not have a short name for PDT. LibUnicode will need to fall back to GMT offset when we have that data.
TestData { "ar"sv, Unicode::CalendarPatternStyle::Short, "America/Vancouver"sv, "غرينتش-٨"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Long, "Europe/London"sv, "Greenwich Mean Time"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Short, "Europe/London"sv, "GMT"sv },
TestData { "ar"sv, Unicode::CalendarPatternStyle::Long, "Europe/London"sv, "توقيت غرينتش"sv },
// The "ar" locale does not have a short name for GMT. LibUnicode will need to fall back to GMT offset when we have that data.
TestData { "ar"sv, Unicode::CalendarPatternStyle::Short, "Europe/London"sv, "غرينتش"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Long, "Africa/Accra"sv, "Greenwich Mean Time"sv },
TestData { "en"sv, Unicode::CalendarPatternStyle::Short, "Africa/Accra"sv, "GMT"sv },
TestData { "ar"sv, Unicode::CalendarPatternStyle::Long, "Africa/Accra"sv, "توقيت غرينتش"sv },
// The "ar" locale does not have a short name for GMT. LibUnicode will need to fall back to GMT offset when we have that data.
TestData { "ar"sv, Unicode::CalendarPatternStyle::Short, "Africa/Accra"sv, "غرينتش"sv },
};
constexpr auto jan_1_2022 = AK::Time::from_seconds(1640995200); // Saturday, January 1, 2022 12:00:00 AM
for (auto const& test : test_data) {
auto time_zone = Unicode::get_time_zone_name(test.locale, test.time_zone, test.style);
VERIFY(time_zone.has_value());
EXPECT_EQ(*time_zone, test.expected_result);
auto time_zone = Unicode::format_time_zone(test.locale, test.time_zone, test.style, jan_1_2022);
EXPECT_EQ(time_zone, test.expected_result);
}
}

19
Userland/Libraries/LibUnicode/DateTimeFormat.cpp
View file

@ -262,7 +262,9 @@ String format_time_zone(StringView locale, StringView time_zone, CalendarPattern
case CalendarPatternStyle::Long:
case CalendarPatternStyle::ShortGeneric:
case CalendarPatternStyle::LongGeneric:
return get_time_zone_name(locale, time_zone, style).value_or(time_zone);
if (auto name = get_time_zone_name(locale, time_zone, style); name.has_value())
return *name;
break;
case CalendarPatternStyle::ShortOffset:
case CalendarPatternStyle::LongOffset:
@ -271,6 +273,21 @@ String format_time_zone(StringView locale, StringView time_zone, CalendarPattern
default:
VERIFY_NOT_REACHED();
}
// If more styles are added, consult the following table to ensure always falling back to GMT offset is still correct:
// https://unicode.org/reports/tr35/tr35-dates.html#dfst-zone
switch (style) {
case CalendarPatternStyle::Short:
case CalendarPatternStyle::ShortGeneric:
return format_time_zone(locale, time_zone, CalendarPatternStyle::ShortOffset, time);
case CalendarPatternStyle::Long:
case CalendarPatternStyle::LongGeneric:
return format_time_zone(locale, time_zone, CalendarPatternStyle::LongOffset, time);
default:
VERIFY_NOT_REACHED();
}
}
}