Add chrono example (#6224)

components/icu/Cargo.toml

@@ -48,7 +48,9 @@ icu_datetime = { path = "../../components/datetime", features = ["serde"] }
 icu_provider_adapters = { path = "../../provider/adapters", features = ["serde"] }
 icu_provider_blob = { path = "../../provider/blob", features = ["alloc"] }
 writeable = { path = "../../utils/writeable" }
-jiff = "0.2"
+jiff = { version = "0.2", default-features = false, features = ["tzdb-bundle-always", "std"] }
+chrono = { version = "0.4", default-features = false }
+chrono-tz = { version = "0.10", default-features = false }
 
 [features]
 default = [
@@ -137,4 +139,4 @@ name = "tui"
 required-features = ["serde"]
 
 [[example]]
-name = "jiff"
+name = "chrono_jiff"

components/icu/examples/chrono_jiff.rs

@@ -0,0 +1,109 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use icu::{
+    calendar::{Date, Iso},
+    datetime::{fieldsets, DateTimeFormatter},
+    locale::locale,
+    time::{
+        zone::{models::Full, IanaParser, TimeZoneVariant, UtcOffset, UtcOffsetCalculator},
+        Time, TimeZoneInfo, ZonedDateTime,
+    },
+};
+
+fn main() {
+    // jiff requires `std` as of 0.2
+    let from_jiff = jiff_to_icu(
+        &jiff::Timestamp::from_nanosecond(1726011440123456789)
+            .unwrap()
+            .to_zoned(jiff::tz::TimeZone::get("Asia/Tokyo").unwrap()),
+    );
+
+    // chrono and chrono_tz are `#[no_std]`
+    let from_chrono = chrono_to_icu(
+        &chrono::DateTime::from_timestamp_nanos(1726011440123456789)
+            .with_timezone(&"Asia/Tokyo".parse().unwrap()),
+    );
+
+    let from_ixdtf = ZonedDateTime::try_from_str(
+        "2024-09-11T08:37:20.123456789+09:00[Asia/Tokyo]",
+        Iso,
+        IanaParser::new(),
+        &UtcOffsetCalculator::new(),
+    )
+    .expect("valid string");
+
+    assert_eq!(from_jiff, from_chrono);
+    assert_eq!(from_chrono, from_ixdtf);
+
+    // A English, Japanese calendar, medium-length, year-month-day-time-specific-zone formatter
+    let formatter = DateTimeFormatter::try_new(
+        locale!("en-GB-u-ca-japanese").into(),
+        fieldsets::YMDT::medium().zone(fieldsets::zone::SpecificLong),
+    )
+    .expect("data is present");
+
+    println!("{}", formatter.format(&from_chrono)); // 11 Sept 6 Reiwa, 08:37:20 Japan Standard Time
+}
+
+fn jiff_to_icu(jiff: &jiff::Zoned) -> ZonedDateTime<Iso, TimeZoneInfo<Full>> {
+    let date = Date::try_new_iso(jiff.year() as i32, jiff.month() as u8, jiff.day() as u8)
+        .expect("jiff returns valid fields");
+
+    let time = Time::try_new(
+        jiff.hour() as u8,
+        jiff.minute() as u8,
+        jiff.second() as u8,
+        jiff.millisecond() as u32 * 1_000_000
+            + jiff.microsecond() as u32 * 1_000
+            + jiff.nanosecond() as u32,
+    )
+    .expect("jiff returns valid fields");
+
+    let zone =
+        // Parse IANA ID into ICU time zone
+        IanaParser::new().parse(jiff.time_zone().iana_name().unwrap())
+        // In ICU's model, a time zone has a fixed offset, as that's required for formatting
+        .with_offset(UtcOffset::try_from_seconds(jiff.offset().seconds()).ok())
+        // Display names might change over time for a given zone (e.g. it might change from Eastern Time to
+        // Central Time), so the ICU timezone needs a reference date and time.
+        .at_time((date, time))
+        // And finally, the zone variant is also required for formatting
+        // TODO(jiff#258): Jiff does not currently guarantee rearguard semantics
+        .with_zone_variant(TimeZoneVariant::from_rearguard_isdst(jiff.time_zone().to_offset_info(jiff.timestamp()).dst().is_dst()));
+
+    ZonedDateTime { date, time, zone }
+}
+
+fn chrono_to_icu(
+    chrono: &chrono::DateTime<chrono_tz::Tz>,
+) -> ZonedDateTime<Iso, TimeZoneInfo<Full>> {
+    use chrono::Datelike;
+    let date = Date::try_new_iso(chrono.year(), chrono.month() as u8, chrono.day() as u8)
+        .expect("chrono returns valid fields");
+
+    use chrono::Timelike;
+    let time = Time::try_new(
+        chrono.hour() as u8,
+        chrono.minute() as u8,
+        chrono.second() as u8,
+        chrono.nanosecond(),
+    )
+    .expect("chrono returns valid fields");
+
+    use chrono_tz::OffsetComponents;
+    let zone =
+        // Parse IANA ID into ICU time zone
+        IanaParser::new().parse(chrono.timezone().name())
+        // In ICU's model, a time zone has a fixed offset, as that's required for formatting
+        .with_offset(UtcOffset::try_from_seconds((chrono.offset().base_utc_offset() + chrono.offset().dst_offset()).num_seconds() as i32).ok())
+        // Display names might change over time for a given zone (e.g. it might change from Eastern Time to
+        // Central Time), so the ICU timezone needs a reference date and time.
+        .at_time((date, time))
+        // And finally, the zone variant is also required for formatting
+        // TODO: chrono_tz does not use rearguard semantics
+        .with_zone_variant(TimeZoneVariant::from_rearguard_isdst(!chrono.offset().dst_offset().is_zero()));
+
+    ZonedDateTime { date, time, zone }
+}