Add full support for U datetime symbol (#7328)

Author: robertbastian

components/datetime/src/format/datetime.rs

@@ -175,21 +175,35 @@ where
         (FieldSymbol::Year(Year::Cyclic), l) => {
             const PART: Part = parts::YEAR_NAME;
             input!(PART, Year, year = input.year);
-            input!(PART, YearCyclic, cyclic = year.cyclic());
+
+            let Some(cyclic) = year.cyclic() else {
+                w.with_part(PART, |w| {
+                    try_write_number(
+                        Part::ERROR,
+                        w,
+                        decimal_formatter,
+                        year.era_year_or_related_iso().into(),
+                        FieldLength::One,
+                    )
+                    .map(|_| ())
+                })?;
+                return Ok(Err(FormattedDateTimePatternError::UnsupportedField(
+                    ErrorField(field),
+                )));
+            };
 
             match datetime_names.get_name_for_cyclic(l, cyclic.year) {
                 Ok(name) => Ok(w.with_part(PART, |w| w.write_str(name))?),
                 Err(e) => {
                     w.with_part(PART, |w| {
-                        w.with_part(Part::ERROR, |w| {
-                            try_write_number_without_part(
-                                w,
-                                decimal_formatter,
-                                cyclic.related_iso.into(),
-                                FieldLength::One,
-                            )
-                            .map(|_| ())
-                        })
+                        try_write_number(
+                            Part::ERROR,
+                            w,
+                            decimal_formatter,
+                            cyclic.related_iso.into(),
+                            FieldLength::One,
+                        )
+                        .map(|_| ())
                     })?;
                     return Ok(Err(match e {
                         GetNameForCyclicYearError::InvalidYearNumber { max } => {

components/datetime/src/pattern/formatter.rs

@@ -257,8 +257,10 @@ impl TryWriteable for FormattedDateTimePattern<'_> {
 #[cfg(test)]
 #[cfg(feature = "compiled_data")]
 mod tests {
+    use crate::provider::fields::Field;
+
     use super::super::*;
-    use icu_calendar::{Date, Gregorian};
+    use icu_calendar::{cal::KoreanTraditional, Date, Gregorian};
     use icu_locale_core::locale;
     use icu_time::{DateTime, Time};
     use writeable::assert_try_writeable_eq;
@@ -606,4 +608,46 @@ mod tests {
             assert_try_writeable_eq!(formatted_pattern, expected, Ok(()), "{cas:?}");
         }
     }
+
+    #[test]
+    fn test_cyclic_year() {
+        use crate::provider::fields::{FieldLength, FieldSymbol, Year};
+
+        let locale = locale!("uk").into();
+        let pattern: DateTimePattern = "UUUU".parse().unwrap();
+
+        let names: FixedCalendarDateTimeNames<Gregorian> =
+            FixedCalendarDateTimeNames::try_new(locale).unwrap();
+        let datetime = DateTime {
+            date: Date::try_new_gregorian(2023, 11, 17).unwrap(),
+            time: Time::try_new(13, 41, 28, 0).unwrap(),
+        };
+
+        assert_try_writeable_eq!(
+            names.with_pattern_unchecked(&pattern).format(&datetime),
+            "2023",
+            Err(FormattedDateTimePatternError::UnsupportedField(ErrorField(
+                Field {
+                    symbol: FieldSymbol::Year(Year::Cyclic),
+                    length: FieldLength::Four
+                }
+            ))),
+        );
+
+        let mut names: FixedCalendarDateTimeNames<KoreanTraditional> =
+            FixedCalendarDateTimeNames::try_new(locale).unwrap();
+        names
+            .load_year_names(&crate::provider::Baked, YearNameLength::Wide)
+            .unwrap();
+        let datetime = DateTime {
+            date: datetime.date.to_calendar(KoreanTraditional::new()),
+            time: datetime.time,
+        };
+
+        assert_try_writeable_eq!(
+            names.with_pattern_unchecked(&pattern).format(&datetime),
+            "gui-mao",
+            Ok(()),
+        );
+    }
 }