Allow different Hijri calendars to use different names

components/datetime/Cargo.toml

@@ -46,6 +46,7 @@ icu_locale = { workspace = true, optional = true }
 
 
 [dev-dependencies]
+calendrical_calculations = { workspace = true }
 icu = { path = "../../components/icu", default-features = false }
 icu_calendar = { path = "../calendar", features = ["ixdtf"] }
 icu_provider_adapters = { path = "../../provider/adapters" }

components/datetime/src/scaffold/calendar.rs

@@ -91,12 +91,67 @@ impl CldrCalendar for Indian {
     type SkeletaV1 = DatetimePatternsDateIndianV1;
 }
 
-impl<R: hijri::Rules> CldrCalendar for Hijri<R> {
+/// [`hijri::Rules`]-specific formatting options.
+/// 
+/// See [`CldrCalendar`].
+/// 
+/// The simplest implementation of this uses the same names
+/// as some provided [`hijri::Rules`]:
+/// 
+/// ```rust
+/// use icu::calendar::cal::hijri;
+/// use icu::datetime::scaffold::FormattableHijriRules;
+/// 
+/// #[derive(Clone, Debug)]
+/// struct MyRules;
+/// 
+/// impl icu::calendar::cal::scaffold::UnstableSealed for MyRules {}
+/// impl hijri::Rules for MyRules {
+///     fn year_data(&self, _year: i32) -> hijri::HijriYearData { todo!() }
+/// }
+/// 
+/// impl FormattableHijriRules for MyRules {
+///     type YearNamesV1 = <hijri::UmmAlQura as FormattableHijriRules>::YearNamesV1;
+///     type MonthNamesV1 = <hijri::UmmAlQura as FormattableHijriRules>::MonthNamesV1;
+///     type SkeletaV1 = <hijri::UmmAlQura as FormattableHijriRules>::SkeletaV1;
+/// }
+/// ```
+// TODO: default associated types would be nice (https://github.com/rust-lang/rust/issues/29661)
+pub trait FormattableHijriRules: hijri::Rules {
+    /// The data marker for loading year symbols for this calendar.
+    type YearNamesV1: DataMarker<DataStruct = YearNames<'static>>;
+
+    /// The data marker for loading month symbols for this calendar.
+    type MonthNamesV1: DataMarker<DataStruct = MonthNames<'static>>;
+
+    /// The data marker for loading skeleton patterns for this calendar.
+    type SkeletaV1: DataMarker<DataStruct = PackedPatterns<'static>>;
+}
+
+impl FormattableHijriRules for hijri::TabularAlgorithm {
+    type YearNamesV1 = DatetimeNamesYearHijriV1;
+    type MonthNamesV1 = DatetimeNamesMonthHijriV1;
+    type SkeletaV1 = DatetimePatternsDateHijriV1;
+}
+
+impl FormattableHijriRules for hijri::UmmAlQura {
     type YearNamesV1 = DatetimeNamesYearHijriV1;
     type MonthNamesV1 = DatetimeNamesMonthHijriV1;
     type SkeletaV1 = DatetimePatternsDateHijriV1;
 }
 
+impl FormattableHijriRules for hijri::AstronomicalSimulation {
+    type YearNamesV1 = DatetimeNamesYearHijriV1;
+    type MonthNamesV1 = DatetimeNamesMonthHijriV1;
+    type SkeletaV1 = DatetimePatternsDateHijriV1;
+}
+
+impl<R: FormattableHijriRules> CldrCalendar for Hijri<R> {
+    type YearNamesV1 = R::YearNamesV1;
+    type MonthNamesV1 = R::MonthNamesV1;
+    type SkeletaV1 = R::SkeletaV1;
+}
+
 impl CldrCalendar for Japanese {
     type YearNamesV1 = DatetimeNamesYearJapaneseV1;
     type MonthNamesV1 = DatetimeNamesMonthJapaneseV1;

components/datetime/src/scaffold/mod.rs

@@ -19,6 +19,7 @@ pub use calendar::ConvertCalendar;
 pub(crate) use calendar::FormattableAnyCalendar;
 pub(crate) use calendar::FormattableAnyCalendarKind;
 pub(crate) use calendar::FormattableAnyCalendarNamesLoader;
+pub use calendar::FormattableHijriRules;
 pub use calendar::FullDataCalMarkers;
 pub use calendar::InFixedCalendar;
 pub use calendar::InSameCalendar;

components/calendar/tests/hijri_iran.rs → components/datetime/tests/hijri_iran.rs

@@ -7,9 +7,13 @@ use icu_calendar::cal::hijri::Rules;
 use icu_calendar::cal::hijri::TabularAlgorithm;
 use icu_calendar::cal::hijri::TabularAlgorithmEpoch;
 use icu_calendar::cal::hijri::TabularAlgorithmLeapYears;
+use icu_calendar::cal::hijri::UmmAlQura;
 use icu_calendar::cal::Hijri;
 use icu_calendar::types::RataDie;
 use icu_calendar::Date;
+use icu_datetime::fieldsets;
+use icu_datetime::scaffold::FormattableHijriRules;
+use icu_datetime::FixedCalendarDateTimeFormatter;
 
 static TEST_RD: [i64; 4] = [727274, 728714, 744313, 764652];
 
@@ -102,6 +106,13 @@ impl Rules for IranTestSighting {
     }
 }
 
+// Use the same display names as for UAQ
+impl FormattableHijriRules for IranTestSighting {
+    type MonthNamesV1 = <UmmAlQura as FormattableHijriRules>::MonthNamesV1;
+    type YearNamesV1 = <UmmAlQura as FormattableHijriRules>::YearNamesV1;
+    type SkeletaV1 = <UmmAlQura as FormattableHijriRules>::SkeletaV1;
+}
+
 #[test]
 fn test_hijri_iran_from_rd() {
     let calendar = Hijri(IranTestSighting);
@@ -123,3 +134,21 @@ fn test_rd_from_hijri_iran() {
         assert_eq!(date.to_rata_die(), RataDie::new(*f_date), "{case:?}");
     }
 }
+
+#[test]
+fn test_format() {
+    let formatter =
+        FixedCalendarDateTimeFormatter::try_new(Default::default(), fieldsets::YMD::long())
+            .unwrap();
+
+    assert_eq!(
+        formatter
+            .format(
+                &Date::try_new_gregorian(2022, 10, 12)
+                    .unwrap()
+                    .to_calendar(Hijri(IranTestSighting))
+            )
+            .to_string(),
+        "AH 1444 Rabiʻ I 16"
+    );
+}