Align Ethiopian eras with CLDR (#6246)

We currently use a `pre-incar` era, which is not defined in CLDR.
Instead, we should use the `mundi` era before the `incar` era.

components/calendar/src/any_calendar.rs

@@ -1793,7 +1793,7 @@ mod tests {
         single_test_roundtrip(ethiopian, "incar", 2000, "M03", 1);
         single_test_roundtrip(ethiopian, "incar", 2000, "M13", 1);
         // Fails ISO roundtrip due to https://github.com/unicode-org/icu4x/issues/2254
-        // single_test_roundtrip(ethiopian, "pre-incar", 100, "M03", 1);
+        // single_test_roundtrip(ethiopian, "mundi", 5400, "M03", 1);
         single_test_error(
             ethiopian,
             "incar",
@@ -1809,15 +1809,15 @@ mod tests {
         );
         single_test_error(
             ethiopian,
-            "pre-incar",
-            0,
+            "mundi",
+            5600,
             "M03",
             1,
             DateError::Range {
                 field: "year",
-                value: 0,
-                min: 1,
-                max: i32::MAX,
+                value: 5600,
+                min: i32::MIN,
+                max: 5500,
             },
         );
         single_test_error(

components/calendar/src/cal/ethiopian.rs

@@ -19,23 +19,23 @@
 use crate::cal::iso::Iso;
 use crate::calendar_arithmetic::{ArithmeticDate, CalendarArithmetic};
 use crate::error::DateError;
+use crate::types::Era;
 use crate::{types, Calendar, Date, DateDuration, DateDurationUnit, RangeError};
 use calendrical_calculations::helpers::I32CastError;
 use calendrical_calculations::rata_die::RataDie;
 use tinystr::tinystr;
 
 /// The number of years the Amete Alem epoch precedes the Amete Mihret epoch
-const AMETE_ALEM_OFFSET: i32 = 5500;
+const INCARNATION_OFFSET: i32 = 5500;
 
 /// Which era style the ethiopian calendar uses
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 #[non_exhaustive]
 pub enum EthiopianEraStyle {
-    /// Use an era scheme of pre- and post- Incarnation eras,
-    /// anchored at the date of the Incarnation of Jesus in this calendar
+    /// Use the Anno Mundi era, anchored at the date of Creation, followed by the
+    /// Incarnation era, anchored at the date of the Incarnation of Jesus
     AmeteMihret,
-    /// Use an era scheme of the Anno Mundi era, anchored at the date of Creation
-    /// in this calendar
+    /// Use the single Anno Mundi era, anchored at the date of Creation
     AmeteAlem,
 }
 
@@ -53,9 +53,8 @@ pub enum EthiopianEraStyle {
 ///
 /// # Era codes
 ///
-/// This calendar supports three era codes, based on what mode it is in. In the Amete Mihret scheme it has
-/// the `"incar"` and `"pre-incar"` eras, 1 Incarnation is 9 CE. In the Amete Alem scheme, it instead has a single era,
-/// `"mundi`, where 1 Anno Mundi is 5493 BCE. Dates before that use negative year numbers.
+/// This calendar always uses the `"mundi` era, where 1 Anno Mundi is 5493 BCE. Dates before that use negative year numbers.
+/// In the Amete Mihret scheme it uses the additional `"incar"` era, 1 Incarnation is 9 CE.
 ///
 /// # Month codes
 ///
@@ -120,8 +119,13 @@ impl Calendar for Ethiopian {
         month_code: types::MonthCode,
         day: u8,
     ) -> Result<Self::DateInner, DateError> {
-        let year = if let Some(era) = era {
-            if era.0 == tinystr!(16, "incar") || era.0 == tinystr!(16, "ethiopic") {
+        const INCAR: Era = Era(tinystr!(16, "incar"));
+        const ETHIOPIC: Era = Era(tinystr!(16, "ethiopic"));
+        const MUNDI: Era = Era(tinystr!(16, "mundi"));
+        const ETHIOAA: Era = Era(tinystr!(16, "ethioaa"));
+
+        let year = match (self.era_style(), era) {
+            (EthiopianEraStyle::AmeteMihret, Some(INCAR | ETHIOPIC) | None) => {
                 if year <= 0 {
                     return Err(DateError::Range {
                         field: "year",
@@ -130,26 +134,23 @@ impl Calendar for Ethiopian {
                         max: i32::MAX,
                     });
                 }
-                year
-            } else if era.0 == tinystr!(16, "pre-incar")
-                || era.0 == tinystr!(16, "ethiopic-inverse")
-            {
-                if year <= 0 {
+                year + INCARNATION_OFFSET
+            }
+            (EthiopianEraStyle::AmeteMihret, Some(MUNDI | ETHIOAA)) => {
+                if year > INCARNATION_OFFSET {
                     return Err(DateError::Range {
                         field: "year",
                         value: year,
-                        min: 1,
-                        max: i32::MAX,
+                        min: i32::MIN,
+                        max: INCARNATION_OFFSET,
                     });
                 }
-                1 - year
-            } else if era.0 == tinystr!(16, "mundi") || era.0 == tinystr!(16, "ethioaa") {
-                year - AMETE_ALEM_OFFSET
-            } else {
+                year
+            }
+            (EthiopianEraStyle::AmeteAlem, Some(MUNDI | ETHIOAA) | None) => year,
+            (_, Some(era)) => {
                 return Err(DateError::UnknownEra(era));
             }
-        } else {
-            year
         };
         ArithmeticDate::new_from_codes(self, year, month_code, day).map(EthiopianDateInner)
     }
@@ -252,7 +253,12 @@ impl Ethiopian {
     }
 
     fn fixed_from_ethiopian(date: ArithmeticDate<Ethiopian>) -> RataDie {
-        calendrical_calculations::ethiopian::fixed_from_ethiopian(date.year, date.month, date.day)
+        // calendrical calculations expects years in the Incarnation era
+        calendrical_calculations::ethiopian::fixed_from_ethiopian(
+            date.year - INCARNATION_OFFSET,
+            date.month,
+            date.day,
+        )
     }
 
     fn ethiopian_from_fixed(date: RataDie) -> EthiopianDateInner {
@@ -266,7 +272,12 @@ impl Ethiopian {
                 }
                 Ok(ymd) => ymd,
             };
-        EthiopianDateInner(ArithmeticDate::new_unchecked(year, month, day))
+        // calendrical calculations returns years in the Incarnation era
+        EthiopianDateInner(ArithmeticDate::new_unchecked(
+            year + INCARNATION_OFFSET,
+            month,
+            day,
+        ))
     }
 
     fn days_in_year_direct(year: i32) -> u16 {
@@ -277,34 +288,24 @@ impl Ethiopian {
         }
     }
     fn year_as_ethiopian(year: i32, amete_alem: bool) -> types::YearInfo {
-        if amete_alem {
+        if amete_alem || year <= INCARNATION_OFFSET {
             types::YearInfo::new(
                 year,
                 types::EraYear {
                     standard_era: tinystr!(16, "ethioaa").into(),
                     formatting_era: types::FormattingEra::Index(0, tinystr!(16, "Anno Mundi")),
-                    era_year: year + AMETE_ALEM_OFFSET,
-                    ambiguity: types::YearAmbiguity::CenturyRequired,
-                },
-            )
-        } else if year > 0 {
-            types::YearInfo::new(
-                year,
-                types::EraYear {
-                    standard_era: tinystr!(16, "ethiopic").into(),
-                    formatting_era: types::FormattingEra::Index(2, tinystr!(16, "Incarnation")),
                     era_year: year,
                     ambiguity: types::YearAmbiguity::CenturyRequired,
                 },
             )
         } else {
             types::YearInfo::new(
-                year,
+                year - INCARNATION_OFFSET,
                 types::EraYear {
-                    standard_era: tinystr!(16, "ethiopic-inverse").into(),
-                    formatting_era: types::FormattingEra::Index(1, tinystr!(16, "Pre-Incarnation")),
-                    era_year: 1 - year,
-                    ambiguity: types::YearAmbiguity::EraAndCenturyRequired,
+                    standard_era: tinystr!(16, "ethiopic").into(),
+                    formatting_era: types::FormattingEra::Index(1, tinystr!(16, "Incarnation")),
+                    era_year: year - INCARNATION_OFFSET,
+                    ambiguity: types::YearAmbiguity::CenturyRequired,
                 },
             )
         }
@@ -314,10 +315,6 @@ impl Ethiopian {
 impl Date<Ethiopian> {
     /// Construct new Ethiopian Date.
     ///
-    /// For the Amete Mihret era style, negative years work with
-    /// year 0 as 1 pre-Incarnation, year -1 as 2 pre-Incarnation,
-    /// and so on.
-    ///
     /// ```rust
     /// use icu::calendar::cal::EthiopianEraStyle;
     /// use icu::calendar::Date;
@@ -337,7 +334,7 @@ impl Date<Ethiopian> {
         day: u8,
     ) -> Result<Date<Ethiopian>, RangeError> {
         if era_style == EthiopianEraStyle::AmeteAlem {
-            year -= AMETE_ALEM_OFFSET;
+            year -= INCARNATION_OFFSET;
         }
         ArithmeticDate::new_from_ordinals(year, month, day)
             .map(EthiopianDateInner)
@@ -353,20 +350,38 @@ mod test {
     fn test_leap_year() {
         // 11th September 2023 in gregorian is 6/13/2015 in ethiopian
         let iso_date = Date::try_new_iso(2023, 9, 11).unwrap();
-        let ethiopian_date = Ethiopian::new().date_from_iso(iso_date);
-        assert_eq!(ethiopian_date.0.year, 2015);
-        assert_eq!(ethiopian_date.0.month, 13);
-        assert_eq!(ethiopian_date.0.day, 6);
+        let date_ethiopian = Date::new_from_iso(iso_date, Ethiopian::new());
+        assert_eq!(date_ethiopian.year().extended_year, 2015);
+        assert_eq!(date_ethiopian.month().ordinal, 13);
+        assert_eq!(date_ethiopian.day_of_month().0, 6);
     }
 
     #[test]
     fn test_iso_to_ethiopian_conversion_and_back() {
         let iso_date = Date::try_new_iso(1970, 1, 2).unwrap();
         let date_ethiopian = Date::new_from_iso(iso_date, Ethiopian::new());
 
-        assert_eq!(date_ethiopian.inner.0.year, 1962);
-        assert_eq!(date_ethiopian.inner.0.month, 4);
-        assert_eq!(date_ethiopian.inner.0.day, 24);
+        assert_eq!(date_ethiopian.year().extended_year, 1962);
+        assert_eq!(date_ethiopian.month().ordinal, 4);
+        assert_eq!(date_ethiopian.day_of_month().0, 24);
+
+        assert_eq!(
+            date_ethiopian.to_iso(),
+            Date::try_new_iso(1970, 1, 2).unwrap()
+        );
+    }
+
+    #[test]
+    fn test_iso_to_ethiopian_aa_conversion_and_back() {
+        let iso_date = Date::try_new_iso(1970, 1, 2).unwrap();
+        let date_ethiopian = Date::new_from_iso(
+            iso_date,
+            Ethiopian::new_with_era_style(EthiopianEraStyle::AmeteAlem),
+        );
+
+        assert_eq!(date_ethiopian.year().extended_year, 7462);
+        assert_eq!(date_ethiopian.month().ordinal, 4);
+        assert_eq!(date_ethiopian.day_of_month().0, 24);
 
         assert_eq!(
             date_ethiopian.to_iso(),

components/calendar/src/types.rs

@@ -155,7 +155,7 @@ pub enum FormattingEra {
     ///
     /// In this context, chronological ordering of eras is obtained by ordering by their start date (or in the case of
     /// negative eras, their end date) first, and for eras sharing a date, put the negative one first. For example,
-    /// bce < ce, and mundi < pre-incar < incar for Ethiopian.
+    /// bce < ce, and mundi < incar for Ethiopian.
     ///
     /// The TInyStr16 is a fallback string for the era when a display name is not available. It need not be an era code, it should
     /// be something sensible (or empty).

components/datetime/tests/fixtures/tests/components-width-differences.json

@@ -44,9 +44,9 @@
                 "en-u-ca-buddhist": "2563 BE",
                 "en-u-ca-coptic": "1736 ERA1",
                 "fr-u-ca-coptic": "1736 ap. D.",
-                "en-u-ca-ethiopic" : "2012 ERA0",
-                "fr-u-ca-ethiopic" : "2012 av. Inc.",
-                "fr-u-ca-ethioaa" : "7512 ERA0"
+                "en-u-ca-ethiopic" : "2012 ERA1",
+                "fr-u-ca-ethiopic" : "2012 ap. Inc.",
+                "fr-u-ca-ethioaa" : "7512 av. Inc."
             }
         }
     },

components/datetime/tests/fixtures/tests/components.json

@@ -48,9 +48,9 @@
                 "fr-u-ca-persian": "mardi 1 bahman 1398 A. P., 08:25:07",
                 "en-u-ca-hebrew": "Tuesday, 24 Tevet 5780 AM, 08:25:07",
                 "fr-u-ca-hebrew": "mardi 24 téveth 5780 A. M., 08:25:07",
-                "en-u-ca-ethiopic": "Tuesday, Ter 12, 2012 ERA0, 08:25:07",
-                "fr-u-ca-ethiopic": "mardi 12 ter 2012 av. Inc., 08:25:07",
-                "fr-u-ca-ethioaa": "mardi 12 ter 7512 ERA0, 08:25:07",
+                "en-u-ca-ethiopic": "Tuesday, Ter 12, 2012 ERA1, 08:25:07",
+                "fr-u-ca-ethiopic": "mardi 12 ter 2012 ap. Inc., 08:25:07",
+                "fr-u-ca-ethioaa": "mardi 12 ter 7512 av. Inc., 08:25:07",
                 "en-u-ca-roc": "Tuesday, January 21, 109 Minguo, 08:25:07",
                 "fr-u-ca-roc": "mardi 21 janvier 109 RdC, 08:25:07",
                 "zh-u-ca-roc": "民国109年1月21日星期二 08:25:07"