DateTimeFormatter AnyCalendarKind getter (unicode-org#5907)

Another part of unicode-org#5900

components/datetime/src/neo.rs

@@ -21,7 +21,7 @@ use crate::MismatchedCalendarError;
 use core::fmt;
 use core::marker::PhantomData;
 use icu_calendar::any_calendar::IntoAnyCalendar;
-use icu_calendar::{AnyCalendar, AnyCalendarPreferences};
+use icu_calendar::{AnyCalendar, AnyCalendarKind, AnyCalendarPreferences};
 use icu_decimal::FixedDecimalFormatterPreferences;
 use icu_locale_core::preferences::extensions::unicode::keywords::{
     CalendarAlgorithm, HourCycle, NumberingSystem,
@@ -765,6 +765,36 @@ impl<FSet: DateTimeMarkers> DateTimeFormatter<FSet> {
             _calendar: PhantomData,
         })
     }
+
+    /// Returns the calendar system used in this formatter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use icu::calendar::AnyCalendarKind;
+    /// use icu::calendar::Date;
+    /// use icu::datetime::fieldsets::YMD;
+    /// use icu::datetime::DateTimeFormatter;
+    /// use icu::locale::locale;
+    /// use writeable::assert_writeable_eq;
+    ///
+    /// let formatter = DateTimeFormatter::try_new(
+    ///     locale!("th").into(),
+    ///     YMD::long(),
+    /// )
+    /// .unwrap();
+    ///
+    /// assert_writeable_eq!(
+    ///     formatter.format_any_calendar(&Date::try_new_iso(2024, 12, 16).unwrap()),
+    ///     "16 ธันวาคม 2567"
+    /// );
+    ///
+    /// assert_eq!(formatter.calendar_kind(), AnyCalendarKind::Buddhist);
+    /// assert_eq!(formatter.calendar_kind().as_bcp47_string(), "buddhist");
+    /// ```
+    pub fn calendar_kind(&self) -> AnyCalendarKind {
+        self.calendar.kind()
+    }
 }
 
 /// A formatter optimized for time and time zone formatting.

ffi/capi/src/datetime_formatter.rs

@@ -13,6 +13,7 @@ pub mod ffi {
     };
 
     use crate::{
+        calendar::ffi::AnyCalendarKind,
         date::ffi::{Date, IsoDate},
         datetime::ffi::{DateTime, IsoDateTime},
         errors::ffi::{DateTimeFormatError, DateTimeFormatterLoadError},
@@ -306,6 +307,12 @@ pub mod ffi {
             let _infallible = self.0.format_any_calendar(&any).write_to(write);
             Ok(())
         }
+
+        /// Returns the calendar system used in this formatter.
+        #[diplomat::rust_link(icu::datetime::DateTimeFormatter::calendar_kind, FnInStruct)]
+        pub fn calendar_kind(&self) -> AnyCalendarKind {
+            self.0.calendar_kind().into()
+        }
     }
 
     #[diplomat::opaque]
@@ -372,5 +379,11 @@ pub mod ffi {
             let _infallible = self.0.format_any_calendar(&any).write_to(write);
             Ok(())
         }
+
+        /// Returns the calendar system used in this formatter.
+        #[diplomat::rust_link(icu::datetime::DateTimeFormatter::calendar_kind, FnInStruct)]
+        pub fn calendar_kind(&self) -> AnyCalendarKind {
+            self.0.calendar_kind().into()
+        }
     }
 }