Followup #6440 (#6461)

Fixes #6386

Author: robertbastian

components/calendar/src/provider/hijri.rs

@@ -75,7 +75,7 @@ impl PackedHijriYearInfo {
         month_lengths: [bool; 12],
         start_day: RataDie,
     ) -> Self {
-        let start_offset = start_day.const_diff(Self::mean_synodic_start_day(extended_year));
+        let start_offset = start_day.until(Self::mean_synodic_start_day(extended_year));
 
         debug_assert!(
             -8 < start_offset && start_offset < 8,
@@ -117,7 +117,7 @@ impl PackedHijriYearInfo {
     const fn mean_synodic_start_day(extended_year: i32) -> RataDie {
         // -1 because the epoch is new year of year 1
         // truncating instead of flooring does not matter, as this is used for positive years only
-        calendrical_calculations::islamic::ISLAMIC_EPOCH_FRIDAY.const_add(
+        calendrical_calculations::islamic::ISLAMIC_EPOCH_FRIDAY.add(
             ((extended_year - 1) as f64 * calendrical_calculations::islamic::MEAN_YEAR_LENGTH)
                 as i64,
         )

utils/calendrical_calculations/src/ethiopian.rs

@@ -11,7 +11,7 @@ use crate::helpers::I32CastError;
 use crate::rata_die::RataDie;
 
 const ETHIOPIC_TO_COPTIC_OFFSET: i64 =
-    super::coptic::COPTIC_EPOCH.const_diff(crate::julian::fixed_from_julian(8, 8, 29));
+    super::coptic::COPTIC_EPOCH.until(crate::julian::fixed_from_julian(8, 8, 29));
 
 /// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/1ee51ecfaae6f856b0d7de3e36e9042100b4f424/calendar.l#L2017>
 pub fn fixed_from_ethiopian(year: i32, month: u8, day: u8) -> RataDie {

utils/calendrical_calculations/src/iso.rs

@@ -53,7 +53,7 @@ pub fn fixed_from_iso(year: i32, month: u8, day: u8) -> RataDie {
 /// Lisp code reference: <https://github.com/EdReingold/calendar-code2/blob/1ee51ecfaae6f856b0d7de3e36e9042100b4f424/calendar.l#L1191-L1217>
 pub(crate) const fn iso_year_from_fixed(date: RataDie) -> i64 {
     // Shouldn't overflow because it's not possbile to construct extreme values of RataDie
-    let date = date.const_diff(EPOCH);
+    let date = date.until(EPOCH);
 
     // 400 year cycles have 146097 days
     let (n_400, date) = (date.div_euclid(146097), date.rem_euclid(146097));

utils/calendrical_calculations/src/rata_die.rs

@@ -14,6 +14,8 @@ use core_maths::*;
 
 /// The *Rata Die*, or *R.D.*: number of days since January 1, 1 CE.
 ///
+/// **The primary definition of this type is in the [`calendrical_calculations`](https://docs.rs/calendrical_calculations) crate.**
+///
 /// See: <https://en.wikipedia.org/wiki/Rata_Die>
 ///
 /// Typically, one should obtain RataDies from other calendrical code, rather than constructing them from integers.
@@ -52,7 +54,7 @@ impl RataDie {
     }
 
     /// A valid `RataDie` that is intended to be below all dates representable in calendars
-    #[doc(hidden)]
+    #[doc(hidden)] // for testing only
     pub const fn big_negative() -> Self {
         Self::new(i64::MIN / 256 / 256)
     }
@@ -68,13 +70,16 @@ impl RataDie {
     }
 
     /// Calculate the number of days between two `RataDie` in a const-friendly way
-    pub const fn const_diff(self, rhs: Self) -> i64 {
+    pub const fn until(self, rhs: Self) -> i64 {
         self.0 - rhs.0
     }
 
     /// Adds a number of days to this `RataDie` in a const-friendly way
-    pub const fn const_add(self, rhs: i64) -> Self {
-        Self(self.0 + rhs)
+    pub const fn add(self, rhs: i64) -> Self {
+        let result = Self(self.0 + rhs);
+        #[cfg(debug_assertions)]
+        result.check();
+        result
     }
 
     /// Convert this to a [`Moment`]
@@ -98,18 +103,13 @@ impl fmt::Debug for RataDie {
 impl Add<i64> for RataDie {
     type Output = Self;
     fn add(self, rhs: i64) -> Self::Output {
-        let result = Self(self.0 + rhs);
-        #[cfg(debug_assertions)]
-        result.check();
-        result
+        self.add(rhs)
     }
 }
 
 impl AddAssign<i64> for RataDie {
     fn add_assign(&mut self, rhs: i64) {
         self.0 += rhs;
-        #[cfg(debug_assertions)]
-        self.check();
     }
 }
 
@@ -127,16 +127,14 @@ impl Sub<i64> for RataDie {
 impl SubAssign<i64> for RataDie {
     fn sub_assign(&mut self, rhs: i64) {
         self.0 -= rhs;
-        #[cfg(debug_assertions)]
-        self.check();
     }
 }
 
 /// Calculate the number of days between two RataDie
 impl Sub for RataDie {
     type Output = i64;
     fn sub(self, rhs: Self) -> Self::Output {
-        self.0 - rhs.0
+        self.until(rhs)
     }
 }