Add NaiveDateTime::checked_(add|sub)_offset

src/naive/datetime/mod.rs

@@ -19,8 +19,9 @@ use crate::format::{Fixed, Item, Numeric, Pad};
 use crate::naive::{Days, IsoWeek, NaiveDate, NaiveTime};
 use crate::offset::Utc;
 use crate::oldtime::Duration as OldDuration;
-use crate::{DateTime, Datelike, LocalResult, Months, TimeZone, Timelike, Weekday};
-
+use crate::{
+    try_opt, DateTime, Datelike, FixedOffset, LocalResult, Months, TimeZone, Timelike, Weekday,
+};
 #[cfg(feature = "rustc-serialize")]
 pub(super) mod rustc_serialize;
 
@@ -663,6 +664,16 @@ impl NaiveDateTime {
         Some(Self { date: self.date.checked_add_months(rhs)?, time: self.time })
     }
 
+    /// Adds given `FixedOffset` to the current datetime.
+    /// Returns `None` if the result would be outside the valid range for [`NaiveDateTime`].
+    ///
+    /// This method is similar to [`checked_add_signed`], but preserves leap seconds.
+    #[must_use]
+    pub(crate) const fn checked_add_offset(self, rhs: FixedOffset) -> Option<NaiveDateTime> {
+        let (time, days) = self.time.overflowing_add_offset(rhs);
+        Some(NaiveDateTime { date: try_opt!(self.date.add_days(days)), time })
+    }
+
     /// Subtracts given `Duration` from the current date and time.
     ///
     /// As a part of Chrono's [leap second handling](./struct.NaiveTime.html#leap-second-handling),
@@ -739,6 +750,16 @@ impl NaiveDateTime {
         Some(NaiveDateTime { date, time })
     }
 
+    /// Subtracts given `FixedOffset` from the current datetime.
+    /// Returns `None` if the result would be outside the valid range for [`NaiveDateTime`].
+    ///
+    /// This method is similar to [`checked_sub_signed`], but preserves leap seconds.
+    #[must_use]
+    pub(crate) const fn checked_sub_offset(self, rhs: FixedOffset) -> Option<NaiveDateTime> {
+        let (time, days) = self.time.overflowing_sub_offset(rhs);
+        Some(NaiveDateTime { date: try_opt!(self.date.add_days(days)), time })
+    }
+
     /// Subtracts given `Months` from the current date and time.
     ///
     /// Uses the last day of the month if the day does not exist in the resulting month.

src/naive/datetime/tests.rs

@@ -377,3 +377,57 @@ fn test_and_utc() {
     assert_eq!(dt_utc.naive_local(), ndt);
     assert_eq!(dt_utc.timezone(), Utc);
 }
+
+#[test]
+fn test_checked_add_offset() {
+    let ymdhmsm = |y, m, d, h, mn, s, mi| {
+        NaiveDate::from_ymd_opt(y, m, d).unwrap().and_hms_milli_opt(h, mn, s, mi)
+    };
+
+    let positive_offset = FixedOffset::east_opt(2 * 60 * 60).unwrap();
+    // regular date
+    let dt = ymdhmsm(2023, 5, 5, 20, 10, 0, 0).unwrap();
+    assert_eq!(dt.checked_add_offset(positive_offset), ymdhmsm(2023, 5, 5, 22, 10, 0, 0));
+    // leap second is preserved
+    let dt = ymdhmsm(2023, 6, 30, 23, 59, 59, 1_000).unwrap();
+    assert_eq!(dt.checked_add_offset(positive_offset), ymdhmsm(2023, 7, 1, 1, 59, 59, 1_000));
+    // out of range
+    assert!(NaiveDateTime::MAX.checked_add_offset(positive_offset).is_none());
+
+    let negative_offset = FixedOffset::west_opt(2 * 60 * 60).unwrap();
+    // regular date
+    let dt = ymdhmsm(2023, 5, 5, 20, 10, 0, 0).unwrap();
+    assert_eq!(dt.checked_add_offset(negative_offset), ymdhmsm(2023, 5, 5, 18, 10, 0, 0));
+    // leap second is preserved
+    let dt = ymdhmsm(2023, 6, 30, 23, 59, 59, 1_000).unwrap();
+    assert_eq!(dt.checked_add_offset(negative_offset), ymdhmsm(2023, 6, 30, 21, 59, 59, 1_000));
+    // out of range
+    assert!(NaiveDateTime::MIN.checked_add_offset(negative_offset).is_none());
+}
+
+#[test]
+fn test_checked_sub_offset() {
+    let ymdhmsm = |y, m, d, h, mn, s, mi| {
+        NaiveDate::from_ymd_opt(y, m, d).unwrap().and_hms_milli_opt(h, mn, s, mi)
+    };
+
+    let positive_offset = FixedOffset::east_opt(2 * 60 * 60).unwrap();
+    // regular date
+    let dt = ymdhmsm(2023, 5, 5, 20, 10, 0, 0).unwrap();
+    assert_eq!(dt.checked_sub_offset(positive_offset), ymdhmsm(2023, 5, 5, 18, 10, 0, 0));
+    // leap second is preserved
+    let dt = ymdhmsm(2023, 6, 30, 23, 59, 59, 1_000).unwrap();
+    assert_eq!(dt.checked_sub_offset(positive_offset), ymdhmsm(2023, 6, 30, 21, 59, 59, 1_000));
+    // out of range
+    assert!(NaiveDateTime::MIN.checked_sub_offset(positive_offset).is_none());
+
+    let negative_offset = FixedOffset::west_opt(2 * 60 * 60).unwrap();
+    // regular date
+    let dt = ymdhmsm(2023, 5, 5, 20, 10, 0, 0).unwrap();
+    assert_eq!(dt.checked_sub_offset(negative_offset), ymdhmsm(2023, 5, 5, 22, 10, 0, 0));
+    // leap second is preserved
+    let dt = ymdhmsm(2023, 6, 30, 23, 59, 59, 1_000).unwrap();
+    assert_eq!(dt.checked_sub_offset(negative_offset), ymdhmsm(2023, 7, 1, 1, 59, 59, 1_000));
+    // out of range
+    assert!(NaiveDateTime::MAX.checked_sub_offset(negative_offset).is_none());
+}