From 225cfaaa88b3e72d0ef9e27220e64d7b2b7817b6 Mon Sep 17 00:00:00 2001
From: Paul Dicker <pitdicker@gmail.com>
Date: Fri, 19 May 2023 14:51:22 +0200
Subject: [PATCH 1/2] Move `Add` and `Sub` impls for `Fixedoffset` to
 `datetime` modules

---
 src/datetime/mod.rs | 28 ++++++++++++++++++++++++++++
 src/offset/fixed.rs | 38 +-------------------------------------
 2 files changed, 29 insertions(+), 37 deletions(-)

diff --git a/src/datetime/mod.rs b/src/datetime/mod.rs
index d0e63d5732..b6fbb823b0 100644
--- a/src/datetime/mod.rs
+++ b/src/datetime/mod.rs
@@ -1247,6 +1247,25 @@ impl<Tz: TimeZone> AddAssign<Duration> for DateTime<Tz> {
     }
 }
 
+fn add_with_leapsecond<T>(lhs: &T, rhs: i32) -> T
+where
+    T: Timelike + Add<OldDuration, Output = T>,
+{
+    // extract and temporarily remove the fractional part and later recover it
+    let nanos = lhs.nanosecond();
+    let lhs = lhs.with_nanosecond(0).unwrap();
+    (lhs + OldDuration::seconds(i64::from(rhs))).with_nanosecond(nanos).unwrap()
+}
+
+impl<Tz: TimeZone> Add<FixedOffset> for DateTime<Tz> {
+    type Output = DateTime<Tz>;
+
+    #[inline]
+    fn add(self, rhs: FixedOffset) -> DateTime<Tz> {
+        add_with_leapsecond(&self, rhs.local_minus_utc())
+    }
+}
+
 impl<Tz: TimeZone> Add<Months> for DateTime<Tz> {
     type Output = DateTime<Tz>;
 
@@ -1294,6 +1313,15 @@ impl<Tz: TimeZone> SubAssign<Duration> for DateTime<Tz> {
     }
 }
 
+impl<Tz: TimeZone> Sub<FixedOffset> for DateTime<Tz> {
+    type Output = DateTime<Tz>;
+
+    #[inline]
+    fn sub(self, rhs: FixedOffset) -> DateTime<Tz> {
+        add_with_leapsecond(&self, -rhs.local_minus_utc())
+    }
+}
+
 impl<Tz: TimeZone> Sub<Months> for DateTime<Tz> {
     type Output = DateTime<Tz>;
 
diff --git a/src/offset/fixed.rs b/src/offset/fixed.rs
index 013f822479..6d3aebdb68 100644
--- a/src/offset/fixed.rs
+++ b/src/offset/fixed.rs
@@ -4,17 +4,14 @@
 //! The time zone which has a fixed offset from UTC.
 
 use core::fmt;
-use core::ops::{Add, Sub};
 use core::str::FromStr;
 
 #[cfg(feature = "rkyv")]
 use rkyv::{Archive, Deserialize, Serialize};
 
 use super::{LocalResult, Offset, TimeZone};
-use crate::duration::Duration as OldDuration;
-use crate::format::{scan, OUT_OF_RANGE};
+use crate::format::{scan, ParseError, OUT_OF_RANGE};
 use crate::naive::{NaiveDate, NaiveDateTime};
-use crate::{DateTime, ParseError, Timelike};
 
 /// The time zone with fixed offset, from UTC-23:59:59 to UTC+23:59:59.
 ///
@@ -184,39 +181,6 @@ impl arbitrary::Arbitrary<'_> for FixedOffset {
     }
 }
 
-// addition or subtraction of FixedOffset to/from Timelike values is the same as
-// adding or subtracting the offset's local_minus_utc value
-// but keep keeps the leap second information.
-// this should be implemented more efficiently, but for the time being, this is generic right now.
-
-fn add_with_leapsecond<T>(lhs: &T, rhs: i32) -> T
-where
-    T: Timelike + Add<OldDuration, Output = T>,
-{
-    // extract and temporarily remove the fractional part and later recover it
-    let nanos = lhs.nanosecond();
-    let lhs = lhs.with_nanosecond(0).unwrap();
-    (lhs + OldDuration::seconds(i64::from(rhs))).with_nanosecond(nanos).unwrap()
-}
-
-impl<Tz: TimeZone> Add<FixedOffset> for DateTime<Tz> {
-    type Output = DateTime<Tz>;
-
-    #[inline]
-    fn add(self, rhs: FixedOffset) -> DateTime<Tz> {
-        add_with_leapsecond(&self, rhs.local_minus_utc)
-    }
-}
-
-impl<Tz: TimeZone> Sub<FixedOffset> for DateTime<Tz> {
-    type Output = DateTime<Tz>;
-
-    #[inline]
-    fn sub(self, rhs: FixedOffset) -> DateTime<Tz> {
-        add_with_leapsecond(&self, -rhs.local_minus_utc)
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::FixedOffset;

From 018be06145db22c727865d7ce5dc97dd2af15fa5 Mon Sep 17 00:00:00 2001
From: Paul Dicker <pitdicker@gmail.com>
Date: Fri, 19 May 2023 14:52:26 +0200
Subject: [PATCH 2/2] Use `checked_(add|sub)_offset` in `Add` and `Sub` impls
 of `DateTime`

---
 src/datetime/mod.rs | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/src/datetime/mod.rs b/src/datetime/mod.rs
index b6fbb823b0..59178743dc 100644
--- a/src/datetime/mod.rs
+++ b/src/datetime/mod.rs
@@ -1247,22 +1247,13 @@ impl<Tz: TimeZone> AddAssign<Duration> for DateTime<Tz> {
     }
 }
 
-fn add_with_leapsecond<T>(lhs: &T, rhs: i32) -> T
-where
-    T: Timelike + Add<OldDuration, Output = T>,
-{
-    // extract and temporarily remove the fractional part and later recover it
-    let nanos = lhs.nanosecond();
-    let lhs = lhs.with_nanosecond(0).unwrap();
-    (lhs + OldDuration::seconds(i64::from(rhs))).with_nanosecond(nanos).unwrap()
-}
-
 impl<Tz: TimeZone> Add<FixedOffset> for DateTime<Tz> {
     type Output = DateTime<Tz>;
 
     #[inline]
-    fn add(self, rhs: FixedOffset) -> DateTime<Tz> {
-        add_with_leapsecond(&self, rhs.local_minus_utc())
+    fn add(mut self, rhs: FixedOffset) -> DateTime<Tz> {
+        self.datetime = self.naive_utc().checked_add_offset(rhs).unwrap();
+        self
     }
 }
 
@@ -1317,8 +1308,9 @@ impl<Tz: TimeZone> Sub<FixedOffset> for DateTime<Tz> {
     type Output = DateTime<Tz>;
 
     #[inline]
-    fn sub(self, rhs: FixedOffset) -> DateTime<Tz> {
-        add_with_leapsecond(&self, -rhs.local_minus_utc())
+    fn sub(mut self, rhs: FixedOffset) -> DateTime<Tz> {
+        self.datetime = self.naive_utc().checked_sub_offset(rhs).unwrap();
+        self
     }
 }