Fix potential panic in edge case

Author: jhpratt

src/lib.rs

@@ -216,12 +216,12 @@ macro_rules! cascade {
         cascade!(@ordinal $ordinal);
         cascade!(@year $year);
         #[allow(unused_assignments)]
-        if $ordinal > crate::util::days_in_year($year) {
+        if $ordinal > crate::util::days_in_year($year) as i16 {
+            $ordinal -= crate::util::days_in_year($year) as i16;
             $year += 1;
-            $ordinal = 1;
-        } else if $ordinal == 0 {
+        } else if $ordinal < 1 {
             $year -= 1;
-            $ordinal = crate::util::days_in_year($year);
+            $ordinal += crate::util::days_in_year($year) as i16;
         }
     };
 }

src/offset_date_time.rs

@@ -152,7 +152,8 @@ impl OffsetDateTime {
         let mut minute =
             self.minute() as i16 - from.minutes_past_hour() as i16 + to.minutes_past_hour() as i16;
         let mut hour = self.hour() as i8 - from.whole_hours() + to.whole_hours();
-        let (mut year, mut ordinal) = self.to_ordinal_date();
+        let (mut year, ordinal) = self.to_ordinal_date();
+        let mut ordinal = ordinal as i16;
 
         // Cascade the values twice. This is needed because the values are adjusted twice above.
         cascade!(second in 0..60 => minute);
@@ -163,9 +164,12 @@ impl OffsetDateTime {
         cascade!(hour in 0..24 => ordinal);
         cascade!(ordinal => year);
 
+        debug_assert!(ordinal > 0);
+        debug_assert!(ordinal <= crate::util::days_in_year(year) as i16);
+
         (
             year,
-            ordinal,
+            ordinal as _,
             Time::__from_hms_nanos_unchecked(
                 hour as _,
                 minute as _,

tests/integration/offset_date_time.rs

@@ -55,6 +55,14 @@ fn to_offset_panic() {
     assert_panic!(PrimitiveDateTime::MIN.assume_utc().to_offset(offset!(-1)));
 }
 
+#[test]
+fn to_offset_invalid_regression() {
+    assert_eq!(
+        datetime!(2019-01-01 0:00 +13).to_offset(offset!(-13)),
+        datetime!(2018-12-30 22:00:00 -13),
+    );
+}
+
 #[test]
 fn from_unix_timestamp() {
     assert_eq!(