From b7d02133f132c1fd7e315eaba8b53ec83b4c35da Mon Sep 17 00:00:00 2001
From: b3t33 <>
Date: Tue, 19 Jan 2021 22:58:32 +0100
Subject: [PATCH]  Fix possible panic in NaiveDate::from_num_days_from_ce_opt

Add some test including panic triggering example
`NaiveDate::from_num_days_from_ce_opt(i32::MAX)`.
As the function already yields `None` for `i32::Max - 365`, this fix
does not change the behaviour, while preventing a panic.
---
 CHANGELOG.md      |  1 +
 src/naive/date.rs | 20 +++++++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 16a9063b60..29cf0c0a1c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ Versions with only mechanical changes will be omitted from the following list.
 * Add support for microseconds timestamps serde serialization/deserialization (#304)
 * Fix `DurationRound` is not TZ aware (#495)
 * Implement `DurationRound` for `NaiveDateTime`
+* Fix `NaiveDate::from_num_days_from_ce_opt` panic on overflow
 
 ## 0.4.19
 
diff --git a/src/naive/date.rs b/src/naive/date.rs
index 989254ae5f..a9a5d341e6 100644
--- a/src/naive/date.rs
+++ b/src/naive/date.rs
@@ -415,11 +415,13 @@ impl NaiveDate {
     /// assert_eq!(from_ndays_opt(-100_000_000), None);
     /// ```
     pub fn from_num_days_from_ce_opt(days: i32) -> Option<NaiveDate> {
-        let days = days + 365; // make December 31, 1 BCE equal to day 0
-        let (year_div_400, cycle) = div_mod_floor(days, 146_097);
-        let (year_mod_400, ordinal) = internals::cycle_to_yo(cycle as u32);
-        let flags = YearFlags::from_year_mod_400(year_mod_400 as i32);
-        NaiveDate::from_of(year_div_400 * 400 + year_mod_400 as i32, Of::new(ordinal, flags))
+        // make December 31, 1 BCE equal to day 0
+        days.checked_add(365).and_then(|days| {
+            let (year_div_400, cycle) = div_mod_floor(days, 146_097);
+            let (year_mod_400, ordinal) = internals::cycle_to_yo(cycle as u32);
+            let flags = YearFlags::from_year_mod_400(year_mod_400 as i32);
+            NaiveDate::from_of(year_div_400 * 400 + year_mod_400 as i32, Of::new(ordinal, flags))
+        })
     }
 
     /// Makes a new `NaiveDate` by counting the number of occurrences of a particular day-of-week
@@ -2027,6 +2029,14 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_date_from_num_days_from_ce_opt() {
+        let ndays_from_ce = |days| NaiveDate::from_num_days_from_ce_opt(days);
+        ndays_from_ce(i32::MAX);
+        assert!(ndays_from_ce(0).is_some());
+        ndays_from_ce(i32::MIN);
+    }
+
     #[test]
     fn test_date_from_num_days_from_ce() {
         let from_ndays_from_ce = |days| NaiveDate::from_num_days_from_ce_opt(days);