fix: Negative UNIX timestamps accepted by from_timestamp_millis

src/naive/datetime/mod.rs

@@ -35,6 +35,11 @@ mod tests;
 /// touching that call when we are already sure that it WILL overflow...
 const MAX_SECS_BITS: usize = 44;
 
+/// Number of nanoseconds in a millisecond
+const NANOS_IN_MILLISECOND: u32 = 1_000_000;
+/// Number of nanoseconds in a second
+const NANOS_IN_SECOND: u32 = 1000 * NANOS_IN_MILLISECOND;
+
 /// The minimum possible `NaiveDateTime`.
 #[deprecated(since = "0.4.20", note = "Use NaiveDateTime::MIN instead")]
 pub const MIN_DATETIME: NaiveDateTime = NaiveDateTime::MIN;
@@ -126,7 +131,8 @@ impl NaiveDateTime {
         let datetime = NaiveDateTime::from_timestamp_opt(secs, nsecs);
         datetime.expect("invalid or out-of-range datetime")
     }
-    /// Creates a new [NaiveDateTime] from milliseconds since the UNIX Epoch.
+
+    /// Creates a new [NaiveDateTime] from milliseconds since the UNIX epoch.
     ///
     /// The UNIX epoch starts on midnight, January 1, 1970, UTC.
     ///
@@ -140,12 +146,24 @@ impl NaiveDateTime {
     /// let naive_datetime = NaiveDateTime::from_timestamp_millis(timestamp_millis);
     /// assert!(naive_datetime.is_some());
     /// assert_eq!(timestamp_millis, naive_datetime.unwrap().timestamp_millis());
+    ///
+    /// // Negative timestamps (before the UNIX epoch) are supported as well.
+    /// let timestamp_millis: i64 = -2208936075; //Mon Jan 01 1900 14:38:45 GMT+0000
+    /// let naive_datetime = NaiveDateTime::from_timestamp_millis(timestamp_millis);
+    /// assert!(naive_datetime.is_some());
+    /// assert_eq!(timestamp_millis, naive_datetime.unwrap().timestamp_millis());
     /// ```
     #[inline]
     pub fn from_timestamp_millis(millis: i64) -> Option<NaiveDateTime> {
-        let secs = millis / 1000;
-        let nsecs = (millis % 1000) as u32 * 1_000_000;
-        NaiveDateTime::from_timestamp_opt(secs, nsecs)
+        if millis < 0 {
+            let secs = millis / 1000;
+            let nsecs = (millis % 1000).abs() as u32 * NANOS_IN_MILLISECOND;
+            NaiveDateTime::from_timestamp_opt(secs - 1, NANOS_IN_SECOND - nsecs)
+        } else {
+            let secs = millis / 1000;
+            let nsecs = (millis % 1000) as u32 * NANOS_IN_MILLISECOND;
+            NaiveDateTime::from_timestamp_opt(secs, nsecs)
+        }
     }
 
     /// Makes a new `NaiveDateTime` corresponding to a UTC date and time,