apply same fix to parsing and add failing test cases as per issue #961

src/format/parsed.rs

@@ -380,8 +380,8 @@ impl Parsed {
         let verify_ordinal = |date: NaiveDate| {
             let ordinal = date.ordinal();
             let weekday = date.weekday();
-            let week_from_sun = (ordinal as i32 - weekday.num_days_from_sunday() as i32 + 7) / 7;
-            let week_from_mon = (ordinal as i32 - weekday.num_days_from_monday() as i32 + 7) / 7;
+            let week_from_sun = (ordinal as i32 - weekday.num_days_from_sunday() as i32 + 6) / 7;
+            let week_from_mon = (ordinal as i32 - weekday.num_days_from_monday() as i32 + 6) / 7;
             self.ordinal.unwrap_or(ordinal) == ordinal
                 && self.week_from_sun.map_or(week_from_sun, |v| v as i32) == week_from_sun
                 && self.week_from_mon.map_or(week_from_mon, |v| v as i32) == week_from_mon

src/naive/date.rs

@@ -2831,6 +2831,16 @@ mod tests {
         assert!(NaiveDate::parse_from_str("Sat, 09 Aug 2013", "%a, %d %b %Y").is_err());
         assert!(NaiveDate::parse_from_str("2014-57", "%Y-%m-%d").is_err());
         assert!(NaiveDate::parse_from_str("2014", "%Y").is_err()); // insufficient
+
+        assert_eq!(
+            NaiveDate::parse_from_str("2020-01-0", "%Y-%W-%w").ok(),
+            NaiveDate::from_ymd_opt(2020, 1, 12),
+        );
+
+        assert_eq!(
+            NaiveDate::parse_from_str("2019-01-0", "%Y-%W-%w").ok(),
+            NaiveDate::from_ymd_opt(2019, 1, 13),
+        );
     }
 
     #[test]