Add #[must_use] to some methods

src/naive/date.rs

@@ -469,6 +469,7 @@ impl NaiveDate {
     ///
     /// Returns `None` if `n` out-of-range; ie. if `n` is larger than the number of `weekday` in
     /// `month` (eg. the 6th Friday of March 2017), or if `n == 0`.
+    #[must_use]
     pub fn from_weekday_of_month_opt(
         year: i32,
         month: u32,
@@ -549,6 +550,7 @@ impl NaiveDate {
     ///     Some(NaiveDate::from_ymd_opt(2022, 9, 30).unwrap())
     /// );
     /// ```
+    #[must_use]
     pub fn checked_add_months(self, months: Months) -> Option<Self> {
         if months.0 == 0 {
             return Some(self);
@@ -579,6 +581,7 @@ impl NaiveDate {
     ///     None
     /// );
     /// ```
+    #[must_use]
     pub fn checked_sub_months(self, months: Months) -> Option<Self> {
         if months.0 == 0 {
             return Some(self);
@@ -591,6 +594,7 @@ impl NaiveDate {
         }
     }
 
+    #[must_use]
     fn diff_months(self, months: i32) -> Option<Self> {
         let (years, left) = ((months / 12), (months % 12));
 
@@ -652,6 +656,7 @@ impl NaiveDate {
     ///     None
     /// );
     /// ```
+    #[must_use]
     pub fn checked_add_days(self, days: Days) -> Option<Self> {
         if days.0 == 0 {
             return Some(self);
@@ -675,6 +680,7 @@ impl NaiveDate {
     ///     None
     /// );
     /// ```
+    #[must_use]
     pub fn checked_sub_days(self, days: Days) -> Option<Self> {
         if days.0 == 0 {
             return Some(self);
@@ -683,6 +689,7 @@ impl NaiveDate {
         i64::try_from(days.0).ok().and_then(|d| self.diff_days(-d))
     }
 
+    #[must_use]
     fn diff_days(self, days: i64) -> Option<Self> {
         let secs = days.checked_mul(86400)?; // 86400 seconds in one day
         if secs >= core::i64::MAX / 1000 || secs <= core::i64::MIN / 1000 {
@@ -706,6 +713,7 @@ impl NaiveDate {
     /// assert_eq!(dt.time(), t);
     /// ```
     #[inline]
+    #[must_use]
     pub const fn and_time(&self, time: NaiveTime) -> NaiveDateTime {
         NaiveDateTime::new(*self, time)
     }