Add From impls for Days, Months and std::time::Duration

src/calendar_duration.rs

@@ -1,7 +1,9 @@
 use core::fmt;
 use core::num::NonZeroU32;
+use core::time::Duration;
 
 use crate::{expect, try_opt};
+use crate::{Days, Months};
 
 /// ISO 8601 duration type.
 ///
@@ -268,9 +270,31 @@ impl CalendarDuration {
     }
 }
 
+impl From<Days> for CalendarDuration {
+    fn from(value: Days) -> Self {
+        let days = u32::try_from(value.0).expect("value of `Days` out of range");
+        Self::new().days(days)
+    }
+}
+
+impl From<Months> for CalendarDuration {
+    fn from(value: Months) -> Self {
+        Self::new().months(value.0)
+    }
+}
+
+impl From<Duration> for CalendarDuration {
+    fn from(value: Duration) -> Self {
+        let seconds = u32::try_from(value.as_secs()).expect("value of `Duration` out of range");
+        Self::new().seconds(seconds).nanos(value.subsec_nanos()).unwrap()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::CalendarDuration;
+    use crate::{Days, Months};
+    use std::time::Duration;
 
     #[test]
     fn test_basic_functionality() {
@@ -301,6 +325,28 @@ mod tests {
         assert!(CalendarDuration::new().is_zero());
     }
 
+    #[test]
+    fn test_from_impls() {
+        assert_eq!(CalendarDuration::new().days(5), Days::new(5).into());
+        assert_eq!(CalendarDuration::new().months(5), Months::new(5).into());
+        assert_eq!(
+            CalendarDuration::new().seconds(7).nanos(8).unwrap(),
+            Duration::new(7, 8).into()
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_from_extreme_days_panics() {
+        let _ = CalendarDuration::from(Days::new(1 << 32));
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_from_extreme_duration_panics() {
+        let _ = CalendarDuration::from(Duration::new(1 << 32, 0));
+    }
+
     #[test]
     fn test_display_format() {
         assert_eq!(