Add test and some documentation

src/naive/internals.rs

@@ -266,6 +266,8 @@ const OL_TO_MDL: &[u8; MAX_OL as usize + 1] = &[
 ///
 /// The whole bits except for the least 3 bits are referred as `Ol` (ordinal and leap flag),
 /// which is an index to the `OL_TO_MDL` lookup table.
+///
+/// The methods implemented on `Of` always return a valid value.
 #[derive(PartialEq, PartialOrd, Copy, Clone)]
 pub(super) struct Of(u32);
 
@@ -384,13 +386,17 @@ impl fmt::Debug for Of {
 /// The whole bits except for the least 3 bits are referred as `Mdl`
 /// (month, day of month and leap flag),
 /// which is an index to the `MDL_TO_OL` lookup table.
+///
+/// The methods implemented on `Mdf` do not always return a valid value.
+/// Dates than can't exist, like February 30, can still be represented.
+/// Use `Mdl::valid` to check whether the date is valid.
 #[derive(PartialEq, PartialOrd, Copy, Clone)]
 pub(super) struct Mdf(u32);
 
 impl Mdf {
     #[inline]
     pub(super) const fn new(month: u32, day: u32, YearFlags(flags): YearFlags) -> Option<Mdf> {
-        match month <= 12 && day <= 31 {
+        match month >= 1 && month <= 12 && day >= 1 && day <= 31 {
             true => Some(Mdf((month << 9) | (day << 4) | flags as u32)),
             false => None,
         }
@@ -829,4 +835,33 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn test_invalid_returns_none() {
+        let regular_year = YearFlags::from_year(2023);
+        let leap_year = YearFlags::from_year(2024);
+        assert!(Of::new(0, regular_year).is_none());
+        assert!(Of::new(366, regular_year).is_none());
+        assert!(Of::new(366, leap_year).is_some());
+        assert!(Of::new(367, regular_year).is_none());
+
+        assert!(Mdf::new(0, 1, regular_year).is_none());
+        assert!(Mdf::new(13, 1, regular_year).is_none());
+        assert!(Mdf::new(1, 0, regular_year).is_none());
+        assert!(Mdf::new(1, 32, regular_year).is_none());
+        assert!(Mdf::new(2, 31, regular_year).is_some());
+
+        assert!(Of::from_mdf(Mdf::new(2, 30, regular_year).unwrap()).is_none());
+        assert!(Of::from_mdf(Mdf::new(2, 30, leap_year).unwrap()).is_none());
+        assert!(Of::from_mdf(Mdf::new(2, 29, regular_year).unwrap()).is_none());
+        assert!(Of::from_mdf(Mdf::new(2, 29, leap_year).unwrap()).is_some());
+        assert!(Of::from_mdf(Mdf::new(2, 28, regular_year).unwrap()).is_some());
+
+        assert!(Of::new(365, regular_year).unwrap().succ().is_none());
+        assert!(Of::new(365, leap_year).unwrap().succ().is_some());
+        assert!(Of::new(366, leap_year).unwrap().succ().is_none());
+
+        assert!(Of::new(1, regular_year).unwrap().pred().is_none());
+        assert!(Of::new(1, leap_year).unwrap().pred().is_none());
+    }
 }