Display: preserve fractional seconds when present

When nanoseconds are non-zero, include them in Display output as
`.NNNNNNNNN` between seconds and the offset. This avoids silently
dropping sub-second precision from the formatted representation.

src/extended.rs

@@ -297,11 +297,28 @@ impl fmt::Display for ExtendedDateTime {
         let abs = self.offset_seconds.unsigned_abs();
         let oh = abs / 3600;
         let om = (abs % 3600) / 60;
-        write!(
-            f,
-            "{:04}-{:02}-{:02} {:02}:{:02}:{:02}{}{:02}:{:02}",
-            self.year, self.month, self.day, self.hour, self.minute, self.second, sign, oh, om,
-        )
+        if self.nanosecond != 0 {
+            write!(
+                f,
+                "{:04}-{:02}-{:02} {:02}:{:02}:{:02}.{:09}{}{:02}:{:02}",
+                self.year,
+                self.month,
+                self.day,
+                self.hour,
+                self.minute,
+                self.second,
+                self.nanosecond,
+                sign,
+                oh,
+                om,
+            )
+        } else {
+            write!(
+                f,
+                "{:04}-{:02}-{:02} {:02}:{:02}:{:02}{}{:02}:{:02}",
+                self.year, self.month, self.day, self.hour, self.minute, self.second, sign, oh, om,
+            )
+        }
     }
 }
 

src/lib.rs

@@ -63,7 +63,14 @@ impl ParsedDateTime {
 impl fmt::Display for ParsedDateTime {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            ParsedDateTime::InRange(z) => write!(f, "{}", z.strftime("%Y-%m-%d %H:%M:%S%:z")),
+            ParsedDateTime::InRange(z) => {
+                let ns = z.datetime().time().subsec_nanosecond();
+                if ns != 0 {
+                    write!(f, "{}", z.strftime("%Y-%m-%d %H:%M:%S%.9f%:z"))
+                } else {
+                    write!(f, "{}", z.strftime("%Y-%m-%d %H:%M:%S%:z"))
+                }
+            }
             ParsedDateTime::Extended(dt) => write!(f, "{dt}"),
         }
     }