hand implemented fmt::Debug for ArchivedDateTime

src/datetime/mod.rs

@@ -1506,6 +1506,31 @@ impl<Tz: TimeZone> fmt::Debug for DateTime<Tz> {
     }
 }
 
+// `fmt::Debug` is hand implemented for the `rkyv::Archive` variant of `DateTime` because
+// deriving a trait recursively does not propagate trait defined associated types with their own
+// constraints:
+// In our case `<<Tz as offset::TimeZone>::Offset as Archive>::Archived`
+// cannot be formatted using `{:?}` because it doesn't implement `Debug`.
+// See below for further discussion:
+// * https://github.com/rust-lang/rust/issues/26925
+// * https://github.com/rkyv/rkyv/issues/333
+// * https://github.com/dtolnay/syn/issues/370
+#[cfg(feature = "rkyv-validation")]
+impl<Tz: TimeZone> fmt::Debug for ArchivedDateTime<Tz>
+where
+    Tz: Archive,
+    <Tz as Archive>::Archived: fmt::Debug,
+    <<Tz as TimeZone>::Offset as Archive>::Archived: fmt::Debug,
+    <Tz as TimeZone>::Offset: fmt::Debug + Archive,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("ArchivedDateTime")
+            .field("datetime", &self.datetime)
+            .field("offset", &self.offset)
+            .finish()
+    }
+}
+
 impl<Tz: TimeZone> fmt::Display for DateTime<Tz>
 where
     Tz::Offset: fmt::Display,