Support serializing dynamically sized field

Author: dtolnay

src/lib.rs

@@ -76,7 +76,7 @@ pub use crate::bytebuf::ByteBuf;
 /// ```
 pub fn serialize<T, S>(bytes: &T, serializer: S) -> Result<S::Ok, S::Error>
 where
-    T: Serialize,
+    T: ?Sized + Serialize,
     S: Serializer,
 {
     Serialize::serialize(bytes, serializer)

tests/test_derive.rs

@@ -28,3 +28,9 @@ struct Test<'a> {
     #[serde(with = "serde_bytes")]
     boxed_bytes: Box<Bytes>,
 }
+
+#[derive(Serialize)]
+struct Dst {
+    #[serde(with = "serde_bytes")]
+    bytes: [u8],
+}