Made the Cow Encode constraints more permissive (#524)

* Made the Cow Encode constraints more permissive

* Made Decode more permissive for Cow

src/features/impl_alloc.rs

@@ -285,7 +285,7 @@ where
 
 impl<'cow, T> Decode for Cow<'cow, T>
 where
-    T: ToOwned,
+    T: ToOwned + ?Sized,
     <T as ToOwned>::Owned: Decode,
 {
     fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError> {
@@ -296,7 +296,8 @@ where
 
 impl<'cow, T> Encode for Cow<'cow, T>
 where
-    T: Encode + Clone,
+    T: ToOwned + ?Sized,
+    for<'a> &'a T: Encode,
 {
     fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
         self.as_ref().encode(encoder)

tests/issues.rs

@@ -20,3 +20,6 @@ mod issue_498;
 
 #[path = "issues/issue_500.rs"]
 mod issue_500;
+
+#[path = "issues/issue_523.rs"]
+mod issue_523;

tests/issues/issue_523.rs

@@ -0,0 +1,9 @@
+#![cfg(all(feature = "derive", feature = "std"))]
+
+extern crate std;
+
+use bincode::{Decode, Encode};
+use std::borrow::Cow;
+
+#[derive(Clone, Encode, Decode)]
+pub struct Foo<'a>(Cow<'a, str>);