swarm-derive/: Add where clause of behaviour to generated out event (#2819)

When generating the `OutEvent` for a `NetworkBehaviour`, add the `where` clause of the
`NetworkBehaviour` `struct` to the generated `enum`.

swarm-derive/src/lib.rs

@@ -159,7 +159,9 @@ fn build_struct(ast: &DeriveInput, data_struct: &DataStruct) -> TokenStream {
                     let visibility = &ast.vis;
 
                     Some(quote! {
-                        #visibility enum #name #impl_generics {
+                        #visibility enum #name #impl_generics
+                            #where_clause
+                        {
                             #(#fields),*
                         }
                     })

swarm-derive/tests/test.rs

@@ -272,7 +272,7 @@ fn custom_event_mismatching_field_names() {
 }
 
 #[test]
-fn where_clause() {
+fn bound() {
     #[allow(dead_code)]
     #[derive(NetworkBehaviour)]
     struct Foo<T: Copy + NetworkBehaviour> {
@@ -281,6 +281,19 @@ fn where_clause() {
     }
 }
 
+#[test]
+fn where_clause() {
+    #[allow(dead_code)]
+    #[derive(NetworkBehaviour)]
+    struct Foo<T>
+    where
+        T: Copy + NetworkBehaviour,
+    {
+        ping: libp2p::ping::Ping,
+        bar: T,
+    }
+}
+
 #[test]
 fn nested_derives_with_import() {
     #[allow(dead_code)]