Disambiguate calls to NetworkBehaviour::inject_event

There is a gnarly edge-case with the custom-derive where rustc
cannot disambiguate the call if:

- The NetworkBehaviourEventProcess trait is imported
- We nest NetworkBehaviours that use the custom-derive

misc/core-derive/src/lib.rs

@@ -293,8 +293,8 @@ fn build_struct(ast: &DeriveInput, data_struct: &DataStruct) -> TokenStream {
         }
 
         Some(match field.ident {
-            Some(ref i) => quote!{ #elem => self.#i.inject_event(peer_id, connection_id, ev) },
-            None => quote!{ #elem => self.#field_n.inject_event(peer_id, connection_id, ev) },
+            Some(ref i) => quote!{ #elem => ::libp2p::swarm::NetworkBehaviour::inject_event(&mut self.#i, peer_id, connection_id, ev) },
+            None => quote!{ #elem => ::libp2p::swarm::NetworkBehaviour::inject_event(&mut self.#field_n, peer_id, connection_id, ev) },
         })
     });
 

misc/core-derive/tests/test.rs

@@ -204,3 +204,35 @@ fn where_clause() {
         bar: T,
     }
 }
+
+#[test]
+fn nested_derives_with_import() {
+    use libp2p::swarm::NetworkBehaviourEventProcess;
+
+    #[allow(dead_code)]
+    #[derive(NetworkBehaviour)]
+    struct Foo {
+        ping: libp2p::ping::Ping,
+    }
+
+    #[allow(dead_code)]
+    #[derive(NetworkBehaviour)]
+    struct Bar {
+        foo: Foo,
+    }
+
+    impl NetworkBehaviourEventProcess<libp2p::ping::PingEvent> for Foo {
+        fn inject_event(&mut self, _: libp2p::ping::PingEvent) {
+        }
+    }
+
+    impl NetworkBehaviourEventProcess<()> for Bar {
+        fn inject_event(&mut self, _: ()) {
+        }
+    }
+
+    #[allow(dead_code)]
+    fn bar() {
+        require_net_behaviour::<Bar>();
+    }
+}