Deriving NetworkBehaviour without specifying OutEvent gives compilation error: use of undeclared type NetworkBehaviour

[folex]

Summary

The following snippet gives a compilation error

use libp2p::identify::Identify;
use libp2p::NetworkBehaviour;
use libp2p::ping::Ping;

#[derive(NetworkBehaviour)]
pub struct Behaviour {
    identify: Identify,
    ping: Ping,
}

Here's a repo with that snippet, it reproduces the error on compilation https://github.com/folex/libp2p-network-behaviour-derive-error/tree/master

Expected behaviour

I expect macro to derive OutEvent enum automatically, as specified in doc

// If we find a #[behaviour(out_event = "Foo")] attribute on the
// struct, we set Foo as the out event. If not, the OutEvent is
// generated.

Actual behaviour

Compilation error

error[E0433]: failed to resolve: use of undeclared type `NetworkBehaviour`
 --> src/main.rs:5:10
  |
5 | #[derive(NetworkBehaviour)]
  |          ^^^^^^^^^^^^^^^^ use of undeclared type `NetworkBehaviour`
  |
  = note: this error originates in the derive macro `NetworkBehaviour` (in Nightly builds, run with -Z macro-backtrace for more info)

Debug Output

<output>

Possible Solution

Adding an out_event with a enum name yields no compilation errors.

Version

libp2p = "0.48.0"
libp2p-core = { version = "0.36.0", default-features = false, features = [ "secp256k1" ] }
libp2p-metrics = { version = "0.9.0", features = ["kad"] }
libp2p-noise = "0.39.0"
libp2p-swarm = "0.39.0"

$ rustup show
active toolchain
----------------
nightly-x86_64-apple-darwin (default)

$ cargo --version
cargo 1.65.0-nightly (4ed54cecc 2022-08-27)

Would you like to work on fixing this bug?

Maybe

[elenaf9]

Thank you for the detailed bug report @folex!
I believe the issue is that when generating the out event the macro references the NetworkBehavour trait, which you don't have imported:

rust-libp2p/swarm-derive/src/lib.rs

Line 128 in 39d6351

quote! {#variant(<#ty as NetworkBehaviour>::OutEvent)}

So quick fix for you would be to just import the trait from libp2p::swarm::NetworkBehaviour (right now you only have the macro itself imported).

That being said, ideally this shouldn't be necessary if we reference the full path in the swarm-derive code like it is done here:

rust-libp2p/swarm-derive/src/lib.rs

Line 50 in 39d6351

let trait_to_impl = quote! {::libp2p::swarm::NetworkBehaviour};

Would you be interested in doing a PR with this fix?

[folex]

Thanks for the explanation, sorry I didn't see it myself. Name clashing confused me a bunch.

Yep, I will submit a PR today!

[elenaf9]

Fixed with #2932. Thanks @folex!