feat(swarm): report outcome of handling SwarmEvent

[thomaseizinger]

Description

Previously, a user wouldn't know whether passing a SwarmEvent to ListenAddresses or ExternalAddresses changed the state. We now return a boolean where true indicates that we handled the event and changed state as a result.

The API is inspired by HashSet::insert and the like.

Notes & open questions

Extracted out of #3651.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[mergify]

This pull request has merge conflicts. Could you please resolve them @thomaseizinger? 🙏

[mxinden]

Looks good to me. Though I would prefer not using once_cell::Lazy here for the sake of simplicity.

[mxinden]

What is the value of a static over a const here? Why does it warrant introducing once_cell as a dependency?

[thomaseizinger]

Multiaddr::empty and Multiaddr::with are unfortunately not const.

[mxinden]

Ah, right. I missed that.

I am hesitant to introduce a dependency just for the sake of more succinct test code. That said, once_cell seems to be everywhere, thus not really an additional dependency.

[thomaseizinger]

It is on the pathway to being stabilized and part of std: rust-lang/rust#105587

[mxinden]

Ah, right. I missed that.

I am hesitant to introduce a dependency just for the sake of more succinct test code. That said, once_cell seems to be everywhere, thus not really an additional dependency.