Make bevy_scene dependency on serde optional

[alice-i-cecile]

In bevy_scene, the dependency to serde is not optional and the code is always enabled... but it would be nice to make it optional. maybe another PR 🙂

Originally posted by @mockersf in #6023 (comment)

[LinusKall]

I've never contributed before, but I would like to give this a shot!

[LinusKall]

Would it be a good idea to make custom SceneSerializer and SceneDeserializer implementations in a new module or make variants within the serde.rs module?

[alice-i-cecile]

Thanks! For this particular issue I think we can probably do a very scoped change :) This line is the suspicious one:

bevy/crates/bevy_scene/Cargo.toml

Line 24 in 2b80a3f

serde = { version = "1.0", features = ["derive"] }

Here's the reference page I use when mucking about with dependencies.

[LinusKall]

Thank you!

I've changed serde to be optional, but is that enough? Wouldn't it also be necessary to define a feature that we can use to "activate" serde again?

I'm also uncertain because wouldn't the case of this serde feature being "deactivated" have to be handled? That is why I'm wondering about custom implementations.

Perhaps I'm just missing something? 😅

[alice-i-cecile]

Oh right! You need to add a serde feature, then add it to the top-level bevy feature. Check out what was done in these commits: https://github.com/bevyengine/bevy/pull/6023/commits

I'm also uncertain because wouldn't the case of this serde feature being "deactivated" have to be handled? That is why I'm wondering about custom implementations.

If the serde feature is deactivated, users don't care about implementing serde's traits one way or another :)

[LinusKall]

I see, thank you for your patience!

I will try it out 😄

[LinusKall]

Hi,

I've taken a look and it seems like most things could be solved by using #[cfg(feature = "serialize)].

The only thing that needs to be handled differently is the AssetLoader implementation for the SceneLoader struct, this is because it uses the SceneDeserializer struct.

I'm thinking that perhaps this implementation and the current Plugin implementation for the ScenePlugin could be connected to the serialize feature.

Then I could make a "blank" Plugin implementation that does nothing when the serialize feature isn't activated.

Would this be reasonable?

[alice-i-cecile]

Yep, that seems basically correct. Feel free to open PRs early (and stick them in draft mode); it's often easier to figure out the exact technical details when there's a change set in front of you :)

[LinusKall]

Okay, I'll try opening a PR tomorrow! :)

Edit: sorry, I meant on friday