Add BRP method to mutate a component

[purplg]

Objective

Add a method to mutate components with BRP.

Currently the only way to modify a component on an entity with BRP is to insert a new one with the new values. This isn't ideal for several reasons, one reason being that the client has to know what all the fields are of the component and stay in sync with the server.

Solution

Add a new BRP method called bevy/mutate_component to mutate a single field in a component on an entity.

Testing

Tested on a simple scene on all Transform, Name, and a custom component.

---

Showcase

Example JSON-RPC request to change the Name of an entity to "New name!"

{
    "jsonrpc": "2.0",
    "id": 0,
    "method": "bevy/mutate_component",
    "params": {
        "entity": 4294967308,
        "component": "bevy_ecs::name::Name",
        "path": ".name",
        "value": "New name!"
    }
}

Or setting the X translation to 10.0 on a Transform:

{
    "jsonrpc": "2.0",
    "id": 0,
    "method": "bevy/mutate_component",
    "params": {
        "entity": 4294967308,
        "component": "bevy_transform::components::transform::Transform",
        "path": ".translation.x",
        "value": 10.0
    }
}

Clip of my Emacs BRP package using this method:

output.mp4

[purplg]

I'm not sure what the convention is for multiple words in a method name is. Should the method be named differently? I'm trying to consider future methods for modifying other things like Resource's.

I had a few other ideas for methods:

• bevy/modify/component
• bevy/mutate/component
• bevy/component_mut this feels too Rusty in this context

[cBournhonesque]

This generally LGTM.
It's a shame that we don't have unit tests for BRP

[purplg]

It's a shame that we don't have unit tests for BRP

I agree. I did look at writing tests for this, but I didn't see an existing way to do this.

[LiamGallagher737]

It would be useful to link to the following docs in the crate level docs for this method to show how the path field should be structured.

https://docs.rs/bevy/latest/bevy/prelude/trait.GetPath.html#syntax

[github-actions]

Your PR increases Bevy Minimum Supported Rust Version. Please update the rust-version field in the root Cargo.toml file.

[purplg]

Good point on that doc link. Added.