API inconsistency with `Handle` as component or field of component

[benfrankel]

Question

Should components with associated assets (e.g. Sprite + Handle<Image>) include their Handle as a field, or as a separate component on the same entity, or something else?

• Handle-as-field: May make generic systems impossible (see the asset_decompression example).
• Handle-as-component: May create ambiguity (see EnvironmentMapLight).

From the Discord discussion, this is blocked on Bevy scenes before a design decision can be made.

Status quo

Bevy's answer to this question is inconsistent (as of March 6th, 2024):

Component with a wrapped Handle field:

• UiImage::texture: Handle<Image>
• TextureAtlas::layout: Handle<TextureAtlasLayout>
• Skybox::image: Handle<Image>
• Mesh2dHandle::0: Handle<Mesh>
• SkinnedMesh::inverse_bindposes: Handle<SkinnedMeshInverseBindposes>
• Lightmap::image: Handle<Image>
• IrradianceVolume::voxels: Handle<Image>
• EnvironmentMapLight::diffuse_map: Handle<Image>
• EnvironmentMapLight::specular_map: Handle<Image>

Component with an associated Handle-as-component:

• Sprite + Handle<Image>
• more? hard to ripgrep for this

Bundle with a Handle-as-component field:

• SpriteBundle::texture: Handle<Image>
• SceneBundle::scene: Handle<Scene>
• DynamicSceneBundle::scene: Handle<DynamicScene>
• MaterialMesh2dBundle<M>::material: Handle<M>
• MaterialMeshBundle<M>::material: Handle<M>
• MaterialMeshBundle<M>::mesh: Handle<Mesh>
• MaterialNodeBundle<M>::material: Handle<M>
• AudioSourceBundle<Source>::source: Handle<Source>

[alice-i-cecile]

I agree; this design has annoyed me since the Component trait was implemented. I think these should all be newtyped personally.

[benfrankel]

This seems to be unblocked now, with required components landed and the scene overhaul generally being underway.

[alice-i-cecile]

This was discussed informally today, with both @cart and I being broadly on board with moving to wrapper components: https://discordapp.com/channels/691052431525675048/1264881140007702558/1278098028536008827

[bushrat011899]

Resolved in #15796. Handle should now be used as a field in a Component.