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DynamicScene (de)serialization to postcard and bincode fails for some components. #6713
Description
Bevy version
0.9.0
What you did
According to the changelog, Bevy 0.9.0 should now support the (de)serialization of the DynamicScene with postcard and bincode. #6140 was merged and includes tests for both bincode and postcard, which do work for me.
However, when I try to (de)serialize to binary in practice, bevy fails. When deserializing SpotLightBundle and CameraBundle, for example, bincode fails with no field at index 0 on struct bevy_render::primitives::Frustum. For the PointLightBundle it's no field at index 0 on struct bevy_render::primitives::CubemapFrusta. There could be other examples too.
What surprised me the most is the behaviour of a seemingly innocent empty entity marker:
#[derive(Component, Serialize, Deserialize, Reflect, Default)]
#[reflect(Component)]
struct Marker;It seems to work at first, but if I call app.register_type::<Marker>(), it gives an error on deserialization. When transferring data over the network, I register the incoming types on the client side, so it is important for me that it works.
(De)serializing into ron works as expected.
What went wrong
what were you expecting?
I expect the (de)serialization to work identically well whether I serialize to ron, or to binary formats. I also expect the component to (de)serialize regardless of whether it was registered manually or automatically.
I would also like the postcard to give more informative errors. As you can see from the error output provided below, they are very generic and unhepful.
Additional information
Here is an example that tests different entities (de)serialization into ron, postcard and bincode: https://pastebin.com/wxGvE9ke
Due to the issue #6573, I am using the unmerged PR #6580 to avoid failing on deserializing GlobalTransform.
Update: The actual error happens during deserialization, so made some edits to avoid confusion. However, I am not sure whether the actual issue is due to incorrect serialization or deserialization or both.
Output
Test #0: Automatically registered marker
ron : OK
bincode : OK
postcard : OK
Test #1: Pre-registered marker
ron : OK
bincode : Error! no field at index 0 on struct test_postcard_roundtrip::RegisteredMarker
postcard : Error! Serde Deserialization Error
Test #2: PbrBundle
ron : OK
bincode : OK
postcard : OK
Test #3: Spot Light
ron : OK
bincode : Error! no field at index 0 on struct bevy_render::primitives::Frustum
postcard : Error! Serde Deserialization Error
Test #4: Point Light
ron : OK
bincode : Error! no field at index 0 on struct bevy_render::primitives::CubemapFrusta
postcard : Error! Serde Deserialization Error
Test #5: Camera
ron : OK
bincode : Error! no field at index 0 on struct bevy_render::primitives::Frustum
postcard : Error! Serde Deserialization Error
Activity
[-]`DynamicScene` serialization to postcard and bincode fails for some components.[/-][+]`DynamicScene` (de)serialization to postcard and bincode fails for some components.[/+]MrGVSV commentedon Nov 21, 2022
Hm, looks like the deserializer is not properly accounting for structs with zero reflectable fields, including unit structs and structs where all fields are ignored (e.g.
FrustumandCubemapFrusta).Will look into this. Thank you for such a detailed writeup, this is very helpful!
MrGVSV commentedon Nov 21, 2022
@sQu1rr could you run your tests using the changes made in #6722 and verify it resolves this issue?
sQu1rr commentedon Nov 21, 2022
I am now getting a seemingly unrelated error
Looks like it is about the changes in: #6305
Not sure how I can work around it to test
MrGVSV commentedon Nov 21, 2022
Sounds like it just needs to be registered in
bevy_render. Can you try registering it manually temporarily? I'll put up a PR (or issue) for the registration.sQu1rr commentedon Nov 21, 2022
ComputedVisibilityFlags is not public, so I cannot access it at the moment
MrGVSV commentedon Nov 21, 2022
Could you register it directly in the source of
bevy_renderjust for testing purposes?sQu1rr commentedon Nov 22, 2022
I can confirm that pub ComputedVisibilityFlags + registration + #6580 together with #6722 fix all issues for me (https://github.com/sQu1rr/bevy/tree/testing-dynamicscene-reflect). I tested it on the minimal example I provided, and also in my networking code, where I discovered the issue in the first place. It works like a charm so far with both bincode and postcard.
Would be very useful to fix the postcard errors though, as new issues may appear in the future, and they are quite unhelpful.
MrGVSV commentedon Nov 22, 2022
Awesome! Glad to hear that, I'll work on getting the registration fixes underway. Could you give it your review/approval?
I agree. I'm not sure why the error gets replaced when deserializing with
postcard. But that might be an upstream issue rather than something Bevy is doing wrong (I think). Maybe consider making an issue on thepostcardrepo?MrGVSV commentedon Nov 22, 2022
For reference, I just registered the missing
bevy_rendertypes in this PR.bevy_reflect: Fix binary deserialization not working for unit structs (…
bevy_reflect: Fix binary deserialization not working for unit structs (…
bevy_reflect: Fix binary deserialization not working for unit structs (…
bevy_reflect: Fix binary deserialization not working for unit structs (…