Cannot reflect struct with Option fields

[inodentry]

Bevy cannot derive Reflect on structs that contain Option<T> fields, even though T is Reflect.

This compiles:

#[derive(Component, Reflect)]
struct MyComponent {
    sz: Size<Val>,
}

(Size<Val> is Reflect)

This does not:

#[derive(Component, Reflect)]
struct MyComponent {
    sz: Option<Size<Val>>,
}

error[E0277]: the trait bound `bevy::prelude::Size<bevy::prelude::Val>: bevy::reflect::erased_serde::private::serde::Serialize` is not satisfied
 --> src/main.rs:3:21
  |
3 | #[derive(Component, Reflect)]
  |                     ^^^^^^^ the trait `bevy::reflect::erased_serde::private::serde::Serialize` is not implemented for `bevy::prelude::Size<bevy::prelude::Val>`
  |
  = note: required because of the requirements on the impl of `bevy::prelude::Reflect` for `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>`
  = note: required for the cast to the object type `dyn bevy::prelude::Reflect`
  = note: this error originates in the derive macro `Reflect` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `for<'de> bevy::prelude::Size<bevy::prelude::Val>: Deserialize<'de>` is not satisfied
 --> src/main.rs:3:21
  |
3 | #[derive(Component, Reflect)]
  |                     ^^^^^^^ the trait `for<'de> Deserialize<'de>` is not implemented for `bevy::prelude::Size<bevy::prelude::Val>`
  |
  = note: required because of the requirements on the impl of `bevy::prelude::Reflect` for `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>`
  = note: required for the cast to the object type `dyn bevy::prelude::Reflect`
  = note: this error originates in the derive macro `Reflect` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `bevy::prelude::Size<bevy::prelude::Val>: bevy::reflect::erased_serde::private::serde::Serialize` is not satisfied
 --> src/main.rs:3:21
  |
3 | #[derive(Component, Reflect)]
  |                     ^^^^^^^ the trait `bevy::reflect::erased_serde::private::serde::Serialize` is not implemented for `bevy::prelude::Size<bevy::prelude::Val>`
  |
  = note: required because of the requirements on the impl of `bevy::prelude::Reflect` for `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>`
  = note: required for the cast to the object type `(dyn bevy::prelude::Reflect + 'static)`
  = note: this error originates in the derive macro `Reflect` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `for<'de> bevy::prelude::Size<bevy::prelude::Val>: Deserialize<'de>` is not satisfied
 --> src/main.rs:3:21
  |
3 | #[derive(Component, Reflect)]
  |                     ^^^^^^^ the trait `for<'de> Deserialize<'de>` is not implemented for `bevy::prelude::Size<bevy::prelude::Val>`
  |
  = note: required because of the requirements on the impl of `bevy::prelude::Reflect` for `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>`
  = note: required for the cast to the object type `(dyn bevy::prelude::Reflect + 'static)`
  = note: this error originates in the derive macro `Reflect` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0599]: the method `clone_value` exists for enum `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>`, but its trait bounds were not satisfied
   --> src/main.rs:3:21
    |
3   | #[derive(Component, Reflect)]
    |                     ^^^^^^^ method cannot be called on `std::option::Option<bevy::prelude::Size<bevy::prelude::Val>>` due to unsatisfied trait bounds
    |
   ::: /home/iyes/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:515:1
    |
515 | pub enum Option<T> {
    | ------------------ doesn't satisfy `_: bevy::prelude::Reflect`
    |
   ::: /home/iyes/.cargo/registry/src/github.com-1ecc6299db9ec823/bevy_math-0.6.0/src/geometry.rs:8:1
    |
8   | pub struct Size<T: Reflect + PartialEq = f32> {
    | ---------------------------------------------
    | |
    | doesn't satisfy `_: Deserialize<'de>`
    | doesn't satisfy `_: bevy::reflect::erased_serde::private::serde::Serialize`
    |
note: the following trait bounds were not satisfied because of the requirements of the implementation of `bevy::prelude::Reflect` for `_`:
      `bevy::prelude::Size<bevy::prelude::Val>: bevy::reflect::erased_serde::private::serde::Serialize`
      `bevy::prelude::Size<bevy::prelude::Val>: Deserialize<'de>`
   --> src/main.rs:3:21
    |
3   | #[derive(Component, Reflect)]
    |                     ^^^^^^^
4   | struct MyTest {
    |        ^^^^^^
    = note: this error originates in the derive macro `Reflect` (in Nightly builds, run with -Z macro-backtrace for more info)

[Davier]

Reflect is implemented there for Option:

bevy/crates/bevy_reflect/src/impls/std.rs

Line 34 in 44bf66e

impl_reflect_value!(Option<T: Serialize + Clone + for<'de> Deserialize<'de> + Reflect + 'static>(Serialize, Deserialize));

Since it is an enum, we currently have to reflect "as a value", and implement Serialize and Deserialize.
Instead of implementing Serialize and Deserialize on Size<Val>, I think the easiest fix is to also reflect your component as a value:

#[derive(Component, Reflect, Serialize, Deserialize)]
#[reflect_value(Component, Serialize, Deserialize)]
struct MyComponent {
    sz: Option<Size<Val>>,
}

Eventually #1347 will fix this issue.

[alice-i-cecile]

#4761 is the follow-up PR that will fix this.

[TheNeikos]

I think this has been solved?

https://learnbevy.com/playground?share=50a7cd2beb4a72e3c506197684999f785d6bccdd361c2f8f33d3f1bbcc294bed