derive `FromTemplate` is preventing `TilemapChunkTileData` to be used in `template_value`

[hxYuki]

Bevy version and features

• main@3c37a4d9035a

What you did

use template_value(TilemapChunkTileData(...)) in bsn!.

What went wrong

This type does not manually implement `FromTemplate`, ...

...

the trait bound `TilemapChunkTileData std::marker::Unpin` is not satisfied ...

Additional information

Not sure if there is something wrong with the marco itself, or just simply to be a misuse for FromTemplate.

For convenience, the following demonstration uses a similar type S.

#[derive(Component, Clone, Debug, Deref, DerefMut, Reflect, FromTemplate)]
#[reflect(Component, Clone, Debug)]
pub struct S(Vec<Option<TileData>>);

If replace FromTemplate to Default, it works:

[jiher974brand-web]

#[derive(Component, Clone, Debug, Deref, DerefMut, Reflect, Default)]
#[reflect(Component, Clone, Debug)]
pub struct S(Vec<Option>);

[jiher974brand-web]

¿Por qué funciona?

Porque:

Default

sí puede derivarse automáticamente para:

Vec<Option>

mientras que:

FromTemplate

requiere restricciones adicionales (Template, Unpin, etc.) que tu tipo no cumple.

[hxYuki]

It was the #[derive(FromTemplate)] that makes S to become !Unpin. While template_value actually accepts the generated STemplate. But if you use STemplate, you cannot reuse functions constructing S.

That's what happens on TilemapChunkTileData. I speculate that it should actually derive Default rather than FromTemplate.

[laundmo]

If you read the full error carefully, it states that the reason is a field not implementing FromTemplate.
The solution is either a custom implementation, ir ensuring all fields implement FromTemplate.

[hxYuki]

The easiest solution seems to be replacing FromTemplate to Default.

Since it doesn't refers to a world context when constructing a TilemapChunkTileData, Default + Clone should be enough. And TileData has derived Default + Clone already, cannot implement FromTemplate easily.