bevy_reflect: Feature-gate function reflection

[MrGVSV]

Objective

Function reflection requires a lot of macro code generation in the form of several all_tuples! invocations, as well as impls generated in the Reflect derive macro.

Seeing as function reflection is currently a bit more niche, it makes sense to gate it all behind a feature.

Solution

Add a functions feature to bevy_reflect, which can be enabled in Bevy using the reflect_functions feature.

Testing

You can test locally by running:

cargo test --package bevy_reflect

That should ensure that everything still works with the feature disabled.

To test with the feature on, you can run:

cargo test --package bevy_reflect --features functions

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Changelog

• Moved function reflection behind a Cargo feature (bevy/reflect_functions and bevy_reflect/functions)
• Add IntoFunction export in bevy_reflect::prelude

Internal Migration Guide

Important

Function reflection was introduced as part of the 0.15 dev cycle. This migration guide was written for developers relying on main during this cycle, and is not a breaking change coming from 0.14.

Function reflection is now gated behind a feature. To use function reflection, enable the feature:

• If using bevy_reflect directly, enable the functions feature
• If using bevy, enable the reflect_functions feature

[MrGVSV]

Thoughts on naming? I originally had function_reflection, but I switched it to reflect_functions since it sounds a bit more like the bevy_reflect/functions.

I'm also trying to think about potential future features. For example, we have a bevy_reflect/documentation feature. Using this naming strategy, it could be reflect_documentation. And so on.

[alice-i-cecile]

Yeah, I like this naming.

[MrGVSV]

While I was at it, I also included a prelude export for IntoFunction because I feel it would be useful to not have to import it every time. If we don't want to include it in the prelude, though, let me know and I can revert this!