Put #[repr(transparent)] attr to bevy_ptr types

[fgrust]

Objective

Fix #9064

Solution

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Changelog

Enhanced: bevy_ptr types would be FFI-sefe

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[NiklasEi]

I am not familiar with repr(transparent), but according to https://doc.rust-lang.org/nomicon/other-reprs.html#reprtransparent it should only be used on structs with a single non-zero sized field. So if I understand correctly, this should not be added to Aligned and Unaligned.

I guess the ptr types below are fine because phantom data has no size? 🤔

[fgrust]

alright, As far as I took reading docs, it's unnecessary to put repr(transparent) into Aligned and Unaligned, which not used for FFI-boundary. Thanks for catching me up.

[fgrust]

@NiklasEi thought?

[NiklasEi]

Yes, I think that makes sense

[rlidwka]

So if I understand correctly, this should not be added to Aligned and Unaligned.

Yes, repr(transparent) makes no sense with ZST.

So this is wrong (not technically wrong, just useless):

#[repr(transparent)]
struct A;

I guess the ptr types below are fine because phantom data has no size?

It is okay to have any number of ZSTs in addition to real type, and this kind of code is all over physx-rs (for example, here).

So this is fine:

#[repr(transparent)]
struct B<T, U> {
    data: T,
    _phantom: PhantomData<U>,
}

[fgrust]

lint checks fail due to issue #9150