bevy_ecs: Allow using i32 for entity ID cursor on platforms without AtomicI64 support #4451
Description
What problem does this solve or what need does it fill?
I have been trying to get bits and pieces of Bevy building for an unusual target platform (armv6k-nintendo-3ds), and to my surprise bevy_ecs almost compiles already!
The only issue I ran into was in https://github.com/bevyengine/bevy/blob/main/crates/bevy_ecs/src/entity/mod.rs#L35 – since the platform does not have atomic load/stores for i64, there is no AtomicI64 available for import. I imagine that some other 32-bit platforms may also run into this problem, but have probably not been the focus of the project thus far.
What solution would you like?
With Rust 1.60.0 the #[cfg(target_has_atomic = "64")] flag has just been stabilized: rust-lang/rust#93824. I propose using this to conditionally compile using AtomicI32 on platforms that do not support 64-bit atomics.
I'm not sure if there might be any further-reaching consequences of such a change, but this platform is already not supported, so it seems like adding support in this way would still be "experimental" or possibly unstable, but still an improvement on the status quo. Existing platforms' implementation would not be impacted.
What alternative(s) have you considered?
No action; effectively require using a fork for platforms without atomic i64 support.
Additional context
I already have a local change with which I have successfully built for armv6k-nintendo-3ds – I'm happy to open a PR if this proposed solution is accepted.