76e9bf9c99
# Objective - Contributes to #15460 - Reduce quantity and complexity of feature gates across Bevy ## Solution - Used `target_has_atomic` configuration variable to automatically detect impartial atomic support and automatically switch to `portable-atomic` over the standard library on an as-required basis. ## Testing - CI ## Notes To explain the technique employed here, consider getting `Arc` either from `alloc::sync` _or_ `portable-atomic-util`. First, we can inspect the `alloc` crate to see that you only have access to `Arc` _if_ `target_has_atomic = "ptr"`. We add a target dependency for this particular configuration _inverted_: ```toml [target.'cfg(not(target_has_atomic = "ptr"))'.dependencies] portable-atomic-util = { version = "0.2.4", default-features = false } ``` This ensures we only have the dependency when it is needed, and it is entirely excluded from the dependency graph when it is not. Next, we adjust our configuration flags to instead of checking for `feature = "portable-atomic"` to instead check for `target_has_atomic = "ptr"`: ```rust // `alloc` feature flag hidden for brevity #[cfg(not(target_has_atomic = "ptr"))] use portable_atomic_util as arc; #[cfg(target_has_atomic = "ptr")] use alloc::sync as arc; pub use arc::{Arc, Weak}; ``` The benefits of this technique are three-fold: 1. For platforms without full atomic support, the functionality is enabled automatically. 2. For platforms with atomic support, the dependency is never included, even if a feature was enabled using `--all-features` (for example) 3. The `portable-atomic` feature no longer needs to virally spread to all user-facing crates, it's instead something handled within `bevy_platform_support` (with some extras where other dependencies also need their features enabled). |
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Bevy Platform Support
Rust is a fantastic multi-platform language with extensive support for modern targets through its standard library.
However, some items within the standard library have alternatives that are better suited for Bevy and game engines in general.
Additionally, to support embedded and other esoteric platforms, it's often necessary to shed reliance on std, making your crate no_std.
These needs are handled by this crate, bevy_platform_support.
The goal of this crate is to provide alternatives and extensions to the Rust standard library which minimize friction when developing with and for Bevy across multiple platforms.
Getting Started
Like any dependency from crates.io, use cargo to add it to your Cargo.toml file:
cargo add bevy_platform_support
Now, instead of importing from std you can use bevy_platform_support for items it has alternative for.
See the documentation for what items are available, and explanations for why you may want to use them.
no_std Support
By default, bevy_platform_support will activate the std feature, requiring access to the std crate for whichever platforms you're targeting.
To use this crate on no_std platforms, disable default features:
bevy_platform_support = { version = "x.y.z", default-features = false }
Features
std (default)
Enables usage of the standard library. Note that where this crate has alternatives to the standard library that it considers better than what's provided, it will provide the alternative even when std is enabled.
This is explicitly incompatible with no_std targets.
alloc (default)
Enables usage of the alloc crate. Note that this feature is automatically enabled when enabling std.
This is compatible with most no_std targets, but not all.
portable-atomic
Switches to using portable-atomic as a backend for atomic types, such as Arc, AtomicU8, etc.
You may need to enable this feature on platforms without full support for atomic types or certain operations, such as atomic CAS.
critical-section
Switches to using critical-section as a backend for synchronization.
You may need to enable this feature on platforms with little to no support for atomic operations, and is often paired with the portable-atomic feature.