0403948aa2
# Background In `no_std` compatible crates, there is often an `std` feature which will allow access to the standard library. Currently, with the `std` feature _enabled_, the [`std::prelude`](https://doc.rust-lang.org/std/prelude/index.html) is implicitly imported in all modules. With the feature _disabled_, instead the [`core::prelude`](https://doc.rust-lang.org/core/prelude/index.html) is implicitly imported. This creates a subtle and pervasive issue where `alloc` items _may_ be implicitly included (if `std` is enabled), or must be explicitly included (if `std` is not enabled). # Objective - Make the implicit imports for `no_std` crates consistent regardless of what features are/not enabled. ## Solution - Replace the `cfg_attr` "double negative" `no_std` attribute with conditional compilation to _include_ `std` as an external crate. ```rust // Before #![cfg_attr(not(feature = "std"), no_std)] // After #![no_std] #[cfg(feature = "std")] extern crate std; ``` - Fix imports that are currently broken but are only now visible with the above fix. ## Testing - CI ## Notes I had previously used the "double negative" version of `no_std` based on general consensus that it was "cleaner" within the Rust embedded community. However, this implicit prelude issue likely was considered when forming this consensus. I believe the reason why is the items most affected by this issue are provided by the `alloc` crate, which is rarely used within embedded but extensively used within Bevy.
61 lines
1.5 KiB
Rust
61 lines
1.5 KiB
Rust
#![doc = include_str!("../README.md")]
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#![cfg_attr(docsrs, feature(doc_auto_cfg))]
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#![doc(
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html_logo_url = "https://bevyengine.org/assets/icon.png",
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html_favicon_url = "https://bevyengine.org/assets/icon.png"
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)]
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#![no_std]
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#[cfg(feature = "std")]
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extern crate std;
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#[cfg(feature = "alloc")]
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extern crate alloc;
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#[cfg(feature = "bevy-support")]
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pub mod commands;
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/// The basic components of the transform crate
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pub mod components;
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/// Transform related bundles
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#[cfg(feature = "bevy-support")]
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pub mod bundles;
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/// Transform related traits
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pub mod traits;
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/// Transform related plugins
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#[cfg(feature = "bevy-support")]
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pub mod plugins;
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/// [`GlobalTransform`]: components::GlobalTransform
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/// Helpers related to computing global transforms
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#[cfg(feature = "bevy-support")]
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pub mod helper;
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/// Systems responsible for transform propagation
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#[cfg(feature = "bevy-support")]
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pub mod systems;
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/// The transform prelude.
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///
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/// This includes the most common types in this crate, re-exported for your convenience.
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#[doc(hidden)]
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#[expect(deprecated)]
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pub mod prelude {
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#[doc(hidden)]
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pub use crate::components::*;
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#[cfg(feature = "bevy-support")]
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#[doc(hidden)]
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pub use crate::{
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bundles::TransformBundle,
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commands::BuildChildrenTransformExt,
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helper::TransformHelper,
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plugins::{TransformPlugin, TransformSystem},
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traits::TransformPoint,
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};
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}
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#[cfg(feature = "bevy-support")]
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pub use prelude::{TransformPlugin, TransformPoint, TransformSystem};
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