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# 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. |
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| .. | ||
| components | ||
| child_builder.rs | ||
| events.rs | ||
| hierarchy.rs | ||
| lib.rs | ||
| query_extension.rs | ||
| valid_parent_check_plugin.rs | ||