Remove Implicit std Prelude from no_std Crates
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BenjaminBrienen
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Patch relied on `ToString` which was not already imported anymore. Using `ToOwned` (which is imported) is equivalent. Expectation on `unsafe_code` fails now, so I've moved it closer to the unsafe-sites and now it seems fine?
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Ok @alice-i-cecile I'm ready for the next attempt at merging this thing! |
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Ok one last CI action is failing in the merge queue. Back to the IDE... |
The `run-examples-on-wasm` timeout appears unrelated to my PR, but this commit includes a fix for a warning noticed when running that action. Hoping it solves everything...somehow
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Marking as ready again. I believe I have resolved all CI issues, but the |
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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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Background
In
no_stdcompatible crates, there is often anstdfeature which will allow access to the standard library. Currently, with thestdfeature enabled, thestd::preludeis implicitly imported in all modules. With the feature disabled, instead thecore::preludeis implicitly imported. This creates a subtle and pervasive issue whereallocitems may be implicitly included (ifstdis enabled), or must be explicitly included (ifstdis not enabled).Objective
no_stdcrates consistent regardless of what features are/not enabled.Solution
cfg_attr"double negative"no_stdattribute with conditional compilation to includestdas an external crate.Testing
Notes
I had previously used the "double negative" version of
no_stdbased 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 thealloccrate, which is rarely used within embedded but extensively used within Bevy.