40 lines
1.6 KiB
Rust
40 lines
1.6 KiB
Rust
//! A workaround for the `!` type in stable Rust.
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//!
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//! This approach is taken from the [`never_say_never`] crate,
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//! reimplemented here to avoid adding a new dependency.
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//!
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//! This module exists due to a change in [never type fallback inference] in the Rust 2024 edition.
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//! This caused failures in `bevy_ecs`'s traits which are implemented for functions
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//! (like [`System`](crate::system::System)) when working with panicking closures.
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//!
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//! Note that using this hack is not recommended in general;
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//! by doing so you are knowingly opting out of rustc's stability guarantees.
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//! Code that compiles due to this hack may break in future versions of Rust.
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//!
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//! Please read [issue #18778](https://github.com/bevyengine/bevy/issues/18778) for an explanation of why
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//! Bevy has chosen to use this workaround.
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//!
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//! [`never_say_never`]: https://crates.io/crates/never_say_never
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//! [never type fallback inference]: https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html
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mod fn_ret {
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/// A helper trait for naming the ! type.
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#[doc(hidden)]
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pub trait FnRet {
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/// The return type of the function.
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type Output;
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}
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/// This blanket implementation allows us to name the never type,
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/// by using the associated type of this trait for `fn() -> !`.
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impl<R> FnRet for fn() -> R {
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type Output = R;
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}
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}
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/// A hacky type alias for the `!` (never) type.
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///
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/// This knowingly opts out of rustc's stability guarantees.
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/// Read the module documentation carefully before using this!
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pub type Never = <fn() -> ! as fn_ret::FnRet>::Output;
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