140 lines
4.2 KiB
Markdown
140 lines
4.2 KiB
Markdown
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Compiler version cfg
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====================
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[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/rustversion-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/rustversion)
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[<img alt="crates.io" src="https://img.shields.io/crates/v/rustversion.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/rustversion)
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[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-rustversion-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/rustversion)
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[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/rustversion/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/rustversion/actions?query=branch%3Amaster)
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This crate provides macros for conditional compilation according to rustc
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compiler version, analogous to [`#[cfg(...)]`][cfg] and
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[`#[cfg_attr(...)]`][cfg_attr].
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[cfg]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute
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[cfg_attr]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute
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```toml
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[dependencies]
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rustversion = "1.0"
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```
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<br>
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## Selectors
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- <b>`#[rustversion::stable]`</b>
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—<br>
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True on any stable compiler.
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- <b>`#[rustversion::stable(1.34)]`</b>
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—<br>
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True on exactly the specified stable compiler.
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- <b>`#[rustversion::beta]`</b>
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—<br>
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True on any beta compiler.
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- <b>`#[rustversion::nightly]`</b>
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—<br>
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True on any nightly compiler or dev build.
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- <b>`#[rustversion::nightly(2019-01-01)]`</b>
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—<br>
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True on exactly one nightly.
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- <b>`#[rustversion::since(1.34)]`</b>
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—<br>
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True on that stable release and any later compiler, including beta and
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nightly.
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- <b>`#[rustversion::since(2019-01-01)]`</b>
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—<br>
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True on that nightly and all newer ones.
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- <b>`#[rustversion::before(`</b><i>version or date</i><b>`)]`</b>
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—<br>
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Negative of *#[rustversion::since(...)]*.
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- <b>`#[rustversion::not(`</b><i>selector</i><b>`)]`</b>
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—<br>
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Negative of any selector; for example *#[rustversion::not(nightly)]*.
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- <b>`#[rustversion::any(`</b><i>selectors...</i><b>`)]`</b>
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—<br>
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True if any of the comma-separated selectors is true; for example
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*#[rustversion::any(stable, beta)]*.
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- <b>`#[rustversion::all(`</b><i>selectors...</i><b>`)]`</b>
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—<br>
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True if all of the comma-separated selectors are true; for example
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*#[rustversion::all(since(1.31), before(1.34))]*.
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- <b>`#[rustversion::attr(`</b><i>selector</i><b>`, `</b><i>attribute</i><b>`)]`</b>
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—<br>
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For conditional inclusion of attributes; analogous to `cfg_attr`.
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<br>
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## Use cases
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Providing additional trait impls as types are stabilized in the standard library
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without breaking compatibility with older compilers; in this case Pin\<P\>
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stabilized in [Rust 1.33][pin]:
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[pin]: https://blog.rust-lang.org/2019/02/28/Rust-1.33.0.html#pinning
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```rust
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#[rustversion::since(1.33)]
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use std::pin::Pin;
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#[rustversion::since(1.33)]
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impl<P: MyTrait> MyTrait for Pin<P> {
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/* ... */
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}
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```
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Similar but for language features; the ability to control alignment greater than
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1 of packed structs was stabilized in [Rust 1.33][packed].
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[packed]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1330-2019-02-28
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```rust
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#[rustversion::attr(before(1.33), repr(packed))]
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#[rustversion::attr(since(1.33), repr(packed(2)))]
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struct Six(i16, i32);
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fn main() {
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println!("{}", std::mem::align_of::<Six>());
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}
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```
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Augmenting code with `const` as const impls are stabilized in the standard
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library. This use of `const` as an attribute is recognized as a special case by
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the rustversion::attr macro.
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```rust
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use std::time::Duration;
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#[rustversion::attr(since(1.32), const)]
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fn duration_as_days(dur: Duration) -> u64 {
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dur.as_secs() / 60 / 60 / 24
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}
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```
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<br>
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#### License
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<sup>
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Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
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2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
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</sup>
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<br>
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<sub>
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
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be dual licensed as above, without any additional terms or conditions.
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</sub>
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