Compiler version cfg
====================
[](https://travis-ci.com/dtolnay/rustversion)
[](https://crates.io/crates/rustversion)
[](https://docs.rs/rustversion)
This crate provides macros for conditional compilation according to rustc
compiler version, analogous to [`#[cfg(...)]`][cfg] and
[`#[cfg_attr(...)]`][cfg_attr].
[cfg]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute
[cfg_attr]: https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute
```toml
[dependencies]
rustversion = "0.1"
```
<br>
## Selectors
- <b>`#[rustversion::stable]`</b>
—<br>
True on any stable compiler.
- <b>`#[rustversion::stable(1.34)]`</b>
—<br>
True on exactly the specified stable compiler.
- <b>`#[rustversion::beta]`</b>
—<br>
True on any beta compiler.
- <b>`#[rustversion::nightly]`</b>
—<br>
True on any nightly compiler or dev build.
- <b>`#[rustversion::nightly(2019-01-01)]`</b>
—<br>
True on exactly one nightly.
- <b>`#[rustversion::since(1.34)]`</b>
—<br>
True on that stable release and any later compiler, including beta and
nightly.
- <b>`#[rustversion::since(2019-01-01)]`</b>
—<br>
True on that nightly and all newer ones.
- <b>`#[rustversion::before(`</b><i>version or date</i><b>`)]`</b>
—<br>
Negative of *#[rustversion::since(...)]*.
- <b>`#[rustversion::not(`</b><i>selector</i><b>`)]`</b>
—<br>
Negative of any selector; for example *#[rustversion::not(nightly)]*.
- <b>`#[rustversion::any(`</b><i>selectors...</i><b>`)]`</b>
—<br>
True if any of the comma-separated selectors is true; for example
*#[rustversion::any(stable, beta)]*.
- <b>`#[rustversion::all(`</b><i>selectors...</i><b>`)]`</b>
—<br>
True if all of the comma-separated selectors are true; for example
*#[rustversion::all(since(1.31), before(1.34))]*.
- <b>`#[rustversion::attr(`</b><i>selector</i><b>`, `</b><i>attribute</i><b>`)]`</b>
—<br>
For conditional inclusion of attributes; analogous to `cfg_attr`.
<br>
## Use cases
Providing additional trait impls as types are stabilized in the standard library
without breaking compatibility with older compilers; in this case Pin\<P\>
stabilized in [Rust 1.33][pin]:
[pin]: https://blog.rust-lang.org/2019/02/28/Rust-1.33.0.html#pinning
```rust
#[rustversion::since(1.33)]
use std::pin::Pin;
#[rustversion::since(1.33)]
impl<P: MyTrait> MyTrait for Pin<P> {
/* ... */
}
```
Similar but for language features; the ability to control alignment greater than
1 of packed structs was stabilized in [Rust 1.33][packed].
[packed]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1330-2019-02-28
```rust
#[rustversion::attr(before(1.33), repr(packed))]
#[rustversion::attr(since(1.33), repr(packed(2)))]
struct Six(i16, i32);
fn main() {
println!("{}", std::mem::align_of::<Six>());
}
```
Augmenting code with `const` as const impls are stabilized in the standard
library. This use of `const` as an attribute is recognized as a special case by
the rustversion::attr macro.
```rust
use std::time::Duration;
#[rustversion::attr(since(1.32), const)]
fn duration_as_days(dur: Duration) -> u64 {
dur.as_secs() / 60 / 60 / 24
}
```
<br>
#### License
<sup>
Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
</sup>
<br>
<sub>
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.
</sub>