README.md
1autocfg
2=======
3
4[![autocfg crate](https://img.shields.io/crates/v/autocfg.svg)](https://crates.io/crates/autocfg)
5[![autocfg documentation](https://docs.rs/autocfg/badge.svg)](https://docs.rs/autocfg)
6![minimum rustc 1.0](https://img.shields.io/badge/rustc-1.0+-red.svg)
7[![Travis Status](https://travis-ci.org/cuviper/autocfg.svg?branch=master)](https://travis-ci.org/cuviper/autocfg)
8
9A Rust library for build scripts to automatically configure code based on
10compiler support. Code snippets are dynamically tested to see if the `rustc`
11will accept them, rather than hard-coding specific version support.
12
13
14## Usage
15
16Add this to your `Cargo.toml`:
17
18```toml
19[build-dependencies]
20autocfg = "0.1"
21```
22
23Then use it in your `build.rs` script to detect compiler features. For
24example, to test for 128-bit integer support, it might look like:
25
26```rust
27extern crate autocfg;
28
29fn main() {
30 let ac = autocfg::new();
31 ac.emit_has_type("i128");
32
33 // (optional) We don't need to rerun for anything external.
34 autocfg::rerun_path(file!());
35}
36```
37
38If the type test succeeds, this will write a `cargo:rustc-cfg=has_i128` line
39for Cargo, which translates to Rust arguments `--cfg has_i128`. Then in the
40rest of your Rust code, you can add `#[cfg(has_i128)]` conditions on code that
41should only be used when the compiler supports it.
42
43
44## Release Notes
45
46- 0.1.4 (2019-05-22)
47 - Relax `std`/`no_std` probing to a warning instead of an error.
48 - Improve `rustc` bootstrap compatibility.
49
50- 0.1.3 (2019-05-21)
51 - Auto-detects if `#![no_std]` is needed for the `$TARGET`
52
53- 0.1.2 (2018-01-16)
54 - Add `rerun_env(ENV)` to print `cargo:rerun-if-env-changed=ENV`
55 - Add `rerun_path(PATH)` to print `cargo:rerun-if-changed=PATH`
56
57
58## Minimum Rust version policy
59
60This crate's minimum supported `rustc` version is `1.0.0`. Compatibility is
61its entire reason for existence, so this crate will be extremely conservative
62about raising this requirement. If this is ever deemed necessary, it will be
63treated as a major breaking change for semver purposes.
64
65
66## License
67
68This project is licensed under either of
69
70 * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
71 http://www.apache.org/licenses/LICENSE-2.0)
72 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
73 http://opensource.org/licenses/MIT)
74
75at your option.
76