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 = "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("build.rs"); 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- 1.0.0 (2020-01-08) 47 - Release 1.0! (no breaking changes) 48 - Add `probe_expression` and `emit_expression_cfg` to test arbitrary expressions. 49 - Add `probe_constant` and `emit_constant_cfg` to test arbitrary constant expressions. 50 51- 0.1.7 (2019-10-20) 52 - Apply `RUSTFLAGS` when probing `$TARGET != $HOST`, mainly for sysroot, by @roblabla. 53 54- 0.1.6 (2019-08-19) 55 - Add `probe`/`emit_sysroot_crate`, by @leo60228. 56 57- 0.1.5 (2019-07-16) 58 - Mask some warnings from newer rustc. 59 60- 0.1.4 (2019-05-22) 61 - Relax `std`/`no_std` probing to a warning instead of an error. 62 - Improve `rustc` bootstrap compatibility. 63 64- 0.1.3 (2019-05-21) 65 - Auto-detects if `#![no_std]` is needed for the `$TARGET`. 66 67- 0.1.2 (2019-01-16) 68 - Add `rerun_env(ENV)` to print `cargo:rerun-if-env-changed=ENV`. 69 - Add `rerun_path(PATH)` to print `cargo:rerun-if-changed=PATH`. 70 71 72## Minimum Rust version policy 73 74This crate's minimum supported `rustc` version is `1.0.0`. Compatibility is 75its entire reason for existence, so this crate will be extremely conservative 76about raising this requirement. If this is ever deemed necessary, it will be 77treated as a major breaking change for semver purposes. 78 79 80## License 81 82This project is licensed under either of 83 84 * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or 85 http://www.apache.org/licenses/LICENSE-2.0) 86 * MIT license ([LICENSE-MIT](LICENSE-MIT) or 87 http://opensource.org/licenses/MIT) 88 89at your option. 90