vendor/autocfg-0.1.7/README.md

   1 autocfg
   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
   9 A Rust library for build scripts to automatically configure code based on
  10 compiler support.  Code snippets are dynamically tested to see if the `rustc`
  11 will accept them, rather than hard-coding specific version support.
  12
  13
  14 ## Usage
  15
  16 Add this to your `Cargo.toml`:
  17
  18 ```toml
  19 [build-dependencies]
  20 autocfg = "0.1"
  21 ```
  22
  23 Then use it in your `build.rs` script to detect compiler features.  For
  24 example, to test for 128-bit integer support, it might look like:
  25
  26 ```rust
  27 extern crate autocfg;
  28
  29 fn 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
  38 If the type test succeeds, this will write a `cargo:rustc-cfg=has_i128` line
  39 for Cargo, which translates to Rust arguments `--cfg has_i128`.  Then in the
  40 rest of your Rust code, you can add `#[cfg(has_i128)]` conditions on code that
  41 should only be used when the compiler supports it.
  42
  43
  44 ## Release Notes
  45
  46 - 0.1.7 (2019-10-20)
  47   - Apply `RUSTFLAGS` when probing `$TARGET != $HOST`, mainly for sysroot, by @roblabla.
  48
  49 - 0.1.6 (2019-08-19)
  50   - Add `probe`/`emit_sysroot_crate`, by @leo60228.
  51
  52 - 0.1.5 (2019-07-16)
  53   - Mask some warnings from newer rustc.
  54
  55 - 0.1.4 (2019-05-22)
  56   - Relax `std`/`no_std` probing to a warning instead of an error.
  57   - Improve `rustc` bootstrap compatibility.
  58
  59 - 0.1.3 (2019-05-21)
  60   - Auto-detects if `#![no_std]` is needed for the `$TARGET`.
  61
  62 - 0.1.2 (2019-01-16)
  63   - Add `rerun_env(ENV)` to print `cargo:rerun-if-env-changed=ENV`.
  64   - Add `rerun_path(PATH)` to print `cargo:rerun-if-changed=PATH`.
  65
  66
  67 ## Minimum Rust version policy
  68
  69 This crate's minimum supported `rustc` version is `1.0.0`.  Compatibility is
  70 its entire reason for existence, so this crate will be extremely conservative
  71 about raising this requirement.  If this is ever deemed necessary, it will be
  72 treated as a major breaking change for semver purposes.
  73
  74
  75 ## License
  76
  77 This project is licensed under either of
  78
  79  * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
  80    http://www.apache.org/licenses/LICENSE-2.0)
  81  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
  82    http://opensource.org/licenses/MIT)
  83
  84 at your option.