autocfg
=======
[](https://crates.io/crates/autocfg)
[](https://docs.rs/autocfg)
A Rust library for build scripts to automatically configure code based on
compiler support. Code snippets are dynamically tested to see if the `rustc`
will accept them, rather than hard-coding specific version support.
## Usage
Add this to your `Cargo.toml`:
```toml
[build-dependencies]
autocfg = "1"
```
Then use it in your `build.rs` script to detect compiler features. For
example, to test for 128-bit integer support, it might look like:
```rust
extern crate autocfg;
fn main() {
let ac = autocfg::new();
ac.emit_has_type("i128");
// (optional) We don't need to rerun for anything external.
autocfg::rerun_path("build.rs");
}
```
If the type test succeeds, this will write a `cargo:rustc-cfg=has_i128` line
for Cargo, which translates to Rust arguments `--cfg has_i128`. Then in the
rest of your Rust code, you can add `#[cfg(has_i128)]` conditions on code that
should only be used when the compiler supports it.
## Release Notes
- 1.1.0 (2022-02-07)
- Use `CARGO_ENCODED_RUSTFLAGS` when it is set.
- 1.0.1 (2020-08-20)
- Apply `RUSTFLAGS` for more `--target` scenarios, by @adamreichold.
- 1.0.0 (2020-01-08)
- �� Release 1.0! �� (no breaking changes)
- Add `probe_expression` and `emit_expression_cfg` to test arbitrary expressions.
- Add `probe_constant` and `emit_constant_cfg` to test arbitrary constant expressions.
- 0.1.7 (2019-10-20)
- Apply `RUSTFLAGS` when probing `$TARGET != $HOST`, mainly for sysroot, by @roblabla.
- 0.1.6 (2019-08-19)
- Add `probe`/`emit_sysroot_crate`, by @leo60228.
- 0.1.5 (2019-07-16)
- Mask some warnings from newer rustc.
- 0.1.4 (2019-05-22)
- Relax `std`/`no_std` probing to a warning instead of an error.
- Improve `rustc` bootstrap compatibility.
- 0.1.3 (2019-05-21)
- Auto-detects if `#![no_std]` is needed for the `$TARGET`.
- 0.1.2 (2019-01-16)
- Add `rerun_env(ENV)` to print `cargo:rerun-if-env-changed=ENV`.
- Add `rerun_path(PATH)` to print `cargo:rerun-if-changed=PATH`.
## Minimum Rust version policy
This crate's minimum supported `rustc` version is `1.0.0`. Compatibility is
its entire reason for existence, so this crate will be extremely conservative
about raising this requirement. If this is ever deemed necessary, it will be
treated as a major breaking change for semver purposes.
## License
This project is licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or
http://opensource.org/licenses/MIT)
at your option.
