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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![build status](https://github.com/cuviper/autocfg/workflows/master/badge.svg)
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- 1.4.0 (2024-09-26)
47
48  - Add `emit_possibility` for Rust 1.80's [checked cfgs], and call that
49    automatically for methods that conditionally `emit`, by @Techcable.
50
51[checked cfgs]: https://blog.rust-lang.org/2024/05/06/check-cfg.html
52
53- 1.3.0 (2024-05-03)
54
55  - Add `probe_raw` for direct control of the code that will be test-compiled.
56  - Use wrappers when querying the `rustc` version information too.
57
58- 1.2.0 (2024-03-25)
59
60  - Add `no_std` and `set_no_std` to control the use of `#![no_std]` in probes.
61  - Use `RUSTC_WRAPPER` and `RUSTC_WORKSPACE_WRAPPER` when they are set.
62
63- 1.1.0 (2022-02-07)
64  - Use `CARGO_ENCODED_RUSTFLAGS` when it is set.
65
66- 1.0.1 (2020-08-20)
67  - Apply `RUSTFLAGS` for more `--target` scenarios, by @adamreichold.
68
69- 1.0.0 (2020-01-08)
70  - �� Release 1.0! �� (no breaking changes)
71  - Add `probe_expression` and `emit_expression_cfg` to test arbitrary expressions.
72  - Add `probe_constant` and `emit_constant_cfg` to test arbitrary constant expressions.
73
74- 0.1.7 (2019-10-20)
75  - Apply `RUSTFLAGS` when probing `$TARGET != $HOST`, mainly for sysroot, by @roblabla.
76
77- 0.1.6 (2019-08-19)
78  - Add `probe`/`emit_sysroot_crate`, by @leo60228.
79
80- 0.1.5 (2019-07-16)
81  - Mask some warnings from newer rustc.
82
83- 0.1.4 (2019-05-22)
84  - Relax `std`/`no_std` probing to a warning instead of an error.
85  - Improve `rustc` bootstrap compatibility.
86
87- 0.1.3 (2019-05-21)
88  - Auto-detects if `#![no_std]` is needed for the `$TARGET`.
89
90- 0.1.2 (2019-01-16)
91  - Add `rerun_env(ENV)` to print `cargo:rerun-if-env-changed=ENV`.
92  - Add `rerun_path(PATH)` to print `cargo:rerun-if-changed=PATH`.
93
94
95## Minimum Rust version policy
96
97This crate's minimum supported `rustc` version is `1.0.0`.  Compatibility is
98its entire reason for existence, so this crate will be extremely conservative
99about raising this requirement.  If this is ever deemed necessary, it will be
100treated as a major breaking change for semver purposes.
101
102
103## License
104
105This project is licensed under either of
106
107 * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
108   https://www.apache.org/licenses/LICENSE-2.0)
109 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
110   https://opensource.org/licenses/MIT)
111
112at your option.
113