# `⚙️ cfg-expr`
**A parser and evaluator for Rust `cfg()` expressions. Targets as of [Rust 1.58.0](https://forge.rust-lang.org/release/platform-support.html) are supported.**
[](https://github.com/EmbarkStudios/cfg-expr/actions?workflow=CI)
[](https://crates.io/crates/cfg-expr)
[](https://docs.rs/cfg-expr)
[](https://blog.rust-lang.org/2021/05/06/Rust-1.52.0.html)
[](https://forge.rust-lang.org/release/platform-support.html)
[](CODE_OF_CONDUCT.md)
[](https://embark.dev)
## Alternatives
- [cargo-platform](https://crates.io/crates/cargo-platform)
- [parse_cfg](https://crates.io/crates/parse_cfg)
## Usage
```rust
use cfg_expr::{targets::get_builtin_target_by_triple, Expression, Predicate};
fn main() {
let specific = Expression::parse(
r#"all(
target_os = "windows",
target_arch = "x86",
windows,
target_env = "msvc",
target_feature = "fxsr",
target_feature = "sse",
target_feature = "sse2",
target_pointer_width = "32",
target_endian = "little",
not(target_vendor = "uwp"),
feature = "cool_thing",
)"#,
)
.unwrap();
// cfg_expr includes a list of every builtin target in rustc (as of 1.41)
let x86_win = get_builtin_target_by_triple("i686-pc-windows-msvc").unwrap();
let x86_pentium_win = get_builtin_target_by_triple("i586-pc-windows-msvc").unwrap();
let uwp_win = get_builtin_target_by_triple("i686-uwp-windows-msvc").unwrap();
let mac = get_builtin_target_by_triple("x86_64-apple-darwin").unwrap();
let avail_targ_feats = ["fxsr", "sse", "sse2"];
// This will satisfy all requirements
assert!(specific.eval(|pred| {
match pred {
Predicate::Target(tp) => tp.matches(x86_win),
Predicate::TargetFeature(feat) => avail_targ_feats.contains(feat),
Predicate::Feature(feat) => *feat == "cool_thing",
_ => false,
}
}));
// This won't, it doesnt' have the cool_thing feature!
assert!(!specific.eval(|pred| {
match pred {
Predicate::Target(tp) => tp.matches(x86_pentium_win),
Predicate::TargetFeature(feat) => avail_targ_feats.contains(feat),
_ => false,
}
}));
// This will *not* satisfy the vendor predicate
assert!(!specific.eval(|pred| {
match pred {
Predicate::Target(tp) => tp.matches(uwp_win),
Predicate::TargetFeature(feat) => avail_targ_feats.contains(feat),
_ => false,
}
}));
// This will *not* satisfy the vendor, os, or env predicates
assert!(!specific.eval(|pred| {
match pred {
Predicate::Target(tp) => tp.matches(mac),
Predicate::TargetFeature(feat) => avail_targ_feats.contains(feat),
_ => false,
}
}));
}
```
## Contributing
We welcome community contributions to this project.
Please read our [Contributor Guide](CONTRIBUTING.md) for more information on how to get started.
## License
Licensed under either of
- Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or )
- MIT license ([LICENSE-MIT](LICENSE-MIT) or )
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.