⚙️ cfg-expr

A parser and evaluator for Rust cfg() expressions. Targets as of Rust 1.58.0 are supported.

Alternatives

• cargo-platform
• parse_cfg

Usage

cfg-expr is a crate that can be used to parse and evaluate Rust cfg() expressions, both as declarable in Rust code itself, as well in cargo manifests' [target.'cfg()'.dependencies] sections.

It contains a list of all builtin targets known to rustc as of 1.58.0 that can be used to determine if a particular cfg expression is satisfiable.

use cfg_expr::{targets::get_builtin_target_by_triple, Expression, Predicate};

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
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_target_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_target_feats.contains(feat),
        Predicate::Feature(feat) => *feat == "cool_thing",
        _ => false,
    }
}));

// This won't, it doesn't have the cool_thing feature!
assert!(!specific.eval(|pred| {
    match pred {
        Predicate::Target(tp) => tp.matches(x86_pentium_win),
        Predicate::TargetFeature(feat) => avail_target_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_target_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_target_feats.contains(feat),
        _ => false,
    }
}));

Contributing

We welcome community contributions to this project.

Please read our Contributor Guide for more information on how to get started.

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

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.