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.
```rust use cfgexpr::{targets::getbuiltintargetby_triple, Expression, Predicate};
let specific = Expression::parse( r#"all( targetos = "windows", targetarch = "x86", windows, targetenv = "msvc", targetfeature = "fxsr", targetfeature = "sse", targetfeature = "sse2", targetpointerwidth = "32", targetendian = "little", not(targetvendor = "uwp"), feature = "cool_thing", )"#, ).unwrap();
// cfgexpr includes a list of every builtin target in rustc let x86win = getbuiltintargetbytriple("i686-pc-windows-msvc").unwrap(); let x86pentiumwin = getbuiltintargetbytriple("i586-pc-windows-msvc").unwrap(); let uwpwin = getbuiltintargetbytriple("i686-uwp-windows-msvc").unwrap(); let mac = getbuiltintargetbytriple("x8664-apple-darwin").unwrap();
let availtargetfeats = ["fxsr", "sse", "sse2"];
// This will satisfy all requirements assert!(specific.eval(|pred| { match pred { Predicate::Target(tp) => tp.matches(x86win), Predicate::TargetFeature(feat) => availtargetfeats.contains(feat), Predicate::Feature(feat) => *feat == "coolthing", _ => false, } }));
// This won't, it doesn't have the coolthing feature! assert!(!specific.eval(|pred| { match pred { Predicate::Target(tp) => tp.matches(x86pentiumwin), Predicate::TargetFeature(feat) => availtarget_feats.contains(feat), _ => false, } }));
// This will not satisfy the vendor predicate assert!(!specific.eval(|pred| { match pred { Predicate::Target(tp) => tp.matches(uwpwin), Predicate::TargetFeature(feat) => availtarget_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) => availtargetfeats.contains(feat), _ => false, } })); ```
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