pub fn eval(&self, platform: &Platform) -> Option<bool> {
        self.inner.eval(|pred| {
            match pred {
                Predicate::Target(target) => Some(platform.triple().matches(target)),
                Predicate::TargetFeature(feature) => platform.target_features().matches(feature),
                Predicate::Test | Predicate::DebugAssertions | Predicate::ProcMacro => {
                    // Known families that always evaluate to false. See
                    // https://docs.rs/cargo-platform/0.1.1/src/cargo_platform/lib.rs.html#76.
                    Some(false)
                }
                Predicate::Feature(_) => {
                    // NOTE: This is not supported by Cargo which always evaluates this to false. See
                    // https://github.com/rust-lang/cargo/issues/7442 for more details.
                    Some(false)
                }
                Predicate::Flag(flag) => {
                    // This returns false by default but true in some cases.
                    Some(platform.has_flag(flag))
                }
                Predicate::KeyValue { .. } => {
                    // This is always interpreted by Cargo as false.
                    Some(false)
                }
            }
        })
    }
Evaluates this expression against the given platform.

Returns `Some(true)` if there's a match, `Some(false)` if there's none, or `None` if the
result of the evaluation is unknown (typically found if target features are involved).
target-spec/src/spec.rs