Macro shadow_rs::shadow

macro_rules! shadow {
    ($build_mod : ident) => { ... };
}

Add a mod in project with $build_mod.

You can use shadow!(build_shadow). Then shadow-rs can help you add a mod with name build_shadow. Next, use mod with name build_shadow,and also use const like:build_shadow::BRANCH.

Normally, you just config shadow!(build).It looks more concise.