Function build 

pub fn build(
    export: &str,
    target: &str,
    options: &BuildOptions,
) -> Result<Build, Verdict>

Build a package and its producing receipt. Refuses only when no package can be formed at all (an export the importer does not accept, a target it does not declare); a package whose checks fail is returned with the failure on its receipt, so a refusal can be inspected and replayed.