Function compile 

pub fn compile(
    builtins: Vec<BuiltinPolicy>,
    startup: &HashMap<String, ParsedPolicy>,
    declared: &HashMap<String, ParsedPolicy>,
    across: &AcrossBuilds,
) -> (PolicyTree, LoadReport)

Compiles declared beside the two sources that are not the operator’s, whole.

across must be the one a deployment holds for the length of its run: it is what lets a policy whose new revision will not compile keep enforcing the revision that did. See AcrossBuilds.