Function broken_references 

pub fn broken_references(
    report: &ValidationReport,
) -> BTreeMap<&Utf8Path, Vec<String>>

Resolve every reference a report collected, keeping the ones that lead nowhere.

Keyed by the referring recipe, as ValidationReport::references is, and carrying the references in the order that recipe writes them — so a recipe making the same broken reference twice reports it twice. Recipes all of whose references resolve are left out entirely, so an empty map means every reference in the collection is good.

Every reference is resolved by [find::resolve_reference], the same way the shopping list follows one: from ValidationReport::base_dir, the root that was validated, except for a .., which steps up from the directory of the recipe making it. A reference is judged by whether the collection holds a recipe of that name, so one pointing outside the validated root is broken however readable the file it lands on happens to be.

“Broken” is the whole of “could not be resolved to a readable recipe”: a reference naming a file that exists but cannot be opened counts, exactly as one naming nothing at all does. Reporting them apart would need a reason on every entry, which nothing has yet asked for.

Nothing here fails, so there is no Result: this is the check, and what it finds is the answer. It does touch the filesystem, once per reference — which is why it is a function rather than a method on the report.