Function relative_to_root 

fn relative_to_root(root: &Path, path: &Path) -> Option<String>

A path as the repository-relative, /-separated string a message should name.

crate::generated_doc::repo_root is …/crates/atune_dev/../.., so a child path carries the ../.. in the middle and cannot simply be string-stripped; it is canonicalised on both sides first.