Function walk_module_tree 

pub fn walk_module_tree<F>(
    namespace: Arc<Path>,
    root: Arc<Path>,
    current_dir: PathBuf,
    submodules: Vec<SubmoduleDecl>,
    source_manager: Arc<dyn SourceManager>,
    warnings_as_errors: bool,
    callback: F,
) -> Result<(), Report>
where
    F: FnMut(Box<Module>) -> Result<(), Report>,