Function foreign_paths 

pub fn foreign_paths(
    manifest: &BundleManifest,
    out_dir: &Path,
) -> Vec<ForeignPath>

The entries of manifest whose path under out_dir holds something that a pull of the same entry may replace without the user’s say: a file, directory or link that no record in the skip-cache in out_dir vouches for. A record vouches for a path when the file there still has the recorded size and mtime, and the record names this entry (this manifest hash and manifest path) or holds this entry’s bytes. A caller that did not choose out_dir can refuse the pull first.

An entry whose path escapes out_dir, or that lands on the pull’s own state, is not named: the pull fails that entry and writes nothing there.