Function collect_files_in_dir 

fn collect_files_in_dir(path: impl AsRef<Path>) -> Result<Vec<PathBuf>, Error>

Collects all regular files in a directory in the order of an OpenPGP Transferable Public Key.

All top-level regular files in the directory are considered. Regular files located in the following list of directories (if they exist) are considered, in the following order:

• revocation: for Revocation Signature packets
• directkey: for Direct Key Signature packets
• uid: for User ID or User Attribute packets
• subkey: for Subkey packets

Errors

Returns an error if

• entries in path cannot be retrieved,
• reading an entry in path fails,
• or collecting files in any of the subdirectories (revocation, directkey, uid or subkey) fails.