Function file_stem 

pub fn file_stem(path: &str, fmt: PathFormat) -> &str

Get the file stem (file_name without the last extension).

Matches Python pathlib’s rule: a suffix exists only when the rightmost . is neither at the start of the name (which marks a hidden-file name like .hidden) nor at the end (which is a trailing dot that does not delimit a real extension — foo. has stem foo. and no suffix).