Function long 

fn long(
    s: &Session,
    json: bool,
    job: Option<&str>,
    work: impl FnOnce(&mut dyn FnMut(&Progress), &Cancel) -> Result<Report, String>,
) -> Result<(), String>

A long command: its progress on standard error (one line per step or folder when piped), its report at the end; or, as a job (--job), its progress and its end written into the job’s file, stopping when asked.