Function start 

pub fn start(label: &'static str, total: Option<usize>, enabled: bool) -> Guard

Install a thread-local progress reporter for the duration of the returned Guard. enabled = false installs no reporter, so report stays a cheap no-op — used when stderr isn’t interactive or --quiet was passed (see should_report).

total, when known ahead of time (the push side plans its pack before building it), renders as done/total; None (the fetch/pull side, where the object count isn’t known until each pack is downloaded) renders as a running count only — never a fabricated total.