Function published_tips 

pub fn published_tips(
    updates: &[PushUpdate],
    prior_commits: &BTreeMap<String, String>,
    tracking: &BTreeMap<String, Vec<String>>,
) -> BTreeMap<String, Vec<String>>

What: The published tips of each remote: its tracking commits and the commits of its prior destination values. Why: Every update to one remote contributes its prior value, so a second branch is bounded by the first’s prior state.

In TS you’d write (pseudocode):

function publishedTips({ updates, peeled, tracking }): ReadonlyMap<string, readonly GitObjectId[]>;