Function walked 

pub fn walked(
    repo: &Path,
    known_as: Remembered<'_>,
    probing: &Probing<'_>,
    shown: &[String],
    commits: &[String],
    known: &HashMap<&str, Snapshot>,
) -> Result<Walk, Box<dyn Error>>

Works out a line: what was probed, what each step did, and what was said.

shown is what a range named; commits is that plus the one underneath, which is probed and never drawn as a stop of its own.