Function adds_no_conflicts 

fn adds_no_conflicts(
    units: &[Unit],
    extents: &[Extent],
    index: &ExtentIndex<'_>,
    outputs: usize,
) -> bool

Whether merging units into outputs files adds no more conflicts than their files have with other files. Outputs stay inside the bounding box of the inputs, so each of them may conflict with every file intruding on that box. An interval without intruders is closed and adds no conflicts.