 update the children that do have coverage data.
                    for (const coverage_node of coverage_nodes) {
                        let index = coverage_node[0];
                        let coverage = coverage_node[1];
                        let node = parent.children.get(index);

                        let span_ids = new Set();
                        coverage_spans(file, coverage, span_ids);

                        // Update the node overlaps based on the coverage spans.
                        