Function squashSegmentGroup

packages/router/src/url_tree.ts:851–872

(segmentGroup: UrlSegmentGroup)

 * root but the `a` route lives under an empty path primary route.
 */
export function squashSegmentGroup(segmentGroup: UrlSegmentGroup): UrlSegmentGroup {
  // Keyed by outlet name, which can be `__proto__`, so use a null-prototype map (see `parseParens`).
  const newChildren: Record<string, UrlSegmentGroup> = Object.create(null);
  for (const [childOutlet, child] of Object.entries(segmentGroup.children)) {
    const childCandidate = squashSegmentGroup(child);
    // moves named children in an empty path primary child into this group
    if (
      childOutlet === PRIMARY_OUTLET &&
      childCandidate.segments.length === 0 &&
      childCandidate.hasChildren()
    ) {
      for (const [grandChildOutlet, grandChild] of Object.entries(childCandidate.children)) {
        newChildren[grandChildOutlet] = grandChild;
      }
    } // don't add empty children
    else if (childCandidate.segments.length > 0 || childCandidate.hasChildren()) {
      newChildren[childOutlet] = childCandidate;
    }
  }
  const s = new UrlSegmentGroup(segmentGroup.segments, newChildren);
  return mergeTrivialChildren(s);
}

/**
 * When possible, merges the primary outlet child into the parent `UrlSegmentGroup`.