Function mergeEmptyPathMatches

packages/router/src/recognize.ts:552–584

* Finds `TreeNode`s with matching empty path route configs and merges them into `TreeNode` with * the children from each duplicate. This is necessary because different outlets can match a * single empty path route config and the results need to then be merged.

(
  nodes: Array<TreeNode<ActivatedRouteSnapshot>>,
)

 * single empty path route config and the results need to then be merged.
 */
function mergeEmptyPathMatches(
  nodes: Array<TreeNode<ActivatedRouteSnapshot>>,
): Array<TreeNode<ActivatedRouteSnapshot>> {
  const result: Array<TreeNode<ActivatedRouteSnapshot>> = [];
  // The set of nodes which contain children that were merged from two duplicate empty path nodes.
  const mergedNodes: Set<TreeNode<ActivatedRouteSnapshot>> = new Set();

  for (const node of nodes) {
    if (!hasEmptyPathConfig(node)) {
      result.push(node);
      continue;
    }

    const duplicateEmptyPathNode = result.find(
      (resultNode) => node.value.routeConfig === resultNode.value.routeConfig,
    );
    if (duplicateEmptyPathNode !== undefined) {
      duplicateEmptyPathNode.children.push(...node.children);
      mergedNodes.add(duplicateEmptyPathNode);
    } else {
      result.push(node);
    }
  }
  // For each node which has children from multiple sources, we need to recompute a new `TreeNode`
  // by also merging those children. This is necessary when there are multiple empty path configs
  // in a row. Put another way: whenever we combine children of two nodes, we need to also check
  // if any of those children can be combined into a single node as well.
  for (const mergedNode of mergedNodes) {
    const mergedChildren = mergeEmptyPathMatches(mergedNode.children);
    result.push(new TreeNode(mergedNode.value, mergedChildren));
  }
  return result.filter((n) => !mergedNodes.has(n));
}

function checkOutletNameUniqueness(nodes: TreeNode<ActivatedRouteSnapshot>[]): void {
  const names: {[k: string]: ActivatedRouteSnapshot} = {};