Function toggleExpanded

packages/core/src/widgets/tree.ts:309–326

(
  expanded: readonly string[],
  key: string,
)

 * @returns New expanded set and whether it's now expanded
 */
export function toggleExpanded(
  expanded: readonly string[],
  key: string,
): { expanded: readonly string[]; isExpanded: boolean } {
  const isCurrentlyExpanded = expanded.includes(key);

  if (isCurrentlyExpanded) {
    return {
      expanded: collapseNode(expanded, key),
      isExpanded: false,
    };
  }

  return {
    expanded: expandNode(expanded, key),
    isExpanded: true,
  };
}

/**
 * Expand all siblings of a node (nodes at the same depth with same parent).