Chris@13: Frequently Asked Questions
Chris@13: ==========================
Chris@13: 
Chris@13:  * [How can the parent of a node be obtained?](#how-can-the-parent-of-a-node-be-obtained)
Chris@13:  * [How can the next/previous sibling of a node be obtained?](#how-can-the-nextprevious-sibling-of-a-node-be-obtained)
Chris@13: 
Chris@13: How can the parent of a node be obtained?
Chris@13: -----
Chris@13: 
Chris@13: The AST does not store parent nodes by default. However, it is easy to add a custom parent node
Chris@13: attribute using a custom node visitor:
Chris@13: 
Chris@13: ```php
Chris@13: use PhpParser\Node;
Chris@13: use PhpParser\NodeVisitorAbstract;
Chris@13: 
Chris@13: class ParentConnector extends NodeVisitorAbstract {
Chris@13:     private $stack;
Chris@13:     public function beforeTraverse(array $nodes) {
Chris@13:         $this->stack = [];
Chris@13:     }
Chris@13:     public function enterNode(Node $node) {
Chris@13:         if (!empty($this->stack)) {
Chris@13:             $node->setAttribute('parent', $this->stack[count($this->stack)-1]);
Chris@13:         }
Chris@13:         $this->stack[] = $node;
Chris@13:     }
Chris@13:     public function leaveNode(Node $node) {
Chris@13:         array_pop($this->stack);
Chris@13:     }
Chris@13: }
Chris@13: ```
Chris@13: 
Chris@13: After running this visitor, the parent node can be obtained through `$node->getAttribute('parent')`.
Chris@13: 
Chris@13: How can the next/previous sibling of a node be obtained?
Chris@13: -----
Chris@13: 
Chris@13: Again, siblings are not stored by default, but the visitor from the previous entry can be easily
Chris@13: extended to store the previous / next node with a common parent as well:
Chris@13: 
Chris@13: ```php
Chris@13: use PhpParser\Node;
Chris@13: use PhpParser\NodeVisitorAbstract;
Chris@13: 
Chris@13: class NodeConnector extends NodeVisitorAbstract {
Chris@13:     private $stack;
Chris@13:     private $prev;
Chris@13:     public function beforeTraverse(array $nodes) {
Chris@13:         $this->stack = [];
Chris@13:         $this->prev = null;
Chris@13:     }
Chris@13:     public function enterNode(Node $node) {
Chris@13:         if (!empty($this->stack)) {
Chris@13:             $node->setAttribute('parent', $this->stack[count($this->stack)-1]);
Chris@13:         }
Chris@13:         if ($this->prev && $this->prev->getAttribute('parent') == $node->getAttribute('parent')) {
Chris@13:             $node->setAttribute('prev', $this->prev);
Chris@13:             $this->prev->setAttribute('next', $node);
Chris@13:         }
Chris@13:         $this->stack[] = $node;
Chris@13:     }
Chris@13:     public function leaveNode(Node $node) {
Chris@13:         $this->prev = $node;
Chris@13:         array_pop($this->stack);
Chris@13:     }
Chris@13: }
Chris@13: ```