GraphQL\Validator\Rules\QueryDepth::nodeDepth PHP Method

    private function nodeDepth(Node $node, $depth = 0, $maxDepth = 0)
    {
        switch ($node->kind) {
            case NodeKind::FIELD:
                /* @var FieldNode $node */
                // node has children?
                if (null !== $node->selectionSet) {
                    // update maxDepth if needed
                    if ($depth > $maxDepth) {
                        $maxDepth = $depth;
                    }
                    $maxDepth = $this->fieldDepth($node, $depth + 1, $maxDepth);
                }
                break;
            case NodeKind::INLINE_FRAGMENT:
                /* @var InlineFragmentNode $node */
                // node has children?
                if (null !== $node->selectionSet) {
                    $maxDepth = $this->fieldDepth($node, $depth, $maxDepth);
                }
                break;
            case NodeKind::FRAGMENT_SPREAD:
                /* @var FragmentSpreadNode $node */
                $fragment = $this->getFragment($node);
                if (null !== $fragment) {
                    $maxDepth = $this->fieldDepth($fragment, $depth, $maxDepth);
                }
                break;
        }
        return $maxDepth;
    }