class AnonCollector implements Collector
{
    public function getNodeType(): string {
        return InClassNode::class;
    }

    public function processNode(Node $node, Scope $scope): ?array {
        return [$node->getClassReflection()->getName()];
    }
}

class AnonRule implements Rule
{
    public function __construct(private ReflectionProvider $reflectionProvider) {}

    public function getNodeType(): string {
        return CollectedDataNode::class;
    }

    public function processNode(Node $node, Scope $scope): array
    {
        $data = $node->get(AnonCollector::class);

        foreach ($data as $dataInFile) {
            foreach ($dataInFile as $fileData) {
                foreach ($fileData as $classString) {
                    $this->reflectionProvider->getClass($classString);
                }
            }
        }
        return [];
    }

}

// anon.php
$foo = new class {};