public function documentSymbol(TextDocumentIdentifier $textDocument): Promise
    {
        return $this->documentLoader->getOrLoad($textDocument->uri)->then(function (PhpDocument $document) {
            $symbols = [];
            foreach ($document->getDefinitions() as $fqn => $definition) {
                $symbols[] = $definition->symbolInformation;
            }
            return $symbols;
        });
    }