installation-bundle/src/Config/ParameterDumper.php
private function getEscapedValues(): array
    {
        $parameters = [];

        foreach ($this->parameters['parameters'] as $key => $value) {
            if (\is_string($value)) {
                if (0 === strncmp($value, '@', 1)) {
                    $value = '@'.$value;
                }

                if (false !== strpos($value, '%')) {
                    $value = str_replace('%', '%%', $value);
                }
            }

            $parameters[$key] = $value;
        }

        return ['parameters' => $parameters];
    }
private function getEscapedValues(): array
    {
        $parameters = [];

        foreach ($this->parameters['parameters'] as $key => $value) {
            if (\is_string($value)) {
                if (0 === strncmp($value, '@', 1)) {
                    $value = '@'.$value;
                }

                if (false !== strpos($value, '%')) {
                    $value = str_replace('%', '%%', $value);
                }
            }

            $parameters[$key] = $value;
        }

        return ['parameters' => $parameters];
    }
Escapes % and @.

@return array<string,string[]>

@see http://symfony.com/doc/current/service_container/parameters.html#parameters-in-configuration-files