protected function readExtensionConfig(PackageInterface $package, $file)
    {
        $path = $this->preparePath($package, $file);
        if (!file_exists($path)) {
            $this->io->writeError('<error>Non existent extension config file</error> ' . $file . ' in ' . $package->getName());
            exit(1);
        }
        return require $path;
    }