Composer.php

<?php

namespace Drupal\Composer;

use Composer\Composer as ComposerApp;
use Composer\Script\Event;
use Composer\Semver\Comparator;
use Drupal\Composer\Generator\PackageGenerator;

/**
 * Provides static functions for composer script events. See also
 * core/lib/Drupal/Composer/Composer.php, which contains similar
 * scripts needed by projects that include drupal/core. Scripts that
 * are only needed by drupal/drupal go here.
 *
 * @see https://getcomposer.org/doc/articles/scripts.md
 */
class Composer {
    
    /**
     * Update metapackages whenever composer.lock is updated.
     *
     * @param \Composer\Script\Event $event
     */
    public static function generateMetapackages(Event $event) {
        $generator = new PackageGenerator();
        $generator->generate($event->getIO(), getcwd());
    }
    
    /**
     * Ensure that the minimum required version of Composer is running.
     * Throw an exception if Composer is too old.
     */
    public static function ensureComposerVersion() {
        $composerVersion = method_exists(ComposerApp::class, 'getVersion') ? ComposerApp::getVersion() : ComposerApp::VERSION;
        if (Comparator::lessThan($composerVersion, '1.9.0')) {
            throw new \RuntimeException("Drupal core development requires Composer 1.9.0, but Composer {$composerVersion} is installed. Please run 'composer self-update'.");
        }
    }
    
    /**
     * Return the branch name the current Drupal version is associated with.
     *
     * @return string
     *   A branch name, e.g. 8.9.x or 9.0.x.
     */
    public static function drupalVersionBranch() {
        return preg_replace('#\\.[0-9]+-dev#', '.x-dev', \Drupal::VERSION);
    }

}