trait InstallerRedirectTrait

trait InstallerRedirectTrait {
    
    /**
     * Returns whether the current PHP process runs on CLI.
     *
     * @return bool
     */
    protected function isCli() {
        return PHP_SAPI === 'cli';
    }
    
    /**
     * Determines if an exception handler should redirect to the installer.
     *
     * @param \Exception $exception
     *   The exception to check.
     * @param \Drupal\Core\Database\Connection|null $connection
     *   (optional) The default database connection. If not provided, a less
     *   comprehensive check will be performed. This can be the case if the
     *   exception occurs early enough that a database connection object isn't
     *   available from the container yet.
     *
     * @return bool
     *   TRUE if the exception handler should redirect to the installer because
     *   Drupal is not installed yet, or FALSE otherwise.
     */
    protected function shouldRedirectToInstaller(\Exception $exception, Connection $connection = NULL) {
        // Never redirect on the command line.
        if ($this->isCli()) {
            return FALSE;
        }
        // Never redirect if we're already in the installer.
        if (InstallerKernel::installationAttempted()) {
            return FALSE;
        }
        // If the database wasn't found, assume the user hasn't entered it properly
        // and redirect to the installer. This check needs to come first because a
        // DatabaseNotFoundException is also an instance of DatabaseException.
        if ($exception instanceof DatabaseNotFoundException) {
            return TRUE;
        }
        // To avoid unnecessary queries, only act if the exception is one that is
        // expected to occur when Drupal has not yet been installed. This includes
        // NotFoundHttpException because an uninstalled site won't have route
        // information available yet and therefore can return 404 errors.
        if (!($exception instanceof \PDOException || $exception instanceof DatabaseException || $exception instanceof NotFoundHttpException)) {
            return FALSE;
        }
        // Redirect if there isn't even any database connection information in
        // settings.php yet, since that means Drupal is not installed.
        if (!Database::getConnectionInfo()) {
            return TRUE;
        }
        // Redirect if the database is empty.
        if ($connection) {
            try {
                return !$connection->schema()
                    ->tableExists('sessions');
            } catch (\Exception $e) {
                // If we still have an exception at this point, we need to be careful
                // since we should not redirect if the exception represents an error on
                // an already-installed site (for example, if the database server went
                // down). Assume we shouldn't redirect, just in case.
                return FALSE;
            }
        }
        // When in doubt, don't redirect.
        return FALSE;
    }

}