src/Composer/Util/Silencer.php
public static function suppress($mask = null)
    {
        if (!isset($mask)) {
            $mask = E_WARNING | E_NOTICE | E_USER_WARNING | E_USER_NOTICE | E_DEPRECATED | E_USER_DEPRECATED | E_STRICT;
        }
        $old = error_reporting();
        self::$stack[] = $old;
        error_reporting($old & ~$mask);

        return $old;
    }
public static function suppress($mask = null)
    {
        if (!isset($mask)) {
            $mask = E_WARNING | E_NOTICE | E_USER_WARNING | E_USER_NOTICE | E_DEPRECATED | E_USER_DEPRECATED | E_STRICT;
        }
        $old = error_reporting();
        self::$stack[] = $old;
        error_reporting($old & ~$mask);

        return $old;
    }
Suppresses given mask or errors.

@param  int|null $mask Error levels to suppress, default value NULL indicates all warnings and below.
@return int      The old error reporting level.