The majority of code is derived from bhyve and therefore the general
coding style should follow the
FreeBSD coding style guidelines
(which are also accessible via man 9 style on Mac OS X).
You may use tools like uncrustify with this config file for new code, though the result may not be perfect.
Keep in mind that, especially for most of the bhyve derived code, it
is more important to try to keep the code in line with bhyve if
possible.