qmk_firmware/keyboards/9key/9key.h

#pragma once

#include "quantum.h"

#define LAYOUT( \
    k00, k01, k02, \
    k10, k11, k12, \
    k20, k21, k22 \
) { \
    { k00, k01, k02 }, \
    { k10, k11, k12 }, \
    { k20, k21, k22 } \
}