improved-combo-auto-mod.c

#  define NEW_RECORD(press)                  \
    .event = {                               \
        .key     = {.col = 254, .row = 254}, \
        .time    = timer_read() | 1,         \
        .pressed = press,                    \
    }

bool process_combo_key_release(uint16_t combo_index, combo_t *combo, uint8_t key_index, uint16_t keycode) {
  // count the number of keys that were held down before
  uint8_t count = __builtin_popcount(combo->state);
  // if the key being released is the first that breaks the combo
  if (pgm_read_word(&combo->keys[count]) == COMBO_END) {
    // loop through all keys that are still held down
    for (uint8_t i = 0; i < count; ++i) {
      // don't touch the key that was released
      if (i == key_index) continue;
      // get the keycode of the keys still being pressed
      uint16_t other = pgm_read_word(&combo->keys[i]);
      switch (other) {
        case QK_MOD_TAP ... QK_MOD_TAP_MAX: {
          // in the case that the keycode is a MT, get the mod and apply it
          uint8_t mod = (other >> 8) & 0x1F;
          action_tapping_process((keyrecord_t){
              NEW_RECORD(true),
              .keycode = MT(mod, KC_NO),
          });
          break;
        }
        case QK_LAYER_TAP ... QK_LAYER_TAP_MAX: {
          // in the case that the keycode is a LT, get the layer and apply it
          uint8_t layer = (other >> 8) & 0x1F;
          action_tapping_process((keyrecord_t){
              NEW_RECORD(true),
              .keycode = LT(layer, KC_NO),
          });
          break;
        }
      }
    }
  } else {
    // release all the tap-holds one by one
    switch (keycode) {
      case QK_MOD_TAP ... QK_MOD_TAP_MAX: {
        uint8_t mod = (keycode >> 8) & 0x1F;
        action_tapping_process((keyrecord_t){
            NEW_RECORD(false),
            .keycode = MT(mod, KC_NO),
        });
        break;
      }
      case QK_LAYER_TAP ... QK_LAYER_TAP_MAX: {
        uint8_t layer = (keycode >> 8) & 0x1F;
        action_tapping_process((keyrecord_t){
            NEW_RECORD(false),
            .keycode = LT(layer, KC_NO),
        });
        break;
      }
    }
  }
  return false;
}

simplified-combo-auto-mod.c

#  define NEW_RECORD(press)                  \
    .event = {                               \
        .key     = {.col = 254, .row = 254}, \
        .time    = timer_read() | 1,         \
        .pressed = press,                    \
    }

bool process_combo_key_release(uint16_t combo_index, combo_t *combo, uint8_t key_index, uint16_t keycode) {
  // count the number of keys that were held down before
  uint8_t count = __builtin_popcount(combo->state);
  // if the key being released is the first that breaks the combo
  if (pgm_read_word(&combo->keys[count]) == COMBO_END) {
    // loop through all keys that are still held down
    for (uint8_t i = 0; i < count; ++i) {
      // don't touch the key that was released
      if (i == key_index) continue;
      // get the keycode of the keys still being pressed
      uint16_t other = pgm_read_word(&combo->keys[i]);
      switch (other) {
        case QK_MOD_TAP ... QK_MOD_TAP_MAX:
        case QK_LAYER_TAP ... QK_LAYER_TAP_MAX:
          // process the tap-hold, while making the keycode = KC_NO
          action_tapping_process((keyrecord_t){NEW_RECORD(true), .keycode = other & 0xFF00});
      }
    }
  } else {
    // release all the tap-holds one by one
    switch (keycode) {
      case QK_MOD_TAP ... QK_MOD_TAP_MAX:
      case QK_LAYER_TAP ... QK_LAYER_TAP_MAX:
        action_tapping_process((keyrecord_t){NEW_RECORD(false), .keycode = keycode & 0xFF00});
    }
  }
  return false;
}