# QMK Breaking Change - 2019 Aug 30 | QMK Firmware
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# QMK Breaking Change - 2019 Aug 30 ​

Four times a year QMK runs a process for merging Breaking Changes. A Breaking Change is any change which modifies how QMK behaves in a way that is incompatible or potentially dangerous. We limit these changes to 4 times per year so that users can have confidence that updating their QMK tree will not break their keymaps.

This document marks the inaugural Breaking Change merge. A list of changes follows.

## Core code formatting with clang-format ​

- All core files (`drivers/`, `quantum/`, `tests/`, and `tmk_core/`) have been formatted with clang-format
- A travis process to reformat PRs on merge has been instituted
- You can use the new CLI command `qmk cformat` to format before submitting your PR if you wish.

## LUFA USB descriptor cleanup ​

- Some code cleanups related to the USB HID descriptors on AVR keyboards, to make them easier to read and understand
- More information: see https://github.com/qmk/qmk_firmware/pull/4871
- No behaviour changes anticipated and no keymaps modified

## Migrating `ACTION_LAYER_MOMENTARY()` entries in `fn_actions` to `MO()` keycodes ​

- `fn_actions` is deprecated, and its functionality has been superseded by direct keycodes and `process_record_user()`
- The end result of removing this obsolete feature should result in a decent reduction in firmware size and code complexity
- All keymaps affected are recommended to switch away from `fn_actions` in favour of the custom keycode and macro features

## Update Atreus to current code conventions ​

- Duplicate include guards have bypassed the expected header processing behavior
- All keymaps affected are recommended to remove duplication of `<keyboard>/config.h` to `<keyboard>/keymaps/<user>/config.h` and only provide overrides at the keymap level

## Backport changes to keymap language files from ZSA fork ​

- Fixes an issue in the `keymap_br_abnt2.h` file that includes the wrong source (`keymap_common.h` instead of `keymap.h`)
- Updates the `keymap_swedish.h` file to be specific to swedish, and not just "nordic" in general.
- Any keymaps using this will need to remove `NO_*` and replace it with `SE_*`.

## Update repo to use LUFA as a git submodule ​

- `/lib/LUFA` removed from the repo
- LUFA set as a submodule, pointing to qmk/lufa
- This should allow more flexibility with LUFA, and allow us to keep the sub-module up to date, a lot more easily. It was ~2 years out of date with no easy path to fix that. This prevents that from being an issue in the future

## Migrating `ACTION_BACKLIGHT_*()` entries in `fn_actions` to `BL_` keycodes ​

- `fn_actions` is deprecated, and its functionality has been superseded by direct keycodes and `process_record_user()`
- All keymaps using these actions have had the relevant `KC_FN*` keys replaced with the equivalent `BL_*` keys
- If you currently use `KC_FN*` you will need to replace `fn_actions` with the custom keycode and macro features

## Remove `KC_DELT` alias in favor of `KC_DEL` ​

- `KC_DELT` was a redundant, undocumented alias for `KC_DELETE`
- It has been removed and all its uses replaced with the more common `KC_DEL` alias
- Around 90 keymaps (mostly for ErgoDox boards) have been modified as a result