build: add Python code formatting with black

NOTE: this will fail tests as of this commit, as the code is not
formatted yet.

We didn't explicitly specify a minimum Python version before that, so I
used v3.7 here, because it's the minimal version Ruff - a Python linter
I will add in the next commit - supports.

.github/workflows/main.yml

@@ -8,7 +8,7 @@ env:
     libjson-glib-dev libsystemd-dev libudev-dev libunistring-dev
     python3-dev python3-evdev swig python3-sphinx
   UBUNTU_DEP_TEST: check python3-gi python3-lxml valgrind
-  PIP_PACKAGES: meson ninja libevdev pyudev pytest sphinx_rtd_theme
+  PIP_PACKAGES: meson ninja libevdev pyudev pytest sphinx_rtd_theme black
 
 jobs:
   build-and-dist:

meson.build

@@ -556,6 +556,8 @@ configure_file(input : 'tools/ratbagctl.test.py.in',
 
 env_test = environment()
 env_test.set('LIBRATBAG_DATA_DIR', libratbag_data_dir_devel)
+# See: https://github.com/mesonbuild/meson/issues/3306.
+env_test.set('MESON_SOURCE_ROOT', meson.source_root())
 ratbagctl_test = find_program(join_paths(meson.build_root(), 'ratbagctl.test'))
 test('ratbagctl-test', ratbagctl_test, args: ['-v'], env : env_test)
 
@@ -630,4 +632,21 @@ custom_target('ratbag-command',
 #### output files ####
 configure_file(output: 'config.h', install: false, configuration: config_h)
 
+#### code formatting #####
+run_target(
+  'python-black',
+  command : 'tools/python-black.sh',
+)
+
+python_black_check = find_program(join_paths(meson.source_root(), 'test/python-black-check.sh'))
+run_target(
+  'python-black-check',
+  command : python_black_check,
+)
+test(
+  'python-black-check',
+  python_black_check,
+  env: env_test,
+)
+
 subdir('doc')

pyproject.toml

@@ -0,0 +1,2 @@
+[tool.black]
+target-version = ["py37"]

test/python-black-check.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+if [ -z "$MESON_SOURCE_ROOT" ]; then
+	echo "Expected \$MESON_SOURCE_ROOT to be set. Are you sure you are running this through ninja?"
+	exit 100
+fi
+
+cd "$MESON_SOURCE_ROOT" || exit 101
+
+black --check $(git ls-files "*.py" "*.py.in")

tools/python-black.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+if [ -z "$MESON_SOURCE_ROOT" ]; then
+	echo "Expected \$MESON_SOURCE_ROOT to be set. Are you sure you are running this through ninja?"
+	exit 100
+fi
+
+cd "$MESON_SOURCE_ROOT" || exit 101
+
+black $(git ls-files "*.py" "*.py.in")

tools/ratbagctl.body.py.in

@@ -26,7 +26,10 @@ import sys
 import argparse
 import re
 
+# This must be on a single line, as we replace it using merge_ratbagd.py while building.
+# fmt: off
 from ratbagd import Ratbagd, RatbagdDevice, RatbagdProfile, RatbagdMacro, RatbagdResolution, RatbagdButton, RatbagdLed, RatbagdUnavailable, RatbagError, RatbagErrorCode, RatbagErrorCapability, RatbagDeviceType  # NOQA
+# fmt: on
 
 
 RATBAGD_API_VERSION = int("@RATBAGD_API_VERSION@")