Introduce the php-cs-fixer and enforce the formatting

.github/workflows/php.yml

@@ -49,3 +49,8 @@ jobs:
 
     - name: Run test suite
       run: composer run-script test
+
+    - name: Lint the code
+      env:
+        PHP_CS_FIXER_IGNORE_ENV: '1'  # make cs-fixer stop complaining when using PHP 8.3
+      run: composer run-script lint

.gitignore

@@ -3,3 +3,4 @@
 .phpunit.result.cache
 .phpunit.cache
 example.php
+.php-cs-fixer.cache

.php-cs-fixer.php

@@ -0,0 +1,17 @@
+<?php
+
+$finder = PhpCsFixer\Finder::create()
+  ->in(__DIR__ . '/src/')
+  ->in(__DIR__ . '/tests/')
+;
+
+$config = new PhpCsFixer\Config();
+
+// https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/master/doc/rules/index.rst
+// https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/master/doc/ruleSets/index.rst
+return $config
+  ->setRules([
+      '@PSR2' => true,
+  ])
+  ->setFinder($finder)
+;

composer.json

@@ -22,9 +22,16 @@
       "php": "^8.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^10.3"
+        "phpunit/phpunit": "^10.3",
+        "friendsofphp/php-cs-fixer": "^3.22"
     },
     "scripts": {
-        "test": "phpunit --testdox"
+        "test": "phpunit --testdox",
+        "lint": [
+            "php-cs-fixer fix --config=.php-cs-fixer.php --dry-run --verbose"
+        ],
+        "format": [
+            "php-cs-fixer fix --config=.php-cs-fixer.php"
+        ]
     }
 }