minor #5840 DX: drop v2 compatible config in project itself (keradus)

This PR was squashed before being merged into the 3.0 branch.

Discussion
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DX: drop v2 compatible config in project itself

Commits
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b45be67 DX: drop v2 compatible config in project itself

.php-cs-fixer.dist.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /*
  * This file is part of PHP CS Fixer.
  *
@@ -10,6 +12,55 @@
  * with this source code in the file LICENSE.
  */
 
-// @TODO 3.x: make this file the only distributed config file and remove `.php_cs.dist` file.
+$header = <<<'EOF'
+This file is part of PHP CS Fixer.
+
+(c) Fabien Potencier <fabien@symfony.com>
+    Dariusz Rumiński <dariusz.ruminski@gmail.com>
+
+This source file is subject to the MIT license that is bundled
+with this source code in the file LICENSE.
+EOF;
+
+$finder = PhpCsFixer\Finder::create()
+    ->exclude('tests/Fixtures')
+    ->in(__DIR__)
+    ->append([
+        __DIR__.'/dev-tools/doc.php',
+        // __DIR__.'/php-cs-fixer', disabled, as we want to be able to run bootstrap file even on lower PHP version, to show nice message
+        __FILE__,
+    ])
+;
+
+$config = new PhpCsFixer\Config();
+$config
+    ->setRiskyAllowed(true)
+    ->setRules([
+        '@PHP71Migration:risky' => true,
+        '@PHPUnit75Migration:risky' => true,
+        '@PhpCsFixer' => true,
+        '@PhpCsFixer:risky' => true,
+        'general_phpdoc_annotation_remove' => ['annotations' => ['expectedDeprecation']],
+        'header_comment' => ['header' => $header],
+    ])
+    ->setFinder($finder)
+;
+
+// special handling of fabbot.io service if it's using too old PHP CS Fixer version
+if (false !== getenv('FABBOT_IO')) {
+    try {
+        PhpCsFixer\FixerFactory::create()
+            ->registerBuiltInFixers()
+            ->registerCustomFixers($config->getCustomFixers())
+            ->useRuleSet(new PhpCsFixer\RuleSet($config->getRules()))
+        ;
+    } catch (PhpCsFixer\ConfigurationException\InvalidConfigurationException $e) {
+        $config->setRules([]);
+    } catch (UnexpectedValueException $e) {
+        $config->setRules([]);
+    } catch (InvalidArgumentException $e) {
+        $config->setRules([]);
+    }
+}
 
-return require '.php_cs.dist';
+return $config;