Start experimenting with PHP7.4 transpiling via rector

composer.json

@@ -17,6 +17,7 @@
 		"ext-json": "*",
 		"phpunit/phpunit": "^9.5.0",
 		"phpstan/phpstan": "^0.12.19",
+	  	"rector/rector": "^0.10.9",
 		"spatie/phpunit-snapshot-assertions": "^4.2.0"
     },
 	"scripts": {
@@ -27,6 +28,6 @@
 	},
 	"require": {
 		"ext-ffi": "*",
-	  	"php": ">= 8.0.0"
+	  	"php": ">= 7.4.0"
 	}
 }

rector.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Core\Configuration\Option;
+use Rector\DowngradePhp80\Rector\Catch_\DowngradeNonCapturingCatchesRector;
+use Rector\DowngradePhp80\Rector\Class_\DowngradePropertyPromotionRector;
+use Rector\DowngradePhp80\Rector\ClassConstFetch\DowngradeClassOnObjectToGetClassRector;
+use Rector\DowngradePhp80\Rector\ClassMethod\DowngradeStaticTypeDeclarationRector;
+use Rector\DowngradePhp80\Rector\ClassMethod\DowngradeTrailingCommasInParamUseRector;
+use Rector\DowngradePhp80\Rector\Expression\DowngradeMatchToSwitchRector;
+use Rector\DowngradePhp80\Rector\FunctionLike\DowngradeMixedTypeDeclarationRector;
+use Rector\DowngradePhp80\Rector\FunctionLike\DowngradeUnionTypeDeclarationRector;
+use Rector\DowngradePhp80\Rector\NullsafeMethodCall\DowngradeNullsafeToTernaryOperatorRector;
+use Rector\DowngradePhp80\Rector\Property\DowngradeUnionTypeTypedPropertyRector;
+use Rector\Generics\Rector\Class_\GenericsPHPStormMethodAnnotationRector;
+use Rector\Set\ValueObject\SetList;
+use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+return static function (ContainerConfigurator $containerConfigurator): void {
+    // get parameters
+//    $parameters = $containerConfigurator->parameters();
+//
+//    // Define what rule sets will be applied
+//    $parameters->set(Option::SETS, [
+//        SetList::DEAD_CODE,
+//		SetList::PHP_80,
+//    ]);
+
+    // get services (needed for register a single rule)
+    $services = $containerConfigurator->services();
+
+
+    $rules = [
+    	// PHP8 downgrade
+		DowngradeClassOnObjectToGetClassRector::class,
+		DowngradeMatchToSwitchRector::class,
+		DowngradeMixedTypeDeclarationRector::class,
+		DowngradeNonCapturingCatchesRector::class,
+		DowngradeNullsafeToTernaryOperatorRector::class,
+		DowngradePropertyPromotionRector::class,
+		DowngradeStaticTypeDeclarationRector::class,
+		DowngradeTrailingCommasInParamUseRector::class,
+		DowngradeUnionTypeDeclarationRector::class,
+		DowngradeUnionTypeTypedPropertyRector::class,
+
+		GenericsPHPStormMethodAnnotationRector::class,
+	];
+
+    foreach ($rules as $rule)
+	{
+		$services->set($rule);
+	}
+};