bug #75 Replace eval by require_once in ForwardCompatTypeExtensionTrait (l-vo)

This PR was merged into the 2.0 branch.

Discussion
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Replace eval by require_once in ForwardCompatTypeExtensionTrait

When an application use the ForwardCompatTypeExtensionTrait trait with return types, an error is triggered since the Symfony container can't determine and include the file that created the trait:

`Warning: include_once(/var/www/html/vendor/exercise/html-purifier-bundle/src/Form/TypeExtension/ForwardCompatTypeExtensionTrait.php(8) : eval()'d code): failed to open stream: No such file or directory`

This PR aims to fix this issue.

Commits
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98d3456 Replace eval by require_once for ForwardCompatTypeExtensionTrait

Author: HeahDude

src/Form/TypeExtension/ForwardCompatTypeExtensionTrait.php

@@ -5,24 +5,7 @@
 use Symfony\Component\Form\FormTypeExtensionInterface;
 
 if (method_exists(FormTypeExtensionInterface::class, 'getExtendedTypes')) {
-    eval('
-    namespace Exercise\HTMLPurifierBundle\Form\TypeExtension;
-
-    /**
-     * @internal
-     */
-    trait ForwardCompatTypeExtensionTrait
-    {
-        private static function doGetExtendedTypes(): iterable
-        {
-        }
-
-        public static function getExtendedTypes(): iterable
-        {
-            return self::doGetExtendedTypes();
-        }
-    }
-');
+    require_once __DIR__.'/forward_compat_trait.inc.php';
 } else {
     /**
      * @internal

src/Form/TypeExtension/forward_compat_trait.inc.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Exercise\HTMLPurifierBundle\Form\TypeExtension;
+
+/**
+ * @internal
+ */
+trait ForwardCompatTypeExtensionTrait
+{
+    private static function doGetExtendedTypes(): iterable
+    {
+    }
+
+    public static function getExtendedTypes(): iterable
+    {
+        return self::doGetExtendedTypes();
+    }
+}