VM: gc_collect_cycles invokes __destruct on cyclic graphs (#6519)

lib/VM/CycleCollector.php

@@ -55,6 +55,7 @@ public static function collect(Context $ctx): int
             if (isset($marked[$object->id])) {
                 continue;
             }
+            ObjectLifetime::invokeDestructorBeforeGcRelease($object);
             ObjectRegistry::release($object);
             ++$collected;
         }

lib/VM/ObjectLifetime.php

@@ -87,6 +87,15 @@ public static function releaseDirectObject(Variable $var): void
      *
      * @see https://github.com/php/php-src/blob/master/Zend/zend_objects.c zend_objects_destroy_object
      */
+    /** Invoke __destruct before gc_collect_cycles() frees an unreachable object (#6519, zend_gc.c). */
+    public static function invokeDestructorBeforeGcRelease(ObjectEntry $object): void
+    {
+        $vm = self::$vm;
+        if (null !== $vm && !$object->destructorInvoked) {
+            $vm->invokeUserDestructor($object);
+        }
+    }
+
     public static function invokeUnsetDestructor(VM $vm, Variable $var): void
     {
         $var = $var->resolveIndirect();

test/compliance/cases/runtime/gc_collect_cycles_destruct.phpt

@@ -0,0 +1,19 @@
+--TEST--
+runtime gc_collect_cycles() — cyclic objects invoke __destruct (#6519)
+--FILE--
+<?php
+#[\AllowDynamicProperties]
+class Node {
+    public function __destruct() {
+        echo "dtor\n";
+    }
+}
+$a = new Node();
+$b = new Node();
+$a->next = $b;
+$b->next = $a;
+unset($a, $b);
+gc_collect_cycles();
+--EXPECT--
+dtor
+dtor

test/unit/GcCollectCyclesDestructTest.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+use PHPUnit\Framework\TestCase;
+
+/** gc_collect_cycles() invokes __destruct on cyclic graphs (#6519). */
+final class GcCollectCyclesDestructTest extends TestCase
+{
+    public function testVmGcCollectCyclesInvokesDestructorsOnCycle(): void
+    {
+        $code = <<<'PHP'
+<?php
+#[\AllowDynamicProperties]
+class Node {
+    public function __destruct()
+    {
+        echo "dtor\n";
+    }
+}
+$a = new Node();
+$b = new Node();
+$a->next = $b;
+$b->next = $a;
+unset($a, $b);
+gc_collect_cycles();
+PHP;
+        $rt = new Runtime();
+        $block = $rt->parseAndCompile($code, 'gc_cycle_destruct.php');
+        ob_start();
+        $rt->run($block);
+        $this->assertSame("dtor\ndtor\n", ob_get_clean());
+    }
+}