Fix phpGH-7958: Nested CallbackFilterIterator is leaking memory

We implement `zend_object_iterator_funcs.get_gc` for user iterators to
avoid the memory leak.

Zend/tests/gh7958.phpt

@@ -0,0 +1,43 @@
+--TEST--
+GH-7958 (Nested CallbackFilterIterator is leaking memory)
+--FILE--
+<?php
+class Action
+{
+    public \Iterator $iterator;
+
+    public function __construct(array $data)
+    {
+        $this->iterator = new ArrayIterator($data);
+        echo '-- c ' . spl_object_id($this) . "\n";
+    }
+
+    public function __destruct()
+    {
+        echo '-- d ' . spl_object_id($this) . "\n";
+    }
+
+    public function filter()
+    {
+        $this->iterator = new \CallbackFilterIterator($this->iterator, fn() => true);
+        $this->iterator->rewind();
+    }
+}
+
+$action = new Action(['a', 'b']);
+$action->filter();
+$action->filter();
+print_r(iterator_to_array($action->iterator));
+$action = null;
+gc_collect_cycles();
+echo "==DONE==\n";
+?>
+--EXPECT--
+-- c 1
+Array
+(
+    [0] => a
+    [1] => b
+)
+-- d 1
+==DONE==

Zend/zend_interfaces.c

@@ -182,6 +182,17 @@ ZEND_API void zend_user_it_rewind(zend_object_iterator *_iter)
 }
 /* }}} */
 
+ZEND_API HashTable *zend_user_it_get_gc(zend_object_iterator *_iter, zval **table, int *n)
+{
+	zend_user_iterator *iter = (zend_user_iterator*)_iter;
+	zend_get_gc_buffer *gc_buffer = zend_get_gc_buffer_create();
+	if (!Z_ISUNDEF(iter->it.data)) {
+		zend_get_gc_buffer_add_zval(gc_buffer, &iter->it.data);
+	}
+	zend_get_gc_buffer_use(gc_buffer, table, n);
+	return NULL;
+}
+
 static const zend_object_iterator_funcs zend_interface_iterator_funcs_iterator = {
 	zend_user_it_dtor,
 	zend_user_it_valid,
@@ -190,7 +201,7 @@ static const zend_object_iterator_funcs zend_interface_iterator_funcs_iterator =
 	zend_user_it_move_forward,
 	zend_user_it_rewind,
 	zend_user_it_invalidate_current,
-	NULL, /* get_gc */
+	zend_user_it_get_gc,
 };
 
 /* {{{ zend_user_it_get_iterator */

Zend/zend_interfaces.h

@@ -55,6 +55,7 @@ ZEND_API void zend_user_it_get_current_key(zend_object_iterator *_iter, zval *ke
 ZEND_API zval *zend_user_it_get_current_data(zend_object_iterator *_iter);
 ZEND_API void zend_user_it_move_forward(zend_object_iterator *_iter);
 ZEND_API void zend_user_it_invalidate_current(zend_object_iterator *_iter);
+ZEND_API HashTable *zend_user_it_get_gc(zend_object_iterator *_iter, zval **table, int *n);
 
 ZEND_API void zend_user_it_new_iterator(zend_class_entry *ce, zval *object, zval *iterator);
 ZEND_API zend_object_iterator *zend_user_it_get_new_iterator(zend_class_entry *ce, zval *object, int by_ref);