Add iterator get_gc function for generators

Closes GH-5787.

Zend/tests/generators/iterator_wrapper_leak.phpt

@@ -0,0 +1,33 @@
+--TEST--
+A generator iterator wrapper involved in a cycle should not leak
+--FILE--
+<?php
+
+class Test {
+    public function method() {
+        $this->gen1 = (function () {
+            yield 1;
+            yield 2;
+            yield 3;
+        })();
+        $gen2 = function() {
+            foreach ($this->gen1 as $x) {
+                echo "$x\n";
+                yield $x;
+            }
+        };
+        $this->gen2 = $gen2();
+        foreach ($this->gen2 as $x) {
+            if ($x == 2) {
+                break;
+            }
+        }
+    }
+}
+(new Test)->method();
+gc_collect_cycles();
+
+?>
+--EXPECT--
+1
+2

Zend/zend_generators.c

@@ -1087,6 +1087,14 @@ static void zend_generator_iterator_rewind(zend_object_iterator *iterator) /* {{
 }
 /* }}} */
 
+static HashTable *zend_generator_iterator_get_gc(
+		zend_object_iterator *iterator, zval **table, int *n)
+{
+	*table = &iterator->data;
+	*n = 1;
+	return NULL;
+}
+
 static const zend_object_iterator_funcs zend_generator_iterator_functions = {
 	zend_generator_iterator_dtor,
 	zend_generator_iterator_valid,
@@ -1095,7 +1103,7 @@ static const zend_object_iterator_funcs zend_generator_iterator_functions = {
 	zend_generator_iterator_move_forward,
 	zend_generator_iterator_rewind,
 	NULL,
-	NULL, /* get_gc */
+	zend_generator_iterator_get_gc,
 };
 
 zend_object_iterator *zend_generator_get_iterator(zend_class_entry *ce, zval *object, int by_ref) /* {{{ */