don't let root objects go out of scope

hphp/runtime/ext/ext_simplexml.cpp

@@ -39,6 +39,9 @@ class XmlDocWrapper : public SweepableResourceData {
   DECLARE_RESOURCE_ALLOCATION_NO_SWEEP(XmlDocWrapper)
 
   CLASSNAME_IS("xmlDoc");
+
+  Object m_element;
+
   // overriding ResourceData
   virtual CStrRef o_getClassNameHook() const { return classnameof(); }
 
@@ -285,9 +288,9 @@ Variant f_simplexml_import_dom(CObjRef node,
   }
 
   if (nodep && nodep->type == XML_ELEMENT_NODE) {
-    Resource obj =
-      Resource(NEWOBJ(XmlDocWrapper)(nodep->doc, class_name, node));
-    return create_element(nullptr, obj, nodep, String(), false);
+    XmlDocWrapper *obj = NEWOBJ(XmlDocWrapper)(nodep->doc, class_name, node);
+    obj->m_element = create_element(nullptr, Resource(obj), nodep, String(), false);
+    return obj->m_element;
   } else {
     raise_warning("Invalid Nodetype to import");
     return uninit_null();
@@ -324,9 +327,9 @@ Variant f_simplexml_load_string(CStrRef data,
     return false;
   }
 
-  return create_element(nullptr,
-                        Resource(NEWOBJ(XmlDocWrapper)(doc, cls->nameRef())),
-                        root, ns, is_prefix);
+  XmlDocWrapper *obj = NEWOBJ(XmlDocWrapper)(doc, cls->nameRef());
+  obj->m_element = create_element(nullptr, Resource(obj), root, ns, is_prefix);
+  return obj->m_element;
 }
 
 Variant f_simplexml_load_file(CStrRef filename,
@@ -399,9 +402,9 @@ void c_SimpleXMLElement::t___construct(CStrRef data, int64_t options /* = 0 */,
   xmlDocPtr doc = xmlReadMemory(xml.data(), xml.size(),
                                 nullptr, nullptr, options);
   if (doc) {
-    m_root = this;
-    m_doc =
-      Resource(NEWOBJ(XmlDocWrapper)(doc, o_getClassName()));
+    XmlDocWrapper *obj = NEWOBJ(XmlDocWrapper)(doc, o_getClassName());
+    obj->m_element = m_root = this;
+    m_doc = Resource(obj);
     m_node = xmlDocGetRootElement(doc);
     if (m_node) {
       m_children = create_children(m_root, m_doc, m_node, ns, is_prefix);

hphp/test/slow/simple_xml/xpath_scope.php

@@ -0,0 +1,24 @@
+<?php
+
+class Config {
+
+  protected $_sections;
+
+  public function __construct() {
+    $config = simplexml_load_string('<config><sections><payment type="group" /><a /><b /></sections></config>');
+    $this->_sections = $config->sections;
+  }
+
+  public function getSections() {
+    return $this->_sections;
+  }
+
+}
+
+$config = new Config();
+$sections = $config->getSections();
+
+// We should still have our original root object here,
+// so we can do xpath lookups in the tree.
+$node = $sections->xpath('payment[@type="group"]');
+var_dump($node);

hphp/test/slow/simple_xml/xpath_scope.php.expect

@@ -0,0 +1,10 @@
+array(1) {
+  [0]=>
+  object(SimpleXMLElement)#4 (1) {
+    ["@attributes"]=>
+    array(1) {
+      ["type"]=>
+      string(5) "group"
+    }
+  }
+}