_PyInstance_Lookup returns a borrowed reference

from_cpython/Include/classobject.h

@@ -81,7 +81,7 @@ PyAPI_FUNC(PyObject *) PyMethod_Class(PyObject *) PYSTON_NOEXCEPT;
  * can't fail, never sets an exception, and NULL is not an error (it just
  * means "not found").
  */
-PyAPI_FUNC(PyObject *) _PyInstance_Lookup(PyObject *pinst, PyObject *name) PYSTON_NOEXCEPT;
+PyAPI_FUNC(BORROWED(PyObject *)) _PyInstance_Lookup(PyObject *pinst, PyObject *name) PYSTON_NOEXCEPT;
 
 // Pyston change: no longer macros
 #if 0

from_cpython/Lib/test/test_shutil.py

-# expected: reffail
-# - leaked refs, some test failures?
 # Copyright (C) 2003 Python Software Foundation
 
 import unittest

src/runtime/classobj.cpp

@@ -77,7 +77,7 @@ static BORROWED(Box*) classLookup(BoxedClassobj* cls, BoxedString* attr) {
     return classLookup<NOT_REWRITABLE>(cls, attr, NULL);
 }
 
-extern "C" PyObject* _PyInstance_Lookup(PyObject* pinst, PyObject* pname) noexcept {
+extern "C" BORROWED(PyObject*) _PyInstance_Lookup(PyObject* pinst, PyObject* pname) noexcept {
     RELEASE_ASSERT(PyInstance_Check(pinst), "");
     BoxedInstance* inst = (BoxedInstance*)pinst;
 
@@ -92,7 +92,7 @@ extern "C" PyObject* _PyInstance_Lookup(PyObject* pinst, PyObject* pname) noexce
         Box* v = inst->getattr(name);
         if (v == NULL)
             v = classLookup(inst->inst_cls, name);
-        return xincref(v);
+        return v;
     } catch (ExcInfo e) {
         setCAPIException(e);
         return NULL;