From 3242428c52852718abe3929481a2446c9e43482f Mon Sep 17 00:00:00 2001
From: Jafnee <jafnee.jesmee@jewelpaymentech.com>
Date: Wed, 23 Sep 2020 18:34:58 +0800
Subject: [PATCH] add Undefined.__aiter__

---
 CHANGES.rst           |  1 +
 src/jinja2/runtime.py |  4 ++++
 tests/test_async.py   | 14 ++++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index 2dccbfc3..45ff1444 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -54,6 +54,7 @@ Unreleased
     :issue:`1170`
 -   ``Undefined.__contains__`` (``in``) raises an ``UndefinedError``
     instead of a ``TypeError``. :issue:`1198`
+-   ``Undefined`` is iterable in an async environment. :issue:`1294`
 
 
 Version 2.11.3
diff --git a/src/jinja2/runtime.py b/src/jinja2/runtime.py
index ca49db76..c3d6fa4c 100644
--- a/src/jinja2/runtime.py
+++ b/src/jinja2/runtime.py
@@ -778,6 +778,10 @@ class Undefined:
     def __iter__(self):
         yield from ()
 
+    async def __aiter__(self):
+        for _ in ():
+            yield
+
     def __bool__(self):
         return False
 
diff --git a/tests/test_async.py b/tests/test_async.py
index 5cc8ba68..44b4bf13 100644
--- a/tests/test_async.py
+++ b/tests/test_async.py
@@ -2,6 +2,7 @@ import asyncio
 
 import pytest
 
+from jinja2 import ChainableUndefined
 from jinja2 import DictLoader
 from jinja2 import Environment
 from jinja2 import Template
@@ -588,3 +589,16 @@ def test_namespace_awaitable(test_env_async):
         assert actual == "Bar"
 
     run(_test())
+
+
+def test_chainable_undefined_aiter():
+    async def _test():
+        t = Template(
+            "{% for x in a['b']['c'] %}{{ x }}{% endfor %}",
+            enable_async=True,
+            undefined=ChainableUndefined,
+        )
+        rv = await t.render_async(a={})
+        assert rv == ""
+
+    run(_test())
-- 
2.47.2