Native Jinja2: raise undefined error immediately (#52237)

Fixes #52158

test/units/template/test_native_concat.py

@@ -0,0 +1,28 @@
+# Copyright: (c) 2019, Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import pytest
+
+from ansible import constants as C
+from ansible.errors import AnsibleUndefinedVariable
+
+# need to mock DEFAULT_JINJA2_NATIVE here so native modules are imported
+# correctly within the template module
+C.DEFAULT_JINJA2_NATIVE = True
+from ansible.template import Templar
+
+from units.mock.loader import DictDataLoader
+
+
+# https://github.com/ansible/ansible/issues/52158
+def test_undefined_variable():
+    fake_loader = DictDataLoader({})
+    variables = {}
+    templar = Templar(loader=fake_loader, variables=variables)
+
+    with pytest.raises(AnsibleUndefinedVariable):
+        templar.template("{{ missing }}")