Check that AnsibleUndefinedVariable doesn't occur when an unused variable references an undefined variable (#35571)

* Check that AnsibleUndefinedVariable doesn't occur

* AnsibleUndefinedVariable exc.: don't modify type

lib/ansible/template/vars.py

@@ -23,7 +23,7 @@ from collections import Mapping
 
 from jinja2.utils import missing
 
-from ansible.errors import AnsibleError
+from ansible.errors import AnsibleError, AnsibleUndefinedVariable
 from ansible.module_utils.six import iteritems
 from ansible.module_utils._text import to_native
 
@@ -105,6 +105,8 @@ class AnsibleJ2Vars(Mapping):
             value = None
             try:
                 value = self._templar.template(variable)
+            except AnsibleUndefinedVariable:
+                raise
             except Exception as e:
                 msg = getattr(e, 'message') or to_native(e)
                 raise AnsibleError("An unhandled exception occurred while templating '%s'. "

test/integration/targets/template/runme.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -eux
+
+ANSIBLE_ROLES_PATH=../ ansible-playbook template.yml -i ../../inventory -e @../../integration_config.yml -v "$@"
+
+# Test for #35571
+ansible testhost -i testhost, -m debug -a 'msg={{ hostvars["localhost"] }}' -e "vars1={{ undef }}" -e "vars2={{ vars1 }}"

test/integration/targets/template/template.yml

@@ -0,0 +1,4 @@
+- hosts: testhost
+  gather_facts: yes
+  roles:
+    - { role: template }