Add path_join compatibility shim (#2172)

* Add path_join compatibility shim.

* Add myself as maintainer.

plugins/filter/path_join_shim.py

@@ -0,0 +1,28 @@
+# -*- coding: utf-8 -*-
+
+# Copyright: (c) 2020-2021, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+import os.path
+
+
+def path_join(list):
+    '''Join list of paths.
+
+    This is a minimal shim for ansible.builtin.path_join included in ansible-base 2.10.
+    This should only be called by Ansible 2.9 or earlier. See meta/runtime.yml for details.
+    '''
+    return os.path.join(*list)
+
+
+class FilterModule(object):
+    '''Ansible jinja2 filters'''
+
+    def filters(self):
+        return {
+            'path_join': path_join,
+        }