module_helper.py Breakdown (#2393) (#2492)

* break down of module_helper into smaller pieces, keeping compatibility

* removed abc.ABC (py3 only) from code + fixed reference to vars.py

* multiple changes:

- mh.base - moved more functionalities to ModuleHelperBase
- mh.mixins.(cmd, state) - CmdMixin no longer inherits from ModuleHelperBase
- mh.mixins.deps - DependencyMixin now overrides run() method to test dependency
- mh.mixins.vars - created class VarsMixin
- mh.module_helper - moved functions to base class, added VarsMixin
- module_helper - importing AnsibleModule as well, for backward compatibility in test

* removed unnecessary __all__

* make pylint happy

* PR adjustments + bot config + changelog frag

* Update plugins/module_utils/mh/module_helper.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update plugins/module_utils/mh/module_helper.py

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit d22dd5056e)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

plugins/module_utils/mh/mixins/deps.py

@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+# (c) 2020, Alexei Znamensky <russoz@gmail.com>
+# Copyright: (c) 2020, Ansible Project
+# Simplified BSD License (see licenses/simplified_bsd.txt or https://opensource.org/licenses/BSD-2-Clause)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+import traceback
+
+from ansible_collections.community.general.plugins.module_utils.mh.base import ModuleHelperBase
+from ansible_collections.community.general.plugins.module_utils.mh.deco import module_fails_on_exception
+
+
+class DependencyCtxMgr(object):
+    def __init__(self, name, msg=None):
+        self.name = name
+        self.msg = msg
+        self.has_it = False
+        self.exc_type = None
+        self.exc_val = None
+        self.exc_tb = None
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.has_it = exc_type is None
+        self.exc_type = exc_type
+        self.exc_val = exc_val
+        self.exc_tb = exc_tb
+        return not self.has_it
+
+    @property
+    def text(self):
+        return self.msg or str(self.exc_val)
+
+
+class DependencyMixin(ModuleHelperBase):
+    _dependencies = []
+
+    @classmethod
+    def dependency(cls, name, msg):
+        cls._dependencies.append(DependencyCtxMgr(name, msg))
+        return cls._dependencies[-1]
+
+    def fail_on_missing_deps(self):
+        for d in self._dependencies:
+            if not d.has_it:
+                self.module.fail_json(changed=False,
+                                      exception="\n".join(traceback.format_exception(d.exc_type, d.exc_val, d.exc_tb)),
+                                      msg=d.text,
+                                      **self.output)
+
+    @module_fails_on_exception
+    def run(self):
+        self.fail_on_missing_deps()
+        super(DependencyMixin, self).run()