Deprecate module_utils.redhat (#6663)

This module contains bits that are either unused (the Rhsm* classes), or
used only by deprecated modules (the RegistrationBase class).
Considering that the bits here have not seen updates in years, it is
unlikely that anyone is actually using them as "library".

Hence, deprecate the whole module altogether:
- the Rhsm* classes, as not used by anything, are slated for removal in
  9.0.0
- the RegistrationBase class is slated for removal in 10.0.0, together
  with its only user (i.e. the rhn_register module)

changelogs/fragments/6663-deprecate-module_utils-redhat.yml

@@ -0,0 +1,11 @@
+deprecated_features:
+  - |
+    redhat module utils - the ``module_utils.redhat`` module is deprecated, as
+    effectively unused: the ``Rhsm``, ``RhsmPool``, and ``RhsmPools`` classes
+    will be removed in community.general 9.0.0; the ``RegistrationBase`` class
+    will be removed in community.general 10.0.0 together with the
+    ``rhn_register`` module, as it is the only user of this class; this means
+    that the whole ``module_utils.redhat`` module will be dropped in
+    community.general 10.0.0, so importing it without even using anything of it
+    will fail
+    (https://github.com/ansible-collections/community.general/pull/6663).

plugins/module_utils/redhat.py

@@ -24,6 +24,14 @@ from ansible.module_utils.six.moves import configparser
 
 
 class RegistrationBase(object):
+    """
+    DEPRECATION WARNING
+
+    This class is deprecated and will be removed in community.general 10.0.0.
+    There is no replacement for it; please contact the community.general
+    maintainers in case you are using it.
+    """
+
     def __init__(self, module, username=None, password=None):
         self.module = module
         self.username = username
@@ -71,10 +79,23 @@ class RegistrationBase(object):
 
 
 class Rhsm(RegistrationBase):
+    """
+    DEPRECATION WARNING
+
+    This class is deprecated and will be removed in community.general 9.0.0.
+    There is no replacement for it; please contact the community.general
+    maintainers in case you are using it.
+    """
+
     def __init__(self, module, username=None, password=None):
         RegistrationBase.__init__(self, module, username, password)
         self.config = self._read_config()
         self.module = module
+        self.module.deprecate(
+            'The Rhsm class is deprecated with no replacement.',
+            version='9.0.0',
+            collection_name='community.general',
+        )
 
     def _read_config(self, rhsm_conf='/etc/rhsm/rhsm.conf'):
         '''
@@ -200,14 +221,25 @@ class Rhsm(RegistrationBase):
 
 
 class RhsmPool(object):
-    '''
+    """
-        Convenience class for housing subscription information
+    Convenience class for housing subscription information
-    '''
+
+    DEPRECATION WARNING
+
+    This class is deprecated and will be removed in community.general 9.0.0.
+    There is no replacement for it; please contact the community.general
+    maintainers in case you are using it.
+    """
 
     def __init__(self, module, **kwargs):
         self.module = module
         for k, v in kwargs.items():
             setattr(self, k, v)
+        self.module.deprecate(
+            'The RhsmPool class is deprecated with no replacement.',
+            version='9.0.0',
+            collection_name='community.general',
+        )
 
     def __str__(self):
         return str(self.__getattribute__('_name'))
@@ -223,11 +255,23 @@ class RhsmPool(object):
 
 class RhsmPools(object):
     """
-        This class is used for manipulating pools subscriptions with RHSM
+    This class is used for manipulating pools subscriptions with RHSM
+
+    DEPRECATION WARNING
+
+    This class is deprecated and will be removed in community.general 9.0.0.
+    There is no replacement for it; please contact the community.general
+    maintainers in case you are using it.
     """
+
     def __init__(self, module):
         self.module = module
         self.products = self._load_product_list()
+        self.module.deprecate(
+            'The RhsmPools class is deprecated with no replacement.',
+            version='9.0.0',
+            collection_name='community.general',
+        )
 
     def __iter__(self):
         return self.products.__iter__()