fix: facts being gathered unnecessarily

Cause: The comparison of the present facts with the required facts is
being done on unsorted lists.

Consequence: The comparison may fail if the only difference is the
order.  Facts are gathered unnecessarily.

Fix: Use `difference` which works no matter what the order is.  Ensure
that the fact gathering subsets used are the absolute minimum required.

Result: The role gathers only the facts it requires, and does
not unnecessarily gather facts.

Signed-off-by: Rich Megginson <rmeggins@redhat.com>

Author: richm

vars/main.yml

@@ -8,11 +8,14 @@ __firewall_required_facts:
   - python_version
   - service_mgr
 
+# these facts cannot be used as a gather_subset
+__firewall_no_subset_facts: [python_interpreter]
+
 # the subsets of ansible_facts that need to be gathered in case any of the
 # facts in required_facts is missing; see the documentation of
 # the 'gather_subset' parameter of the 'setup' module
 __firewall_required_facts_subsets: "{{ ['!all', '!min'] +
-  __firewall_required_facts }}"
+  __firewall_required_facts | difference(__firewall_no_subset_facts) }}"
 
 __firewall_packages_base: [firewalld]