fix: facts being gathered unnecessarily

tasks/set_vars.yml

@@ -1,9 +1,9 @@
 ---
 - name: Ensure ansible_facts used by role
   setup:
-    gather_subset: min
-  when: not ansible_facts.keys() | list |
-    intersect(__storage_required_facts) == __storage_required_facts
+    gather_subset: "{{ __storage_required_facts_subsets }}"
+  when: __storage_required_facts |
+    difference(ansible_facts.keys() | list) | length > 0
 
 - name: Set platform/version specific variables
   include_vars: "{{ __vars_file }}"

vars/main.yml

@@ -5,3 +5,9 @@ __storage_required_facts:
   - distribution_major_version
   - distribution_version
   - os_family
+
+# 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
+__storage_required_facts_subsets: "{{ ['!all', '!min'] +
+  __storage_required_facts }}"