Always set the discovered interpreter on the delegated host (#64906)

* Always set the discovered interpreter on the delegated host. Fixes #63180

* Make code a little more generic

* Move code into a function

* Implement some changes based on reviews

* Add changelog fragment

changelogs/fragments/64906-always-delegate-fact-prefixes.yml

@@ -0,0 +1,4 @@
+bugfixes:
+- Fact Delegation - Add ability to indicate which facts must always be delegated. Primarily
+  for ``discovered_interpreter_python`` right now, but extensible later.
+  (https://github.com/ansible/ansible/issues/61002)

lib/ansible/plugins/strategy/__init__.py

@@ -55,6 +55,12 @@ display = Display()
 
 __all__ = ['StrategyBase']
 
+# This list can be an exact match, or start of string bound
+# does not accept regex
+ALWAYS_DELEGATE_FACT_PREFIXES = frozenset((
+    'discovered_interpreter_',
+))
+
 
 class StrategySentinel:
     pass
@@ -389,6 +395,34 @@ class StrategyBase:
         host_name = result.get('_ansible_delegated_vars', {}).get('ansible_delegated_host', None)
         return [host_name or task.delegate_to]
 
+    def _set_always_delegated_facts(self, result, task):
+        """Sets host facts for ``delegate_to`` hosts for facts that should
+        always be delegated
+
+        This operation mutates ``result`` to remove the always delegated facts
+
+        See ``ALWAYS_DELEGATE_FACT_PREFIXES``
+        """
+        if task.delegate_to is None:
+            return
+
+        facts = result['ansible_facts']
+        always_keys = set()
+        _add = always_keys.add
+        for fact_key in facts:
+            for always_key in ALWAYS_DELEGATE_FACT_PREFIXES:
+                if fact_key.startswith(always_key):
+                    _add(fact_key)
+        if always_keys:
+            _pop = facts.pop
+            always_facts = {
+                'ansible_facts': dict((k, _pop(k)) for k in list(facts) if k in always_keys)
+            }
+            host_list = self.get_delegated_hosts(result, task)
+            _set_host_facts = self._variable_manager.set_host_facts
+            for target_host in host_list:
+                _set_host_facts(target_host, always_facts)
+
     @debug_closure
     def _process_pending_results(self, iterator, one_pass=False, max_passes=None):
         '''
@@ -606,11 +640,13 @@ class StrategyBase:
                         self._add_group(original_host, result_item)
 
                     if 'ansible_facts' in result_item:
-
                         # if delegated fact and we are delegating facts, we need to change target host for them
                         if original_task.delegate_to is not None and original_task.delegate_facts:
                             host_list = self.get_delegated_hosts(result_item, original_task)
                         else:
+                            # Set facts that should always be on the delegated hosts
+                            self._set_always_delegated_facts(result_item, original_task)
+
                             host_list = self.get_task_hosts(iterator, original_host, original_task)
 
                         if original_task.action == 'include_vars':