Add new `loop_control.extended_allitems` option (#75760)

* Add new `loop_control.extended_allitems` option. Fixes #75216

* Add test for extended_allitems

* docs code block fix

changelogs/fragments/75216-loop-control-extended-allitems.yml

@@ -0,0 +1,3 @@
+minor_changes:
+- Loops - Add new ``loop_control.extended_allitems`` to allow users to disable tracking all loop items for each loop
+  (https://github.com/ansible/ansible/issues/75216)

docs/docsite/rst/user_guide/playbooks_loops.rst

@@ -452,6 +452,16 @@ Variable                    Description
 
 .. note:: When using ``loop_control.extended`` more memory will be utilized on the control node. This is a result of ``ansible_loop.allitems`` containing a reference to the full loop data for every loop. When serializing the results for display in callback plugins within the main ansible process, these references may be dereferenced causing memory usage to increase.
 
+.. versionadded:: 2.14
+
+To disable the ``ansible_loop.allitems`` item, to reduce memory consumption, set ``loop_control.extended_allitems: no``.
+
+::
+
+      loop_control:
+        extended: yes
+        extended_allitems: no
+
 Accessing the name of your loop_var
 -----------------------------------
 .. versionadded:: 2.8

lib/ansible/executor/task_executor.py

@@ -283,6 +283,7 @@ class TaskExecutor:
             index_var = templar.template(self._task.loop_control.index_var)
             loop_pause = templar.template(self._task.loop_control.pause)
             extended = templar.template(self._task.loop_control.extended)
+            extended_allitems = templar.template(self._task.loop_control.extended_allitems)
 
             # This may be 'None',so it is templated below after we ensure a value and an item is assigned
             label = self._task.loop_control.label
@@ -310,7 +311,6 @@ class TaskExecutor:
 
             if extended:
                 task_vars['ansible_loop'] = {
-                    'allitems': items,
                     'index': item_index + 1,
                     'index0': item_index,
                     'first': item_index == 0,
@@ -319,6 +319,8 @@ class TaskExecutor:
                     'revindex': items_len - item_index,
                     'revindex0': items_len - item_index - 1,
                 }
+                if extended_allitems:
+                    task_vars['ansible_loop']['allitems'] = items
                 try:
                     task_vars['ansible_loop']['nextitem'] = items[item_index + 1]
                 except IndexError:

lib/ansible/playbook/loop_control.py

@@ -30,6 +30,7 @@ class LoopControl(FieldAttributeBase):
     _label = FieldAttribute(isa='str')
     _pause = FieldAttribute(isa='float', default=0)
     _extended = FieldAttribute(isa='bool')
+    _extended_allitems = FieldAttribute(isa='bool', default=True)
 
     def __init__(self):
         super(LoopControl, self).__init__()

test/integration/targets/loop_control/extended.yml

@@ -10,3 +10,14 @@
         - third
       loop_control:
         extended: yes
+
+    - debug:
+        var: ansible_loop
+      loop:
+        - first
+        - second
+        - third
+      loop_control:
+        extended: yes
+        extended_allitems: no
+      failed_when: ansible_loop.allitems is defined