[stable-2.7] Ensure loop with delegate_to can short circuit the same as without delegate_to. Fixes #45189 (#45231)

(cherry picked from commit 2ac647d)

Co-authored-by: Matt Martz <matt@sivel.net>

changelogs/fragments/loop_undefined_delegate_to.yaml

@@ -0,0 +1,4 @@
+bugfixes:
+- loop - Ensure that a loop with a when condition that evaluates to false and delegate_to, will short circuit if the
+  loop references an undefined variable. This matches the behavior in the same scenario without delegate_to
+  (https://github.com/ansible/ansible/issues/45189)

lib/ansible/vars/manager.py

@@ -512,7 +512,12 @@ class VariableManager:
             else:
                 raise AnsibleError("Failed to find the lookup named '%s' in the available lookup plugins" % task.loop_with)
         elif task.loop is not None:
-            items = templar.template(task.loop)
+            try:
+                items = templar.template(task.loop)
+            except AnsibleUndefinedVariable:
+                # This task will be skipped later due to this, so we just setup
+                # a dummy array for the later code so it doesn't fail
+                items = [None]
         else:
             has_loop = False
             items = [None]

test/integration/targets/loops/tasks/main.yml

@@ -233,3 +233,22 @@
 - assert:
     that:
       - ansible_search_path == loop_search_path.results.0.item
+
+# https://github.com/ansible/ansible/issues/45189
+- name: with_X conditional delegate_to shortcircuit on templating error
+  debug:
+    msg: "loop"
+  when: false
+  delegate_to: localhost
+  with_list: "{{ fake_var }}"
+  register: result
+  failed_when: result is not skipped
+
+- name: loop conditional delegate_to shortcircuit on templating error
+  debug:
+      msg: "loop"
+  when: false
+  delegate_to: localhost
+  loop: "{{ fake_var }}"
+  register: result
+  failed_when: result is not skipped