Template run_once for handlers (#54030)

Fixes #27237

changelogs/fragments/27237-handlers-template-run_once.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+  - Fix handlers to allow for templated values in run_once (https://github.com/ansible/ansible/issues/27237)

lib/ansible/plugins/strategy/__init__.py

@@ -846,9 +846,7 @@ class StrategyBase:
             #        we consider the ability of meta tasks to flush handlers
             for handler in handler_block.block:
                 if handler.notified_hosts:
-                    handler_vars = self._variable_manager.get_vars(play=iterator._play, task=handler)
-                    handler_name = handler.get_name()
-                    result = self._do_handler_run(handler, handler_name, iterator=iterator, play_context=play_context)
+                    result = self._do_handler_run(handler, handler.get_name(), iterator=iterator, play_context=play_context)
                     if not result:
                         break
         return result
@@ -871,11 +869,11 @@ class StrategyBase:
             self._tqm.send_callback('v2_playbook_on_handler_task_start', handler)
             handler.name = saved_name
 
-        run_once = False
+        bypass_host_loop = False
         try:
             action = action_loader.get(handler.action, class_only=True)
-            if handler.run_once or getattr(action, 'BYPASS_HOST_LOOP', False):
-                run_once = True
+            if getattr(action, 'BYPASS_HOST_LOOP', False):
+                bypass_host_loop = True
         except KeyError:
             # we don't care here, because the action may simply not have a
             # corresponding action plugin
@@ -887,7 +885,9 @@ class StrategyBase:
                 task_vars = self._variable_manager.get_vars(play=iterator._play, host=host, task=handler)
                 self.add_tqm_variables(task_vars, play=iterator._play)
                 self._queue_task(host, handler, task_vars, play_context)
-                if run_once:
+
+                templar = Templar(loader=self._loader, variables=task_vars)
+                if templar.template(handler.run_once) or bypass_host_loop:
                     break
 
         # collect the results from the handler run

test/integration/targets/handlers/runme.sh

@@ -75,3 +75,10 @@ set -e
 
 # https://github.com/ansible/ansible/issues/47287
 [ "$(ansible-playbook test_handlers_including_task.yml -i ../../inventory -v "$@" | egrep -o 'failed=[0-9]+')" = "failed=0" ]
+
+# https://github.com/ansible/ansible/issues/27237
+set +e
+result="$(ansible-playbook test_handlers_template_run_once.yml -i inventory.handlers "$@" 2>&1)"
+set -e
+grep -q "handler A" <<< "$result"
+grep -q "handler B" <<< "$result"

test/integration/targets/handlers/test_handlers_template_run_once.yml

@@ -0,0 +1,12 @@
+- hosts: A,B
+  gather_facts: no
+  tasks:
+    - debug:
+      changed_when: true
+      notify:
+        - handler
+  handlers:
+    - name: handler
+      debug:
+        msg: "handler {{ inventory_hostname }}"
+      run_once: "{{ testvar | default(False) }}"