Register handlers immediately if currently iterating handlers (#80898)

This fixes the issue where handlers notifying other handlers are
not properly run because the notification is not registered unless
another flush_handlers occurs. Instead, if the current host state
is iterating handlers we immediately register the handler to be
run so the notification is not lost.

Fixes #80880

changelogs/fragments/80880-register-handlers-immediately-if-iterating-handlers.yml

@@ -0,0 +1,4 @@
+bugfixes:
+- "From issue https://github.com/ansible/ansible/issues/80880, when notifying a
+  handler from another handler, handler notifications must be registered
+  immediately as the flush_handler call is not recursive."

lib/ansible/plugins/strategy/__init__.py

@@ -652,20 +652,28 @@ class StrategyBase:
                         # only ensure that notified handlers exist, if so save the notifications for when
                         # handlers are actually flushed so the last defined handlers are exexcuted,
                         # otherwise depending on the setting either error or warn
+                        host_state = iterator.get_state_for_host(original_host.name)
                         for notification in result_item['_ansible_notify']:
-                            if any(self.search_handlers_by_notification(notification, iterator)):
-                                iterator.add_notification(original_host.name, notification)
-                                display.vv(f"Notification for handler {notification} has been saved.")
-                                continue
-
-                            msg = (
-                                f"The requested handler '{notification}' was not found in either the main handlers"
-                                " list nor in the listening handlers list"
-                            )
-                            if C.ERROR_ON_MISSING_HANDLER:
-                                raise AnsibleError(msg)
+                            for handler in self.search_handlers_by_notification(notification, iterator):
+                                if host_state.run_state == IteratingStates.HANDLERS:
+                                    # we're currently iterating handlers, so we need to expand this now
+                                    if handler.notify_host(original_host):
+                                        # NOTE even with notifications deduplicated this can still happen in case of handlers being
+                                        # notified multiple times using different names, like role name or fqcn
+                                        self._tqm.send_callback('v2_playbook_on_notify', handler, original_host)
+                                else:
+                                    iterator.add_notification(original_host.name, notification)
+                                    display.vv(f"Notification for handler {notification} has been saved.")
+                                break
                             else:
-                                display.warning(msg)
+                                msg = (
+                                    f"The requested handler '{notification}' was not found in either the main handlers"
+                                    " list nor in the listening handlers list"
+                                )
+                                if C.ERROR_ON_MISSING_HANDLER:
+                                    raise AnsibleError(msg)
+                                else:
+                                    display.warning(msg)
 
                     if 'add_host' in result_item:
                         # this task added a new host (add_host module)

test/integration/targets/handlers/80880.yml

@@ -0,0 +1,34 @@
+---
+- name: Test notification of handlers from other handlers
+  hosts: localhost
+  gather_facts: no
+  handlers:
+    - name: Handler 1
+      debug:
+        msg: Handler 1
+      changed_when: true
+      notify: Handler 2
+      register: handler1_res
+    - name: Handler 2
+      debug:
+        msg: Handler 2
+      changed_when: true
+      notify: Handler 3
+      register: handler2_res
+    - name: Handler 3
+      debug:
+        msg: Handler 3
+      register: handler3_res
+  tasks:
+    - name: Trigger handlers
+      ansible.builtin.debug:
+        msg: Task 1
+      changed_when: true
+      notify: Handler 1
+  post_tasks:
+    - name: Assert results
+      ansible.builtin.assert:
+        that:
+        - "handler1_res is defined and handler1_res is success"
+        - "handler2_res is defined and handler2_res is success"
+        - "handler3_res is defined and handler3_res is success"

test/integration/targets/handlers/runme.sh

@@ -50,6 +50,9 @@ for strategy in linear free; do
   [ "$(ansible-playbook test_force_handlers.yml -i inventory.handlers -v "$@" --tags force_false_in_play --force-handlers \
   | grep -E -o CALLED_HANDLER_. | sort | uniq | xargs)" = "CALLED_HANDLER_B" ]
 
+  # https://github.com/ansible/ansible/pull/80898
+  [ "$(ansible-playbook 80880.yml -i inventory.handlers -vv "$@" 2>&1)" ]
+
   unset ANSIBLE_STRATEGY
 
 done