Add config to fail on invalid task attributes. Fixes #42479

lib/ansible/config/base.yml

@@ -1375,6 +1375,17 @@ HOST_KEY_CHECKING:
   ini:
   - {key: host_key_checking, section: defaults}
   type: boolean
+INVALID_TASK_ATTRIBUTE_FAILED:
+  name: Controls whether invalid attributes for a task result in errors instead of warnings
+  default: false
+  description: If 'true', invalid attributes for a task will result in errors instead of warnings
+  type: boolean
+  env:
+    - name: ANSIBLE_INVALID_TASK_ATTRIBUTE_FAILED
+  ini:
+    - key: invalid_task_attribute_failed
+      section: defaults
+  version_added: "2.7"
 INVENTORY_ANY_UNPARSED_IS_FAILED:
   name: Controls whether any unparseable inventory source is a fatal error
   default: False

lib/ansible/playbook/task.py

@@ -231,7 +231,7 @@ class Task(Base, Conditional, Taggable, Become):
                                        " Please see:\nhttps://docs.ansible.com/ansible/playbooks_roles.html#task-include-files-and-encouraging-reuse\n\n"
                                        " for currently supported syntax regarding included files and variables", version="2.7")
                     new_ds['vars'][k] = v
-                elif k in self._valid_attrs:
+                elif C.INVALID_TASK_ATTRIBUTE_FAILED or k in self._valid_attrs:
                     new_ds[k] = v
                 else:
                     display.warning("Ignoring invalid attribute: %s" % k)