Swap default for INVALID_TASK_ATTRIBUTE_FAILED to True, add additional info to exception (#44138)

lib/ansible/config/base.yml

@@ -1385,8 +1385,8 @@ HOST_KEY_CHECKING:
   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
+  default: True
+  description: If 'false', invalid attributes for a task will result in warnings instead of errors
   type: boolean
   env:
     - name: ANSIBLE_INVALID_TASK_ATTRIBUTE_FAILED

lib/ansible/playbook/task.py

@@ -248,6 +248,13 @@ class Task(Base, Conditional, Taggable, Become):
 
         return LoopControl.load(data=ds, variable_manager=self._variable_manager, loader=self._loader)
 
+    def _validate_attributes(self, ds):
+        try:
+            super(Task, self)._validate_attributes(ds)
+        except AnsibleParserError as e:
+            e.message += '\nThis error can be suppressed as a warning using the "invalid_task_attribute_failed" configuration'
+            raise e
+
     def post_validate(self, templar):
         '''
         Override of base class post_validate, to also do final validation on