Looking for thoughts on the idea of adding a new TriggerRule which will never fire. The use case I have in mind is system tests. Airflow docs pages harvest code snippets from the system tests and on occasion I have run into a situation where the snippet can't run in the context of the test (run duration too long to be practical, requires some external paid account, etc) but the snippet is still desired. So far I have used a TaskGroup with a BranchingOperator as a workaround in the (two or three?) instances where I've hit this, but I wonder if it's something that others might find useful enough to make it worth discussing. I could also see it being a useful debugging tool for DAG authors; they could just easily "comment out" entire tasks while leaving them displayed in the DAG graph, for example.
The natural progression from that could be a TriggerRule:Callable where the callable returns a bool and the TriggerRule is satisfied if/when the callable evaluates to True... in which case my goal here would be covered simply using `TriggerRule:False` (or maybe it would have to be something like `TriggerRule:lambda x: False`, I haven't really put any thought into this part) which may or may not be just as easy to implement if we decide we want to do this at all. Down side: Obviously it's not great to have untested code snippets in the docs. We probably shouldn't be encouraging this behavior. - ferruzzi
