[GitHub] [airflow] uranusjr commented on issue #16764: TaskGroup dependencies handled inconsistently

[GitBox <gi...@apache.org>]

uranusjr commented on issue #16764:
URL: https://github.com/apache/airflow/issues/16764#issuecomment-1015058864


   One way I can think of to get rid of all the complexity is to _prohibit_ the task group from being used before the context manager exits, i.e.
   
   ```python
   with TaskGroup('tg') as taskgroup:
       task1 = ...
       task2 = ...
       task1 >> task2  # Fine.
       start >> taskgroup >> end  # Throws error!
   ```
   
   ```python
   with TaskGroup('tg') as taskgroup:
       task1 = ...
       task2 = ...
       task1 >> task2
   start >> taskgroup >> end  # Must do this instead.
   ```
   
   This essentially ensures the step 3 happens after step 2, and leaves only steps 3 and 4 to be interchangable. Does
   
   ```python
   with TaskGroup('tg') as taskgroup:
       task1 = ...
       task2 = ...
   start >> taskgroup >> end
   task1 >> task2
   ```
   
   produce an “expected” graph? If it does, all problems would be solved from what I can tell; if not, this is the only thing we need to fix (aside from implementing logic to prohibit a task gorup to be used before exiting).
   
   This would break some of the existing usages, but I _think_ we might be able to get away with the breaking change because most of the usages that would break does not work very well right now anyway (as shown in this issue), and therefore are unlikely to be widely in use right now.


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