Release the airflow 1.7.1 tag.
There are three issues blocking this release caused by this commit:
1. DAGs with a lot of tasks take much longer to parse (~25x slowdown)
2. The following kind of patterns fail:
This is because set_upstream now calls add_task and a task can't be added more than once.
3. Airflow losing queued tasks (see linked issue)
4. Airflow putting dags in a stuck state ( AIRFLOW-92)
I'm working with the owner of the commit to resolve these issues.
The way to catch (1) in the future is an integration test that asserts a given non-trivial DAG parses under X seconds