Add /files/dags to PYTHONPATH in Breeze

[jason810496]

Why

The default dags path in Breeze will be /files/dags, but /files/dags is not in PYTHONPATH, which cause the triggers defined in Dag file are not able to import by Triggerer, and have to workaround by copying Dag file to some directories that are in PYTHONPATH. Pointed out in: #58676 (comment)

What

We should add /files/dags to PYTHONPATH in Breeze in case the triggers are defined in dags, and cause "unable to import trigger" during Triggerer runtime.

Before: /files/dags is not in PYTHONPATH

>>> import sys; import pprint; pprint.pprint(sys.path)
['',
 '/opt/airflow',
 '/opt/airflow/providers/standard/tests',
 '/usr/python/lib/python310.zip',
 '/usr/python/lib/python3.10',
# ...
 '/opt/airflow/providers/yandex/src',

After: /files/dags is now in PYTHONPATH

>>> import sys; import pprint; pprint.pprint(sys.path)
['',
 '/opt/airflow',
 '/files/dags',  # <----------------------------- added!
 '/opt/airflow/providers/standard/tests',
 '/usr/python/lib/python310.zip',
 '/usr/python/lib/python3.10',
 '/usr/python/lib/python3.10/lib-dynload',
 '/usr/python/lib/python3.10/site-packages',
 '/opt/airflow/airflow-core/src',
 '/opt/airflow/airflow-ctl/src',
 ...

[potiuk]

Hmm. I think that should not be the case - at least by default when Airflow imports Dags (whether it's in Triggerer, worker or Dag Processor), it should add bundle root to the PYTHONPATH automatically - and we should avoid adding it externally- if we see a problem that it is not added, we should fix it.

@jedcunningham @ephraimbuddy - am I right ?

[jedcunningham]

Correct (edit: mostly). In fact, triggers from Dag files was pretty broken before anyways, so we intentionally removed that ability in AF3.

edit:

whether it's in Triggerer, worker or Dag Processor), it should add bundle root to the PYTHONPATH automatically

Yes for worker and dag processor. But not for the triggerer - the single process architecture means you can't do it reliably.

[jedcunningham]

See #48603.