kyungjunleeme opened a new pull request, #68180:
URL: https://github.com/apache/airflow/pull/68180
`[scheduler] ignore_first_depends_on_past_by_default` became a **dead
config** in Airflow 3: it is still declared in `config.yml` with default
`"True"`, but no code reads it. The Task SDK hardcoded the default:
```python
DEFAULT_IGNORE_FIRST_DEPENDS_ON_PAST: bool = False
```
so the regression that #22491 fixed in 2.3.0 came back. Adding a new task to
an existing DAG whose `default_args` set `depends_on_past=True` leaves the new
task in no-status forever (`PrevDagrunDep`: *"previous task instance has not
run yet"*) and the DAG run never leaves the running state. A `grep` for
`ignore_first_depends_on_past_by_default` across `main` matches only the
`config.yml` declaration — zero readers. (2.10.5 read it at
`airflow/models/abstractoperator.py`.)
### Fix
Wire the default back to the config, the same way 2.10.5 did and the way
`DEFAULT_RETRIES` and friends in the same module still do:
```python
DEFAULT_IGNORE_FIRST_DEPENDS_ON_PAST: bool = conf.getboolean(
"scheduler", "ignore_first_depends_on_past_by_default"
)
```
The value flows through `OPERATOR_DEFAULTS` into the serialization
`client_defaults`, so **both regular and mapped operators** pick up the
configured default on the scheduler side. The server-side schema default stays
`False`, so setting the config to `False` continues to disable the behavior (no
`client_defaults` entry is emitted in that case).
### Tests
- `task-sdk`: default is `True`, explicit override wins, and the default
follows the config (reload guard against the dead-config regression).
- `airflow-core` `PrevDagrunDep`: a new task with `depends_on_past=True`
passes its first run using only the config default.
- Updated default-value assertions in `test_dag_serialization` and
`test_mappedoperator`.
related: #17585, #22491
---
##### Was generative AI tooling used to co-author this PR?
- [X] Yes — Claude Code (Opus 4.8)
Generated-by: Claude Code (Opus 4.8) following [the
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