sjyangkevin opened a new pull request, #64653:
URL: https://github.com/apache/airflow/pull/64653
…on previous dag run
<!-- SPDX-License-Identifier: Apache-2.0
https://www.apache.org/licenses/LICENSE-2.0 -->
<!--
Thank you for contributing!
Please provide above a brief description of the changes made in this pull
request.
Write a good git commit message following this guide:
http://chris.beams.io/posts/git-commit/
Please make sure that your code changes are covered with tests.
And in case of new features or big changes remember to adjust the
documentation.
Feel free to ping (in general) for the review if you do not see reaction for
a few days
(72 Hours is the minimum reaction time you can expect from volunteers) - we
sometimes miss notifications.
In case of an existing issue, reference it using one of the following:
* closes: #ISSUE
* related: #ISSUE
-->
closes: #60328
### Why
Add a new `depends_on_previous_tasks` parameter to BaseOperator that allows
a task to declare cross-dagrun dependencies on specific tasks from the previous
DagRun.
- `depends_on_past=True` only blocks a task instance until the same task in
the previous DagRun has succeeded.
- `wait_for_downstream=True` extends this to downstream tasks of the same
task.
```
A → B → C → D → E
dag_run_1 fails at task D.
For dag_run_2, task C should not start until C, D, and E from dag_run_1 have
all succeeded.
```
### Usage
```python
C = PythonOperator(
task_id="C",
python_callable=process_data,
depends_on_previous_tasks=["C", "D", "E"],
)
```
In `DagRun(N)`, task C is scheduled only if tasks C, D, and E in
`DagRun(N-1)` all finished with success or skipped. The first DagRun is never
blocked (same behavior as `depends_on_past`). Fully opt-in and backward
compatible.
### Design Trade-offs
**Mutual exclusivity vs. composition with `depends_on_past`**
`depends_on_previous_tasks` is mutually exclusive with `depends_on_past` and
`wait_for_downstream`. Combining them raises a ValueError at task construction
time.
Rationale: `depends_on_previous_tasks` is a strict superset, to replicate
`depends_on_past=True`, include the task's own `task_id` in the list. Allowing
both simultaneously would create confusing semantics. Failing fast at
definition time prevents silent misconfiguration.
3. Reusing `PrevDagrunDep` vs. a new dependency class
The implementation adds a branch to the existing
`PrevDagrunDep._get_dep_statuses()` method rather than creating a separate
dependency class.
Rationale: both `depends_on_past` and `depends_on_previous_tasks` share the
same lifecycle; look up the previous DagRun, check task states, push the
`PAST_DEPENDS_MET` xcom. Sharing the same dep class avoids duplicating the
DagRun-lookup logic and ensures the existing `ignore_depends_on_past` flag and
`DepContext` integration work for both paths without additional wiring.
### Caveats
- `uv.lock` is updated by pre-commit hook
---
##### Was generative AI tooling used to co-author this PR?
<!--
If generative AI tooling has been used in the process of authoring this PR,
please
change below checkbox to `[X]` followed by the name of the tool, uncomment
the "Generated-by".
-->
- [X] Yes (please specify the tool below)
Generated-by: [Antigravity] following [the
guidelines](https://github.com/apache/airflow/blob/main/contributing-docs/05_pull_requests.rst#gen-ai-assisted-contributions)
---
* Read the **[Pull Request
Guidelines](https://github.com/apache/airflow/blob/main/contributing-docs/05_pull_requests.rst#pull-request-guidelines)**
for more information. Note: commit author/co-author name and email in commits
become permanently public when merged.
* For fundamental code changes, an Airflow Improvement Proposal
([AIP](https://cwiki.apache.org/confluence/display/AIRFLOW/Airflow+Improvement+Proposals))
is needed.
* When adding dependency, check compliance with the [ASF 3rd Party License
Policy](https://www.apache.org/legal/resolved.html#category-x).
* For significant user-facing changes create newsfragment:
`{pr_number}.significant.rst`, in
[airflow-core/newsfragments](https://github.com/apache/airflow/tree/main/airflow-core/newsfragments).
You can add this file in a follow-up commit after the PR is created so you
know the PR number.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
