[AIRFLOW-5636] Allow adding or overriding existing Operator Links for…

[kaxil]

… an Operator

This will be done via Airflow Plugins

Make sure you have checked all steps below.

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-5636

Description

• Here are some details about my PR, including screenshots of any UI changes:
  Currently, we can add Operator link globally for all tasks or add operator links in existing tasks.

We should be able to add Operator links on a Single Operator or override existing Operator link on an operator.

This PR adds this functionality. This would also help in adding Operator links once we enable Serialized DAGs #5743

In the future, this will become a de facto way of adding OperatorLinks.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain docstrings that explain what it does
  • If you implement backwards incompatible changes, please leave a note in the Updating.md so we can assign it to a appropriate release

[codecov-io]

Codecov Report

Merging #6302 into master will decrease coverage by 0.02%.
The diff coverage is 97.22%.

@@            Coverage Diff             @@
##           master    #6302      +/-   ##
==========================================
- Coverage   80.41%   80.39%   -0.03%     
==========================================
  Files         612      616       +4     
  Lines       35473    35797     +324     
==========================================
+ Hits        28525    28778     +253     
- Misses       6948     7019      +71

Impacted Files	Coverage Δ
airflow/plugins_manager.py	87.27% <100%> (+0.35%)	⬆️
airflow/models/baseoperator.py	95.62% <100%> (+0.09%)	⬆️
airflow/utils/tests.py	81.08% <95.83%> (+27.23%)	⬆️
airflow/executors/kubernetes_executor.py	58.89% <0%> (-6.34%)	⬇️
airflow/gcp/operators/bigquery.py	86.44% <0%> (-0.17%)	⬇️
airflow/gcp/operators/mlengine.py	89.51% <0%> (ø)	⬆️
...gle/marketing_platform/sensors/campaign_manager.py	100% <0%> (ø)
...oogle/marketing_platform/hooks/campaign_manager.py	100% <0%> (ø)
..._platform/example_dags/example_campaign_manager.py	0% <0%> (ø)
...e/marketing_platform/operators/campaign_manager.py	91.73% <0%> (ø)
... and 8 more

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[milton0825]

This would also help in adding Operator links once we enable Serialized DAGs #5743

Can you share more details around this?

[kaxil]

Tests passes: https://travis-ci.org/kaxil/airflow/builds/597860562