[GitHub] kaxil opened a new pull request #3907: WIP: [AIRFLOW-1195] Add feature to clear tasks in Parent Dag

[GitBox <gi...@apache.org>]

kaxil opened a new pull request #3907: WIP: [AIRFLOW-1195] Add feature to clear tasks in Parent Dag
URL: https://github.com/apache/incubator-airflow/pull/3907
 
 
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR"
     - https://issues.apache.org/jira/browse/AIRFLOW-1195
     - In case you are fixing a typo in the documentation you can prepend your commit with \[AIRFLOW-XXX\], code changes always need a Jira issue.
   
   ### Description
   
   - [x] Here are some details about my PR, including screenshots of any UI changes:
   Details on Jira
   
   Let's say that you had a task fail in a SubDag. You fix the underlying issue and want Airflow to resume the DagRun where it left off. If this were a flat DAG, then all you need to do is clear the failed TaskInstance and its downstream dependencies. The GUI will happily clear all of them for you in a single PUT request! In order to resume a SubDag, you must clear the TaskInstance + downstream dependencies AND you must clear the SubDagOperator + downstream depencies WITHOUT clearing its recursive dependencies. There should be an option to recursively clear task instances in upstream SubDags.
   
   ### Tests
   
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   ### Commits
   
   - [x] 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](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [x] In case of new functionality, my PR adds documentation that describes how to use it.
     - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.
   
   ### Code Quality
   
   - [x] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
   

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