druid/CONTRIBUTING.md

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# How to Contribute

When submitting a pull request (PR), please use the following guidelines:

- Make sure your code respects existing formatting conventions. In general, follow
  the same coding style as the code that you are modifying.
- For Intellij you can import our code style settings xml: [`druid_intellij_formatting.xml`](
  https://github.com/apache/druid/raw/master/dev/druid_intellij_formatting.xml).
- For Eclipse you can import our code style settings xml: [`eclipse_formatting.xml`](
  https://github.com/apache/druid/raw/master/dev/eclipse_formatting.xml).
- Do add/update documentation appropriately for the change you are making.
- If you are introducing a new feature you may want to first write about your idea
  for feedback to [dev@druid.apache.org](https://lists.apache.org/list.html?dev@druid.apache.org). Or create an issue
  using "Feature/Change" template. Non-trivial features should include unit tests covering the new functionality. Open
  a "Proposal" issue for large changes.
- Bugfixes should include a unit test or integration test reproducing the issue.
- Do not use author tags/information in the code.
- Try to keep pull requests short and submit separate ones for unrelated
  features, but feel free to combine simple bugfixes/tests into one pull request.
- If you are adding or updating a dependency, be sure to update the version, license, or notice information in
  [licenses.yaml](https://github.com/apache/druid/blob/master/licenses.yaml) as appropriate to help ease
  LICENSE and NOTICE management for ASF releases.

You can find more developers' resources in [`dev/`](dev) directory.

## GitHub Workflow

1. Fork the apache/druid repository into your GitHub account

    https://github.com/apache/druid/fork

2. Clone your fork of the GitHub repository

    ```sh
    git clone git@github.com:<username>/druid.git
    ```

    replace `<username>` with your GitHub username.

3. Add a remote to keep up with upstream changes

    ```
    git remote add upstream https://github.com/apache/druid.git
    ```

    If you already have a copy, fetch upstream changes

    ```
    git fetch upstream master
    ```

4. Create a feature branch to work in

    ```
    git checkout -b feature-xxx remotes/upstream/master
    ```

5. _Before submitting a pull request_ periodically rebase your changes
    (but don't do it when a pull request is already submitted)

    ```
    git pull --rebase upstream master
    ```

6. Before submitting a pull request, combine ("squash") related commits into a single one

    ```
    git rebase -i upstream/master
    ```

    This will open your editor and allow you to re-order commits and merge them:
    - Re-order the lines to change commit order (to the extent possible without creating conflicts)
    - Prefix commits using `s` (squash) or `f` (fixup) to merge extraneous commits.

7. Submit a pull-request

    ```
    git push origin feature-xxx
    ```

    Go to your Druid fork main page

    ```
    https://github.com/<username>/druid
    ```

    If you recently pushed your changes GitHub will automatically pop up a
    `Compare & pull request` button for any branches you recently pushed to. If you
    click that button it will automatically offer you to submit your pull-request
    to the apache/druid repository.

    - Give your pull-request a meaningful title.
    - In the description, explain your changes and the problem they are solving.

8. Addressing code review comments

    Address code review comments by committing changes and pushing them to your feature
    branch.

    ```
    git push origin feature-xxx
    ```

### If your pull request shows conflicts with master
  If your pull request shows conflicts with master, merge master into your feature branch:
  

  ```
  git merge upstream/master
  ```
  
  and resolve the conflicts. After resolving conflicts, push your branch again:
  
  ```
  git push origin feature-xxx
  ```

  _Avoid rebasing and force pushes after submitting a pull request,_ since these make it
  difficult for reviewers to see what you've changed in response to their reviews. The Druid
  committer that merges your change will rebase and squash it into a single commit before
  committing it to master.

## Release notes

Release notes are the way that Druid users will learn about your fix or improvement. What does a user need to know? The key is to identify the user impact. Give it your best shot! Druid committers will review and edit your notes.

Here's a non-exhaustive list of the type of changes that have user impact and need release notes: 

* Changes what the user sees in the UI.
* Changes any action that the user takes (in the UI, in the API, in configuration, in install, etc.)
* Changes the results of any query, ingestion, or task.
* Changes performance (preferably making things faster).
* Adds, deprecates, or removes features.
* Anything that changes install, configuration, or operation of Druid.

An example of a change that doesn't need a release note is fixing a flakey test.

Use these tips when writing your release note:

**Summarize your change.** Describe the user impacting parts of your change, but try to be as concise as you can.

**Be accurate, clear, and concise.** If you can't tick all of these off, the order of priority is accurate > clear > concise.

**WIIFM - what's in it for me?** Spell out why the user should care. A release note shouldn't be like a stand-up update that focuses on the details of code changes.

**Give enough context.** Make sure there's enough detail for users to do something with the information if they need to. For example, include the property they need to set and link to the documentation when possible.

**You don't need to be formal and impersonal.** Speak directly to the user ("You can..."). Avoid passive voice (“X has been added”). 

### Example release notes

| Template                                        | Examples |
|-------------------------------------------------|----------|
| New: You can now…                           | New: You can now upload CSV files with a single header row for batch ingestion. Set the `infrerSchemaFromHeader` property of your ingestion spec to `true` to enable this feature. For more information, see [TITLE](/path/to/doc-file.md#anchor).|
| Fixed: X no longer does Y when Z.               | Fixed: Multi-value string array expressions no longer give flattened results when used in  groupBy queries.         |
| Changed: X now does Y. Previously, X did Z. | Changed: The first/last string aggregator now only compares based on values. Previously, the first/last string aggregator’s values were compared based on the `_time` column first and then on values.         |
| Improved: Better / Increased / Updated etc. | Improved: You can now perform Kinesis ingestion even if there are empty shards. Previously, all shards had to have at least one record. |
| Improved: Better / Increased / Updated etc. | Improved: Java 11 is fully supported and is no longer experimental. Java 17 support is improved.         |
| Deprecated: Removed / Will remove X. | Deprecated: Support for ZooKeeper X.Y will be removed in the next release, so consider upgrading ZooKeeper. For information about how to upgrade ZooKeeper, see the ZooKeeper documentation.        |


## FAQ

### Help! I merged changes from upstream and cannot figure out how to resolve conflicts when rebasing!

Never fear! If you occasionally merged upstream/master, here is another way to squash your changes into a single commit:

1. First, rename your existing branch to something else, e.g. `feature-xxx-unclean`
    ```
    git branch -m feature-xxx-unclean
    ```

2.  Checkout a new branch with the original name `feature-xxx` from upstream. This branch will supercede our old one.

    ```
    git checkout -b feature-xxx upstream/master
    ```

3. Then merge your changes in your original feature branch `feature-xxx-unclean` and create a single commit.

    ```
    git merge --squash feature-xxx-unclean
    git commit
    ```

4. You can now submit this new branch and create or replace your existing pull request.

    ```
    git push origin [--force] feature-xxx:feature-xxx
    ```