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/incubator-druid/raw/master/druid_intellij_formatting.xml).
- For Eclipse you can import our code style settings xml: [eclipse_formatting.xml](https://github.com/apache/incubator-druid/raw/master/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).
Non-trivial features should include unit tests covering the new functionality.
- Bugfixes should include a unit test or integration test reproducing the issue.
- Do not use author tags/information in the code.
- Always include license header on each java file your create. See [this example](https://github.com/apache/incubator-druid/blob/master/common/src/main/java/org/apache/druid/metadata/PasswordProvider.java)
- 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.
- Keep the number of commits small and combine commits for related changes.
Each commit should compile on its own and ideally pass tests.
- Keep formatting changes in separate commits to make code reviews easier and
distinguish them from actual code changes.
## GitHub Workflow
1. Fork the apache/incubator-druid repository into your GitHub account
https://github.com/apache/incubator-druid/fork
1. Clone your fork of the GitHub repository
```sh
git clone git@github.com:<username>/druid.git
```
replace `<username>` with your GitHub username.
1. Add a remote to keep up with upstream changes
```
git remote add upstream https://github.com/apache/incubator-druid.git
```
If you already have a copy, fetch upstream changes
```
git fetch upstream master
```
1. Create a feature branch to work in
```
git checkout -b feature-xxx remotes/upstream/master
```
1. _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
```
1. 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.
1. 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/incubator-druid repository.
- Give your pull-request a meaningful title.
- In the description, explain your changes and the problem they are solving.
1. 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.
# 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
```
1. 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
```
1. 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
```
1. You can now submit this new branch and create or replace your existing pull request.
```
git push origin [--force] feature-xxx:feature-xxx
```