RIOT/CONTRIBUTING.md

# Contributing to RIOT

Thank you for your interest in contributing to RIOT! There are many ways to
contribute, and we appreciate all of them. You can jump to the major sections
of this document using the following links:

* [Getting Started][getting-started]
* [Bug Reports and Feature Requests][issues]
* [Contributing code][contributing-code]
* [Writing Documentation][writing-documentation]
* [Working with Git][working with git]

If you have questions, please write a post over at our [forum] or chat on
`#riot-os:matrix.org` on [Matrix].

As a reminder, all contributors are expected to follow our
[Code of Conduct](CODE_OF_CONDUCT.md).

[forum]: https://forum.riot-os.org
[Matrix]: https://matrix.to/#/#riot-os:matrix.org

## Getting Started
[getting-started]: #getting-started
If you are just beginning to work with RIOT you might first want to read our
[documentation]. Especially the following sections might be of interest to you

- [Getting Started](https://doc.riot-os.org/getting-started.html)
- [Creating modules](https://doc.riot-os.org/creating-modules.html)
- [Creating an application](https://doc.riot-os.org/creating-an-application.html)

[documentation]: https://doc.riot-os.org

## Bug reports and feature requests
[issues]: #bug-reports-and-feature-requests
Both bug reports and feature request, big or small, are welcome.

Before submitting a feature request, please check if an [open issue][existing-feature-request]
already exists. If this is not the case, [submit a feature request][feature-request].
Describe your use case, why you need this feature and why this feature is important for RIOT.

Before filing a bug report, please check if an [open issue][existing-bug]
already exists. If this is not the case, [submit a new bug report][bug-report].
If you're not sure if something is a bug or not, feel free to file a bug report anyway.

**If you believe reporting your bug publicly represents a security risk to
RIOT users, please send an email describing the bug to <security@riot-os.org>**.
We would appreciate waiting for a 6 months grace period before reporting it on
public channels, to allow us adequate time to release the fix.

[bug reports]: https://github.com/RIOT-OS/RIOT/issues/new?template=bug_report.md
[feature requests]: https://github.com/RIOT-OS/RIOT/issues/new?template=feature_request.md

[existing-feature-request]: https://github.com/RIOT-OS/RIOT/issues?q=state:open+type:issue+label:"Type:+new+feature"
[feature-request]: https://github.com/RIOT-OS/RIOT/issues/new?template=feature_request.md&title=Feature+Request:
[existing-bug]: https://github.com/RIOT-OS/RIOT/issues?q=state:open+type:issue+label:"Type:+bug"
[bug-report]: https://github.com/RIOT-OS/RIOT/issues/new?template=bug_report.md&title=Bug:

## Contributing code
[contributing-code]: #contributing-code
If you think your work should be integrated in the main RIOT repository, take
the following steps:

  1. Fork the RIOT git repository (if you haven't done this already).
  1. Create a branch for your contribution.
  1. Make sure your code is in compliance with RIOT's [coding conventions].
  1. Make commits. Make sure to follow RIOT's [commit conventions].
  1. Push this branch to your fork on GitHub.
  1. Open a [pull request][open-a-pull-request]. See [pull requests].
  1. RIOT maintainers will set [labels] and provide feedback.
  1. Address this feedback. See [working with git].
  1. Your code is merged in RIOT master branch when it passes review.

Be sure to read the [general tips] below.

[open-an-issue]: https://github.com/RIOT-OS/RIOT/issues?q=state:open+type:issue+label:"Type:+bug"
[labels]: https://github.com/RIOT-OS/RIOT/wiki/RIOT%27s-labeling-system
[open-a-pull-request]: https://help.github.com/articles/using-pull-requests

### General Tips
[general tips]: #general-tips
From experience, the following recommendations help to get a software
contribution into RIOT master faster:

- **Ask around for help!** Either offline or through one of our communication
  channels (see above). The earlier you check your feature design with other
  people, the less likely it is that it is denied during the review process.
- **Verify your concept early!** If you work on your own until the code
  *looks* good enough to show publicly, you might miss some design flaws others
  might have spotted earlier.
- **Keep it simple!** Try to use what is already there and don't change existing
  APIs if not absolutely necessary.
- **Keep it small!** A PR with >1000 lines of changes will very likely make
  even the most active reviewer put your review on their long to-do list.
- **Keep it modular!** Make extensions to a feature or new features for a
  platform optionally to use.
- **Provide tests!** They should be comprehensible and easy to be executed.
  Alternatively comprehensive testing procedures should be provided with your
  pull request.

### Coding conventions
[coding conventions]: #coding-conventions

RIOT has extensive [coding conventions][coding-conventions].
It is possible to check if your code follows these conventions:

* You can [uncrustify] `.c` and `.h` files:

  ```console
  $ uncrustify -c $RIOTBASE/uncrustify-riot.cfg --no-backup <your file>
  ```

  **Note**: The `--no-backup` flag makes uncrustify *replace* the current file
   with a formatted version.

* RIOT provides static test tools to verify the quality of changes (cppcheck,
  trailing whitespaces, documentation, etc). These tools are wrapped in a
  single `make` target: `static-test`.

  *Watch out:* the command below will rebase your branch on your master branch,
  so make sure they can be rebased (e.g. there's no potential conflict).

  ```console
  $ make static-test
  ```

  Use it before opening a PR to perform last time checks.

[coding-conventions]: CODING_CONVENTIONS.md

### Commit conventions
[commit conventions]: #commit-conventions

* Each commit should target changes of specific parts/modules of RIOT. The
  commits use the following pattern:

  ```
  area of code: description of changes
  ```

  You can use multi-line commit messages if you want to detail more the
  changes.
  For example:

  ```
  periph/timer: Document that set_absolute is expected to wrap

  Most timers are implemented this way already, and keeping (documenting)
  it that way allows the generic timer_set implementation to stay as
  simple as it is.
  ```

### Pull Requests
[pull requests]: #pull-requests

GitHub's Pull Request (PR) feature is the primary mechanism used to make
contributions to the RIOT codebase. GitHub itself has some great documentation
on [using the Pull Request feature][about-pull-requests].
We use the [fork and pull model][development-models], where contributors push
changes to their personal fork and create pull requests to bring those changes
into the source repository.

* Before opening a new Pull Request, have a look at
  [existing ones][existing-pull-requests]. Maybe someone has already opened one
  about the same thing. If it's the case, you might be able to help with the
  contribution. Just comment on the PR and ask. Include closed PR's in your
  search, as previous work might have been closed for lack of interest.
  Old and stalled [PRs are sometimes archived][archived-pull-requests] with the
  "State: archived" label, maybe one of them is also about the same topic.

* The Pull Request title should reflect what it is about and be in the same form
  as the [commit conventions].

* Each Pull Request form uses a template that is there to help
  maintainers understand your contribution and help them in testing it.
  Please fill each section with as much information as possible.

* We recommend that you leave the *'Allow edits from maintainers'* check box ticked.
  This will allow maintainer finalizing your PR by pushing in your branch.
  In general, this speeds up the PR merge in the main repository.
  Note that this is not an obligation.

* Remember that smaller PRs tend to be merged faster, so keep your changes as
  concise as possible. They should be confined to a single explainable
  change, and be runnable on their own. So don't hesitate to split your PRs
  into smaller ones when possible.

* Maintainers try their best to review every PR as fast as possible, but they
  are also only human and it can happen that they miss a few PRs or might be
  preoccupied with other PRs. If it happens that your PR receives no review for
  a long time, don't hesitate to gently solicit a review by commenting or
  by explicitly mentioning a maintainer that you know is knowledgeable in the
  area of the PR. You can also advertise the PR on the [forum] and ask for a
  review there.

* Try to answer reviews as quickly as possible to speed up the review process
  and avoid stalled PRs.

[about-pull-requests]: https://help.github.com/articles/about-pull-requests/
[development-models]: https://help.github.com/articles/creating-a-pull-request-from-a-fork
[existing-pull-requests]: https://github.com/RIOT-OS/RIOT/pulls
[archived-pull-requests]: https://github.com/RIOT-OS/RIOT/pulls?q=is:pr+label:"State:+archived"
[uncrustify]: http://uncrustify.sourceforge.net

## Writing Documentation
[writing-documentation]: #writing-documentation

Documentation improvements are always welcome and a good starting point for
new contributors. This kind of contribution is merged quite quickly in general.

RIOT documentation is built with [doxygen][doxygen]. Doxygen is configured to
parse header (.h) and `doc.txt` files in the RIOT source code to generate
the modules, cpus, boards and packages documentation.
General documentation pages are written in Markdown and located in
`doc/doxygen/src`.

To generate the documentation, simply run the following
from the base directory of the RIOT source code.

```console
$ make doc
```

The generated documentation is located in `doc/doxygen/html`

[doxygen]: http://www.doxygen.nl/

## Working with Git
[working with git]: #working-with-git
Using git is a bit difficult for newcomers. If you are completely new to git,
we recommend that you [start by learning it][try-github-io] a bit. You can also
read the official [getting started documentation][git-scm-getting-started].

In this section, we give the bare minimum for a better experience with our
development workflow on GitHub.

[try-github-io]: https://try.github.io/
[git-scm-getting-started]: https://git-scm.com/book/en/v2/Getting-Started-Git-Basics

### Setup your local RIOT repository

Before you start modifying code, you need to fork the RIOT upstream repository
from the [RIOT main GitHub page][riot-github].

If it's your first time with git, configure your name and emails:

```console
$ git config --global user.name = "<your name here>"
$ git config --global user.email = "<your email address here>"
```

Then clone locally your fork of RIOT (replace `account name` with your actual
login on GitHub):

```console
$ git clone git@github.com:<account name>/RIOT.git
```

You can keep any branch of your local repository up-to-date with the upstream
master branch with the following commands:

```console
$ git checkout <branch name>
$ git pull --rebase https://github.com/RIOT-OS/RIOT.git
```

Use it before opening a PR. This will at least ensure the PR is mergeable but
also that it is up-to-date with the upstream repository.

[riot-github]: https://github.com/RIOT-OS/RIOT

### Work on branches

Avoid opening PR from the `master` branch of your fork to the master branch of
the RIOT upstream repository: update your master branch and start a new branch
from it.

```console
$ git checkout master
$ git pull --rebase https://github.com/RIOT-OS/RIOT.git
$ git checkout -b <new branch>
```

Do your changes, commit, update with latest upstream master

```console
$ git push
```

### Add fixup commits during review

To keep the history of changes easier to track for reviewers, it is recommended
to push your review request updates in fixup commits.

Let's say your PR contains 3 commits with comments: `prefix1: change 1`,
`prefix2: change 2` and `prefix3: change 3`.

Instead of committing changes in `prefix2` in a 4th commit `prefix2: change 4`,
you can use the `--fixup` option:

```console
$ git add /path/of/prefix2
$ git commit --fixup <prefix2 commit hash>
```

### Squash commits after review

Squashing a commit is done using the rebase subcommand of git in interactive
mode:

```console
$ git rebase master -i
```

You can find information on rebasing in
[GitHub rebase documentation][about-git-rebase].

[about-git-rebase]: https://help.github.com/articles/about-git-rebase/

If you used [fixup commits](#add-fixup-commits-during-review) during the review
phase, squashing commits can be performed in a single command:

```console
$ git rebase -i --autosquash
```

**Watch out: Don't squash your commit until a maintainer asks you to do it.**

Otherwise the history of review changes is lost and for large PRs, it
makes it difficult for the reviewer to follow them. It might also happen that
you introduce regression and won't be able to recover them from previous
commits.

If you encounter a merge conflict you could either resolve it by hand with an
editor and use

```console
$ git add -p
```

To add your changes or use a merge tool like [meld](https://meldmerge.org/) to
resolve your merge conflict.

```console
$ git mergetool
```

After the merge conflict is resolved you can continue to rebase by using

```console
$ git rebase --continue
```

Once squashing is done, you will have to force push your branch to update the
PR:

```console
$ git push --force-with-lease
```