# How to contribute

Note: contributing implies licensing those contributions
under the terms of [COPYING](COPYING), which is an MIT-like license.

## Opening issues

* Make sure you have a [GitHub account](https://github.com/signup/free)
* Make sure there is no open issue on the topic
* [Submit a new issue](https://github.com/NixOS/nixpkgs/issues/new/choose) by choosing the kind of topic and fill out the template

## Submitting changes

Read the ["Submitting changes"](https://nixos.org/nixpkgs/manual/#chap-submitting-changes) section of the nixpkgs manual. It explains how to write, test, and iterate on your change, and which branch to base your pull request against.

Below is a short excerpt of some points in there:

* Format the commit messages in the following way:

  ```
  (pkg-name | nixos/<module>): (from -> to | init at version | refactor | etc)

  (Motivation for change. Link to release notes. Additional information.)
  ```

  For consistency, there should not be a period at the end of the commit message's summary line (the first line of the commit message).

  Examples:

  * nginx: init at 2.0.1
  * firefox: 54.0.1 -> 55.0
    https://www.mozilla.org/en-US/firefox/55.0/releasenotes/
  * nixos/hydra: add bazBaz option

    Dual baz behavior is needed to do foo.
  * nixos/nginx: refactor config generation

    The old config generation system used impure shell scripts and could break in specific circumstances (see #1234).

* `meta.description` should:
  * Be capitalized.
  * Not start with the package name.
  * Not have a period at the end.
* `meta.license` must be set and fit the upstream license.
  * If there is no upstream license, `meta.license` should default to `lib.licenses.unfree`.
* `meta.maintainers` must be set.

See the nixpkgs manual for more details on [standard meta-attributes](https://nixos.org/nixpkgs/manual/#sec-standard-meta-attributes).

## Writing good commit messages

In addition to writing properly formatted commit messages, it's important to include relevant information so other developers can later understand *why* a change was made. While this information usually can be found by digging code, mailing list/Discourse archives, pull request discussions or upstream changes, it may require a lot of work.

For package version upgrades and such a one-line commit message is usually sufficient.

## Rebasing between branches (i.e. from master to staging)

From time to time, changes between branches must be rebased, for example, if the
number of new rebuilds they would cause is too large for the target branch. When
rebasing, care must be taken to include only the intended changes, otherwise
many CODEOWNERS will be inadvertently requested for review.  To achieve this,
rebasing should not be performed directly on the target branch, but on the merge
base between the current and target branch.

In the following example, we see a rebase from `master` onto the merge base
between `master` and `staging`, so that a change can eventually be retargeted to
`staging`. The example uses `upstream` as the remote for `NixOS/nixpkgs.git`
while the `origin` remote is used for the remote you are pushing to.


```console
# Find the common base between two branches
common=$(git merge-base upstream/master upstream/staging)
# Find the common base between your feature branch and master
commits=$(git merge-base $(git branch --show-current) upstream/master)
# Rebase all commits onto the common base
git rebase --onto=$common $commits
# Force push your changes
git push origin $(git branch --show-current) --force-with-lease
```

Then change the base branch in the GitHub PR using the *Edit* button in the upper
right corner, and switch from `master` to `staging`. After the PR has been
retargeted it might be necessary to do a final rebase onto the target branch, to
resolve any outstanding merge conflicts.

```console
# Rebase onto target branch
git rebase upstream/staging
# Review and fixup possible conflicts
git status
# Force push your changes
git push origin $(git branch --show-current) --force-with-lease
```

## Backporting changes

Follow these steps to backport a change into a release branch in compliance with the [commit policy](https://nixos.org/nixpkgs/manual/#submitting-changes-stable-release-branches).

You can add a label such as `backport release-22.05` to a PR, so that merging it will
automatically create a backport (via [a GitHub Action](.github/workflows/backport.yml)).
This also works for PR's that have already been merged, and might take a couple of minutes to trigger.

You can also create the backport manually:

1. Take note of the commits in which the change was introduced into `master` branch.
2. Check out the target _release branch_, e.g. `release-22.05`. Do not use a _channel branch_ like `nixos-22.05` or `nixpkgs-22.05-darwin`.
3. Create a branch for your change, e.g. `git checkout -b backport`.
4. When the reason to backport is not obvious from the original commit message, use `git cherry-pick -xe <original commit>` and add a reason. Otherwise use `git cherry-pick -x <original commit>`. That's fine for minor version updates that only include security and bug fixes, commits that fixes an otherwise broken package or similar. Please also ensure the commits exists on the master branch; in the case of squashed or rebased merges, the commit hash will change and the new commits can be found in the merge message at the bottom of the master pull request.
5. Push to GitHub and open a backport pull request. Make sure to select the release branch (e.g. `release-22.05`) as the target branch of the pull request, and link to the pull request in which the original change was comitted to `master`. The pull request title should be the commit title with the release version as prefix, e.g. `[22.05]`.
6. When the backport pull request is merged and you have the necessary privileges you can also replace the label `9.needs: port to stable` with `8.has: port to stable` on the original pull request. This way maintainers can keep track of missing backports easier.

## Criteria for Backporting changes

Anything that does not cause user or downstream dependency regressions can be backported. This includes:
- New Packages / Modules
- Security / Patch updates
- Version updates which include new functionality (but no breaking changes)
- Services which require a client to be up-to-date regardless. (E.g. `spotify`, `steam`, or `discord`)
- Security critical applications (E.g. `firefox`)

## Generating 22.11 Release Notes

Documentation in nixpkgs is transitioning to a markdown-centric workflow. Release notes now require a translation step to convert from markdown to a compatible docbook document.

Steps for updating 22.11 Release notes:

1. Edit `nixos/doc/manual/release-notes/rl-2211.section.md` with the desired changes
2. Run `./nixos/doc/manual/md-to-db.sh` to render `nixos/doc/manual/from_md/release-notes/rl-2211.section.xml`
3. Include changes to `rl-2211.section.md` and `rl-2211.section.xml` in the same commit.

## Reviewing contributions

See the nixpkgs manual for more details on how to [Review contributions](https://nixos.org/nixpkgs/manual/#chap-reviewing-contributions).
