path: root/CONTRIBUTING.md

# Contributing to Nixpkgs

This document is for people wanting to contribute to the implementation of Nixpkgs.
This involves interacting with implementation changes that are proposed using [GitHub](https://github.com/) [pull requests](https://docs.github.com/pull-requests) to the [Nixpkgs](https://github.com/nixos/nixpkgs/) repository (which you're in right now).

As such, a GitHub account is recommended, which you can sign up for [here](https://github.com/signup).
See [here](https://discourse.nixos.org/t/about-the-patches-category/477) for how to contribute without a GitHub account.

Additionally this document assumes that you already know how to use GitHub and Git.
If that's not the case, we recommend learning about it first [here](https://docs.github.com/en/get-started/quickstart/hello-world).

## Overview
[overview]: #overview

This file contains general contributing information, but individual parts also have more specific information to them in their respective `README.md` files, linked here:
- [`lib`](./lib/README.md): Sources and documentation of the [library functions](https://nixos.org/manual/nixpkgs/stable/#chap-functions)
- [`maintainers`](./maintainers/README.md): Nixpkgs maintainer and team listings, maintainer scripts
- [`pkgs`](./pkgs/README.md): Package and [builder](https://nixos.org/manual/nixpkgs/stable/#part-builders) definitions
- [`doc`](./doc/README.md): Sources and infrastructure for the [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/)
- [`nixos`](./nixos/README.md): Implementation of [NixOS](https://nixos.org/manual/nixos/stable/)

# How to's

## How to create pull requests
[pr-create]: #how-to-create-pull-requests

This section describes in some detail how changes can be made and proposed with pull requests.

> [!Note]
> Be aware that contributing implies licensing those contributions under the terms of [COPYING](./COPYING), an MIT-like license.

0. Set up a local version of Nixpkgs to work with using GitHub and Git
   1. [Fork](https://docs.github.com/en/get-started/quickstart/fork-a-repo#forking-a-repository) the [Nixpkgs repository](https://github.com/nixos/nixpkgs/).
   1. [Clone the forked repository](https://docs.github.com/en/get-started/quickstart/fork-a-repo#cloning-your-forked-repository) into a local `nixpkgs` directory.
   1. [Configure the upstream Nixpkgs repository](https://docs.github.com/en/get-started/quickstart/fork-a-repo#configuring-git-to-sync-your-fork-with-the-upstream-repository).

1. Figure out the branch that should be used for this change by going through [this section][branch].
   If in doubt use `master`, that's where most changes should go.
   This can be changed later by [rebasing][rebase].

2. Create and switch to a new Git branch, ideally such that:
   - The name of the branch hints at the change you'd like to implement, e.g. `update-hello`.
   - The base of the branch includes the most recent changes on the base branch from step 1, we'll assume `master` here.

   ```bash
   # Make sure you have the latest changes from upstream Nixpkgs
   git fetch upstream

   # Create and switch to a new branch based off the master branch in Nixpkgs
   git switch --create update-hello upstream/master
   ```

   To avoid having to download and build potentially many derivations, at the expense of using a potentially outdated version, you can base the branch off a specific [Git commit](https://www.git-scm.com/docs/gitglossary#def_commit) instead:
   - The commit of the latest `nixpkgs-unstable` channel, available [here](https://channels.nixos.org/nixpkgs-unstable/git-revision).
   - The commit of a local Nixpkgs downloaded using [nix-channel](https://nixos.org/manual/nix/stable/command-ref/nix-channel), available using `nix-instantiate --eval --expr '(import <nixpkgs/lib>).trivial.revisionWithDefault null'`
   - If you're using NixOS, the commit of your NixOS installation, available with `nixos-version --revision`.

   Once you have an appropriate commit you can use it instead of `upstream/master` in the above command:
   ```bash
   git switch --create update-hello <the desired base commit>
   ```

3. Make the desired changes in the local Nixpkgs repository using an editor of your choice.
   Make sure to:
   - Adhere to both the [general code conventions][code-conventions], and the code conventions specific to the part you're making changes to.
     See the [overview section][overview] for more specific information.
   - Test the changes.
     See the [overview section][overview] for more specific information.
   - If necessary, document the change.
     See the [overview section][overview] for more specific information.

4. Commit your changes using `git commit`.
   Make sure to adhere to the [commit conventions](#commit-conventions).

   Repeat the steps 3-4 as many times as necessary.
   Advance to the next step if all the commits (viewable with `git log`) make sense together.

5. Push your commits to your fork of Nixpkgs.
   ```
   git push --set-upstream origin HEAD
   ```

   The above command will output a link that allows you to directly quickly do the next step:
   ```
   remote: Create a pull request for 'update-hello' on GitHub by visiting:
   remote:      https://github.com/myUser/nixpkgs/pull/new/update-hello
   ```

6. [Create a pull request](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request#creating-the-pull-request) from the new branch in your Nixpkgs fork to the upstream Nixpkgs repository.
   Use the branch from step 2 as the pull requests base branch.
   Go through the [pull request template](#pull-request-template) in the pre-filled default description.

7. Respond to review comments, potential CI failures and potential merge conflicts by updating the pull request.
   Always keep the pull request in a mergeable state.

   The custom [OfBorg](https://github.com/NixOS/ofborg) CI system will perform various checks to help ensure code quality, whose results you can see at the bottom of the pull request.
   See [the OfBorg Readme](https://github.com/NixOS/ofborg#readme) for more details.

   - To add new commits, repeat steps 3-4 and push the result using
     ```
     git push
     ```

   - To change existing commits you will have to [rewrite Git history](https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History).
     Useful Git commands that can help a lot with this are `git commit --patch --amend` and `git rebase --interactive`.
     With a rewritten history you need to force-push the commits using
     ```
     git push --force-with-lease
     ```

   - In case of merge conflicts you will also have to [rebase the branch](https://git-scm.com/book/en/v2/Git-Branching-Rebasing) on top of current `master`.
     Sometimes this can be done [on GitHub directly](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/keeping-your-pull-request-in-sync-with-the-base-branch#updating-your-pull-request-branch), but if not you will have to rebase locally using
     ```
     git fetch upstream
     git rebase upstream/master
     git push --force-with-lease
     ```

   - If you need to change the base branch of the pull request, you can do so by [rebasing][rebase].

8. If your pull request is merged and [acceptable for releases][release-acceptable] you may [backport][pr-backport] the pull request.

### Pull request template
[pr-template]: #pull-request-template

The pull request template helps determine what steps have been made for a contribution so far, and will help guide maintainers on the status of a change. The motivation section of the PR should include any extra details the title does not address and link any existing issues related to the pull request.

When a PR is created, it will be pre-populated with some checkboxes detailed below:

#### Tested using sandboxing

When sandbox builds are enabled, Nix will set up an isolated environment for each build process.
It is used to remove further hidden dependencies set by the build environment to improve reproducibility.
This includes access to the network during the build outside of `fetch*` functions and files outside the Nix store.
Depending on the operating system, access to other resources is blocked as well (e.g., inter-process communication is isolated on Linux); see [sandbox](https://nixos.org/manual/nix/stable/command-ref/conf-file#conf-sandbox) in the Nix manual for details.

In pull requests for [nixpkgs](https://github.com/NixOS/nixpkgs/) people are asked to test builds with sandboxing enabled (see `Tested using sandboxing` in the pull request template) because in [Hydra](https://nixos.org/hydra/) sandboxing is also used.

If you are on Linux, sandboxing is enabled by default.
On other platforms, sandboxing is disabled by default due to a small performance hit on each build.

Please enable sandboxing **before** building the package by adding the following to: `/etc/nix/nix.conf`:

  ```ini
  sandbox = true
  ```

#### Built on platform(s)

Many Nix packages are designed to run on multiple platforms. As such, it’s important to let the maintainer know which platforms your changes have been tested on. It’s not always practical to test a change on all platforms, and is not required for a pull request to be merged. Only check the systems you tested the build on in this section.

#### Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)

Packages with automated tests are much more likely to be merged in a timely fashion because it doesn’t require as much manual testing by the maintainer to verify the functionality of the package. If there are existing tests for the package, they should be run to verify your changes do not break the tests. Tests can only be run on Linux. For more details on writing and running tests, see the [section in the NixOS manual](https://nixos.org/nixos/manual/index.html#sec-nixos-tests).

#### Tested compilation of all pkgs that depend on this change using `nixpkgs-review`

If you are modifying a package, you can use `nixpkgs-review` to make sure all packages that depend on the updated package still compile correctly. The `nixpkgs-review` utility can look for and build all dependencies either based on uncommitted changes with the `wip` option or specifying a GitHub pull request number.

Review changes from pull request number 12345:

```ShellSession
nix-shell -p nixpkgs-review --run "nixpkgs-review pr 12345"
```

Alternatively, with flakes (and analogously for the other commands below):

```ShellSession
nix run nixpkgs#nixpkgs-review -- pr 12345
```

Review uncommitted changes:

```ShellSession
nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
```

Review changes from last commit:

```ShellSession
nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD"
```

#### Tested execution of all binary files (usually in `./result/bin/`)

It’s important to test any executables generated by a build when you change or create a package in nixpkgs. This can be done by looking in `./result/bin` and running any files in there, or at a minimum, the main executable for the package. For example, if you make a change to texlive, you probably would only check the binaries associated with the change you made rather than testing all of them.

#### Meets Nixpkgs contribution standards

The last checkbox is about whether it fits the guidelines in this `CONTRIBUTING.md` file. This document has detailed information on standards the Nix community has for commit messages, reviews, licensing of contributions you make to the project, etc... Everyone should read and understand the standards the community has for contributing before submitting a pull request.

### Rebasing between branches (i.e. from master to staging)
[rebase]: #rebasing-between-branches-ie-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. As an additional precautionary measure,
you should temporarily mark the PR as draft for the duration of the operation.
This reduces the probability of mass-pinging people. (OfBorg might still
request a couple of persons for reviews though.)

In the following example, we assume that the current branch, called `feature`,
is based on `master`, and we rebase it onto the merge base between
`master` and `staging` so that the PR can eventually be retargeted to
`staging` without causing a mess. The example uses `upstream` as the remote for `NixOS/nixpkgs.git`
while `origin` is the remote you are pushing to.


```console
# Rebase your commits onto the common merge base
git rebase --onto upstream/staging... upstream/master
# Force push your changes
git push origin feature --force-with-lease
```

The syntax `upstream/staging...` is equivalent to `upstream/staging...HEAD` and
stands for the merge base between `upstream/staging` and `HEAD` (hence between
`upstream/staging` and `upstream/master`).

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 feature --force-with-lease
```

#### Something went wrong and a lot of people were pinged

It happens. Remember to be kind, especially to new contributors.
There is no way back, so the pull request should be closed and locked
(if possible). The changes should be re-submitted in a new PR, in which the people
originally involved in the conversation need to manually be pinged again.
No further discussion should happen on the original PR, as a lot of people
are now subscribed to it.

The following message (or a version thereof) might be left when closing to
describe the situation, since closing and locking without any explanation
is kind of rude:

```markdown
It looks like you accidentally mass-pinged a bunch of people, which are now subscribed
and getting notifications for everything in this pull request. Unfortunately, they
cannot be automatically unsubscribed from the issue (removing review request does not
unsubscribe), therefore development cannot continue in this pull request anymore.

Please open a new pull request with your changes, link back to this one and ping the
people actually involved in here over there.

In order to avoid this in the future, there are instructions for how to properly
rebase between branches in our [contribution guidelines](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#rebasing-between-branches-ie-from-master-to-staging).
Setting your pull request to draft prior to rebasing is strongly recommended.
In draft status, you can preview the list of people that are about to be requested
for review, which allows you to sidestep this issue.
This is not a bulletproof method though, as OfBorg still does review requests even on draft PRs.
```

## How to backport pull requests
[pr-backport]: #how-to-backport-pull-requests

Once a pull request has been merged into `master`, a backport pull request to the corresponding `release-YY.MM` branch can be created either automatically or manually.

### Automatically backporting changes

> [!Note]
> You have to be a [Nixpkgs maintainer](./maintainers) to automatically create a backport pull request.

Add the [`backport release-YY.MM` label](https://github.com/NixOS/nixpkgs/labels?q=backport) to the pull request on the `master` branch.
This will cause [a GitHub Action](.github/workflows/backport.yml) to open a pull request to the `release-YY.MM` branch a few minutes later.
This can be done on both open or already merged pull requests.

### Manually backporting changes

To manually create a backport pull request, follow [the standard pull request process][pr-create], with these notable differences:

- Use `release-YY.MM` for the base branch, both for the local branch and the pull request.

> [!Warning]
> Do not use the `nixos-YY.MM` branch, that is a branch pointing to the tested release channel commit

- Instead of manually making and committing the changes, use [`git cherry-pick -x`](https://git-scm.com/docs/git-cherry-pick) for each commit from the pull request you'd like to backport.
  Either `git cherry-pick -x <commit>` when the reason for the backport is obvious (such as minor versions, fixes, etc.), otherwise use `git cherry-pick -xe <commit>` to add a reason for the backport to the commit message.
  Here is [an example](https://github.com/nixos/nixpkgs/commit/5688c39af5a6c5f3d646343443683da880eaefb8) of this.

> [!Warning]
> 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.

- In the pull request description, link to the original pull request to `master`.
  The pull request title should include `[YY.MM]` matching the release you're backporting to.

- 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.

## How to review pull requests
[pr-review]: #how-to-review-pull-requests

> [!Warning]
> The following section is a draft, and the policy for reviewing is still being discussed in issues such as [#11166](https://github.com/NixOS/nixpkgs/issues/11166) and [#20836](https://github.com/NixOS/nixpkgs/issues/20836).

The Nixpkgs project receives a fairly high number of contributions via GitHub pull requests. Reviewing and approving these is an important task and a way to contribute to the project.

The high change rate of Nixpkgs makes any pull request that remains open for too long subject to conflicts that will require extra work from the submitter or the merger. Reviewing pull requests in a timely manner and being responsive to the comments is the key to avoid this issue. GitHub provides sort filters that can be used to see the [most recently](https://github.com/NixOS/nixpkgs/pulls?q=is%3Apr+is%3Aopen+sort%3Aupdated-desc) and the [least recently](https://github.com/NixOS/nixpkgs/pulls?q=is%3Apr+is%3Aopen+sort%3Aupdated-asc) updated pull requests. We highly encourage looking at [this list of ready to merge, unreviewed pull requests](https://github.com/NixOS/nixpkgs/pulls?q=is%3Apr+is%3Aopen+review%3Anone+status%3Asuccess+-label%3A%222.status%3A+work-in-progress%22+no%3Aproject+no%3Aassignee+no%3Amilestone).

When reviewing a pull request, please always be nice and polite. Controversial changes can lead to controversial opinions, but it is important to respect every community member and their work.

GitHub provides reactions as a simple and quick way to provide feedback to pull requests or any comments. The thumb-down reaction should be used with care and if possible accompanied with some explanation so the submitter has directions to improve their contribution.

Pull request reviews should include a list of what has been reviewed in a comment, so other reviewers and mergers can know the state of the review.

All the review template samples provided in this section are generic and meant as examples. Their usage is optional and the reviewer is free to adapt them to their liking.

To get more information about how to review specific parts of Nixpkgs, refer to the documents linked to in the [overview section][overview].

If a pull request contains documentation changes that might require feedback from the documentation team, ping [@NixOS/documentation-reviewers](https://github.com/orgs/nixos/teams/documentation-reviewers) on the pull request.

If you consider having enough knowledge and experience in a topic and would like to be a long-term reviewer for related submissions, please contact the current reviewers for that topic. They will give you information about the reviewing process. The main reviewers for a topic can be hard to find as there is no list,