pyrox.dev
1# Contributing to Nixpkgs
2
3This document is for people wanting to contribute to the implementation of Nixpkgs.
4This 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).
5
6As such, a GitHub account is recommended, which you can sign up for [here](https://github.com/signup).
7See [here](https://discourse.nixos.org/t/about-the-patches-category/477) for how to contribute without a GitHub account.
8
9Additionally this document assumes that you already know how to use GitHub and Git.
10If that's not the case, we recommend learning about it first [here](https://docs.github.com/en/get-started/quickstart/hello-world).
11
12## Overview
13[overview]: #overview
14
15This file contains general contributing information, but individual parts also have more specific information to them in their respective `README.md` files, linked here:
16- [`lib`](./lib/README.md): Sources and documentation of the [library functions](https://nixos.org/manual/nixpkgs/stable/#chap-functions)
17- [`maintainers`](./maintainers/README.md): Nixpkgs maintainer and team listings, maintainer scripts
18- [`pkgs`](./pkgs/README.md): Package and [builder](https://nixos.org/manual/nixpkgs/stable/#part-builders) definitions
19- [`doc`](./doc/README.md): Sources and infrastructure for the [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/)
20- [`nixos`](./nixos/README.md): Implementation of [NixOS](https://nixos.org/manual/nixos/stable/)
21
22# How to's
23
24## How to create pull requests
25[pr-create]: #how-to-create-pull-requests
26
27This section describes in some detail how changes can be made and proposed with pull requests.
28
29> **Note**
30> Be aware that contributing implies licensing those contributions under the terms of [COPYING](./COPYING), an MIT-like license.
31
320. Set up a local version of Nixpkgs to work with using GitHub and Git
33 1. [Fork](https://docs.github.com/en/get-started/quickstart/fork-a-repo#forking-a-repository) the [Nixpkgs repository](https://github.com/nixos/nixpkgs/).
34 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.
35 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).
36
371. Figure out the branch that should be used for this change by going through [this section][branch].
38 If in doubt use `master`, that's where most changes should go.
39 This can be changed later by [rebasing][rebase].
40
412. Create and switch to a new Git branch, ideally such that:
42 - The name of the branch hints at the change you'd like to implement, e.g. `update-hello`.
43 - The base of the branch includes the most recent changes on the base branch from step 1, we'll assume `master` here.
44
45 ```bash
46 # Make sure you have the latest changes from upstream Nixpkgs
47 git fetch upstream
48
49 # Create and switch to a new branch based off the master branch in Nixpkgs
50 git switch --create update-hello upstream/master
51 ```
52
53 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:
54 - The commit of the latest `nixpkgs-unstable` channel, available [here](https://channels.nixos.org/nixpkgs-unstable/git-revision).
55 - 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'`
56 - If you're using NixOS, the commit of your NixOS installation, available with `nixos-version --revision`.
57
58 Once you have an appropriate commit you can use it instead of `upstream/master` in the above command:
59 ```bash
60 git switch --create update-hello <the desired base commit>
61 ```
62
633. Make the desired changes in the local Nixpkgs repository using an editor of your choice.
64 Make sure to:
65 - Adhere to both the [general code conventions][code-conventions], and the code conventions specific to the part you're making changes to.
66 See the [overview section][overview] for more specific information.
67 - Test the changes.
68 See the [overview section][overview] for more specific information.
69 - If necessary, document the change.
70 See the [overview section][overview] for more specific information.
71
724. Commit your changes using `git commit`.
73 Make sure to adhere to the [commit conventions](#commit-conventions).
74
75 Repeat the steps 3-4 as many times as necessary.
76 Advance to the next step if all the commits (viewable with `git log`) make sense together.
77
785. Push your commits to your fork of Nixpkgs.
79 ```
80 git push --set-upstream origin HEAD
81 ```
82
83 The above command will output a link that allows you to directly quickly do the next step:
84 ```
85 remote: Create a pull request for 'update-hello' on GitHub by visiting:
86 remote: https://github.com/myUser/nixpkgs/pull/new/update-hello
87 ```
88
896. [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.
90 Use the branch from step 2 as the pull requests base branch.
91 Go through the [pull request template](#pull-request-template) in the pre-filled default description.
92
937. Respond to review comments, potential CI failures and potential merge conflicts by updating the pull request.
94 Always keep the pull request in a mergeable state.
95
96 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.
97 See [the OfBorg Readme](https://github.com/NixOS/ofborg#readme) for more details.
98
99 - To add new commits, repeat steps 3-4 and push the result using
100 ```
101 git push
102 ```
103
104 - To change existing commits you will have to [rewrite Git history](https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History).
105 Useful Git commands that can help a lot with this are `git commit --patch --amend` and `git rebase --interactive`.
106 With a rewritten history you need to force-push the commits using
107 ```
108 git push --force-with-lease
109 ```
110
111 - 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`.
112 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
113 ```
114 git fetch upstream
115 git rebase upstream/master
116 git push --force-with-lease
117 ```
118
119 - If you need to change the base branch of the pull request, you can do so by [rebasing][rebase].
120
1218. If your pull request is merged and [acceptable for releases][release-acceptable] you may [backport][pr-backport] the pull request.
122
123### Pull request template
124[pr-template]: #pull-request-template
125
126The 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.
127
128When a PR is created, it will be pre-populated with some checkboxes detailed below:
129
130#### Tested using sandboxing
131
132When sandbox builds are enabled, Nix will setup 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 are blocked as well (ex. 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.
133
134Sandboxing is not enabled by default in Nix due to a small performance hit on each build. 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.
135
136Depending if you use NixOS or other platforms you can use one of the following methods to enable sandboxing **before** building the package:
137
138- **Globally enable sandboxing on NixOS**: add the following to `configuration.nix`
139
140 ```nix
141 nix.settings.sandbox = true;
142 ```
143
144- **Globally enable sandboxing on non-NixOS platforms**: add the following to: `/etc/nix/nix.conf`
145
146 ```ini
147 sandbox = true
148 ```
149
150#### Built on platform(s)
151
152Many 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.
153
154#### Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
155
156Packages 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).
157
158#### Tested compilation of all pkgs that depend on this change using `nixpkgs-review`
159
160If 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.
161
162Review changes from pull request number 12345:
163
164```ShellSession
165nix-shell -p nixpkgs-review --run "nixpkgs-review pr 12345"
166```
167
168Alternatively, with flakes (and analogously for the other commands below):
169
170```ShellSession
171nix run nixpkgs#nixpkgs-review -- pr 12345
172```
173
174Review uncommitted changes:
175
176```ShellSession
177nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
178```
179
180Review changes from last commit:
181
182```ShellSession
183nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD"
184```
185
186#### Tested execution of all binary files (usually in `./result/bin/`)
187
188It’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.
189
190#### Meets Nixpkgs contribution standards
191
192The 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.
193
194### Rebasing between branches (i.e. from master to staging)
195[rebase]: #rebasing-between-branches-ie-from-master-to-staging
196
197From time to time, changes between branches must be rebased, for example, if the
198number of new rebuilds they would cause is too large for the target branch. When
199rebasing, care must be taken to include only the intended changes, otherwise
200many CODEOWNERS will be inadvertently requested for review. To achieve this,
201rebasing should not be performed directly on the target branch, but on the merge
202base between the current and target branch. As an additional precautionary measure,
203you should temporarily mark the PR as draft for the duration of the operation.
204This reduces the probability of mass-pinging people. (OfBorg might still
205request a couple of persons for reviews though.)
206
207In the following example, we assume that the current branch, called `feature`,
208is based on `master`, and we rebase it onto the merge base between
209`master` and `staging` so that the PR can eventually be retargeted to
210`staging` without causing a mess. The example uses `upstream` as the remote for `NixOS/nixpkgs.git`
211while `origin` is the remote you are pushing to.
212
213
214```console
215# Rebase your commits onto the common merge base
216git rebase --onto upstream/staging... upstream/master
217# Force push your changes
218git push origin feature --force-with-lease
219```
220
221The syntax `upstream/staging...` is equivalent to `upstream/staging...HEAD` and
222stands for the merge base between `upstream/staging` and `HEAD` (hence between
223`upstream/staging` and `upstream/master`).
224
225Then change the base branch in the GitHub PR using the *Edit* button in the upper
226right corner, and switch from `master` to `staging`. *After* the PR has been
227retargeted it might be necessary to do a final rebase onto the target branch, to
228resolve any outstanding merge conflicts.
229
230```console
231# Rebase onto target branch
232git rebase upstream/staging
233# Review and fixup possible conflicts
234git status
235# Force push your changes
236git push origin feature --force-with-lease
237```
238
239#### Something went wrong and a lot of people were pinged
240
241It happens. Remember to be kind, especially to new contributors.
242There is no way back, so the pull request should be closed and locked
243(if possible). The changes should be re-submitted in a new PR, in which the people
244originally involved in the conversation need to manually be pinged again.
245No further discussion should happen on the original PR, as a lot of people
246are now subscribed to it.
247
248The following message (or a version thereof) might be left when closing to
249describe the situation, since closing and locking without any explanation
250is kind of rude:
251
252```markdown
253It looks like you accidentally mass-pinged a bunch of people, which are now subscribed
254and getting notifications for everything in this pull request. Unfortunately, they
255cannot be automatically unsubscribed from the issue (removing review request does not
256unsubscribe), therefore development cannot continue in this pull request anymore.
257
258Please open a new pull request with your changes, link back to this one and ping the
259people actually involved in here over there.
260
261In order to avoid this in the future, there are instructions for how to properly
262rebase between branches in our [contribution guidelines](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#rebasing-between-branches-ie-from-master-to-staging).
263Setting your pull request to draft prior to rebasing is strongly recommended.
264In draft status, you can preview the list of people that are about to be requested
265for review, which allows you to sidestep this issue.
266This is not a bulletproof method though, as OfBorg still does review requests even on draft PRs.
267```
268
269## How to backport pull requests
270[pr-backport]: #how-to-backport-pull-requests
271
272Once 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.
273
274### Automatically backporting changes
275
276> **Note**
277> You have to be a [Nixpkgs maintainer](./maintainers) to automatically create a backport pull request.
278
279Add the [`backport release-YY.MM` label](https://github.com/NixOS/nixpkgs/labels?q=backport) to the pull request on the `master` branch.
280This will cause [a GitHub Action](.github/workflows/backport.yml) to open a pull request to the `release-YY.MM` branch a few minutes later.
281This can be done on both open or already merged pull requests.
282
283### Manually backporting changes
284
285To manually create a backport pull request, follow [the standard pull request process][pr-create], with these notable differences:
286
287- Use `release-YY.MM` for the base branch, both for the local branch and the pull request.
288 > **Warning**
289 > Do not use the `nixos-YY.MM` branch, that is a branch pointing to the tested release channel commit
290
291- 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.
292 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.
293 Here is [an example](https://github.com/nixos/nixpkgs/commit/5688c39af5a6c5f3d646343443683da880eaefb8) of this.
294
295 > **Warning**
296 > Ensure the commits exists on the master branch.
297 > 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.
298
299- In the pull request description, link to the original pull request to `master`.
300 The pull request title should include `[YY.MM]` matching the release you're backporting to.
301
302- 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.
303 This way maintainers can keep track of missing backports easier.
304
305## How to review pull requests
306[pr-review]: #how-to-review-pull-requests
307
308> **Warning**
309> 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).
310
311The 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.
312
313The 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).
314
315When 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.
316
317GitHub 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.
318
319Pull 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.
320
321All 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.
322
323To get more information about how to review specific parts of Nixpkgs, refer to the documents linked to in the [overview section][overview].
324
325If a pull request contains documentation changes that might require feedback from the documentation team, ping @NixOS/documentation-team on the pull request.
326
327If 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, but checking past pull requests to see who reviewed or git-blaming the code to see who committed to that topic can give some hints.
328
329Container system, boot system and library changes are some examples of the pull requests fitting this category.
330
331## How to merge pull requests
332[pr-merge]: #how-to-merge-pull-requests
333
334The *Nixpkgs committers* are people who have been given
335permission to merge.
336
337It is possible for community members that have enough knowledge and experience on a special topic to contribute by merging pull requests.
338
339In case the PR is stuck waiting for the original author to apply a trivial
340change (a typo, capitalisation change, etc.) and the author allowed the members
341to modify the PR, consider applying it yourself (or commit the existing review
342suggestion). You should pay extra attention to make sure the addition doesn't go
343against the idea of the original PR and would not be opposed by the author.
344
345<!--
346The following paragraphs about how to deal with unactive contributors is just a proposition and should be modified to what the community agrees to be the right policy.
347
348Please note that contributors with commit rights unactive for more than three months will have their commit rights revoked.
349-->
350
351Please see the discussion in [GitHub nixpkgs issue #50105](https://github.com/NixOS/nixpkgs/issues/50105) for information on how to proceed to be granted this level of access.
352
353In a case a contributor definitively leaves the Nix community, they should create an issue or post on [Discourse](https://discourse.nixos.org) with references of packages and modules they maintain so the maintainership can be taken over by other contributors.
354
355# Flow of merged pull requests
356
357After a pull request is merged, it eventually makes it to the [official Hydra CI](https://hydra.nixos.org/).
358Hydra regularly evaluates and builds Nixpkgs, updating [the official channels](https://channels.nixos.org/) when specific Hydra jobs succeeded.
359See [Nix Channel Status](https://status.nixos.org/) for the current channels and their state.
360Here's a brief overview of the main Git branches and what channels they're used for:
361
362- `master`: The main branch, used for the unstable channels such as `nixpkgs-unstable`, `nixos-unstable` and `nixos-unstable-small`.
363- `release-YY.MM` (e.g. `release-23.05`): The NixOS release branches, used for the stable channels such as `nixos-23.05`, `nixos-23.05-small` and `nixpkgs-23.05-darwin`.
364
365When a channel is updated, a corresponding Git branch is also updated to point to the corresponding commit.
366So e.g. the [`nixpkgs-unstable` branch](https://github.com/nixos/nixpkgs/tree/nixpkgs-unstable) corresponds to the Git commit from the [`nixpkgs-unstable` channel](https://channels.nixos.org/nixpkgs-unstable).
367
368Nixpkgs in its entirety is tied to the NixOS release process, which is documented in the [NixOS Release Wiki](https://nixos.github.io/release-wiki/).
369
370See [this section][branch] to know when to use the release branches.
371
372## Staging
373[staging]: #staging
374
375The staging workflow exists to batch Hydra builds of many packages together.
376
377It works by directing commits that cause [mass rebuilds][mass-rebuild] to a separate `staging` branch that isn't directly built by Hydra.
378Regularly, the `staging` branch is _manually_ merged into a `staging-next` branch to be built by Hydra using the [`nixpkgs:staging-next` jobset](https://hydra.nixos.org/jobset/nixpkgs/staging-next).
379The `staging-next` branch should then only receive direct commits in order to fix Hydra builds.
380Once it is verified that there are no major regressions, it is merged into `master` using [a pull requests](https://github.com/NixOS/nixpkgs/pulls?q=head%3Astaging-next).
381This is done manually in order to ensure it's a good use of Hydra's computing resources.
382By keeping the `staging-next` branch separate from `staging`, this batching does not block developers from merging changes into `staging`.
383
384In order for the `staging` and `staging-next` branches to be up-to-date with the latest commits on `master`, there are regular _automated_ merges from `master` into `staging-next` and `staging`.
385This is implemented using GitHub workflows [here](.github/workflows/periodic-merge-6h.yml) and [here](.github/workflows/periodic-merge-24h.yml).
386
387> **Note**
388> Changes must be sufficiently tested before being merged into any branch.
389> Hydra builds should not be used as testing platform.
390
391Here is a Git history diagram showing the flow of commits between the three branches:
392```mermaid
393%%{init: {
394 'theme': 'base',
395 'themeVariables': {
396 'gitInv0': '#ff0000',
397 'gitInv1': '#ff0000',
398 'git2': '#ff4444',
399 'commitLabelFontSize': '15px'
400 },
401 'gitGraph': {
402 'showCommitLabel':true,
403 'mainBranchName': 'master',
404 'rotateCommitLabel': true
405 }
406} }%%
407gitGraph
408 commit id:" "
409 branch staging-next
410 branch staging
411
412 checkout master
413 checkout staging
414 checkout master
415 commit id:" "
416 checkout staging-next
417 merge master id:"automatic"
418 checkout staging
419 merge staging-next id:"automatic "
420
421 checkout staging-next
422 merge staging type:HIGHLIGHT id:"manual"
423 commit id:"fixup"
424
425 checkout master
426 checkout staging
427 checkout master
428 commit id:" "
429 checkout staging-next
430 merge master id:"automatic "
431 checkout staging
432 merge staging-next id:"automatic "
433
434 checkout staging-next
435 commit id:"fixup "
436 checkout master
437 merge staging-next type:HIGHLIGHT id:"manual (PR)"
438```
439
440
441Here's an overview of the different branches:
442
443| branch | `master` | `staging` | `staging-next` |
444| --- | --- | --- | --- |
445| Used for development | ✔️ | ✔️ | ❌ |
446| Built by Hydra | ✔️ | ❌ | ✔️ |
447| [Mass rebuilds][mass-rebuild] | ❌ | ✔️ | ⚠️ Only to fix Hydra builds |
448| Critical security fixes | ✔️ for non-mass-rebuilds | ❌ | ✔️ for mass-rebuilds |
449| Automatically merged into | `staging-next` | - | `staging` |
450| Manually merged into | - | `staging-next` | `master` |
451
452The staging workflow is used for all main branches, `master` and `release-YY.MM`, with corresponding names:
453- `master`/`release-YY.MM`
454- `staging`/`staging-YY.MM`
455- `staging-next`/`staging-next-YY.MM`
456
457# Conventions
458
459## Branch conventions
460<!-- This section is relevant to both contributors and reviewers -->
461[branch]: #branch-conventions
462
463Most changes should go to the `master` branch, but sometimes other branches should be used instead.
464Use the following decision process to figure out which one it should be:
465
466Is the change [acceptable for releases][release-acceptable] and do you wish to have the change in the release?
467- No: Use the `master` branch, do not backport the pull request.
468- Yes: Can the change be implemented the same way on the `master` and release branches?
469 For example, a packages major version might differ between the `master` and release branches, such that separate security patches are required.
470 - Yes: Use the `master` branch and [backport the pull request](#how-to-backport-pull-requests).
471 - No: Create separate pull requests to the `master` and `release-XX.YY` branches.
472
473Furthermore, if the change causes a [mass rebuild][mass-rebuild], use the appropriate staging branch instead:
474- Mass rebuilds to `master` should go to `staging` instead.
475- Mass rebuilds to `release-XX.YY` should go to `staging-XX.YY` instead.
476
477See [this section][staging] for more details about such changes propagate between the branches.
478
479### Changes acceptable for releases
480[release-acceptable]: #changes-acceptable-for-releases
481
482Only changes to supported releases may be accepted.
483The oldest supported release (`YYMM`) can be found using
484```
485nix-instantiate --eval -A lib.trivial.oldestSupportedRelease
486```
487
488The release branches should generally only receive backwards-compatible changes, both for the Nix expressions and derivations.
489Here are some examples of backwards-compatible changes that are okay to backport:
490- ✔️ New packages, modules and functions
491- ✔️ Security fixes
492- ✔️ Package version updates
493 - ✔️ Patch versions with fixes
494 - ✔️ Minor versions with new functionality, but no breaking changes
495
496In addition, major package version updates with breaking changes are also acceptable for:
497- ✔️ Services that would fail without up-to-date client software, such as `spotify`, `steam`, and `discord`
498- ✔️ Security critical applications, such as `firefox` and `chromium`
499
500### Changes causing mass rebuilds
501[mass-rebuild]: #changes-causing-mass-rebuilds
502
503Which changes cause mass rebuilds is not formally defined.
504In order to help the decision, CI automatically assigns [`rebuild` labels](https://github.com/NixOS/nixpkgs/labels?q=rebuild) to pull requests based on the number of packages they cause rebuilds for.
505As a rule of thumb, if the number of rebuilds is **over 500**, it can be considered a mass rebuild.
506To get a sense for what changes are considered mass rebuilds, see [previously merged pull requests to the staging branches](https://github.com/NixOS/nixpkgs/issues?q=base%3Astaging+-base%3Astaging-next+is%3Amerged).
507
508## Commit conventions
509[commit-conventions]: #commit-conventions
510
511- Create a commit for each logical unit.
512
513- Check for unnecessary whitespace with `git diff --check` before committing.
514
515- If you have commits `pkg-name: oh, forgot to insert whitespace`: squash commits in this case. Use `git rebase -i`.
516
517- 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).
518
519- When adding yourself as maintainer in the same pull request, make a separate
520 commit with the message `maintainers: add <handle>`.
521 Add the commit before those making changes to the package or module.
522 See [Nixpkgs Maintainers](./maintainers/README.md) for details.
523
524- Make sure you read about any commit conventions specific to the area you're touching. See:
525 - [Commit conventions](./pkgs/README.md#commit-conventions) for changes to `pkgs`.
526 - [Commit conventions](./lib/README.md#commit-conventions) for changes to `lib`.
527 - [Commit conventions](./nixos/README.md#commit-conventions) for changes to `nixos`.
528 - [Commit conventions](./doc/README.md#commit-conventions) for changes to `doc`, the Nixpkgs manual.
529
530### Writing good commit messages
531
532In 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.
533
534Package version upgrades usually allow for simpler commit messages, including attribute name, old and new version, as well as a reference to the relevant release notes/changelog. Every once in a while a package upgrade requires more extensive changes, and that subsequently warrants a more verbose message.
535
536Pull requests should not be squash merged in order to keep complete commit messages and GPG signatures intact and must not be when the change doesn't make sense as a single commit.
537
538## Code conventions
539[code-conventions]: #code-conventions
540
541### Release notes
542
543If you removed packages or made some major NixOS changes, write about it in the release notes for the next stable release in [`nixos/doc/manual/release-notes`](./nixos/doc/manual/release-notes).
544
545### File naming and organisation
546
547Names of files and directories should be in lowercase, with dashes between words — not in camel case. For instance, it should be `all-packages.nix`, not `allPackages.nix` or `AllPackages.nix`.
548
549### Syntax
550
551- Use 2 spaces of indentation per indentation level in Nix expressions, 4 spaces in shell scripts.
552
553- Do not use tab characters, i.e. configure your editor to use soft tabs. For instance, use `(setq-default indent-tabs-mode nil)` in Emacs. Everybody has different tab settings so it’s asking for trouble.
554
555- Use `lowerCamelCase` for variable names, not `UpperCamelCase`. Note, this rule does not apply to package attribute names, which instead follow the rules in [package naming](./pkgs/README.md#package-naming).
556
557- Function calls with attribute set arguments are written as
558
559 ```nix
560 foo {
561 arg = ...;
562 }
563 ```
564
565 not
566
567 ```nix
568 foo
569 {
570 arg = ...;
571 }
572 ```
573
574 Also fine is
575
576 ```nix
577 foo { arg = ...; }
578 ```
579
580 if it's a short call.
581
582- In attribute sets or lists that span multiple lines, the attribute names or list elements should be aligned:
583
584 ```nix
585 # A long list.
586 list = [
587 elem1
588 elem2
589 elem3
590 ];
591
592 # A long attribute set.
593 attrs = {
594 attr1 = short_expr;
595 attr2 =
596 if true then big_expr else big_expr;
597 };
598
599 # Combined
600 listOfAttrs = [
601 {
602 attr1 = 3;
603 attr2 = "fff";
604 }
605 {
606 attr1 = 5;
607 attr2 = "ggg";
608 }
609 ];
610 ```
611
612- Short lists or attribute sets can be written on one line:
613
614 ```nix
615 # A short list.
616 list = [ elem1 elem2 elem3 ];
617
618 # A short set.
619 attrs = { x = 1280; y = 1024; };
620 ```
621
622- Breaking in the middle of a function argument can give hard-to-read code, like
623
624 ```nix
625 someFunction { x = 1280;
626 y = 1024; } otherArg
627 yetAnotherArg
628 ```
629
630 (especially if the argument is very large, spanning multiple lines).
631
632 Better:
633
634 ```nix
635 someFunction
636 { x = 1280; y = 1024; }
637 otherArg
638 yetAnotherArg
639 ```
640
641 or
642
643 ```nix
644 let res = { x = 1280; y = 1024; };
645 in someFunction res otherArg yetAnotherArg
646 ```
647
648- The bodies of functions, asserts, and withs are not indented to prevent a lot of superfluous indentation levels, i.e.
649
650 ```nix
651 { arg1, arg2 }:
652 assert system == "i686-linux";
653 stdenv.mkDerivation { ...
654 ```
655
656 not
657
658 ```nix
659 { arg1, arg2 }:
660 assert system == "i686-linux";
661 stdenv.mkDerivation { ...
662 ```
663
664- Function formal arguments are written as:
665
666 ```nix
667 { arg1, arg2, arg3 }:
668 ```
669
670 but if they don't fit on one line they're written as:
671
672 ```nix
673 { arg1, arg2, arg3
674 , arg4, ...
675 , # Some comment...
676 argN
677 }:
678 ```
679
680- Functions should list their expected arguments as precisely as possible. That is, write
681
682 ```nix
683 { stdenv, fetchurl, perl }: ...
684 ```
685
686 instead of
687
688 ```nix
689 args: with args; ...
690 ```
691
692 or
693
694 ```nix
695 { stdenv, fetchurl, perl, ... }: ...
696 ```
697
698 For functions that are truly generic in the number of arguments (such as wrappers around `mkDerivation`) that have some required arguments, you should write them using an `@`-pattern:
699
700 ```nix
701 { stdenv, doCoverageAnalysis ? false, ... } @ args:
702
703 stdenv.mkDerivation (args // {
704 ... if doCoverageAnalysis then "bla" else "" ...
705 })
706 ```
707
708 instead of
709
710 ```nix
711 args:
712
713 args.stdenv.mkDerivation (args // {
714 ... if args ? doCoverageAnalysis && args.doCoverageAnalysis then "bla" else "" ...
715 })
716 ```
717
718- Unnecessary string conversions should be avoided. Do
719
720 ```nix
721 rev = version;
722 ```
723
724 instead of
725
726 ```nix
727 rev = "${version}";
728 ```
729
730- Building lists conditionally _should_ be done with `lib.optional(s)` instead of using `if cond then [ ... ] else null` or `if cond then [ ... ] else [ ]`.
731
732 ```nix
733 buildInputs = lib.optional stdenv.isDarwin iconv;
734 ```
735
736 instead of
737
738 ```nix
739 buildInputs = if stdenv.isDarwin then [ iconv ] else null;
740 ```
741
742 As an exception, an explicit conditional expression with null can be used when fixing a important bug without triggering a mass rebuild.
743 If this is done a follow up pull request _should_ be created to change the code to `lib.optional(s)`.