mirror of https://github.com/NixOS/nixpkgs.git synced 2024-11-22 15:03:28 +00:00

Silvan Mosberger 1e1cd398d4 doc/coding-conventions: Rough move to new contribution doc files

No content was changed, new titles are wrapped with () to signal that
they will need to be decided on in a future commit.

Section in the manual have been preserved with a simple redirect to
GitHub, the proper anchors should be filled out in a future commit once
the new section names are decided.

2023-08-13 22:02:34 +02:00

13 KiB

Raw Blame History

Contributing to Nixpkgs

(Proposing a change) | Submitting changes

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

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).

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.

Package 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.

Pull 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. This means that, when addressing review comments in order to keep the pull request in an always mergeable status, you will sometimes need to rewrite your branch's history and then force-push it with git push --force-with-lease. Useful git commands that can help a lot with this are git commit --patch --amend and git rebase --interactive. For more details consult the git man pages or online resources like git-rebase.io or The Pro Git Book.

(Creating a pull request)

When pull requests are made, our tooling automation bot, OfBorg will perform various checks to help ensure expression quality.

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. 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.

# 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.

# 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:

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.

Backporting changes

Follow these steps to backport a change into a release branch in compliance with the commit policy.

You can add a label such as backport release-23.05 to a PR, so that merging it will automatically create a backport (via a GitHub Action). This also works for pull requests that have already been merged, and might take a couple of minutes to trigger.

You can also create the backport manually:

Take note of the commits in which the change was introduced into master branch.
Check out the target release branch, e.g. release-23.05. Do not use a channel branch like nixos-23.05 or nixpkgs-23.05-darwin.
Create a branch for your change, e.g. git checkout -b backport.
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.
Push to GitHub and open a backport pull request. Make sure to select the release branch (e.g. release-23.05) as the target branch of the pull request, and link to the pull request in which the original change was committed to master. The pull request title should be the commit title with the release version as prefix, e.g. [23.05].
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)

(Merging a pull request)

The Nixpkgs committers are people who have been given permission to merge.

(Flow of changes)

Most contributions are based on and merged into these branches:

master is the main branch where all small contributions go
staging is branched from master, changes that have a big impact on Hydra builds go to this branch
staging-next is branched from staging and only fixes to stabilize and security fixes with a big impact on Hydra builds should be contributed to this branch. This branch is merged into master when deemed of sufficiently high quality

Coding conventions

File naming and organisation

Names 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.

Syntax

Use 2 spaces of indentation per indentation level in Nix expressions, 4 spaces in shell scripts.
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.
Use lowerCamelCase for variable names, not UpperCamelCase. Note, this rule does not apply to package attribute names, which instead follow the rules in .
Function calls with attribute set arguments are written as
```
foo {
  arg = ...;
}
```
not
```
foo
{
  arg = ...;
}
```
Also fine is
```
foo { arg = ...; }
```
if it's a short call.

In attribute sets or lists that span multiple lines, the attribute names or list elements should be aligned:

# A long list.
list = [
  elem1
  elem2
  elem3
];

# A long attribute set.
attrs = {
  attr1 = short_expr;
  attr2 =
    if true then big_expr else big_expr;
};

# Combined
listOfAttrs = [
  {
    attr1 = 3;
    attr2 = "fff";
  }
  {
    attr1 = 5;
    attr2 = "ggg";
  }
];

Short lists or attribute sets can be written on one line:

# A short list.
list = [ elem1 elem2 elem3 ];

# A short set.
attrs = { x = 1280; y = 1024; };

Breaking in the middle of a function argument can give hard-to-read code, like

someFunction { x = 1280;
  y = 1024; } otherArg
  yetAnotherArg

(especially if the argument is very large, spanning multiple lines).

Better:

someFunction
  { x = 1280; y = 1024; }
  otherArg
  yetAnotherArg

let res = { x = 1280; y = 1024; };
in someFunction res otherArg yetAnotherArg

The bodies of functions, asserts, and withs are not indented to prevent a lot of superfluous indentation levels, i.e.

{ arg1, arg2 }:
assert system == "i686-linux";
stdenv.mkDerivation { ...

not

{ arg1, arg2 }:
  assert system == "i686-linux";
    stdenv.mkDerivation { ...

Function formal arguments are written as:

{ arg1, arg2, arg3 }:

but if they don't fit on one line they're written as:

{ arg1, arg2, arg3
, arg4, ...
, # Some comment...
  argN
}:

Functions should list their expected arguments as precisely as possible. That is, write

{ stdenv, fetchurl, perl }: ...

instead of

args: with args; ...

{ stdenv, fetchurl, perl, ... }: ...

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:

{ stdenv, doCoverageAnalysis ? false, ... } @ args:

stdenv.mkDerivation (args // {
  ... if doCoverageAnalysis then "bla" else "" ...
})