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Contributing to Nixpkgs packages

This document is for people wanting to contribute specifically to the package collection in Nixpkgs. See the CONTRIBUTING.md document for more general information.

Overview

Quick Start to Adding a Package

We welcome new contributors of new packages to Nixpkgs, arguably the greatest software database known. However, each new package comes with a cost for the maintainers, Continuous Integration, caching servers and users downloading Nixpkgs.

Before adding a new package, please consider the following questions:

  • Is the package ready for general use? We don't want to include projects that are too immature or are going to be abandoned immediately. In case of doubt, check with upstream.
  • Does the project have a clear license statement? Remember that software is unfree by default (all rights reserved), and merely providing access to the source code does not imply its redistribution. In case of doubt, ask upstream.
  • How realistic is it that it will be used by other people? It's good that nixpkgs caters to various niches, but if it's a niche of 5 people it's probably too small.
  • Are you willing to maintain the package? You should care enough about the package to be willing to keep it up and running for at least one complete Nixpkgs' release life-cycle.
    • In case you are not able to maintain the package you wrote, you can seek someone to fill that role, effectively adopting the package.

If any of these questions' answer is no, then you should probably not add the package.

This is section describes a general framework of understanding and exceptions might apply.

Luckily it's pretty easy to maintain your own package set with Nix, which can then be added to the Nix User Repository project.

Now that this is out of the way. To add a package to Nixpkgs:

  1. Checkout the Nixpkgs source tree:

    $ git clone https://github.com/NixOS/nixpkgs
$ cd nixpkgs

  2. Create a package directory pkgs/by-name/so/some-package where some-package is the package name and so is the lowercased 2-letter prefix of the package name:

    $ mkdir -p pkgs/by-name/so/some-package

    For more detailed information, see here.

  3. Create a package.nix file in the package directory, containing a Nix expression — a piece of code that describes how to build the package. In this case, it should be a function that is called with the package dependencies as arguments, and returns a build of the package in the Nix store.

    $ emacs pkgs/by-name/so/some-package/package.nix
$ git add pkgs/by-name/so/some-package/package.nix

    If the package is written in a language other than C, you should use the corresponding language framework.

    You can have a look at the existing Nix expressions under pkgs/ to see how it’s done, some of which are also using the category hierarchy. Here are some good ones:

    Some notes:

    • Add yourself as the maintainer of the package.

    • All other meta attributes are optional, but it’s still a good idea to provide at least the description, homepage and license.

    • The exact syntax and semantics of the Nix expression language, including the built-in functions, are Nix language reference.

  4. To test whether the package builds, run the following command from the root of the nixpkgs source tree:

    $ nix-build -A some-package

    where some-package should be the package name. You may want to add the flag -K to keep the temporary build directory in case something fails. If the build succeeds, a symlink ./result to the package in the Nix store is created.

  5. If you want to install the package into your profile (optional), do

    $ nix-env -f . -iA libfoo

  6. Optionally commit the new package and open a pull request to nixpkgs, or use the Patches category on Discourse for sending a patch without a GitHub account.

Commit conventions

  • Make sure you read about the commit conventions common to Nixpkgs as a whole.

  • Format the commit messages in the following way:

    (pkg-name): (from -> to | init at version | refactor | etc)

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

    Examples:

(using "→" instead of "->" is also accepted)

Category Hierarchy

Most top-level packages are organised in a loosely-categorised directory hierarchy in this directory. See the overview for which directories are part of this.

This category hierarchy is partially deprecated and will be migrated away over time. The new pkgs/by-name directory (docs) should be preferred instead. The category hierarchy may still be used for packages that should be imported using an alternate callPackage, such as python3Packages.callPackage or libsForQt5.callPackage.

If that is the case for a new package, here are some rules for picking the right category. Many packages fall under several categories; what matters is the primary purpose of a package. For example, the libxml2 package builds both a library and some tools; but it’s a library foremost, so it goes under pkgs/development/libraries.

Categories

If it’s used to support software development:

  • If it’s a library used by other packages:

    • development/libraries (e.g. libxml2)

  • If it’s a compiler:

    • development/compilers (e.g. gcc)

  • If it’s an interpreter:

    • development/interpreters (e.g. guile)

  • If it’s a (set of) development tool(s):

    • If it’s a parser generator (including lexers):

      • development/tools/parsing (e.g. bison, flex)

    • If it’s a build manager:

      • development/tools/build-managers (e.g. gnumake)

    • If it’s a language server:

      • development/tools/language-servers (e.g. ccls or nil)

    • Else:

      • development/tools/misc (e.g. binutils)

  • Else:

    • development/misc

If it’s a (set of) tool(s):

(A tool is a relatively small program, especially one intended to be used non-interactively.)

  • If it’s for networking:

    • tools/networking (e.g. wget)

  • If it’s for text processing:

    • tools/text (e.g. diffutils)

  • If it’s a system utility, i.e., something related or essential to the operation of a system:

    • tools/system (e.g. cron)

  • If it’s an archiver (which may include a compression function):

    • tools/archivers (e.g. zip, tar)

  • If it’s a compression program:

    • tools/compression (e.g. gzip, bzip2)

  • If it’s a security-related program:

    • tools/security (e.g. nmap, gnupg)

  • Else:

    • tools/misc

If it’s a shell:

  • shells (e.g. bash)

If it’s a server:

  • If it’s a web server:

    • servers/http (e.g. apache-httpd)

  • If it’s an implementation of the X Windowing System:

    • servers/x11 (e.g. xorg — this includes the client libraries and programs)

  • Else:

    • servers/misc

If it’s a desktop environment:

  • desktops (e.g. kde, gnome, enlightenment)

If it’s a window manager:

  • applications/window-managers (e.g. awesome, stumpwm)

If it’s an application:

A (typically large) program with a distinct user interface, primarily used interactively.

  • If it’s a version management system:

    • applications/version-management (e.g. subversion)

  • If it’s a terminal emulator:

    • applications/terminal-emulators (e.g. alacritty or rxvt or termite)

  • If it’s a file manager:

    • applications/file-managers (e.g. mc or ranger or pcmanfm)

  • If it’s for video playback / editing:

    • applications/video (e.g. vlc)

  • If it’s for graphics viewing / editing:

    • applications/graphics (e.g. gimp)

  • If it’s for networking:

    • If it’s a mailreader:

      • applications/networking/mailreaders (e.g. thunderbird)

    • If it’s a newsreader:

      • applications/networking/newsreaders (e.g. pan)

    • If it’s a web browser:

      • applications/networking/browsers (e.g. firefox)

    • Else:

      • applications/networking/misc

  • Else:

    • applications/misc

If it’s data (i.e., does not have a straight-forward executable semantics):

  • If it’s a font:

    • data/fonts

  • If it’s an icon theme:

    • data/icons

  • If it’s related to SGML/XML processing:

    • If it’s an XML DTD:

      • data/sgml+xml/schemas/xml-dtd (e.g. docbook)

    • If it’s an XSLT stylesheet:

      (Okay, these are executable...)

      • data/sgml+xml/stylesheets/xslt (e.g. docbook-xsl)

  • If it’s a theme for a desktop environment, a window manager or a display manager:

    • data/themes

If it’s a game:

  • games

Else:

  • misc

Conventions

The key words must, must not, required, shall, shall not, should, should not, recommended, may, and optional in this section are to be interpreted as described in RFC 2119. Only emphasized words are to be interpreted in this way.

Package naming

In Nixpkgs, there are generally three different names associated with a package:

  • The pname attribute of the derivation. This is what most users see, in particular when using nix-env.

  • The attribute name used for the package in the pkgs/by-name structure or in all-packages.nix, and when passing it as a dependency in recipes.

  • The filename for (the directory containing) the Nix expression.

Most of the time, these are the same. For instance, the package e2fsprogs has a pname attribute "e2fsprogs", is bound to the attribute name e2fsprogs in all-packages.nix, and the Nix expression is in pkgs/os-specific/linux/e2fsprogs/default.nix.

Follow these guidelines:

  • For the pname attribute:

    • It should be identical to the upstream package name.

    • It must not contain uppercase letters.

      Example: Use "mplayer" instead of "MPlayer"

  • For the package attribute name:

    • It must be a valid identifier in Nix.

    • If the pname starts with a digit, the attribute name should be prefixed with an underscore. Otherwise the attribute name should not be prefixed with an underline.

      Example: The corresponding attribute name for 0ad should be _0ad.

    • New attribute names should be the same as the value in pname.

      Hyphenated names should not be converted to snake case or camel case. This was done historically, but is not necessary any more. The Nix language allows dashes in identifiers since 2012.

    • If there are multiple versions of a package, this should be reflected in the attribute names in all-packages.nix.

      Example: json-c_0_9 and json-c_0_11

      If there is an obvious “default” version, make an extra attribute.

      Example: json-c = json-c_0_9;

      See also versioning.

Versioning

These are the guidelines the version attribute of a package:

  • It must start with a digit. This is required for backwards-compatibility with how nix-env parses derivation names.

    Example: "0.3.1rc2" or "0-unstable-1970-01-01"

  • If a package is a commit from a repository without a version assigned, then the version attribute should be the latest upstream version preceding that commit, followed by -unstable- and the date of the (fetched) commit. The date must be in "YYYY-MM-DD" format.

    Example: Given a project had its latest releases 2.2 in November 2021 and 3.0 in January 2022, a commit authored on March 15, 2022 for an upcoming bugfix release 2.2.1 would have version = "2.2-unstable-2022-03-15".

  • If a project has no suitable preceding releases - e.g., no versions at all, or an incompatible versioning or tagging scheme - then the latest upstream version in the above schema should be 0.

    Example: Given a project that has no tags or released versions at all, or applies versionless tags like latest or YYYY-MM-DD-Build, a commit authored on March 15, 2022 would have version = "0-unstable-2022-03-15".

Because every version of a package in Nixpkgs creates a potential maintenance burden, old versions of a package should not be kept unless there is a good reason to do so. For instance, Nixpkgs contains several versions of GCC because other packages don’t build with the latest version of GCC. Other examples are having both the latest stable and latest pre-release version of a package, or to keep several major releases of an application that differ significantly in functionality.

If there is only one version of a package, its Nix expression should be named (e.g) pkgs/by-name/xy/xyz/package.nix. If there are multiple versions, this should be reflected in the attribute name. If you wish to share code between the Nix expressions of each version, you cannot rely upon pkgs/by-name's automatic attribute creation, and must create the attributes yourself in all-packages.nix. See also pkgs/by-name/README.md's section on this topic.

Meta attributes

  • meta.description must:
    • Be short, just one sentence.
    • Be capitalized.
    • Not start with the definite or an indefinite article.
    • Not start with the package name.
      • More generally, it should not refer to the package name.
    • Not end with a period (or any punctuation for that matter).
    • Provide factual information.
      • Avoid subjective language.
  • meta.license must be set and match the upstream license.
    • If there is no upstream license, meta.license should default to lib.licenses.unfree.
    • If in doubt, try to contact the upstream developers for clarification.
  • meta.mainProgram must be set to the name of the executable which facilitates the primary function or purpose of the package, if there is such an executable in $bin/bin/ (or $out/bin/, if there is no "bin" output).
    • Packages that only have a single executable in the applicable directory above should set meta.mainProgram. For example, the package ripgrep only has a single executable rg under $out/bin/, so ripgrep.meta.mainProgram is set to "rg".
    • Packages like polkit_gnome that have no executables in the applicable directory should not set meta.mainProgram.
    • Packages like e2fsprogs that have multiple executables, none of which can be considered the main program, should not set meta.mainProgram.
    • Packages which are not primarily used for a single executable do not need to set meta.mainProgram.
    • Always prefer using a hardcoded string (don't use pname, for example).
    • When in doubt, ask for reviewer input.
  • meta.maintainers must be set for new packages.

See the Nixpkgs manual for more details on standard meta-attributes.

Import From Derivation

Import From Derivation (IFD) is disallowed in Nixpkgs for performance reasons: Hydra evaluates the entire package set, and sequential builds during evaluation would increase evaluation times to become impractical.

Import From Derivation can be worked around in some cases by committing generated intermediate files to version control and reading those instead.

Sources

Always fetch source files using Nixpkgs fetchers. Use reproducible sources with a high degree of availability. Prefer protocols that support proxies.

A list of schemes for mirror:// URLs can be found in pkgs/build-support/fetchurl/mirrors.nix, and is supported by fetchurl. Other fetchers which end up relying on fetchurl may also support mirroring.

The preferred source hash type is sha256.

Examples going from bad to best practices:

  • Bad: Uses git:// which won't be proxied.

    {
  src = fetchgit {
    url = "git://github.com/NixOS/nix.git";
    rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
    hash = "sha256-7D4m+saJjbSFP5hOwpQq2FGR2rr+psQMTcyb1ZvtXsQ=";
  };
}

  • Better: This is ok, but an archive fetch will still be faster.

    {
  src = fetchgit {
    url = "https://github.com/NixOS/nix.git";
    rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
    hash = "sha256-7D4m+saJjbSFP5hOwpQq2FGR2rr+psQMTcyb1ZvtXsQ=";
  };
}

  • Best: Fetches a snapshot archive for the given revision.

    {
  src = fetchFromGitHub {
    owner = "NixOS";
    repo = "nix";
    rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
    hash = "sha256-7D4m+saJjbSFP5hOwpQq2FGR2rr+psQMTcyb1ZvtXsQ=";
  };
}

Note

When fetching from GitHub, always reference revisions by their full commit hash. GitHub shares commit hashes among all forks and returns 404 Not Found when a short commit hash is ambiguous. It already happened in Nixpkgs for short, 6-character commit hashes.

Pushing large amounts of auto generated commits into forks is a practical vector for a denial-of-service attack, and was already demonstrated against GitHub Actions Beta.

Patches

Sometimes, changes are needed to the source to allow building a derivation in nixpkgs, or to get earlier access to an upstream fix or improvement. When using the patches parameter to mkDerivation, make sure the patch name clearly describes the reason for the patch, or add a comment.

Fetching patches

In the interest of keeping our maintenance burden and the size of Nixpkgs to a minimum, patches already merged upstream or published elsewhere should be retrieved using fetchpatch:

{
  patches = [
    (fetchpatch {
      name = "fix-check-for-using-shared-freetype-lib.patch";
      url = "http://git.ghostscript.com/?p=ghostpdl.git;a=patch;h=8f5d285";
      hash = "sha256-uRcxaCjd+WAuGrXOmGfFeu79cUILwkRdBu48mwcBE7g=";
    })
  ];
}

If a patch is available online but does not cleanly apply, it can be modified in some fixed ways by using additional optional arguments for fetchpatch. Check the fetchpatch reference for details.

Vendoring patches

In the following cases, a .patch file should be added to Nixpkgs repository, instead of retrieved:

  • solves problems unique to packaging in Nixpkgs
  • is already proposed upstream but not merged yet
  • cannot be fetched easily
  • has a high chance to disappear in the future due to unstable or unreliable URLs

The latter avoids link rot when the upstream abandons, squashes or rebases their change, in which case the commit may get garbage-collected.

{
  patches = [ ./0001-add-missing-include.patch ];
}

If you do need to do create this sort of patch file, one way to do so is with git:

  1. Move to the root directory of the source code you're patching.

    $ cd the/program/source

  2. If a git repository is not already present, create one and stage all of the source files.

    $ git init
$ git add .

  3. Edit some files to make whatever changes need to be included in the patch.

  4. Use git to create a diff, and pipe the output to a patch file:

    $ git diff -a > nixpkgs/pkgs/the/package/0001-changes.patch

Deprecating/removing packages

There is currently no policy when to remove a package.

Before removing a package, one should try to find a new maintainer or fix smaller issues first.

Steps to remove a package from Nixpkgs

We use jbidwatcher as an example for a discontinued project here.

  1. Have Nixpkgs checked out locally and up to date.

  2. Create a new branch for your change, e.g. git checkout -b jbidwatcher

  3. Remove the actual package including its directory, e.g. git rm -rf pkgs/applications/misc/jbidwatcher

  4. Remove the package from the list of all packages (pkgs/top-level/all-packages.nix).

  5. Add an alias for the package name in pkgs/top-level/aliases.nix (There is also pkgs/applications/editors/vim/plugins/aliases.nix. Package sets typically do not have aliases, so we can't add them there.)

    For example in this case:

    {
  jbidwatcher = throw "jbidwatcher was discontinued in march 2021"; # added 2021-03-15
}

    The throw message should explain in short why the package was removed for users that still have it installed.

  6. Test if the changes introduced any issues by running nix-env -qaP -f . --show-trace. It should show the list of packages without errors.

  7. Commit the changes. Explain again why the package was removed. If it was declared discontinued upstream, add a link to the source.

    $ git add pkgs/applications/misc/jbidwatcher/default.nix pkgs/top-level/all-packages.nix pkgs/top-level/aliases.nix
$ git commit

    Example commit message:

    jbidwatcher: remove

project was discontinued in march 2021. the program does not work anymore because ebay changed the login.

https://web.archive.org/web/20210315205723/http://www.jbidwatcher.com/

  8. Push changes to your GitHub fork with git push

  9. Create a pull request against Nixpkgs. Mention the package maintainer.

This is how the pull request looks like in this case: NixOS#116470

Package tests

To run the main types of tests locally:

  • Run package-internal tests with nix-build --attr pkgs.PACKAGE.passthru.tests
  • Run NixOS tests with nix-build --attr nixosTests.NAME, where NAME is the name of the test listed in nixos/tests/all-tests.nix
  • Run global package tests with nix-build --attr tests.PACKAGE, where PACKAGE is the name of the test listed in pkgs/test/default.nix
  • See lib/tests/NAME.nix for instructions on running specific library tests

Tests are important to ensure quality and make reviews and automatic updates easy.

The following types of tests exists:

  • NixOS module tests, which spawn one or more NixOS VMs. They exercise both NixOS modules and the packaged programs used within them. For example, a NixOS module test can start a web server VM running the nginx module, and a client VM running curl or a graphical firefox, and test that they can talk to each other and display the correct content.
  • Nix package tests are a lightweight alternative to NixOS module tests. They should be used to create simple integration tests for packages, but cannot test NixOS services, and some programs with graphical user interfaces may also be difficult to test with them.
  • The checkPhase of a package, which should execute the unit tests that are included in the source code of a package.

Here in the nixpkgs manual we describe mostly package tests; for module tests head over to the corresponding section in the NixOS manual.

Writing inline package tests

For very simple tests, they can be written inline:

{ /* ... , */ yq-go }:

buildGoModule rec {
  # …

  passthru.tests = {
    simple = runCommand "${pname}-test" {} ''
      echo "test: 1" | ${yq-go}/bin/yq eval -j > $out
      [ "$(cat $out | tr -d $'\n ')" = '{"test":1}' ]
    '';
  };
}

Any derivation can be specified as a test, even if it's in a different file. Such a derivation that implements a test can depend on the package under test, even in the presence of overrideAttrs.

In the following example, (my-package.overrideAttrs f).passthru.tests will work as expected, as long as the definition of tests does not rely on the original my-package or overrides all occurrences of my-package:

# my-package/default.nix
{ stdenv, callPackage }:
stdenv.mkDerivation (finalAttrs: {
  # ...
  passthru.tests.example = callPackage ./example.nix { my-package = finalAttrs.finalPackage; };
})
# my-package/example.nix
{ runCommand, lib, my-package, ... }:
runCommand "my-package-test" {
  nativeBuildInputs = [ my-package ];
  src = lib.sources.sourcesByRegex ./. [ ".*.in" ".*.expected" ];
} ''
  my-package --help
  my-package <example.in >example.actual
  diff -U3 --color=auto example.expected example.actual
  mkdir $out
''

Writing larger package tests

This is an example using the phoronix-test-suite package with the current best practices.

Add the tests in passthru.tests to the package definition like this:

{ stdenv, lib, fetchurl, callPackage }:

stdenv.mkDerivation {
  # …

  passthru.tests = {
    simple-execution = callPackage ./tests.nix { };
  };

  meta = { /* … */ };
}

Create tests.nix in the package directory:

{ runCommand, phoronix-test-suite }:

let
  inherit (phoronix-test-suite) pname version;
in

runCommand "${pname}-tests" { meta.timeout = 60; }
  ''
    # automatic initial setup to prevent interactive questions
    ${phoronix-test-suite}/bin/phoronix-test-suite enterprise-setup >/dev/null
    # get version of installed program and compare with package version
    if [[ `${phoronix-test-suite}/bin/phoronix-test-suite version` != *"${version}"*  ]]; then
      echo "Error: program version does not match package version"
      exit 1
    fi
    # run dummy command
    ${phoronix-test-suite}/bin/phoronix-test-suite dummy_module.dummy-command >/dev/null
    # needed for Nix to register the command as successful
    touch $out
  ''

Running package tests

You can run these tests with:

$ cd path/to/nixpkgs
$ nix-build -A phoronix-test-suite.tests

Examples of package tests

Here are examples of package tests:

Linking NixOS module tests to a package

Like package tests as shown above, NixOS module tests can also be linked to a package, so that the tests can be easily run when changing the related package.

For example, assuming we're packaging nginx, we can link its module test via passthru.tests:

{ stdenv, lib, nixosTests }:

stdenv.mkDerivation {
  # ...

  passthru.tests = {
    nginx = nixosTests.nginx;
  };

  # ...
}

Automatic package updates

Nixpkgs periodically tries to update all packages that have a passthru.updateScript attribute.

Note

A common pattern is to use the nix-update-script attribute provided in Nixpkgs, which runs nix-update:

{ stdenv, nix-update-script }:
stdenv.mkDerivation {
  # ...
  passthru.updateScript = nix-update-script { };
}

For simple packages, this is often enough, and will ensure that the package is updated automatically by nixpkgs-update when a new version is released. The update bot runs periodically to attempt to automatically update packages, and will run passthru.updateScript if set. While not strictly necessary if the project is listed on Repology, using nix-update-script allows the package to update via many more sources (e.g. GitHub releases).

The passthru.updateScript attribute can contain one of the following:

  • an executable file, either on the file system:

    { stdenv }:
stdenv.mkDerivation {
  # ...
  passthru.updateScript = ./update.sh;
}

    or inside the expression itself:

    { stdenv, writeScript }:
stdenv.mkDerivation {
  # ...
  passthru.updateScript = writeScript "update-zoom-us" ''
    #!/usr/bin/env nix-shell
    #!nix-shell -i bash -p curl pcre2 common-updater-scripts

    set -eu -o pipefail

    version="$(curl -sI https://zoom.us/client/latest/zoom_x86_64.tar.xz | grep -Fi 'Location:' | pcre2grep -o1 '/(([0-9]\.?)+)/')"
    update-source-version zoom-us "$version"
  '';
}

  • a list, a script file followed by arguments to be passed to it:

    { stdenv }:
stdenv.mkDerivation {
  # ...
  passthru.updateScript = [ ../../update.sh pname "--requested-release=unstable" ];
}

  • an attribute set containing:

    • command

      A string or list in the format expected by passthru.updateScript

    • attrPath (optional)

      A string containing the canonical attribute path for the package.

      If present, it will be passed to the update script instead of the attribute path on which the package was discovered during Nixpkgs traversal.

    • supportedFeatures (optional)

      A list of the [extra features the script supports][supported-features].

      { stdenv }:
stdenv.mkDerivation rec {
  pname = "my-package";
  # ...
  passthru.updateScript = {
    command = [ ../../update.sh pname ];
    attrPath = pname;
    supportedFeatures = [ /* ... */ ];
  };
}

How are update scripts executed?

Update scripts are to be invoked by the automatic package update script. You can run nix-shell maintainers/scripts/update.nix in the root of Nixpkgs repository for information on how to use it. update.nix offers several modes for selecting packages to update, and it will execute update scripts for all matched packages that have an updateScript attribute.

Each update script will be passed the following environment variables:

  • [UPDATE_NIX_NAME] – content of the name attribute of the updated package
  • [UPDATE_NIX_PNAME] – content of the pname attribute of the updated package
  • [UPDATE_NIX_OLD_VERSION] – content of the version attribute of the updated package
  • [UPDATE_NIX_ATTR_PATH] – attribute path the update.nix discovered the package on (or the package's specified attrPath when available). Example: pantheon.elementary-terminal

Note

An update script will be usually run from the root of the Nixpkgs repository, but you should not rely on that. Also note that update.nix executes update scripts in parallel by default, so you should avoid running git commit or any other commands that cannot handle that.

While update scripts should not create commits themselves, update.nix supports automatically creating commits when running it with --argstr commit true. If you need to customize commit message, you can have the update script implement the commit feature.

Supported features

  • commit

    This feature allows update scripts to ask update.nix to create Git commits.

    When support of this feature is declared, whenever the update script exits with 0 return status, it is expected to print a JSON list containing an object described below for each updated attribute to standard output. Example:

    [
  {
    "attrPath": "volume_key",
    "oldVersion": "0.3.11",
    "newVersion": "0.3.12",
    "files": [
      "/path/to/nixpkgs/pkgs/development/libraries/volume-key/default.nix"
    ]
  }
]

    :::

    When update.nix is run with --argstr commit true, it will create a separate commit for each of the objects. An empty list can be returned when the script did not update any files; for example, when the package is already at the latest version.

    The commit object contains the following values:

    • attrPath – a string containing the attribute path
    • oldVersion – a string containing the old version
    • newVersion – a string containing the new version
    • files – a non-empty list of file paths (as strings) to add to the commit
    • commitBody (optional) – a string with extra content to be appended to the default commit message (useful for adding changelog links)
    • commitMessage (optional) – a string to use instead of the default commit message

    If the returned list contains exactly one object (e.g. [{}]), all values are optional and will be determined automatically.

Reviewing contributions

Package updates

A package update is the most trivial and common type of pull request. These pull requests mainly consist of updating the version part of the package name and the source hash.

It can happen that non-trivial updates include patches or more complex changes.

Reviewing process:

  • Ensure that the package versioning fits the guidelines.
  • Ensure that the commit text fits the guidelines.
  • Ensure that the package maintainers are notified.
    • CODEOWNERS will make GitHub notify users based on the submitted changes, but it can happen that it misses some of the package maintainers.
  • Ensure that the meta field information fits the guidelines and is correct:
    • License can change with version updates, so it should be checked to match the upstream license.
    • If the package has no maintainer, a maintainer must be set. This can be the update submitter or a community member that accepts to take maintainership of the package.
  • Ensure that the code contains no typos.
  • Build the package locally.

    • Pull requests are often targeted to the master or staging branch, and building the pull request locally when it is submitted can trigger many source builds.

    • It is possible to rebase the changes on nixos-unstable or nixpkgs-unstable for easier review by running the following commands from a nixpkgs clone.

      $ git fetch origin nixos-unstable
$ git fetch origin pull/PRNUMBER/head
$ git rebase --onto nixos-unstable BASEBRANCH FETCH_HEAD
      • The first command fetches the nixos-unstable branch.
      • The second command fetches the pull request changes, PRNUMBER is the number at the end of the pull request title and BASEBRANCH the base branch of the pull request.
      • The third command rebases the pull request changes to the nixos-unstable branch.

    • The nixpkgs-review tool can be used to review a pull request content in a single command. PRNUMBER should be replaced by the number at the end of the pull request title. You can also provide the full github pull request url.

      $ nix-shell -p nixpkgs-review --run "nixpkgs-review pr PRNUMBER"
  • Run every binary.

Sample template for a package update review is provided below.

##### Reviewed points

- [ ] package name fits guidelines
- [ ] package version fits guidelines
- [ ] package builds on ARCHITECTURE
- [ ] executables tested on ARCHITECTURE
- [ ] all depending packages build
- [ ] patches have a comment describing either the upstream URL or a reason why the patch wasn't upstreamed
- [ ] patches that are remotely available are fetched rather than vendored

##### Possible improvements

##### Comments

New packages

New packages are a common type of pull requests. These pull requests consists in adding a new nix-expression for a package.

Review process:

  • Ensure that all file paths fit the guidelines.
  • Ensure that the package name and version fits the guidelines.
  • Ensure that the package versioning fits the guidelines.
  • Ensure that the commit text fits the guidelines.
  • Ensure that the meta fields fits the guidelines and contain the correct information:
    • License must match the upstream license.
    • Platforms should be set (or the package will not get binary substitutes).
    • Maintainers must be set. This can be the package submitter or a community member that accepts taking up maintainership of the package.
    • The meta.mainProgram must be set if a main executable exists.
  • Report detected typos.
  • Ensure the package source:
    • Uses mirror:// URLs when available.
    • Uses the most appropriate functions (e.g. packages from GitHub should use fetchFromGitHub).
  • Build the package locally.
  • Run every binary.

Sample template for a new package review is provided below.

##### Reviewed points

- [ ] package path fits guidelines
- [ ] package name fits guidelines
- [ ] package version fits guidelines
- [ ] package builds on ARCHITECTURE
- [ ] executables tested on ARCHITECTURE
- [ ] `meta.description` is set and fits guidelines
- [ ] `meta.license` fits upstream license
- [ ] `meta.platforms` is set
- [ ] `meta.maintainers` is set
- [ ] `meta.mainProgram` is set, if applicable.
- [ ] build time only dependencies are declared in `nativeBuildInputs`
- [ ] source is fetched using the appropriate function
- [ ] the list of `phases` is not overridden
- [ ] when a phase (like `installPhase`) is overridden it starts with `runHook preInstall` and ends with `runHook postInstall`.
- [ ] patches have a comment describing either the upstream URL or a reason why the patch wasn't upstreamed
- [ ] patches that are remotely available are fetched rather than vendored

##### Possible improvements

##### Comments

Security

Submitting security fixes

Security fixes are submitted in the same way as other changes and thus the same guidelines apply.

  • If a new version fixing the vulnerability has been released, update the package;

  • If the security fix comes in the form of a patch and a CVE is available, then add the patch to the Nixpkgs tree, and apply it to the package. The name of the patch should be the CVE identifier, so e.g. CVE-2019-13636.patch; If a patch is fetched the name needs to be set as well, e.g.:

    (fetchpatch {
  name = "CVE-2019-11068.patch";
  url = "https://gitlab.gnome.org/GNOME/libxslt/commit/e03553605b45c88f0b4b2980adfbbb8f6fca2fd6.patch";
  hash = "sha256-SEKe/8HcW0UBHCfPTTOnpRlzmV2nQPPeL6HOMxBZd14=";
})

If a security fix applies to both master and a stable release then, similar to regular changes, they are preferably delivered via master first and cherry-picked to the release branch.

Critical security fixes may by-pass the staging branches and be delivered directly to release branches such as master and release-*.

Vulnerability Roundup

Issues

Vulnerable packages in Nixpkgs are managed using issues. Currently opened ones can be found using the following:

github.com/NixOS/nixpkgs/issues?q=is:issue+is:open+"Vulnerability+roundup"

Each issue correspond to a vulnerable version of a package; As a consequence:

  • One issue can contain several CVEs;
  • One CVE can be shared across several issues;
  • A single package can be concerned by several issues.

A "Vulnerability roundup" issue usually respects the following format:

<link to relevant package search on search.nix.gsc.io>, <link to relevant files in Nixpkgs on GitHub>

<list of related CVEs, their CVSS score, and the impacted NixOS version>

<list of the scanned Nixpkgs versions>

<list of relevant contributors>

Note that there can be an extra comment containing links to previously reported (and still open) issues for the same package.

Triaging and Fixing

Note: An issue can be a "false positive" (i.e. automatically opened, but without the package it refers to being actually vulnerable). If you find such a "false positive", comment on the issue an explanation of why it falls into this category, linking as much information as the necessary to help maintainers double check.

If you are investigating a "true positive":