path: root/pkgs/README.md

# Contributing to Nixpkgs packages

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

## Overview

- [`top-level`](./top-level): Entrypoints, package set aggregations
  - [`impure.nix`](./top-level/impure.nix), [`default.nix`](./top-level/default.nix), [`config.nix`](./top-level/config.nix): Definitions for the evaluation entry point of `import <nixpkgs>`
  - [`stage.nix`](./top-level/stage.nix), [`all-packages.nix`](./top-level/all-packages.nix), [`by-name-overlay.nix`](./top-level/by-name-overlay.nix), [`splice.nix`](./top-level/splice.nix): Definitions for the top-level attribute set made available through `import <nixpkgs> {…}`
  - `*-packages.nix`, [`linux-kernels.nix`](./top-level/linux-kernels.nix), [`unixtools.nix`](./top-level/unixtools.nix): Aggregations of nested package sets defined in `development`
  - [`aliases.nix`](./top-level/aliases.nix), [`python-aliases.nix`](./top-level/python-aliases.nix): Aliases for package definitions that have been renamed or removed
  - `release*.nix`, [`make-tarball.nix`](./top-level/make-tarball.nix), [`packages-config.nix`](./top-level/packages-config.nix), [`metrics.nix`](./top-level/metrics.nix), [`nixpkgs-basic-release-checks.nix`](./top-level/nixpkgs-basic-release-checks.nix): Entry-points and utilities used by Hydra for continuous integration
- [`development`](./development)
  - `*-modules`, `*-packages`, `*-pkgs`: Package definitions for nested package sets
  - All other directories loosely categorise top-level package definitions, see [category hierarchy][categories]
- [`build-support`](./build-support): [Builders](https://nixos.org/manual/nixpkgs/stable/#part-builders)
  - `fetch*`: [Fetchers](https://nixos.org/manual/nixpkgs/stable/#chap-pkgs-fetchers)
- [`stdenv`](./stdenv): [Standard environment](https://nixos.org/manual/nixpkgs/stable/#part-stdenv)
- [`pkgs-lib`](./pkgs-lib): Definitions for utilities that need packages but are not needed for packages
- [`test`](./test): Tests not directly associated with any specific packages
- [`by-name`](./by-name): Top-level packages organised by name ([docs](./by-name/README.md))
- All other directories loosely categorise top-level packages definitions, see [category hierarchy][categories]

## 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.

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](https://github.com/nix-community/nur) project.

---

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

1. Checkout the Nixpkgs source tree:

   ```ShellSession
   $ 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:

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

   For more detailed information, see [here](./by-name/README.md).

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.

   ```ShellSession
   $ 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](https://nixos.org/manual/nixpkgs/stable/#chap-language-support).

   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](#category-hierarchy).
   Here are some good ones:

   - GNU Hello: [`pkgs/by-name/he/hello/package.nix`](./by-name/he/hello/package.nix). Trivial package, which specifies some `meta` attributes which is good practice.

   - GNU cpio: [`pkgs/tools/archivers/cpio/default.nix`](tools/archivers/cpio/default.nix). Also a simple package. The generic builder in `stdenv` does everything for you. It has no dependencies beyond `stdenv`.

   - GNU Multiple Precision arithmetic library (GMP): [`pkgs/development/libraries/gmp/5.1.x.nix`](development/libraries/gmp/5.1.x.nix). Also done by the generic builder, but has a dependency on `m4`.

   - Pan, a GTK-based newsreader: [`pkgs/applications/networking/newsreaders/pan/default.nix`](applications/networking/newsreaders/pan/default.nix). Has an optional dependency on `gtkspell`, which is only built if `spellCheck` is `true`.

   - Apache HTTPD: [`pkgs/servers/http/apache-httpd/2.4.nix`](servers/http/apache-httpd/2.4.nix). A bunch of optional features, variable substitutions in the configure flags, a post-install hook, and miscellaneous hackery.

   - buildMozillaMach: [`pkgs/applications/networking/browser/firefox/common.nix`](applications/networking/browsers/firefox/common.nix). A reusable build function for Firefox, Thunderbird and Librewolf.

   - JDiskReport, a Java utility: [`pkgs/tools/misc/jdiskreport/default.nix`](tools/misc/jdiskreport/default.nix). Nixpkgs doesn’t have a decent `stdenv` for Java yet so this is pretty ad-hoc.

   - XML::Simple, a Perl module: [`pkgs/top-level/perl-packages.nix`](top-level/perl-packages.nix) (search for the `XMLSimple` attribute). Most Perl modules are so simple to build that they are defined directly in `perl-packages.nix`; no need to make a separate file for them.

   - Adobe Reader: [`pkgs/applications/misc/adobe-reader/default.nix`](applications/misc/adobe-reader/default.nix). Shows how binary-only packages can be supported. In particular the [builder](applications/misc/adobe-reader/builder.sh) uses `patchelf` to set the RUNPATH and ELF interpreter of the executables so that the right libraries are found at runtime.

   Some notes:

   - Add yourself as the maintainer of the package.

   - All other [`meta`](https://nixos.org/manual/nixpkgs/stable/#chap-meta) attributes are optional, but it’s still a good idea to provide at least the `description`, `homepage` and [`license`](https://nixos.org/manual/nixpkgs/stable/#sec-meta-license).

   - You can use `nix-prefetch-url url` to get the SHA-256 hash of source distributions. There are similar commands as `nix-prefetch-git` and `nix-prefetch-hg` available in `nix-prefetch-scripts` package.

   - A list of schemes for `mirror://` URLs can be found in [`pkgs/build-support/fetchurl/mirrors.nix`](build-support/fetchurl/mirrors.nix).

   The exact syntax and semantics of the Nix expression language, including the built-in function, are [described in the Nix manual](https://nixos.org/manual/nix/stable/language/).

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

   ```ShellSession
   $ 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.

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

   ```ShellSession
   $ nix-env -f . -iA libfoo
   ```

7. Optionally commit the new package and open a pull request [to nixpkgs](https://github.com/NixOS/nixpkgs/pulls), or use [the Patches category](https://discourse.nixos.org/t/about-the-patches-category/477) on Discourse for sending a patch without a GitHub account.

## Commit conventions

- Make sure you read about the [commit conventions](../CONTRIBUTING.md#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:

  * nginx: init at 2.0.1
  * firefox: 54.0.1 -> 55.0

    https://www.mozilla.org/en-US/firefox/55.0/releasenotes/

## Category Hierarchy
[categories]: #category-hierarchy

Most top-level packages are organised in a loosely-categorised directory hierarchy in this directory.
See the [overview](#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](./by-name/README.md)) 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`.

<details>
<summary>Categories</summary>

**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_:**

    -