78 lines
5.9 KiB
Markdown
78 lines
5.9 KiB
Markdown
# Quick Start to Adding a Package {#chap-quick-start}
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To add a package to Nixpkgs:
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1. Checkout the Nixpkgs source tree:
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```ShellSession
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$ git clone https://github.com/NixOS/nixpkgs
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$ cd nixpkgs
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```
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2. Find a good place in the Nixpkgs tree to add the Nix expression for your package. For instance, a library package typically goes into `pkgs/development/libraries/pkgname`, while a web browser goes into `pkgs/applications/networking/browsers/pkgname`. See <xref linkend="sec-organisation" /> for some hints on the tree organisation. Create a directory for your package, e.g.
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```ShellSession
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$ mkdir pkgs/development/libraries/libfoo
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```
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3. In the package directory, create 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. The expression should usually be called `default.nix`.
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```ShellSession
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$ emacs pkgs/development/libraries/libfoo/default.nix
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$ git add pkgs/development/libraries/libfoo/default.nix
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```
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You can have a look at the existing Nix expressions under `pkgs/` to see how it’s done. Here are some good ones:
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- GNU Hello: [`pkgs/applications/misc/hello/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/hello/default.nix). Trivial package, which specifies some `meta` attributes which is good practice.
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- GNU cpio: [`pkgs/tools/archivers/cpio/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/archivers/cpio/default.nix). Also a simple package. The generic builder in `stdenv` does everything for you. It has no dependencies beyond `stdenv`.
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- GNU Multiple Precision arithmetic library (GMP): [`pkgs/development/libraries/gmp/5.1.x.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/gmp/5.1.x.nix). Also done by the generic builder, but has a dependency on `m4`.
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- Pan, a GTK-based newsreader: [`pkgs/applications/networking/newsreaders/pan/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/newsreaders/pan/default.nix). Has an optional dependency on `gtkspell`, which is only built if `spellCheck` is `true`.
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- Apache HTTPD: [`pkgs/servers/http/apache-httpd/2.4.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/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.
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- Thunderbird: [`pkgs/applications/networking/mailreaders/thunderbird/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/mailreaders/thunderbird/default.nix). Lots of dependencies.
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- JDiskReport, a Java utility: [`pkgs/tools/misc/jdiskreport/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/tools/misc/jdiskreport/default.nix). Nixpkgs doesn’t have a decent `stdenv` for Java yet so this is pretty ad-hoc.
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- XML::Simple, a Perl module: [`pkgs/top-level/perl-packages.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/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.
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- Adobe Reader: [`pkgs/applications/misc/adobe-reader/default.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/adobe-reader/default.nix). Shows how binary-only packages can be supported. In particular the [builder](https://github.com/NixOS/nixpkgs/blob/master/pkgs/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.
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Some notes:
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- All [`meta`](#chap-meta) attributes are optional, but it’s still a good idea to provide at least the `description`, `homepage` and [`license`](#sec-meta-license).
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- 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.
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- A list of schemes for `mirror://` URLs can be found in [`pkgs/build-support/fetchurl/mirrors.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/fetchurl/mirrors.nix).
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The exact syntax and semantics of the Nix expression language, including the built-in function, are described in the Nix manual in the [chapter on writing Nix expressions](https://hydra.nixos.org/job/nix/trunk/tarball/latest/download-by-type/doc/manual/#chap-writing-nix-expressions).
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4. Add a call to the function defined in the previous step to [`pkgs/top-level/all-packages.nix`](https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/all-packages.nix) with some descriptive name for the variable, e.g. `libfoo`.
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```ShellSession
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$ emacs pkgs/top-level/all-packages.nix
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```
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The attributes in that file are sorted by category (like “Development / Libraries”) that more-or-less correspond to the directory structure of Nixpkgs, and then by attribute name.
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5. To test whether the package builds, run the following command from the root of the nixpkgs source tree:
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```ShellSession
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$ nix-build -A libfoo
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```
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where `libfoo` should be the variable name defined in the previous step. 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.
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6. If you want to install the package into your profile (optional), do
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```ShellSession
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$ nix-env -f . -iA libfoo
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```
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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.
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